Vibration absorption of the Ti-6Al-4V alloy fabricated by laser powder bed fusion additive manufacturing (LPBF-AM) was evaluated following as-built and post-heat treatment (i.e., solution treatment followed by water quenching). The base plate was heated at 50°C or 200°C during building. Results showed that the vibration absorption of the as-built Ti-6Al-4V alloy was higher when the base plate was heated at 50°C than at 200°C. Further, the vibration absorption indicated strong anisotropy, with the highest vibration absorption in the direction perpendicular to the building direction and transverse to the laser scanning direction. However, after solution treatment followed by water quenching, the anisotropy in the vibration absorption of the LPBF-AMed Ti-6Al-4V alloy practically disappeared, and relatively high values were obtained parallel to each direction.

Abstract We developed two methods for three-dimensional (3D) evaluation of spinal alignment in standing position by image matching between biplanar x-ray images and 3D vertebral models. One used a Slot-Scanning 3D x-ray Imager (sterEOS) to obtain biplanar x-ray images, and the other used a conventional x-ray system and a rotating table. The 3D vertebral model was constructed from the CT scan data. The spatial position of the vertebral model was determined by minimizing the contour difference between the projected image of the model and the biplanar x-ray images. Verification experiments were conducted using a torso phantom. The relative positions of the upper vertebrae to the lowest vertebrae of the cervical, thoracic, and lumbar vertebrae were evaluated. The mean, standard deviation, and mean square error of the relative position were less than 1° and 1 mm in all cases for sterEOS. The maximum mean squared errors of the conventional x-ray system and the rotating table were 0.7° and 0.4 mm for the cervical spine, 1.0° and 1.2 mm for the thoracic spine, and 1.1° and 1.2 mm for the lumbar spine. Therefore, both methods could be useful for evaluating the spinal alignment in standing position.

The Co-20Cr-15W-10Ni (CCWN, mass%) alloy, registered as American society of testing and materials (ASTM) F90, has been widely used as a balloon-expandable stent because of its excellent balance between its mechanical properties and corrosion resistance. To realize a less invasive stent placement, the stent diameter must be reduced, which implies that the stent strut thickness must be reduced. As such, the CCWN alloy must be high in strength and ductility while maintaining a low yield stress to facilitate the expansion and suppression of stent recoil. In this study, we focus on the effects of the adding Mn/Fe on the microstructure, mechanical properties, and corrosive properties of CCWN alloys. A 6 mass% Mn-added CCWN alloy with a grain size of approximately 20 μm prepared in this study exhibits excellent balance between tensile strength and ductility. In addition, it exhibits a lower yield stress while maintaining a high tensile strength compared with the ASTM F90 alloy. Meanwhile, a 6 mass% Fe-added CCWN alloy exhibits a higher ductility compared with the ASTM F90 alloy. The addition of Mn or Fe to the CCWN alloy increases the stacking fault energy of the alloy and suppresses strain-induced martensitic transformation during plastic deformation, thus improving the ductility of the alloy. Results of polarization tests show that the 6 mass% Mn-or Fe-added CCWN alloys exhibit the same corrosion current density as the ASTM F90 alloy. Mn-added Co-Cr-W-Ni alloys are suitable for use in balloon-expandable stents.

To study the effect of O on β-Ti alloys with various β phase stability, Ti–xNb–0.4O (x = 30, 32, 34, 36, 38, 40, 42, mass%) alloys were prepared by arc melting followed by homogenization, hot rolling, and solution treatment. To ensure the O content of the alloys, melting and hot rolling were performed under an Ar atmosphere, and homogenization and solution treatment were performed under vacuum conditions. The mass fractions of O in the Ti–Nb–O alloys were finally accurately controlled in the range of 0.4–0.5%. The phase composition of the alloys was determined by analyzing the X-ray diffraction patterns, the microstructure was observed by optical microscopy, and the mechanical properties were measured by tensile tests. The ω phase and α" phase were found in the solution-treated Ti–30Nb–0.4O. Ti–30Nb–0.4O showed the lowest yield strength owing to the existence of the α" phase. O suppressed ω phase and α" phase transformations during quenching, and showed an obvious solution-strengthening effect. Because the O content of the alloys was essentially the same, the Ti–xNb–0.4O alloys showed similar tensile strengths. The Young's moduli of the alloys ranged from 60 to 69 GPa, and the elongations were all higher than 15%. Particularly, Ti–36Nb–0.4O exhibited desirable mechanical properties, including a Young's modulus of 61 GPa, a tensile strength of 760 MPa, and an elongation of approximately 35%.

In this study, the influence of the high-pressure torsion (HPT) processing parameters and solution treatment (ST) on the corrosion and tribocorrosion behavior of CoCrMo (CCM) alloys was investigated for possible usage in biomedical applications. The corrosion behavior of the CCM alloys was investigated by using potentiodynamic scanning (PDS) and electrochemical impedance spectroscopy (EIS) tests. Tribocorrosion tests were carried out in a reciprocating ball-on-plate tribometer at 1 Hz, 1 N load, and 3 mm stroke length for 2 h. All electrochemical measurements were performed using a potentiostat in standard phosphate-buffered saline (PBS) solution at body temperature (37 ± 2 °C). The samples were characterized by using a scanning electron microscope (SEM), transmission electron microscope (TEM), optical microscope (OM), and X-ray diffraction (XRD). The deepness and width of wear tracks were examined by using a profilometer. The results showed that HPT and ST processes did not affect significantly the corrosion resistance of samples. However, the ST-treated samples had a higher material loss during sliding in standard phosphate-buffered saline (PBS) at body temperature as compared to HPT-treated samples.

Zr was added to Ti–Nb–Fe alloys to develop low elastic modulus and high strength β-Ti alloys for biomedical applications. Ingots of Ti–12Nb–2Fe–(2, 4, 6, 8, 10)Zr (at.%) were prepared by arc melting and then subjected to homogenization, cold rolling, and solution treatments. The phases and microstructures of the alloys were analyzed by optical microscopy, X-ray diffraction, and transmission electron microscopy. The mechanical properties were measured by tensile tests. The results indicate that Zr and Fe cause a remarkable solid-solution strengthening effect on the alloys; thus, all the alloys show yield and ultimate tensile strengths higher than 510 MPa and 730 MPa, respectively. Zr plays a weak role in the deformation mechanism. Further, twinning occurs in all the deformed alloys and is beneficial to both strength and plasticity. Ti–12Nb–2Fe–(8, 10)Zr alloys with metastable β phases show low elastic modulus, high tensile strength, and good plasticity and are suitable candidate materials for biomedical implants.

This is the first report presenting the development of a Co–Cr–W–Ni–Mn alloy by adding 6 mass pct Mn to ASTM F90 Co–20Cr–15W–10Ni (CCWN, mass pct) alloy for use as balloon-expandable stents with an excellent balance of mechanical properties and corrosion resistance. The effects of Mn addition on the microstructures as well as the mechanical and corrosion properties were investigated after hot forging, solution treatment, swaging, and static recrystallization. The Mn-added alloy with a grain size of ~ 20 µm (recrystallization condition: 1523 K, 150 seconds) exhibited an ultimate tensile strength of 1131 MPa, 0.2 pct proof stress of 535 MPa, and plastic elongation of 66 pct. Additionally, it exhibited higher ductility and lower yield stress while maintaining high strength compared to the ASTM F90 CCWN alloy. The formation of intersecting stacking faults was suppressed by increasing the stacking fault energy (SFE) with Mn addition, resulting in a lower yield stress. The low-yield stress is effective in suppressing stent recoil. In addition, strain-induced martensitic transformation during plastic deformation was suppressed by increasing the SFE, thereby improving the ductility. The Mn-added alloys also exhibited good corrosion resistance, similar to the ASTM F90 CCWN alloy. Mn-added Co–Cr–W–Ni alloys are suitable for use as balloon-expandable stents.

We investigated changes in the microstructure and mechanical properties of biomedical Co20Cr15W10Ni alloys (mass%) containing 8 mass% Mn and 03 mass% Si due to hot forging, solution treatment, cold swaging, and static recrystallization. The ©-phase (M XM X type cubic structure, M: metallic elements, X: C and/or N, space group: Fd-3m (227)) and CoWSi type Laves phase (C14 MgZn2 type hexagonal structure, space group: P63/mmc (194)) were confirmed as precipitates in the as-cast and as-forged alloys. To the best of our knowledge, this is the first report that reveals the formation of CoWSi type Laves phase precipitates in CoCrWNi-based alloys. The addition of Si promoted the formation of precipitates of both ©-phase and CoWSi type Laves phase. The solution-treated 8Mn+(0, 1)Si-added alloys exhibited TWIP-like plastic deformation behavior with an increasing work-hardening rate during the early to middle stages of plastic deformation. This plastic deformation behavior is effective in achieving both the low yield stress and high strength required to develop a high-performance balloon-expandable stent. The 8Mn+2Si-added alloy retained the CoWSi type Laves phase even after solution treatment, such that the ductility decreased but the strength improved. Additions of Mn and Si are effective in improving the ductility and strength of the CoCrWNi alloy, respectively. 6 12

The Co-20Cr-15W-10Ni (CCWN, mass%) alloy has excellent corrosion resistance and strength-ductility balance and is applied in almost all balloon-expandable stent platforms. To further reduce the invasiveness of stent placement, it is necessary to reduce the diameter of the stent. That is, both high strength and high ductility should be achieved while maintaining a low yield stress. In our previous studies, it was discovered that low-temperature heat-treatment (LTHT) at 873 K improves the elongation of the CCWN alloy. In this study, we focused on the grain refinement by swaging and static recrystallization to improve the strength of the alloy. The as-swaged alloy was recrystallized at 1373-1473 K for 100-300 s, followed by LTHT. A fine grain structure with an average grain size of 3-17 µm was obtained by static recrystallization. The η-phase (M X-M X type precipitates, M: metallic elements, X: C and/or N) formed during the recrystallization at 1373-1448 K. The alloys recrystallized at 1448 and 1473 K had a homogeneous structure with a small variation in the grain size. On the other hand, the alloys recrystallized at 1373 and 1423 K had an inhomogeneous structure in which fine and coarse grains were mixed. Both the strength and ductility of the CCWN alloy were improved by combining high-temperature short-time recrystallization and LTHT. 12 6

© 2020, ASM International. A series of Ti-(38-2x)Nb-xMo (wt.%) alloys are designed using 1% Mo to replace 2% Nb in order to gradually increase the β stability and obtain a low springback. The α″ phase is exhibited in Ti-38Nb and suppressed with an increasing Mo content. The Ti-38Nb and Ti-34Nb-2Mo alloys show stress-induced α″ martensite transformations during cold rolling and double yielding behavior in tensile tests. The Ti-30Nb-4Mo and Ti-26Nb-6Mo alloys exhibit nonlinear deformation owing to the metastable β phase. With an increase in the Mo content, Young’s modulus increases slightly from 68 GPa in Ti-38Nb to 73 GPa in Ti-26Nb-6Mo, owing to the increase in β stability. Mo shows a solution strengthening effect that gradually increases the tensile strength. Although a higher Young’s modulus was not observed to be induced through deformation in Ti-(38-2x)Nb-xMo alloys, low springback was obtained according to the three-point bending loading–unloading test. In particular, the Ti-38Nb and Ti-34Nb-2Mo alloys with stress-induced α″ martensite transformations exhibit low yielding stress and are thus easily deformed. The deformed α″ phase hardly reverts to the β matrix after unloading, and therefore, the plastic deformation is maintained.

A series of Ti-29Nb-(4, 7, 10, 13)Zr-2Cr alloys were fabricated to investigate the influence of Zr content on microstructures and mechanical properties. All the four alloys present a single β phase after solution treatment. With the increase in Zr content, the 0.2% proof stress is gradually increased from 388 MPa in Ti-29Nb-4Zr-2Cr to 713 MPa in Ti-29Nb-13Zr-2Cr. The Young’s modulus gradually is decreased from 80 GPa in Ti-29Nb-4Zr-2Cr to 63 GPa in Ti-29Nb-13Zr-2Cr. The elongation shows the same trend as that of Young’s modulus. The changes of mechanical properties are influenced by the β stability and solid solution strengthening effect, which are both enhanced by Zr addition. The Ti-29Nb-13Zr-2Cr alloy presents a Young’s modulus of 63 GPa, tensile strength of 730 MPa and elongation of 18% and is a promising biomedical material.

The microstructures, tensile properties, and fatigue lives of the forged Ti-17 using a 1500-ton forging simulator subjected to different solution treatments and a common aging treatment under both load- and strain-controlled conditions to evaluate high cycle fatigue and low cycle fatigue lives, respectively were examined. Then, the tensile properties, microstructures, and relationships between fatigue lives and the microstructural factors were discussed. The fatigue limit under load-controlled conditions increases with increasing solution treatment temperature up to 1143 K, which is in the (α + β) region. However, it decreases with further increase in the solution treatment temperature to 1203 K in the b region. The fatigue ratio at fatigue limit is increasing with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase, and it relates well qualitatively with the volume fraction of the primary α phase when the solution treatment temperature is less than the b transus temperature. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life increases with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life relates well quantitatively with the tensile true strain at breaking of the specimen and the volume fraction of the primary α phase for each total strain range.

© 2019 The Japan Society of Applied Physics. Ti-29Nb-13Ta-4.6Zr (TNTZ) is one of the Ti alloys used for orthodontic wire. However, there is a problem that the metallic color of TNTZ may spoil the appearance of a row of teeth. In previous studies, white oxide coating on disk-shaped TNTZ samples was obtained by heat treatment or atmospheric-pressure plasma (APP) treatment. In this study, the fabrication process of white orthodontic wire by applying APP treatment is proposed. As a result, TNTZ wire which has a white oxide layer with comparable brightness to the surface of Japanese teeth has been successfully fabricated.

A process combining swaging, static recrystallization, and heat treatment at 873 K (low-temperature heat-treatment, LTHT) was developed for achieving both high ultimate strength and high ductility in Co-20Cr-15W-10Ni (mass%, CCWN) alloy for stent application. The alloys swaged to a sectional area reduction rate of 58.3% were annealed at 1373-1473 K for 30-300 s. Under annealing at 1373 K for 300 s, a fine grain structure with an average grain size of similar to 6 mu m formed, while under annealing at 1473 K, a structure with an average grain size of 12 mu m formed after 120 s. In the alloys annealed at 1373-1448 K, the formation of eta-phase precipitates (M6X-M12X type, M: metallic elements, X: C and/or N) was observed, while no precipitates were observed in the alloys annealed at 1473 K. The improvement in ultimate strength by grain refinement was confirmed. Alloys annealed at 1473 K showed higher ductility compared to those annealed at 1373-1448 K even if the grain size was similar. It is considered that the eta-phase precipitates deteriorated the ductility of the annealed alloys. LTHT suppressed the strain-induced martensitic gamma-to-epsilon transformation to improve the ductility of the fine-grained as well as coarse-grained alloys. Thus, regardless of the grain size, it is newly evidenced that LTHT effectively improves ductility in CCWN alloy. By combining high-temperature short-time annealing and LTHT, both the ultimate strength and ductility of Co-2OCr-15W-10Ni (mass%) alloy improved, and it was possible to provide properties suitable for next-generation balloon-expandable stents with Co-20Cr-15W-10Ni (mass%) alloy.

β-Type Ti-Nb-based alloys exhibit satisfactory biocompatibility and low Young’s modulus for biomedical applications. The microstructure and mechanical properties of a series of Ti-(14, 16, 18, 20, 22, 24)Nb-2Fe alloys fabricated by arc melting were investigated by XRD, optical microscopy, and tensile tests. Both ω and α″ phases existed in the Ti-14Nb-2Fe alloy, while just a single β phase existed in the other alloys. Twinning is an important deformation mechanism that causes work hardening and twinning-induced plasticity. It was found in the Ti-(14, 16, 18, 20)Nb-2Fe alloys and not in the Ti-22Nb-2Fe alloy. The Ti-14Nb-2Fe alloy exhibited the highest tensile strength and the highest Young’s modulus owing to the existence of the ω phase. The tensile strength decreased gradually from 830 MPa (highest) for the Ti-14Nb-2Fe alloy to 540 MPa (lowest) for the Ti-24Nb-2Fe alloy with an increase in the Nb content. The Young’s modulus decreased from 90 GPa for the Ti-14Nb-2Fe alloy to 63 GPa for the Ti-22Nb-2Fe alloy and then increased to 71 GPa for the Ti-24Nb-2Fe alloy. Elongation shows the same trend as the Young’s modulus. The Ti-22Nb-2Fe alloy, with a low Young’s modulus of 63 GPa, tensile strength of 570 MPa, and 15% elongation, was found suitable for biomedical applications. The Ti-20Nb-2Fe alloy also exhibits a high tensile strength, a Young’s modulus ratio of 9.24 × 10 , and 18% elongation and is thus considered another valuable Ti alloy for biomedical applications. −3

© 2019 The Japan Institute of Metals and Materials Biomedical Ti15Nb25Zr(0, 2, 4, 8)Fe (mol%) alloys are prepared by mixing pure element powders and spark plasma sintering (SPS). Specimens with diameters of 20 mm and thicknesses of 3 mm are obtained by sintering at 1000°C for 10 min followed by cooling in the furnace. Some of the specimens are then heat-treated at 900°C for 1 h followed by water quenching. Zr and Fe are dissolved in Ti; however, segregation of Nb is observed in all of the alloys. The ¢ and ¡AA phases are observed in the as-sintered and heat-treated specimens owing to the insufficient diffusion of the alloying elements. Fe stabilizes the ¢ phase and provides a solution-strengthening effect. With the increase in the Fe content in the as-sintered specimen, the compressive strength and micro-Vickers hardness are improved in the Ti15Nb25Zr(0, 2, 4)Fe alloys and slightly decreased in Ti15Nb25Zr8Fe. The as-sintered Ti15Nb25Zr4Fe alloy exhibits the maximum compressive strength of 1740 MPa. Although the plasticity is decreased by the Fe addition, a fracture strain of approximately 17% is obtained for Ti15Nb25Zr4Fe, indicating a good plasticity. The heat treatment cannot eliminate the segregation of Nb, but can improve the plasticity and slightly increase the strengths of Ti15Nb25Zr(0, 2, 4)Fe. Moreover, the heat-treated Ti15Nb25Zr8Fe exhibits a high strength of approximately 1780 MPa and fracture strain of approximately 19%. Therefore, good comprehensive mechanical properties, including high strengths, high hardnesses, and good plasticities, can be obtained in Fe-added ¢-Ti alloys prepared by SPS and subsequent optional short heat treatment.

© 2019 Japan Institute of Metals (JIM). All rights reserved. Deformation-induced higher Young’s modulus can satisfy the contradictory requirements of Ti alloys for spinal-fixation applications, which demand a high Young’s modulus to reduce springback during operations and a low Young’s modulus to prevent stress shielding effect for patients after surgeries. In this study, TNTZ(1, 3, 5)Mo are designed by adding Mo and Ti to Ti29Nb13Ta4.6Zr (TNTZ) in order to maintain low initial Young’s modulus and achieve low springback. All the solutionized alloys show single ¢ phase with increasing the ¢ stability by Mo addition. They show low Young’s moduli less than 65 GPa, similar ultimate tensile strength of 650 MPa and elongation around 20%. The springback of TNTZ3Mo and TNTZ5Mo is lower than that of TNTZ and TNTZ1Mo owing to their more stable ¢ phase. After cold rolling, TNTZ3Mo shows the largest increasing ratio of 25% in Young’s modulus and the highest ultimate tensile strength owning to the appearance of deformation-induced ½ phase. With the low initial Young’s modulus of 59 GPa, TNTZ3Mo is a potential candidate to make the spinal rods in spinal fixation devices.

The effect of Si addition on the microstructure and mechanical properties of a near-¢ titanium alloy Ti-17 with fully lamella microstructure was investigated. It was found that the microstructure of Ti-17 with silicon exhibited the absence of a continuously thick ¡ layer along prior-¢ grain boundaries (grain boundary ¡), while the grain boundary ¡ was distinctively formed in Ti-17 without Si. The formation of (Ti, Zr) silicide particles at the prior-¢ grain interior and its grain boundaries were observed, and the presence of these particles were related to the disappearance of grain boundary ¡ similar to the oxygen scavenging effect of boride particles reported previously. With regard to mechanical properties, Ti-17 with silicon exhibits higher strength and lower ductility compared with Ti-17 without Si. Ductile transgranular fracture morphology was observed even on the fracture surface of Ti-17 with Si after tensile test.

©2019 The Japan Institute of Metals and Materials. The fatigue lives of forged Ti-17 using a 1500-ton forging simulator subjected to different solution treatments and a common aging treatment were evaluated under both load- and strain-controlled conditions: high and low cycle fatigue lives, respectively. Then, the tensile properties and microstructures were also examined. Finally, the relationships among fatigue lives and the microstructural factors and tensile properties were examined. The microstructure after solution treatment at 1203 K, which is more than the ¢ transus temperature, and aging treatment exhibits equiaxed prior ¢ grains composed of fine acicular ¡. On the other hand, the microstructures after solution treatment at temperatures of 1063, 1123, and 1143 K, which are less than the ¢ transus temperature, and aging treatment exhibit elongated prior ¢ grains composed of two different microstructural feature regions, which are acicular ¡ and fine spheroidal ¡ phase regions. The 0.2% proof stress, ·0.2, and tensile strength, ·B, increase with increasing solution treatment temperature up to 1143 K within the (¡ + ¢) region, but decrease with further increasing solution treatment temperature to 1203 K within the ¢ region. The elongation (EL) and reduction of area (RA) decrease with increasing solution treatment temperature, and it becomes nearly 0% corresponding to a solution treatment temperature of 1203 K. The high cycle fatigue limit increases with increasing solution treatment temperature up to 1143 K, corresponding to the (¡ + ¢) region. However, it decreases with further increase in the solution treatment temperature to 1203 K in the ¢ region. The fatigue ratio in high cycle fatigue life region is increasing with decreasing solution treatment temperature, namely increasing the volume fraction of the primary ¡ phase, and it relates well qualitatively with the volume fraction of the primary ¡ phase when the solution treatment temperature is less than the ¢ transus temperature. The low cycle fatigue life increases with decreasing solution treatment temperature, namely increasing the volume fraction of the primary ¡ phase. The low cycle fatigue life relates well quantitatively with the tensile true strain at breaking of the specimen and the volume fraction of the primary ¡ phase for each total strain range of low cycle fatigue testing.

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. Different amounts of Cr were added to a metastable β-type Ti–22Nb (at.%) alloy to obtain desirable mechanical properties, including a low Young’s modulus, high strength, and good plasticity. The mechanical properties and microstructural changes were investigated. Cr has a high ability to stabilize the β phase, as well as suppress both α″ martensite and ω phase transformations during quenching and the stress-induced α″ martensite transformation during tension. Solid solution strengthening is scarcely achieved by Cr addition. The changes in mechanical properties can be attributed to the different β stabilities. The Ti–22Nb–(0,1)Cr alloys have metastable β phases and exhibit double yielding phenomena, indicating a stress-induced α″ martensite transformation. The Ti–22Nb–(2,3)Cr alloys with stable β phases exhibit distinct work hardening caused by a {332}β<113>β twinning, which also occurs in the Ti–22Nb–(0,1)Cr alloys, but not in the Ti–22Nb–4Cr alloy. Low Young’s moduli of approximately 60 GPa are obtained for the Ti–22Nb–(1,2)Cr alloys. The Ti–22Nb–2Cr alloy exhibits desirable properties for biomedical applications, including an ultimate tensile strength of approximately 600 MPa and elongation of approximately 20%.

The microstructure and tensile properties of Co-27Cr-6Mo (mass%) alloys heat-treated at 673-1373 K were studied. Lower elongation was observed after heat treatment at 1073 K due to formation of carbonitride precipitates. In contrast, when low-temperature heat treatment (LTHT) was applied at 673-873 K, both the ultimate tensile strength and elongation synchronously improved compared with the solution-treated alloy. Electron backscatter diffraction analysis for plastic-strained alloys and in situ X-ray diffraction analysis under stress induced conditions revealed that the strain-induced martensitic transformation (SIMT) of the gamma(fcc)-phase to epsilon(hcp)-phase during plastic deformation was suppressed by the LTHT. Stacking faults (thin epsilon-phase) were observed to collide in the LTHT alloys. The following mechanisms for the synchronous improvement in the tensile strength and elongation after LHTH are proposed. First, stacking faults with multiple variants were formed during LTHT. Then, the epsilon-phase of a single variant formed by SIMT during plastic deformation collides with preexisting multi-variant stacking faults formed during LTHT, increasing the tensile strength. In addition, the SIMT during plastic deformation is suppressed in the high-plastic-strain region by the collision. This decreases the total amount of epsilon-phase formed during plastic deformation, which improves the ductility. We demonstrated that LTHT of Co-Cr-Mo alloys effectively improves the performance and mechanical safety of spinal fixation implants, which often fracture because of fatigue cracking.

Microstructural changes were observed during the plastic deformation of ASTM F90 Co-20Cr-15W-10Ni (mass pct) alloy heat-treated at 873 K (600 °C) for 14.4 ks, and analyzed by electron backscatter diffraction and in situ X-ray diffraction techniques. The obtained results revealed that the area fraction of the ε-phase (fε) in the as-received alloy was higher than that in the heat-treated alloy in the low-to-middle strain region (≤ 50 pct), whereas the fε of the heat-treated alloy was higher than that of the as-received alloy at the fracture point. During plastic deformation, the ε-phase was preferentially formed at the twin boundaries of the heat-treated alloy rather than at the grain boundaries. According to the transmission electron microscopy observations, the thin ε-phase layer formed due to the alloy heat treatment acted as the origin of deformation twinning, which decreased the stress concentration at the grain boundaries. The results of anodic polarization testing showed that neither the heat treatment at 873 K (600 °C) nor plastic deformation affected the alloy corrosion properties. To the best of our knowledge, this is the first study proving that the formation of a thin ε-phase layer during the low-temperature heat treatment of the studied alloy represents an effective method for the enhancement of the alloy ductility without sacrificing its strength and corrosion properties.

In order to know precisely the corrosion behavior of a new developed β type titanium alloy Ti-29Nb-13Ta-4.6Zr (TNTZ) and ordinary titanium alloy Ti-6Al-4V (for comparison) in oral cavity environment, corrosion rate of these alloys in an artificial saliva solution was then investigated. Corrosion measurement was conducted in 600 ml solution of Fusayama-Meyer artificial saliva containing of 0,4 g NaCl, 0.4 g KCl, 0.795 g CaCl2.2H2O, 0.69 g NaH2PO4, and 1 g urea using a potentiostat model (VERSA studio-200) controlled by a personal computer. The solution was maintained at pH 5.2 and 37oC to imitate oral cavity condition. After corrosion test, specimen surfaces were observed by SEM, EDX and XPS. The result show that the averaged corrosion rate of TNTZ and Ti-6Al-4V is 4.5×10-9 mmy-1 and 6.4×10-8 mmy-1, respectively. This indicates that the corrosion resistance of TNTZ is relatively high, and it is better than that of Ti-6Al-4V. This is due to the formation of a multiple layer of Ti, Nb and Zr oxides in the surface of TNTZ. However, formation of micro-pitting corrosion is more intense in TNTZ due mainly to the alloying elements segregation and the presence of high impurities. It is recommended that, therefore, an intense homogenizing process is neccessary to apply in TNTZ for homogenizing the elemental distribution and, subsequently, for minimizing pitting corrosion attack. Having low pitting corrosion attack is an important thing for dental application in order to reduce stress concentration and crack initiation, and then to avoid mechanical failure during application.

In this study, hydroxyapatite (HA) based composite films were successfully syntheses on the β-type Ti29Nb13Ta4.6Zr (TNTZ). The solutionized TNTZ substrates coated with HA and HA/Titania (TiO2) bioactive composite coatings by sol-gel method under various sintering parameters related to sintering temperatures and heating ramp rates. Microstructural observations of the coatings revealed that apatite was formed on the substrates. The hardness values of the coatings increase with increasing both the sintering temperature and the TiO2 concentration in the coatings layer. However, it was found that the heating ramp rate of the sintering was not affecting the hardness values so much. Also, the hardness values of the HA/TiO2 composite coatings at all sintering temperatures were higher than only HA coated TNTZ samples due to the existence TiO2 phases in the HA matrix. Results indicating that the doping of HA with TiO2, improve the physical consistency between the coating layer and the substrates and provide a better inter-particle bonding due to the existence TiO2 phases in the HA.

© 2018 The Japan Institute of Metals and Materials. Oxygen was added to Ti38Nb (mass%) alloys to improve their mechanical properties. Ti38NbxO (x = 0.13, 0.24, 0.46, mass%) alloys were prepared by arc melting, and subsequently subjected to homogenization, hot rolling, and solution treatment. It was found that adding oxygen suppresses the martensite transformation and exhibits strong solution strengthening effect. Single ¢ phase is obtained in Ti38Nb0.24O, whereas Ti38Nb0.13O is composed of both ¡AA and ¢ phases. Both alloys exhibit double yielding phenomena during tension, indicating a stress-induced martensitic transformation. Ti38Nb0.46O exhibits a non-linear deformation, a low Young's modulus of 62 GPa, high tensile strength up to 780 MPa, and elongation around 23%, which are promising characteristics for biomedical applications.

The effects of alloying elements in Ti-29Nb-13Ta-4.6Zr (wt%) (TNTZ) alloys with low Young's modulus for biomedical applications on microstructural evolution during aging, in particular, at an aging temperature of 400 degrees C have been determined. The peak hardness is obtained by co-precipitation of alpha and omega phases. O addition stabilizes omega phases; as a result, formation of omega is enhanced with increasing the O content as an alloying element, resulting in prevention of the growth of the alpha phases due to soft impingement. Because of the stress caused by the omega to alpha transformation, the alpha phase often contains defects within its internal structure. Although Zr is known to be a neutral element within Ti, here we show that Zr acts as weak beta stabilizer. At the beta/alpha interface, Zr enrichment appears to be due to a solute drag mechanism. In addition, a slight increase in Zr composition in the beta/omega interface has also been detected using atom probe. Dispersion of omega phases and segregation of Zr to the beta/alpha interface lead to fine alpha phase precipitation, resulting in an increase in the hardness of the O-added TNTZ alloys.

Good ductility, low magnetic susceptibility, and tunable Young's modulus are highly desirable properties for materials usage as spinal fixation rods. In this study, the effects of niobium content on the microstructure, magnetic susceptibility, and mechanical properties of Zr-xNb (13 <= x <= 23 wt%) alloys were investigated. For the Zr-15Nb and Zr-17Nb alloys, a remarkable increase in Young's modulus was achieved due to the occurrence of deformation-induced o.) phase transformation. This was the result of the competition of two factors associated with the Nb content: an increase of the stability of beta phase and a decrease of the amount of athermal to phase with increasing Nb content. When the Nb content was 15% or 17%, the amount of deformation-induced to phase was maximum. Moreover, the magnetic susceptibility decreased with the deformation-induced beta -> omega to phase transformation, and the Zr-17Nb alloy with apparent kink bands exhibited a smaller amount of springback than the Zr-15Nb alloy with (3 3 2} (1 1 3) mechanical twins. Furthermore, the ions released from the Zr-xNb alloys in accelerated immersion tests were at a very low level. The combination of low initial Young's modulus, and its remarkable variation induced by deformation, low magnetic susceptibility, good ductility, and smaller springback make the Zr-17Nb alloy a potential candidate for spinal fixation rods.

Oxygen was added into biomedical beta-type Ti-29Nb-13Ta-4.6Zr (mass%, TNTZ) alloy to improve its fatigue properties with maintaining its low Young's modulus. The effect of oxygen on the fatigue behaviors of these oxygen-added TNTZ alloys was systematically investigated. A series of TNTZ-(0.1, 0.3, 0.5 and 0.7 mass%)0 alloys were prepared, denoted as 0.10, 0.30, 0.50, and 0.70, respectively. The Young's moduli of the prepared alloys increase slightly with increasing oxygen content; 0.70 possessing the highest oxygen content still shows a quite low Young's modulus. The fatigue limits of the alloys increase monotonically with oxygen content increases. The high-concentration oxygen in 0.70 suppresses the slip plane decohesion and induces the formation of densely-arranged small-scaled alpha" martensite twins that increases the paths and distance for fatigue crack propagation, thus it enhances the resistance to the fatigue crack initiation and propagation in 0.70, which contributes to its excellent fatigue performance. Among all the alloys compared in the present study, 0.70 shows a high fatigue limit of similar to 635 MPa, a high tensile strength of similar to 1100 MPa, a large elongation of similar to 20% as well as a low Young's modulus of similar to 76 GPa, thus it is regarded as a promising biomaterial for next-generation biomedical applications.

Deformation-induced co-phase transformation during tensile deformation was investigated in the developed spinal-support alloy, Ti-9Cr-0.2O. Both preferential single-variant omega transformation along its [0001] direction and growth and/or assembling of uniformly distributed omega particles undergo in the alloy during tensile deformation. It is confirmed that this deformation-induced omega-phase transformation can be triggered by elastic strain or stress without plastic deformation. Furthermore, a re-orientation process works for this transformation; that is, the omega(1) variant may re-orientate into the omega(2) variant via {001} (110) twinning-type mechanism probably related to the external loading condition and the orientations of omega and beta phases. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In recent years, metallic biomaterial applications have demanded a relatively low Young s modulus that is nearly equal to that of bone (around 30 GPa). However, in the case of spinal fixture applications, metallic materials with a relatively high Young s modulus are required to suppress spring-back by elastic and plastic deformation during implantation. We recently proposed Young s modulus control by stress-induced transformation to produce the biomedical beta-type Ti-12Cr alloy. However, the relationship between the microstructure and the mechanical properties of Ti-12Cr has not been fully investigated. In this study, the changes in the mechanical properties of Ti-12Cr were investigated through the heat treatment and the fine particle bombarding process (FPB), which is a surface modification process. Peak aging (PA) of Ti-12Cr heated at 673 K occurred for around 2.4 ks. The Vickers hardness of Ti-12Cr at the PA condition at 673 K (HV 524) was around 90% higher than that after solutionized treatment (ST) (HV 294). Both the 0.2% proof stress and tensile strength of Ti-12Cr at the PA condition at 673 K were also around 50% higher those after ST. However, the ductility of Ti-12Cr at the PA condition at each temperature significantly decreased. Therefore, only ST was judged to be optimal for Ti-12Cr with an excellent combination of strength and ductility. The Vickers hardness and Young s modulus of solutionized Ti-12Cr subjected to FPB increased by around 40% and 70%, respectively, at the edge of the specimen surface compared with the corresponding values of the unprocessed sample. Furthermore, the run-out (770 MPa) of Ti-12Cr subjected to FPB increased by around 70 MPa. The bone contact ratio of Ti-12Cr slightly increased with an increase in the implantation period from 24 to 52 weeks.

A post-weld heat treatment process, that is, solution treatment and aging, was found to be effective in improving the fatigue strength of friction stir welded Ti-6Al-4V butt joints. The stir-zone microstructure was changed by friction stir welding, from an equiaxed-a structure to a lamellar structure, but equiaxed-a structure remained in the base metal. Subsequently, solution treatment and aging modified these microstructures to bimodal structures in both the stir zone and base metal. The hardness in the stir zone differed from the base metal after friction stir welding, but the difference was eliminated by solution treatment and aging. The fatigue strength of friction stir welded Ti-6Al-4V butt joints was successfully increased by solution treatment and aging, which was higher than that of the parent Ti-6Al-4V plate. This indicates that solution treatment and aging increases the fatigue strength of friction stir welded Ti-6Al-4V butt joints by the formation of similar bimodal structures in the stir zone and base metal, resulting in reduced stress concentration at these boundaries and retarded fatigue failure.

Ti-Mn alloys fabricated by metal injection molding (MIM) show promising performance for biomedical applications, but their low ductility (caused by high O content and the presence of pores and carbides) requires improvement. Previously, the addition of Mo to cold crucible levitation melted (CCLM) Ti-Mn alloys efficiently improved the ductility of those alloys by promoting mechanical twinning. In the present study, Mo was added to Ti-Mn alloys fabricated by MIM. Unlike fabrication by CCLM, fabrication by MIM can produce alloys with a smaller grain size, and also introduce microstructures such as pores and Ti carbides. Thus, in order to investigate how Mo addition interacts with these typical MIM features, four alloys for biomedical applications were fabricated by MIM: Ti-5Mn-3Mo (TMM-53), Ti-5Mn-4Mo (TMM-54), Ti-6Mn-3Mo (TMM-63), and Ti-6Mn-4Mo (TMM-64). Their microstructures, mechanical properties, and tensile deformation mechanisms were evaluated. Their hardness values range from 312-359 HV, and their Young s modulus values range from 84-88 GPa; both the Vickers hardness and Young s modulus show little variation among the alloys. Although the alloys show fracture features associated with a predominantly ductile fracture mode and Mo addition successfully promotes mechanical twinning in TMM-54, the elongation of these alloys is still critically low. Compared to the TMM alloys fabricated by CCLM, the TMM alloys fabricated by MIM show slightly lower hardness and Young s modulus, and comparable tensile strength, with their low elongation remaining inadequate for such applications. In particular, TMM-63 shows the best combination of mechanical properties among the present alloys, with an elongation of 4% and an ultimate tensile strength of 1145 MPa.

Oxygen was added to the biomedical beta-type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ, mass pct) in order to improve its strength, while keeping its Young's modulus low. Conventionally, with an increase in the oxygen content, an alloy's tensile strength increases, while its tensile elongation-to-failure decreases. However, an abnormal deformation behavior has been reported in the case of oxygen-modified TNTZ alloys in that their strength increases monotonically while their elongation-to-failure initially decreases and then increases with the increase in the oxygen content. In this study, this abnormal tensile deformation behavior of oxygen-modified TNTZ alloys was investigated systematically. A series of TNTZ-(0.1, 0.3, and 0.7 mass pct)O alloy samples was prepared, treated thermomechanically, and finally solution treated; these samples are denoted as 0.1ST, 0.3ST, and 0.7ST, respectively. The main tensile deformation mechanisms in 0.1ST are a deformation-induced alpha aEuro(3)-martensitic transformation and {332}aOE (c) 113 > mechanical twinning. The large elongation-to-failure of 0.1ST is attributable to multiple deformation mechanisms, including the deformation-induced martensitic transformation and mechanical twinning as well as dislocation glide. In both 0.3ST and 0.7ST, dislocation glide is the predominant deformation mode. 0.7ST shows more homogeneous and extensive dislocation glide along with multiple slip systems and a higher frequency of cross slip. As a result, it exhibits a higher work-hardening rate and greater resistance to local stress concentration, both of which contribute to its elongation-to-failure being greater than that of 0.3ST. (C) The Minerals, Metals & Materials Society and ASM International 2016

The microstructural evolution and its effect on biocompatibility of TNTZ through HPT processing were investigated systematically in this study. TNTZ_AHPT shows an enhanced mechanical biocompatibility, which is characterized by a higher tensile strength (1375 MPa) and hardness (450 HV) than those of TNTZ_ST, TNTZ_AT, and Ti64 ELI while maintaining a relatively low Young’s modulus. In this study, such microstructural refinement of TNTZ and its effect on electrochemical biocompatibility through HPT processing are investigated systematically in this study. The microstructure of TNTZ_AT consists of randomly distributed needle-like α precipitates in the equiaxed β grains with a diameter of approximately 40 m. The microstructure of TNTZ_AHPT consists of nanograined (NG) elongated β grains that have subgrains of non-uniform morphologies resulting from distortion by severe torsional deformation. Furthermore, the β grains and subgrains are surrounded by non-equilibrium grain boundaries. The needle-like α precipitates are completely refined to a nanograined. TNTZ_AHPT exhibits an enhanced combination of excellent corrosion performance and improved cellular response compared to TNTZ_ST, TNTZ_AT, and Ti64 ELI.

The surface treatment technology known as 'cavitation peening' was employed in this study in order to enhance the durability of spinal implant fixture applications, which are subject to fretting fatigue. Cavitation peening can be realized by a technique in which a high-speed water jet is injected into water through a nozzle. It utilizes a phenomenon by which surface impacts due to collapsing cavitation bubbles induce work-hardening by introducing residual compressive stress near the surface. A fretting fatigue test was conducted on a spinal implant rod made of Ti-6Al-4V ELI in accordance with the ASTM F1717 standard, which is the established method for testing spinal implants after they are treated by cavitation peening. The residual stress was evaluated by using X-ray diffraction analysis. The hardness over the cross-sectional area was also measured using an indentation test. The obtained results show that cavitation peening drastically improves the fretting fatigue properties of spinal implant fixtures by as much as 2.2 times compared to untreated ones. This can be attributed to a significant increase in the hardness from 5.0 to 9.6 GPa and a high compressive residual stress of over 600 MPa induced by cavitation peening. (C) 2016 Elsevier Ltd. All rights reserved.

In previous studies, Ti-Mn alloys showed promising performance for biomedical applications, but their elongation required improvement. In this study, Mo was added to Ti-Mn alloys to promote mechanical twinning and improve their ductility. Four alloys for biomedical applications were designed and fabricated by cold crucible levitation melting: Ti-5Mn-3Mo (TMM-53), Ti-5Mn-4Mo (TMM-54), Ti-6Mn-3Mo (TMM-63), and Ti-6Mn-4Mo (TMM-64). The microstructure, mechanical properties, tensile deformation mechanisms, and electrochemical corrosion properties of the alloys were evaluated. Their hardness ranges from 336 to 373 HV. Their Young's modulus ranges from 89 to 100 GPa. Both hardness and Young's modulus tend to decrease with decreasing amount of athermal omega phase, which is caused by increasing alloying elements contents. Mo addition improves the elongation of TMM-53 and TMM-54 by promoting twinning. Conversely, it increases the tensile strength of TMM-63 and TMM-64. Particularly, TMM-54 shows an elongation of 34% with an ultimate tensile strength (UTS) of 935 MPa. TMM-63 shows an elongation of 14% and a UTS of 1220 MPa, associated to the formation of deformation-induced to phase. Moreover, Mo addition decreases the corrosion rate of the Ti-Mn alloys to a level comparable to that of commercially-pure Ti. (C) 2016 Elsevier Ltd. All rights reserved.

The effect of oxygen on stability of isothermal omega precipitates in Ti-29Nb-13Ta-4.6Zr was examined using Xray powder diffraction, transmission electron microscopy, and atom probe tomography. Two alloys with 0.1 and 0.4 mass% oxygen were subjected to single step, and two-step annealing heat-treatments to respectively promote omega and alpha formation. After second step annealing, large volume fraction of omega precipitates was retained in 0.4 mass% 0 alloy while mainly alpha phase was observed in TNTZ-0.10. The enhanced stability of omega in the higher oxygen containing TNTZ alloys questions the conventionally accepted understanding that oxygen destabilizes the omega phase in titanium alloys. (C) 2016 Elsevier Ltd. All rights reserved.

Bioactive oxide layers were fabricated on Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) by three different alkali solution treatments: hydrothermal (H), electrochemical (E), and hydro thermal -electrochemical (HE). The adhesive strength of the oxide layer to the TNTZ substrate was measured to determine whether this process achieves sufficient adhesive strength for implant materials. Samples subjected to the HE process, in which a current of 15 mA/cm(2) was applied at 90 degrees C for 1 h (HE90-1h), exhibited a comparatively higher adhesive strength of approximately 18 MPa while still maintaining a sufficiently high bioactivity. Based on these results, an oxide layer fabricated on TNTZ by HE90-1h is considered appropriate for practical biomaterial application, though thicker oxide layers with many cracks can lead to a reduced adhesive strength. (C) 2016 Elsevier Ltd. All rights reserved.

Osteoporosis is becoming more prevalent due to the aging demographics of many populations. Osteoporotic bone is more prone to fracture than normal bone, and current orthopedic implant materials are not ideal for the osteoporotic cases. A newly developed strontium phosphate (SrPO4) coating is reported herein, and applied to Ti-29Nb-13Ta-4.6Zr (wt%), TNTZ, an implant material with a comparative Young's modulus to that of natural bone. The SrPO4 coating is anticipated to modulate the activity of osteoblast (OB) and osteoclast (OC) cells, in order to promote bone formation. TNTZ, a material with excellent biocompatibility and high bioinertness is pretreated in a concentrated alkaline solution under hydrothermal conditions, followed by a hydrothermal coating growth process to achieve complete SrPO4 surface coverage with high bonding strength. Owing to the release of Sr ions from the SrPO4 coating and its unique surface topography, OB cells demonstrate increased proliferation and differentiation, while the cellular responses of OC are suppressed, compared to the control case, i.e., bare TNTZ. This TNTZ implant with a near physiologic Young's modulus and a functional SrPO4 coating provides a new direction in the design and manufacture of implantable devices used in the management of orthopedic conditions in osteoporotic individuals.

Titanium and its alloys are suitable for biomedical applications owing to their good mechanical properties and biocompatibility. Beta-type Ti-Mn alloys (8-17 mass% Mn) were fabricated by metal injection molding (MIM) as a potential low cost material for use in biomedical applications. The microstructures and mechanical properties of the alloys were evaluated. For up to 13 mass% Mn, the tensile strength (1162-938 MPa) and hardness (308-294 HV) of the MIM fabricated alloys are comparable to those of Ti-Mn alloys fabricated by cold crucible levitation melting. Ti-9Mn exhibits the best balance of ultimate tensile strength (1046 MPa) and elongation (4.7%) among the tested alloys, and has a Young's modulus of 89 GPa. The observed low elongation of the alloys is attributed to the combined effects of high oxygen content, with the presence of interconnected pores and titanium carbides, the formation of which is due to carbon pickup during the debinding process. The elongation and tensile strength of the alloys decrease with increasing Mn content. The Ti-Mn alloys show good compressive properties, with Ti-17Mn showing a compressive 0.2% proof stress of 1034 MPa, and a compressive strain of 50%. (C) 2016 Elsevier Ltd. All rights reserved.

The effects of severe plastic deformation through high-pressure torsion (HPT) on the microstructure and tensile properties of a biomedical Co-Cr-Mo (CCM) alloy were investigated. The microstructure was examined as a function of torsional rotation number, N and equivalent strain, epsilon(eq) in the HPT processing. Electron backscatter diffraction analysis (EBSD) shows that a strain-induced martensitic transformation occurs by the HPT processing. Grain diameter decreases with increasing epsilon(eq), and the HPT-processed alloy (CCMHPT)for epsilon(eq)=45 exhibits an average grain diameter of 47 nm, compared to 70 mu m for the CCM alloy before HPT processing. Blurred and wavy grain boundaries with low-angle of misorientation in the CCMHPT sample for epsilon(eq) <45 become better-defined grain boundaries with high-angle of misorientation after HPT processing for epsilon(eq)=45. Kernel average misorientation (KAM) maps from EBSD indicate that KAM inside grains increases with epsilon(eq) for epsilon(eq)<45, and then decreases for epsilon(eq)=45. The volume fraction of the epsilon (hcp) phase in the CCMHPT samples slightly increases at epsilon(eq)=9, and decreases at epsilon(eq)=45. In addition, the strength of the CCM samples increases at epsilon(eq)=9, and then decrease at epsilon(eq)=45. The decrease in the strength is attributed to the decrease in the volume fraction of e phase, annihilation of dislocations, and decrease in strain in the CCMHPT sample processed at epsilon(eq)=45 by HPT. () 2015 Elsevier Ltd. All rights reserved.

In this study, micro-arc oxidation (MAO) was performed on a beta-type titanium alloy, namely, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ), to improve not only its antibacterial property but also bioactivity in body fluids. The surface oxide layer formed on TNTZ by MAO treatment in a mixture of calcium glycerophosphate, calcium acetate, and silver nitrate was characterized using surface analyses. The resulting porous oxide layer was mainly composed of titanium oxide, and it also contained calcium, phosphorus, and a small amount of silver, all of which were incorporated from the electrolyte during the treatment. The MAO-treated TNTZ showed a strong inhibition effect on anaerobic Gram-negative bacteria when the electrolyte contained more than 0.5 mM silver ions. The formation of calcium phosphate on the surface of the specimens after immersion in Hanks' solution was evaluated to determine the bioactivity of TNTZ with sufficient antibacterial property. As a result, thick calcium phosphate layers formed on the TNTZ specimen that underwent MAO treatment, whereas no precipitate was observed on TNTZ without treatment. Thus, the MAO treatment of titanium-based alloys is confirmed to be effective in realizing both antibacterial and bioactive properties.

In order to develop new low-cost and high-strength beta-type titanium alloys, a Ti-13Mn was fabricated by metal injection molding. For improving its tensile strength, Ti-13Mn was subjected to cold-rolling at reduction ratios of 60% and 90%, respectively. The solutionized Ti-13Mn has pores and titanium carbide (Ti carbide) precipitates and consists of a beta phase and an athermal omega phase. The porosity of the alloy decreases from 6.1% to 0.01% after cold-rolling at a reduction ratio of 90%. Moreover, during cold-rolling, the Ti carbides are fragmented and a deformation-induced omega phase is formed. The ultimate tensile strength, 0.2% proof stress, Vickers hardness, and Young's modulus of Ti-13Mn increase from 888 MPa to 1852 MPa, from 827 MPa to 1823 MPa, from 279 Hv to 461 Hv, and from 96 GPa to 108 GPa, respectively, after cold-rolling at a reduction ratio of 90%. On the other hand, the elongations of both the solutionized and cold rolled Ti-13Mn are less than 2%. Although the elongation of Ti-13Mn is less than 2%, the tensile strength of the cold rolled Ti-13Mn is extremely high compared with that of existing titanium alloys. This large-improvement in the tensile strength of the cold rolled Ti-13Mn is attributed to the increase in the dislocation density, decrease in grain size, decrease in porosity, and formation of a deformation-induced omega phase. (c) 2015 Elsevier B.V. All rights reserved.

A novel method for detecting antimicrobial activity using an innate property of the <i>Salmonella</i> bacteria, namely, the ability of <i>Salmonella</i> to produce hydrogen sulfide (H₂S) was developed in this study. The effectiveness of the method was evaluated by comparing the antibacterial activity of copper to that of aluminum. <i>Salmonella</i> was inoculated over the entire surface of deoxycholate hydrogen sulfide lactose (DHL) agar plates that included Ammonium ferric citrate (C₆H₈FeN). Approximately 25 μL of cupric chloride (CuCl₂, 1% weight ratio) solution or aluminum chloride (AlCl₃, 1% weight ratio) solution was added to the center of the medium. The surface of the medium was covered with plastic PET (polyethylene terephthalate) material to induce an anaerobic state. <i>Salmonella</i> was cultured under anaerobic conditions at 310 K (37℃) for 86.4 ks (24 h). The antibacterial activity of copper was determined by observing the medium surface color change due to iron sulfide (FeS) formation, which was caused by the production of H₂S by <i>Salmonella</i>; blackness indicated presence of newly formed FeS. A quantitative evaluation of copper's antimicrobial activity was performed using a gradient of CuCl₂ concentrations; results were compared with those of the present standard method, Kirby-Bauer disk diffusion method on the Mueller Hinton medium. Finally, in order to evaluate the antibacterial activity of metals, <i>Salmonella</i> was inoculated on DHL agar plates. Subsequently, Japanese coins (1 yen, 5 yen, 10 yen, 50 yen, 100 yen and 500 yen coins) were placed on the agar and cultured at 310 K for 86 ks. <i>Salmonella</i> cultured in the presence of AlCl₃ produces black color, while no blackening is observed with CuCl₂, suggesting that copper possesses an antibacterial property against Salmonella. CuCl₂ suppresses H₂S production by Salmonella, as Cu²⁺ forms a transparent circle or ellipse (new halo) around the point at which CuCl₂ had has been plated. The size of the new halo increases in direct proportion to the concentration of CuCl₂. The halo is no longer visible at 0.034 mg of CuCl₂ in our method, while the halo disappears with 4.34 mg of CuCl₂ in the Kirby-Bauer method. Therefore, the present method is 129 times more sensitive than the standard method, suggesting increased usefulness and effectiveness in testing antibacterial activity. No FeS-dependent black circle is formed under any of the coins, with the exception of the 1-yen coin, which contains aluminum and no copper. Therefore, the copper-containing coins have an antibacterial effect.<br>

The alloy Ti-9Cr-0.20 has been developed as a potential material for implant rods used in spinal fixation applications, since it exhibits good mechanical properties and a remarkably "changeable Young's modulus", which is achieved by suppressing the athermal omega-phase formed upon quenching and enhancing the deformation-induced omega-phase transformation. In this study, athermal and deformation induced omega-phase transformations in Ti-9Cr-0.20 were investigated systematically by transmission electron microscopy. This was done in order to understand the nature of these omega-phase transformations, as well as the specific functionality the "changeable Young's modulus" resulting from them. In solution-treated alloy samples, in addition to ideal omega-structures, structures considered as initial omega-structures associated with incommensurate omega-phase were observed. This might be attributed to the composition heterogeneity, heterogeneity of oxygen distribution, and/or the inhomogeneous distribution of defects such as vacancies and locally strained areas. Following cold rolling, some of the selected area electron diffraction patterns of the alloy showed that the reflections of one omega-variant had increased significantly in intensity while those of the other omega-variant had decreased sharply. This vanishing of one type of variant omega-structures is attributable to two possible mechanisms: (i) a reversal mechanism, under which the particular < 111 > partial dislocations transform the corresponding omega-variants back into beta-phase or (ii) a re-orientation mechanism, according to which the omega-variants unfavorable with regard to the loading direction re-orient and turn into the preferred omega-variants. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Ti-12Cr has been developed for use in various biomedical applications, in particular; it is expected to be used for the rods of the spinal fixation devices. When Ti-12Cr is deformed, its Young's modulus increases because of deformation-induced ω phase transformation. If a spinal rod made of Ti-12Cr is bent during operation, only the Young's modulus of the bent region will increase; this phenomenon decreases the springback of the rod so that the bent shape is maintained. The compression fatigue strength of Ti-12Cr obtained from compression fatigue tests performed according to ASTM F1717 can be significantly improved by cavitation peening. Details of the development of this Ti-Cr alloy for use as spinal rods are discussed.

Proper surface characteristics for a titanium implant are crucial for the formation of different cellular protrusions known as filopodia and lamellipodia, both of which have a significant impact on cell attachment, spreading, migration, and proliferation. Microstructural features such as grain boundaries and defects of implant surface can modulate the cellular components and structure at the leading edge of cells. Here, a nano-grained Ti-29Nb-13Ta-4.6Zr (NG TNTZ) substrate was produced by high-pressure torsion (HPT) for improved biofunctionality. Cellular response of human osteoblast cells on nano-grained TNTZ substrates is evaluated and compared with the cellular response of those on coarse-grained TNTZ. High wettability, which depends on high internal energy due to the nano-sized grains that are full of boundaries, interfaces, and high dislocation density, influenced the hOBs cells on NG TNTZ to form highly developed cellular protrusions. Large number of filopodia protrusions resulted in excellent cell attachment as consistent with high level of vinculin and superior cell proliferation. This study demonstrates the advantages of nanocrystalline surface modification using HPT for processingmetallic biomaterials that are proper for orthopedic implants.

A novel method for detecting antimicrobial activity using an innate property of the Salmonella bacteria, namely, the ability of Salmonella to produce hydrogen sulfide (H2S) was developed in this study. The validity of the method was evaluated by comparing the antibacterial activity of copper to that of aluminum. Salmonella was inoculated over the entire surface of deoxycholate hydrogen sulfide lactose (DHL) agar plates that included Ammonium ferric citrate (C6H8FeN). Approximately 25 mu L of cupric chloride (CuCl2, 1% weight ratio) solution or aluminum chloride (AlCl3, 1% weight ratio) solution was added to the center of the medium. The surface of the medium was covered with polyethylene terephthalate (PET) films to induce an anaerobic state. Salmonella was cultured under anaerobic conditions at 310 K (37 degrees C) for 86.4 ksec (24 h). The antibacterial activity of copper was determined by observing the medium surface color change due to iron sulfide (FeS) formation, which was caused by the production of H2S by Salmonella; blackness indicated presence of newly formed FeS. A quantitative evaluation of copper's antimicrobial activity was performed using a gradient of CuCl2 concentrations; results were compared with those of the present standard method, Kirby-Bauer disk diffusion method on the Mueller Hinton medium. Finally, in order to evaluate the antibacterial activity of metals, Salmonella was inoculated on DHL agar plates. Subsequently, Japanese coins (1-yen, 5-yen, 10-yen, 50-yen, 100-yen, and 500-yen coins) were placed on the agar and cultured at 310 K for 86 ksec. Salmonella cultured in the presence of AlCl3 produces black color, while no blackening is observed with CuCl2, suggesting that copper possesses an antibacterial property against Salmonella. CuCl2 suppresses H2S production by Salmonella, as copper ions form a transparent circle or ellipse (new halo) around the point at which CuCl2 had has been plated. The size of the new halo increases in direct proportion to the concentration of CuCl2. The halo is no longer visible at 0.034 mg of CuCl2 in our method, while the halo disappears with 4.34 mg of CuCl2 in the Kirby-Bauer test. Therefore, the present method is 129 times more sensitive than the standard method, suggesting increased usefulness and effectiveness in testing antibacterial activity. No FeS-dependent black circle is formed under any of the coins, with the exception of the 1-yen coin, which contains aluminum and no copper. Therefore, the copper-containing coins have an antibacterial effect.

The main target of this study is to optimize the microstructure and to achieve an optimization for the mechanical properties in a biomedical Co-Cr-Mo (CCM) alloy with the nominal composition of Co-28Cr-6Mo (mass%) subjected to high-pressure torsion (HPT) and subsequent short annealing. The gamma ->epsilon phase transformation and grain refinement occur in the CCM alloy subjected to HPT processing at an equivalent strain (epsilon(eq)) of 2.25 (CCMHPT). The HPT processing causes a decrease in the elongation due to the formation of an excessive amount of epsilon phase. For removal of the excessive amount of e phases, the CCMHPT was subjected to a short annealing (CCMHPTA). The effect of the short annealing temperature (1073 K, 1273 K, and 1473 K; annealing time was fixed at 0.3 ks) on CCMHPT was investigated. In addition, the effect of the length of duration for the short annealing (0.06 ks, 0.3 ks, and 0.6 ks;) for a fixed annealing temperature of 1273 K on CCMHPT was studied. CCMHPTA(1273 K) annealed for 0.3 ks shows a good optimization of mechanical properties that include high strength and large elongation owing to its ultra fine-grained microstructure, and removal of excessive e phases.

In recent years, metallic biomaterial applications have demanded a relatively low elastic modulus of around 30 GPa that is nearly equal to that of bone. However, in the case of spinal fixture applications, metallic materials with a relatively high Young's modulus are required to suppress spring-back by elastic and plastic deformation during implantation. Therefore, Young's modulus control by stress-induced transformation in a newly developed biomedical beta-type Ti-12Cr alloy, has been proposed by the present authors. However, the relationship between the microstructure and mechanical properties of Ti-12Cr has not been fully investigated up till now. Therefore, changes in the mechanical properties of Ti-12Cr were investigated through heat treatment and the fine particle bombarding process (FPB), which is a surface modification process used in this study. Peak aging of Ti-12Cr heated at 673 K showed for around 2.4 ks. The Vickers hardness of Ti-12Cr in the peak aging condition (PA) at 673 K was around 90% (HV 524) higher than that (HV 294) in the solutionized condition (ST). Meanwhile, both the 0.2% proof stress and tensile strength of Ti-12Cr in the PA at 673 K were also around 50% higher those in the ST. However, the ductility of Ti-12Cr in the PA at each temperature reduced significantly. Therefore, a solo-solution treatment was judged to be the optimal heat treatment for Ti-12Cr with an excellent combination of strength and ductility. The Vickers hardness and Young's modulus of as. solutionized Ti-12Cr subjected to FPB increased by around 40% and 70%, respectively, at the very edge of the specimen surface, as compared to those of the unprocessed sample. Furthermore, the fatigue strength of Ti-12Cr subjected to FPB increased by around 70 MPa. The bone contact ratio of Ti-12Cr rose slightly with an increase in the implantation period from 24 to 52 weeks.

In spinal fixation devices, the activity of the patient can cause fretting of the metal-to-metal contacts between the rod and plug, which may result in failures. In this study, compressive fatigue tests were conducted with rods made of Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) with oxygen contents of 0.06 mass% (06O) and 0.89 mass% (89O) and Ti-6Al-4V extra low interstitial alloy (Ti64) as comparison in both air and saline solution. The fatigue strength increases in the order of 06O < 89O < Ti64 in both air and saline solution. These results indicate that solid-solution strengthening by oxygen improves the fretting fatigue resistance of the TNTZ rod.

Ultrafine-grained materials often possess superior mechanical properties owing to their small grain size. The high-pressure torsion (IIPT) process is a severe plastic deformation method used to induce ultra-large strain and produce ultrafine grains. In this study, the grain refinement mechanisms in the Co-28Cr-6Mo (CCM) alloy, evolution of dislocation density as a result of HPT and its effects on mechanical properties were investigated. The dislocation density and subgrain diameter were also calculated by X-ray line profile analysis. The microstructure of the CCM alloy subjected to HPT processing (CCMHPT) was evaluated as a function of torsional rotation number, N and equivalent strain, epsilon(eq). Strain-induced gamma ->epsilon transformation in neighboring ultrafine grains is observed in CCMHPT processed at epsilon(eq) = 2.25 and epsilon(eq) = 4.5. Low-angle crystal rotation around the [110] fcc direction occurs in different locations in the same elongated grain neighboring ultrafine grains, which suggests the formation of low-angle grain boundaries in CCMHPT processed at epsilon(eq) = 2.25 and epsilon(eq) = 4.5. Two possible grain refinement mechanisms are proposed. The maximum dislocation densities, which are 2.8 x 10(16) m(-2) in gamma phase and 3.8 x 10(16) m(-2) in epsilon phase, and maximum subgrain diameters, which are 21.2 nm in gamma phase and 36 nm in epsilon phase, are achieved in CCMHPT processed at epsilon(eq) = 9. IIPT processing causes a substantial increase in the tensile strength and hardness owing to the grain refinement and a significant increase in the volume fraction of epsilon phase and dislocation density.

In previous studies, it has been concluded that volume losses (V-loss) of the Ti-29Nb-13Ta-4.6Zr (TNTZ) discs and balls are larger than those of the respective Ti-6Al-4V extra-low interstitial (Ti64) discs and balls, both in air and Ringer's solution. These results are related to severe subsurface deformation of TNTZ, which is caused by the lower resistance to plastic shearing of TNTZ than that of Ti64. Therefore, it is necessary to further increase the wear resistance of TNTZ to satisfy the requirements as a biomedical implant. From this viewpoint, interstitial oxygen was added to TNTZ to improve the plastic shear resistance via solid-solution strengthening. Thus, the wear behaviors of combinations comprised of a new titanium alloy, TNTZ with high oxygen content of 0.89 mass% (890) and a conventional titanium alloy, Ti64 were investigated in air and Ringer's solution for biomedical implant applications. The worn surfaces, wear debris, and subsurface damage were analyzed using a scanning electron microscopy and an electron probe microanalysis. V-loss of the 890 discs and balls are smaller than those of the respective TNTZ discs and balls in both air and Ringer's solution. It can be concluded that the solid-solution strengthening by oxygen effectively improves the wear resistance for TNTZ materials. However, the 890 disc/ball combination still exhibits higher V-loss than the Ti64 disc./ball combination in both air and Ringer's solution. Moreover, V-loss of the disc for the 890 disc/Ti64 ball combination significantly decreases in Ringer's solution compared to that in air. This decrease for the 890 disc./Ti64 ball combination in Ringer's solution can be explained by the transition in the wear mechanism from severe delamination wear to abrasive wear. (C) 2015 Elsevier Ltd. All rights reserved.

The microstructures, mechanical properties and biocompatibility of low cost beta-type Ti-(6-18)Mn alloys were investigated after solution treatment. Ti-9Mn exhibits the best combination of tensile strength and elongation among the fabricated alloys, and its performance is comparable to or superior to those of Ti-6Al-4V ELI (Ti-64 ELI) in terms of every parameter evaluated. A hardness of 338 HV, a Young's modulus of 94 GPa, a 0.2% proof stress of 1023 MPa, an ultimate tensile strength of 1048 MPa and elongation of 19% were obtained for Ti-9Mn. Furthermore, the cell viability and metallic ion release ratios are comparable to those of commercially pure titanium, making this alloy promising for biomedical applications. The Young's modulus is also lower than that of Ti-64 ELI (110 GPa), which can possibly reduce the stress shielding effect in implanted patients. Statement of significance This study evaluates mechanical and biological performance of low cost solution treated beta-type Ti-(6, 9, 13 and 18 mass%)Mn alloys. It includes alloys containing a Mn content range higher than most previously published works (which is around or lower than 8 mass%). Furthermore, the effects of the omega phase and the beta phase stability of the alloys over some mechanical properties and microstructures are discussed. Ion release behavior under simulated body fluids and cell viability are also evaluated. For the case of the Ti-9Mn, a mechanical and biological performance that is comparable to or superior than that of the widely used Ti-6Al-4V ELI and commercially pure Ti was observed. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The adhesive strengths between sol-gel fabricated hydroxyapatite (HAp) films and Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) were evaluated before and after immersion in Ringer's solution at 310K for 7 d. The effect of the surface morphology of TNTZ on the adhesion of HAp films was also investigated. The fracture surfaces after adhesion tests were observed and fracture areas at the interface between HAp films and TNTZ were also evaluated before and after immersion in Ringer's solution. No significant differences in the adhesive strengths between HAp films and TNTZ disks with mirror-polished and mechanically polished surfaces were found. The fracture area at the interface between HAp film and mirror-polished TNTZ disk increases after immersion in Ringer's solution, whereas no fracture occurs at the interface between HAp film and mechanically polished TNTZ disk before and after immersion in Ringer's solution. It is supposed that Ringer's solution penetrates along the cracks that are formed in the HAp films during calcination and the regions with weak adhesion between HAp and TNTZ are connected during immersion in Ringer's solution in the case of HAp films fabricated on mirror-polished TNTZ. From these results, it is found that a relatively rougher surface is effective in improving the adhesion of HAp films fabricated on TNTZ before and after immersion in Ringer's solution.

To evaluate the long-term mechanical biocompatibility of Ti-Mn alloys, the microstructures, Young's moduli, and tensile and fatigue properties of the solutionized Ti-8Mn and Ti-13Mn were investigated. In addition, to evaluate the long-term biological biocompatibility of Ti-Mn alloys, the bone formability of the solutionized Ti-12Mn implant was evaluated by animal testing. The solutionized Ti-8Mn and Ti-13Mn consist of equiaxed P-grains with diameters of approximately 420 m and 430 pm, respectively. Moreover, the solutionized Ti-8Mn also contains an athermal < a phase. The 0.2 % proof stress (σ0.2), tensile strength (σb), and elongation of the solutionized Ti-8Mn are 1148 MPa, 1184 MPa, and 2%, respectively. The σ0.2 and σb decrease to 915 MPa and 953 MPa, respectively, and the elongation increases to 7% for the solutionized Ti-13Mn. The higher strength and significantly lower elongation of the solutionized Ti-8Mn are attributed to precipitation of an athermal ω phase. The fatigue strength of the solutionized Ti-8Mn is comparable to that of the aged Ti-6Al-4V ELI in the low-cycle fatigue life region. The striation widths of the solutionized Ti-8Mn and Ti-13Mn are 2.4 m and 7.8 m, respectively. The smaller striation width of the solutionized Ti-8Mn indicates that the crack propagation rate in the solutionized Ti-8Mn is smaller than that in the solutionized Ti-13Mn. The relative bone contact ratio of the solutionized Ti-12Mn increases from 11% to 29% when the implant period increases from 12 to 52 weeks. The relative bone contact ratios of the solutionized Ti-12Mn implant and the commercially pure Ti implant are almost identical for all implantation periods.

Along with a high strength, ductility, and work hardening rate, a variable Young's modulus is crucial for materials used as implant rods in spinal fixation surgery. The potential in this context of Ti-(9, 8, 7)Cr-0.2O (mass%) alloys is reported herein. The microstructural and mechanical properties of the alloys were systematically examined as a function of their chromium content, and the ion release of the optimized alloy was investigated to assess its suitability as an implant material. In terms of the deformation-induced omega-phase transformation required for a variable Young's modulus, the balance between beta-phase stability and athermal omega-phase content is most favorable in the Ti-9Cr-0.2O alloy. In addition, this composition affords a high tensile strength (>1000 MPa), elongation at break (similar to 20%), and work hardening rate to solution-treated (ST) samples. These excellent properties are attributed to the combined effects of deformation-induced omega-phase transformation, deformation twinning, and dislocation gliding. Furthermore, the ST Ti-9Cr-0.2O alloy proves resistant to metal ion release in simulated body fluid. This combination of a good biocompatibility, variable Young's modulus and a high strength, ductility, and work hardening rate is ideal for spinal fixation applications. Statement of significance Extensive efforts have been devoted over the past decades to developing beta-type titanium alloys with low Young's moduli for biomedical applications. In spinal fixation surgery however, along with excellent mechanical properties, the spinal-support materials should possess high Young's modulus for showing small springback during surgery to facilitate manipulation but low Young's modulus close to bone once implanted to avoid stress shielding. None of currently used metallic biomaterials can satisfy these above-mentioned requirements. In the present study, we have developed a novel alloy, Ti-9Cr-0.2O. Remarkably variable Young's modulus and excellent mechanical properties can be achieved in this alloy via phase transformations and complex deformation mechanisms, which makes the Ti-9Cr-0.2O preferred material for spinal fixation surgery. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

This study investigates the effect of heterogeneous precipitation induced by the segregation of substitutional and interstitial elements in Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) on its mechanical properties. For this, samples both with and without segregation of substitutional elements were prepared, with only the latter being subjected to long-term homogenization. It was found that micro-scale segregation of substitutional elements such as Nb, Ta, and Zr does not significantly affect mechanical properties such as fatigue strength, not even if heterogeneous precipitation occurs as a result of this segregation. On the other hand, segregation of interstitial elements was achieved by controlling the aging time. The segregation of interstitial elements creates precipitate-free zones (PFZs), grain boundary (GB) plates, and Widmanstatten alpha phases with migrating O atoms that all significantly affect the mechanical properties. Specifically, the PFZs have the potential to improve fatigue life, while the Widmanstatten alpha phase increases the tensile strength and reduces the fatigue ratio, the GB-plates reduce elongation, These results indicate that the formation of a Widmanstatten alpha phase by the migration of interstitial elements has a varying influence on the tensile and fatigue properties. 0 2015 Elsevier B.V. All rights reserved.

Ti-xMg (x = 17, 33, and 55 mass%) alloy films, which cannot be prepared by conventional melting processes owing to the absence of a solid-solution phase in the phase diagram, were prepared by direct current magnetron sputtering in order to investigate their biocompatibility. Ti and Mg films were also prepared by the same process for comparison. The crystal structures were examined by X-ray diffraction (XRD) analysis and the surfaces were analyzed by X-ray photoelectron spectroscopy. The Ti, Ti-xMg alloy, and Mg films were immersed in a 0.9% NaCl solution at 310 K for 7 d to evaluate the dissolution amounts of Ti and Mg. In addition, to evaluate the formation ability of calcium phosphate in vitro, the Ti, Ti-xMg alloy, and Mg films were immersed in Hanks' solution at 310 K for 30 d. Ti and Mg form solid-solution alloys because the peaks attributed to pure Ti and Mg do not appear in the XRD patterns of any of the Ti-xMg alloy films. The surfaces of the Ti-17Mg alloy and Ti-33Mg alloy films contain Ti oxides and MgO, whereas MgO is the main component of the surface oxide of the Ti-55Mg alloy and Mg films. The dissolution amounts of Ti from all films are below or near the detection limit of inductively coupled plasma-optical emission spectroscopy. On the other hand, the Ti-17Mg alloy, Ti-33Mg alloy, Ti-55Mg alloy, and Mg films exhibit Mg dissolution amounts of approximately 2.5, 1.4, 21, and 41 mu g/cm(2), respectively. The diffraction peaks attributed to calcium phosphate are present in the XRD patterns of the Ti-33Mg alloy, Ti-55Mg alloy, and Mg films after the inimersion in Hanks' solution. Spherical calcium phosphate particles precipitate on the surface of the Ti-33Mg film. However, many cracks are observed in the Ti-55Mg film, and delamination of the film occurs after the immersion in Flanks' solution. The Mg film is dissolved in Flanks' solution and calcium phosphate particles precipitate on the glass substrate. Consequently, it is revealed that the Ti-33Mg alloy film evaluated in this study is suitable for biomedical applications. (C) 2015 Elsevier B.V. All tights reserved.

A beta-type Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy containing various amounts of TiB reinforcements has been developed to achieve higher fatigue strength for biomedical applications. Fatigue tests were performed at room temperature, and the effects of TiB on fatigue crack initiation and propagation were investigated. The results indicate that the fatigue limit of the TNTZ alloy was substantially improved by the TiB reinforcements. However, the fatigue strength first increased and subsequently decreased as the B concentration increased. TNTZ alloy with 0.10% B has the largest fatigue limit, which is 67% greater than that of the TNTZ alloy. The effects of TiB on the improvement of the fatigue properties are due to the following two factors. First, sliding of the dislocations can be blocked by TiB particles, which results in resistance to fatigue crack initiation. In addition, the crack deflection and crack bridging by the TiB particles could delay the crack propagation. Conversely, debonding of some larger TiB particles may occur, especially when the B concentration is higher than 0.20%. Therefore, the crack initiates from the debonding of the TiB particles and easily propagates along the voids from the interfacial decohesion, which could exert a deleterious influence on the fatigue strength. (C) 2015 Elsevier B.V. All rights reserved.

Metal-organic chemical vapour deposition was used to fabricate hydroxyapatite (HAp) and alpha-tricalcium phosphate coatings on the surface of representative biomedical titanium alloys: Ti-29Nb-13Ta-4.6Zr, commercially pure Ti, and Ti-6Al-4V ELI. The effect of the substrate surface roughness, alloy composition and precursor temperature was investigated in relation to the type of calcium phosphate formed and the morphology and thickness of the HAp coating. The surface roughness of substrates mechanically polished by SiC paper was found to vary depending on the type of alloy, whereas the roughness of substrates buff polished using a colloidal SiO2 suspension was comparable. The type of calcium phosphate formed could be controlled by the precursor temperature. A coarse, granular microstructure was observed on the surface of the thicker HAp coatings formed on the rough polished substrates, while the thinner HAp coatings formed on the smooth polished substrates had a relatively dense and fine grained microstructure.

Ag-Pd-Au-Zn alloys are frequently strengthened by an aging treatment after an initial solution treatment. However, Ag-Pd-Au-Zn alloys can be significantly strengthened by solution treatment alone. This phenomenon is unique, as the strength of metallic materials is generally decreased by solution treatment because of the precipitates dissolving into the surrounding matrix. Among the Ag-Pd-Au-Zn alloys, Ag-20Pd-12Au-14.5Cu alloy (in mass %) is the standard compositional alloy used for practical applications. The main source of the solution-treated Ag-20Pd-12Au-14.5Cu alloy strengthening was expected to be a beta' phase formation during the cooling process from the solution treatment's high temperature; this is clarified by changing the solution heat treatment and aging treatment conditions of using as-received wrought Ag-20Pd-12Au-14.5Cu alloy and liquid rapid solidified Ag-20Pd-12Au-14.5Cu alloy.

Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy has been extensively studied as it is promising for use in biomedical applications. Despite its potential, the effects of warm plastic deformation on the alloy have not yet been revealed. This study investigated the differences in phase constitution of two warm-deformed TNTZ alloys and revealed relevant mechanisms with particular attention to martensitic transformation. The influence of phase constituents on mechanical characteristics was discussed as well. The TNTZ alloy deformed at 823 K possessed alpha, beta, and omega phases as well as alpha '' martensite, and demonstrated a low Young's modulus and double-yielding phenomenon. In contrast, the alloy deformed at 723 K had no martensite but more omega phase, leading to increased strength, hardness, and Young's modulus. The absence of alpha '' martensite in the alloy deformed at 723 K was interpreted in light of beta-stability of the parent phase and reduced M-s temperature.

The predominant factor determining the wear properties of a new titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ) and a conventional titanium alloy, Ti-6Al-4V extra-low interstitial (Ti64) was investigated for TNTZ and Ti64 combinations in metal-to-metal contacting bioimplant applications. The worn surfaces, wear debris, and subsurface damages were analyzed using a scanning electron microscopy combined with energy-dispersive spectroscopy and electron-back scattered diffraction analysis. The volume loss of TNTZ is found to be larger than that of Ti64, regardless of the mating material. The wear track of TNTZ exhibits the galled regions and severe plastic deformation with large flake-like debris, indicative of delamination wear, which strongly suggests the occurrence of adhesive wear. Whereas, the wear track of Ti64 have a large number of regular grooves and microcuttings with cutting chip-like wear debris and microfragmentation of fine oxide debris, indicative of abrasive wear combined with oxidative wear. This difference in the wear type is caused by severe and mild subsurface deformations of TNTZ and Ti64, respectively. The lower resistance to plastic shearing for TNTZ compared to that of Ti64 induces delamination, resulting in a higher wear rate. (C) 2014 Elsevier Ltd. All rights reserved.

The wear behaviors of combinations comprised of a new titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ) and a conventional titanium alloy, Ti-6Al-4Vextra-low interstitial (Ti64) were investigated using ball-on-disc type configuration in Ringer's solution for metal-to-metal contacting biomedical implant applications. The worn surfaces, wear debris, and subsurface damage were analyzed using a scanning electron microscopy combined with energy-dispersive spectroscopy and an electron probe microanalysis. Moreover theses wear characteristics are compared to the results obtained from the wear tests in air. Volume loss of both the disc and ball primarily increases for the TNTZ disc/TNTZ ball combination in Ringer's solution compared to that in air. This increase can be explained by the ejection of debris from the contact region induced by the presence of Ringer's solution. Subsequently, this increases the number of areas with asperity junctions between the disc and ball, thereby leading to severe delamination wear. In contrast, the volume loss of both the disc and ball decrease for the Ti64 disc/Ti64 ball combination in Ringer's solution compared to that in air. It is believed that the predominately abrasive wear associated with Ti64 is effectively suppressed by the use of Ringer's solution.

The new p-type Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy containing trace amounts of CeO2 additions has been designed as a biomedical implant with improved fatigue properties achieved by keeping Young's modulus to a low value. The results show that the microstructure is refined by the addition of CeO2; the p grain size becomes a little larger when Ce content increases from 0.05% to 0.10%. This occurs because dispersed CeO2 particles can act as nucleation sites for p grains; thus, the effect of rare earth oxides on microstructure refinement mainly depends on the size and dispersion of the rare earth oxides. Young's moduli of TNTZ with CeO(2)additions are maintained as low as those of TNTZ without CeO2, while the fatigue limit is highly improved. The 0.10% Ce alloy exhibits the best fatigue strength among the experimental alloys; its fatigue strength is increased by 66.7% compared to that of pure TNTZ. The mechanism by which rare earth oxides affect fatigue performance is dominated by dispersion strengthening. The stiff rare earth oxides can hinder the movement of dislocations, resulting in resistance to the formation of fatigue cracks. Rare earth oxides also change the crack propagation direction and the crack propagation route, effectively decreasing the crack propagation rate. (C) 2014 Elsevier B.V. All rights reserved.

In order to elucidate the microstructural refinement mechanism and the effect of secondary phase on the microstructural evolution of beta-type titanium alloy, severe plastic deformation was conducted on samples of a precipitation-hardened Ti-29Nb-13Ta-4.6Zr (TNTZ). Specifically, TNTZ that was precipitation-hardened through an aging treatment (TNTZAT) was subjected to high-pressure torsion (HPT) processing (TNTZ(AHPT)). The microstructure of TNTZ(AHPT), which has been evaluated as a function of the torsional rotation number, N, exhibits ultrafine elongated beta grains. The needle-like alpha precipitates in TNTZ(AT), which exhibit a diameter of approximately 12 nm, are homogeneously distributed within the beta grains. The dislocation density and subgrain diameter, estimated by X-ray line profile analysis, saturate at approximately 4.2 x 10(16) m(-2) and 12.2 nm, respectively, at N >= 10. The beta grains contain nanostructured subgrains having non-uniform morphologies surrounded by blurred and wavy boundaries. A saturated hardness distribution at approximately 450 HV indicates that microstructural homogeneity has been achieved at N >= 10. The alpha precipitates enhance the beta grain refinement and microstructural homogeneity is achieved in TNTZ(AHPT) at N >= 10, whereas this occurs at later stages (N > 20) in TNTZ which is solution-treated and therefore does not contain any alpha precipitates. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Ag-Pd-Au-Cu alloys have been used widely for dental prosthetic applications. Significant enhancement of the mechanical properties of the Ag-20Pd-12Au-14.5Cu alloy as a result of the precipitation of the beta' phase through high-temperature solution treatment (ST), which is different from conventional aging treatment in these alloys, has been reported. The relationship between the unique hardening behavior and precipitation of the beta' phase in Ag-20Pd-12Au-xCu alloys (x=6.5, 13, 14.5, 17, and 20 mass%) subjected to the high-temperature ST at 1123 K for 3.6 ks was investigated in this study. Unique hardening behavior after the high-temperature ST also occurs in Ag-20Pd-12Au-xCu alloys (x=13, 17, and 20) with precipitation of the beta' phase. However, hardening is not observed and the beta' phase does not precipitate in the Ag-20Pd-12Au-6.5Cu alloy after the same ST. The tensile strength and 0.2% proof stress also increase in Ag-20Pd-12Au-xCu alloys (x=13, 14.5, 17, and 20) after the high-temperature ST. In addition, these values after the high-temperature ST increase with increasing Cu content in Ag-20Pd-12Au-xCu alloys (x=14.5, 17, and 20). The formation process of the beta' phase can be explained in terms of diffusion of Ag and Cu atoms and precipitation of the beta' phase. Clarification of the relationship between hardening and precipitation of the beta' phase via high-temperature ST is expected to help the development of more effective heat treatments for hardening in Ag-20Pd-12Au-xCu alloys. (C) 2014 Elsevier Ltd. All rights reserved.

Materials used for implant rods in spinal fixation systems must show changeable Young's moduli, high strength and large elongation-to-failure. A d-electron design method was used to determine the chemical composition of Ti-10Cr, which showed all these properties and significant work-hardening characteristics owing to multiple plastic deformation mechanisms, such as deformationinduced omega-phase transformation, {3 3 2}<1 1 3> mechanical twinning and dislocation gliding. Therefore, Ti-10Cr exhibits great potential for use in spinal fixation applications. (c) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The springback behavior of Ti-12Cr and Ti-29Nb-13Ta-4.6Zr (TNTZ) during deformation by bending was investigated; and the microstructures of the non-deformed and deformed parts of both alloys were systematically examined to clarify the relationship between microstructure and springback behavior. For the deformed Ti-12Cr alloy, deformation-induced omega-phase transformation occurs in both the areas of compression and tension within the deformed part, which increases the Young's modulus. With the deformed TNTZ alloy, deformation-induced omega-phase transformation is observed in the area of compression within the deformed part; while a deformation-induced alpha '' martensite transformation occurs in the area under tension, which is likely to be associated with the pseudoelasticity of TNTZ. Among these two alloys, Ti-12Cr exhibits a smaller springback and a much greater bending strength when compared with TNTZ; making Ti-12Cr the more advantageous for spinal fixation applications. (C) 2014 Elsevier Ltd. All rights reserved.

Dental Ag-20Pd-12Au-14.5Cu alloys exhibit a unique hardening behavior, which the mechanical strengths enhance significantly which enhances the mechanical strength significantly after high-temperature (1123 K) solution treatment without aging treatment. The mechanism of the unique hardening is not clear. The contribution of two precipitates (beta' and beta phases) to the unique hardening behavior in the as-solutionized Ag-20Pd-12Au-14.5Cu alloys was investigated. In addition, the chemical composition of the beta' phase was investigated. The fine beta' phase densely precipitates in a matrix. The beta' phase (semi-coherent precipitate), which causes lattice strain, contributes greatly to the unique hardening behavior. On the other hand, the coarse beta phase sparsely precipitates in the matrix. The contribution of the beta phase (incoherent precipitate), which does not cause lattice strain, is small. The chemical composition of the beta' phase was determined. This study reveals that the fine beta' phase precipitated by high-temperature solution treatment leads to the unique hardening behavior in dental Ag-20Pd-12Au-14.5Cu alloys in the viewpoints of the lattice strain contrast and interface coherency. It is expected to make the heat treatment process more practical for hardening. The determined chemical composition of beta' phase would be helpful to study an unknown formation process of beta' phase. (C) 2014 Elsevier B.V. All rights reserved.

Anodic oxide nanostructures (nanopores and nanotubes) were fabricated on a biomedical beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ), by anodization in order to improve the adhesive strength of a medical polymer, segmented polyurethane (SPU), to TNTZ. TNTZ was anodized in 1.0 M H3PO4 solution with 0.5 mass% NaF using a direct-current power supply at a voltage of 20 V. A nanoporous structure is formed on TNTZ in the first stage of anodization, and the formation of a nanotube structure occurs subsequently beneath the nanoporous structure. The nanostructures formed on TNTZ by anodization for less than 3600 s exhibit higher adhesive strengths than those formed at longer anodization times. The adhesive strength of the SPU coating on the nanoporous structure formed on top of TNTZ by anodization for 1200 s improves by 144% compared to that of the SPU coating on as-polished TNTZ with a mirror surface. The adhesive strength of the SPU coating on the nanotube structure formed on TNTZ by anodization for 3600 s increases by 50%. These improvements in the adhesive strength of SPU are the result of an anchor effect introduced by the nanostructures formed by anodization. Fracture occurs at the interface of the nanoporous structure and the SPU coating layer. In contrast, in the case that SPU coating has been performed on the nanotube structure, fracture occurs inside the nanotubes. (C) 2013 Elsevier B.V. All rights reserved.

The age-hardening behavior of the dental-casting Ag-20Pd-12Au-14.5Cu alloy subjected to aging treatment at around 673 K is well known, and this hardening has been widely employed in various applications. To date, the age-hardening of this alloy has been explained to attribute to the precipitation of a beta phase, which is a B2-type ordered CuPd phase or PdCuxZn1-x phase. In this study, results obtained from microstructural observations using a transmission electron microscopy and a scanning transmission electron microscopy revealed that a fine L1(0)-type ordered beta' phase precipitated in the matrix and a coarse-structure region (consisting of Ag- and Cu-rich regions) appeared after aging treatment at 673 K and contributed to increase in hardness. The microstructure of the coarse beta phase, which existed before aging treatment, did not change by aging treatment. Thus, it is concluded that the fine beta' phase precipitated by aging treatment contributed more to increase in hardness than the coarse-structure region and coarse beta phase. (C) 2013 Elsevier B.V. All rights reserved.

In order to meet the requirements of the patients and surgeons simultaneously for spinal fixation applications, a novel biomedical alloy with a changeable Young's modulus, that is, with a low Young's modulus to prevent the stress-shielding effect for patients and a high Young's modulus to suppress springback for surgeons, was developed. In this study, the chromium and oxygen contents in ternary Ti(11, 12 mass%)Cr-(0.2, 0.4, 0.6 mass%)0 alloys were optimized in order to achieve a changeable Young's modulus via deformation-induced omega-phase transformation with good mechanical properties. The Young's moduli of all the examined alloys increase after cold rolling, which is attributed to the deformation-induced (omega-phase transformation. This transformation is suppressed by oxygen but enhanced with lower chromium content, which is related to the beta(bcc)-lattice stability. Among the examined alloys, the Ti-11Cr-0.2O alloy shows a low Young's modulus of less than 80 GPa in the solution-treated (ST) condition and a high Young's modulus of more than 90 GPa in the cold rolled (CR) condition. The Ti-11Cr-0.2O alloy also exhibits a high tensile strength, above 1000 MPa, with an acceptable elongation of similar to 12% in the ST condition. Furthermore, the Ti-11Cr-0.2O alloy exhibits minimal springback. This value of springback is the closest to that of Ti64 ELI alloy among the compared alloys. Therefore, the Ti-11Cr-0.2O alloy, which has a good balance between large changeable Young's modulus, high tensile strength, good plasticity, and minimal springback, is considered to be a potential candidate for spinal fixation applications. (C) 2013 Elsevier Ltd. All rights reserved.

Newly developed low-modulus beta-type titanium alloys such as Ti-29Nb-13Ta-4.6Zr (TNTZ) and Ti-Cr alloys are expected to be used for rods in spinal fixation devices. As the endurance, i.e., fatigue strength, is one of the most important factors for this application. Various types of fatigue strengths of TNTZ and Ti-Cr alloys as well as their developments were investigated. Compared to conventional Ti-6Al-4V extra low interstitials (ELI) for biomedical applications the uni-axial fatigue strength of TNTZ is increased significantly by thermomechanical processing, which includes solution treatment, severe cold swaging or rolling, and followed by aging treatment. The uni-axial fatigue strength of Ti-12Cr is significantly higher compared to that of Ti-6Al-4V ELI. The four point bending fatigue strengths of the alloys exhibit opposite trends.

Ti-4.5Al-2.5Cr-1.2Fe-0.1C referred to as KS Ti-531C is a newly developed low cost titanium alloy for use in next-generation aircrafts by adding inexpensive elements such as C, Fe, Al and Cr. There is a possibility for the formation of TiCr and/or TiCr2 after a long heat treatment or welding. Therefore, relationships between the microstructures and fatigue properties of KS Ti-531C subjected to several heat treatments as well as laser welding were investigated systematically. The results showed that the fatigue strength of laser-welded KS Ti-531C was lower than that of non-laser welded KS Ti-531C.

A biomedical beta-type titanium, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ), exhibits good biological and mechanical biocompatibilities due to containing non-toxic elements and lower Young's modulus than that of a conventional (alpha+beta)-type titanium alloy, Ti-6Al-4V ELI alloy (Ti64). One of the expected applications for TNTZ is spinal fixation applications. However, screws and rods are contacted each other in this kind of application, while titanium alloys generally exhibit poor wear resistance. Therefore, the wear characteristics of TNTZ and Ti64 were investigated in this study. Balls and discs made of TNTZ and Ti64 were prepared for a ball-on-disc wear test. As the results of microstructural analysis, it was found that the morphologies of wear tracks and debris of TNTZ are different from those of Ti64 because different wear mechanism is predominant in each alloy.

Mechanical biocompatibility, including tensile properties and Young's modulus, of β-type Ti-Mn alloys, namely, Ti-10Mn and Ti-14Mn, fabricated by the metal injection molding method were investigated. The bone formability (biological biocompatibility) of a Ti-Mn alloy, namely, Ti-12Mn, fabricated by the arc-melting method was evaluated by means of an animal test. The tensile strength of sintered Ti-10Mn and Ti-14Mn achieve a maximum value of 860 and 886 MPa, respectively. The Ti-14Mn specimen sintered at 1273 K shows the lowest Young's modulus (76 GPa) among all sintered Ti-10Mn and Ti-14Mn specimens. The tensile strength of Ti-Mn alloys is almost equal to that of Ti64 ELI; further, their Young's modulus is lower than that of Ti-6Al-4V ELI. The relative bone contact ratio of Ti-12Mn increases from 11% to 29% with increasing implantation time from 12 weeks to 52 weeks. Moreover, the relative bone contact ratio of Ti-12Mn and CP-Ti is almost constant for all implantation times. © (2014) Trans Tech Publications, Switzerland.

Ti-29Nb-13Ta-4.6Zr (TNTZ) is a novel beta-type titanium alloy that has great potential use in biomedical implants because of its relatively low Young's modulus (around 60 GPa), which minimise bone atrophy due to stress shielding. However, the biocompatibility and bio-functionality of TNTZ is poor. Therefore, a bioactive ceramic surface modification or soft-tissue-compatible polymer surface modification is advantageous for enhancing the biological properties of TNTZ. The bio-functionality of TNTZ itself, and that modified with a coating hydroxyapatite (HAp) using alkali treatment, electrochemical treatment, and dip-coating treatment with calcium phosphate glass ceramic or metal organic chemical vapour deposition (MOCVD) is assessed. In addition, modification of TNTZ with soft-tissue-compatible segmented polyurethane (SPU) using different silane coupling agents is described. The bonding strength of the bioactive ceramic and soft-tissue compatible polymer with the TNTZ is assessed with respect to variations in surface roughness.

A novel beta-type titanium alloy with a changeable Young's modulus, that is, with a low Young's modulus to prevent the stress-shielding effect for patients and a high Young's modulus to suppress springback for surgeons, should be developed in order to satisfy the conflicting requirements of both the patients and surgeons in spinal fixation operations. In this study, the oxygen content in ternary Ti-11Cr-O alloys was optimized in order to achieve a large changeable Young's modulus with good mechanical properties for spinal fixation applications. The increase in Young's moduli of all the examined alloys by cold rolling is attributed to the deformation-induced omega-phase transformation which is suppressed by oxygen. Among the examined alloys, the Ti-11Cr-0.2O alloy exhibits the largest changeable Young's modulus and a high tensile strength with an acceptable plasticity under both solution-treated (ST) and cold-rolled (CR) conditions. Therefore, the Ti-11Cr-0.2O alloy, which shows a good balance among a changeable Young's modulus, high tensile strength and good plasticity, is considered a potential candidate for spinal fixation applications.

The fatigue strength of the newly developed beta-type titanium alloy Ti-29Nb-13Ta-4.6Zr (referred to as TNTZ) is important for its applications in spinal fixation rods. Enhancements in the fatigue strength of TNTZ upon solution treatmnet and thermo-mechanical processing (aging after severe cold-caliber rolling or sever cold-swaging) have been investigated. Aging the rods at 723 K for 259.2 ks after cold-swaging is shown to be the optimal thermo-mechanical processing method for the TNTZ rod, yeilding a high 0.2% proof stress of about 1200 MPa, high elongation of 18%, and high fatigue strength of 950 MPa. High springback is undesirable for application of TNTZ spinal-fixation rods. To reduce springback, a High Young's modulus is required; on the other hand, a low Young's modulus is beneficial to reduce bone absorption and obtain good bone remodeling. To achieve a balance between these two factors, TNTZ has been modified by adding Cr to obtain an alloy with a high Young's modulus at the deformed region and a low Young's modulus throughout the undeformed region. TNTZ-8Ti-2Cr and TNTZ-16Ti-4Cr are novel alloys whose beta phase is more stable than that of TNTZ. Only the beta phase is present in these alloys, which exhibit relatively low Young's moduli of <65 GPa after solution treatment, and higher Young's moduli after cold rolling, owing to a deformation-induced omega-phase transformation. These modified TNTZ alloys show significantly less springback than the original TNTZ, based on tensile and loading unloading bending tests.

A novel beta-type, Ti-29Nb-13Ta-4.6Zr, referred to as TNTZ has been developed for biomedical applications. Its fatigue strength is one of the most important mechanical biocompatibilities of TNTZ because, in surgical applications, it will be used under cyclic loading conditions. The effect of the microstructural refinement by high-pressure torsion (HPT) on the fatigue behaviour of TNTZ is systematically investigated in this study. TNTZ subjected to HPT processing where the rotation number (N) is 20 (TNTZ(AHPT)) after aging treatment (AT) shows a unique microstructure having ultrafine elongated grains (285 nm in length and 36 nm in width) with high-density dislocations, a large fraction of blurred and wavy boundaries consisting of non-uniform subgrains with high misorientation and nanostructured precipitated alpha phase. Remarkably, a good combination of high mechanical strength (1375 MPa) and low Young's modulus (87 GPa), compared to that of Ti-6Al-4V (Ti64) ELI, is achieved for TNTZ(AHPT) at N = 20. TNTZ(AHPT) a great fatigue strength, which is comparable to those of (Ti64) ELI.

The wear mechanisms of conventional Ti-6Al-4V extra-low interstitial (Ti64) and the new Ti-29Nb-13Ta-4.6Zr (TNTZ) were studied to investigate the wear properties of Ti64/TNTZ for application in spinal fixation devices. Ti64 and TNTZ balls and discs were first prepared as wear-test specimens. A ball-on-disc frictional wear-testing machine was used in air to perform the frictional wear tests of the Ti64 and TNTZ discs mated against Ti64 and TNTZ balls. The wear mechanisms were investigated using a scanning electron microscopy to analyze the worn surfaces and wear debris. The volume losses for the TNTZ discs were larger than those for the Ti64 ones, regardless of the mating ball material. Furthermore, the morphologies of the wear tracks and the debris of the Ti64 and TNTZ discs were different, suggesting that the wear mechanisms for the Ti64 and TNTZ discs were abrasive and delamination wear caused by mild and severe subsurface deformations of the Ti64 and TNTZ, respectively, regardless of the mating ball material.

The effect of high-pressure torsion (HPT) processing on the microstructure and Vickers hardness of Co-Cr-Mo (CCM) alloys were investigated in this study. The microstructure of initial CCM alloy contains equiaxed grains with a grain diameter of approximately 50 mu m and twins. The clear grain boundaries of equiaxed grains and twins disappear after HPT processing at a rotation number, N, of 10. The phase maps of initial CCM alloy and CCM alloy subjected to HPT processing at N = 5 measured by electron backscatter diffraction exhibit that the ratio of. phase decreases from 93.5% to 34.1% and the ratio of e phase increases from 6.5% to 65.9% by applying HPT processing. These results indicate that the e phase is formed by high-strain, which is induced by the HPT processing. The Vickers hardness values on the surfaces of the CCM alloys subjected to HPT processing at N = 1, 5, and 10 increase with increasing the equivalent strain, epsilon(eq). These results suggest that an increase of Vickers hardness is correlated to an increase of the ratio of epsilon phase and the dislocation density, and grain refinement, which are caused by the high-strain induced by HPT processing.

The wear mechanisms of a conventional titanium alloy, Ti-6Al-4V extra-low interstitial (Ti64), and a new titanium alloy, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) were studied to investigate the wear properties of a Ti64/TNTZ combination for spinal fixation devices. Balls and discs made of Ti64 and TNTZ were prepared to be used as wear-test specimens. Frictional wear tests of Ti64 and TNTZ discs were carried out against Ti64 and TNTZ balls in air using a ball-on-disc frictional wear testing system. The wear mechanisms were investigated by analysis of worn surfaces and wear debris using scanning electron microscopy. Volume losses of the TNTZ discs were found to be larger than those of the Ti64 discs, regardless of mating ball. Furthermore, the morphologies of wear tracks and debris were found to be different between TNTZ and Ti64 discs. It is considered that the wear mechanism for a Ti64 disc is oxidative wear, whereas that for a TNTZ disc is delamination wear, regardless of mating ball material. © (2014) Trans Tech Publications, Switzerland.

A novel β-type titanium alloy Ti-29Nb-13Ta-4.6Zr (TNTZ) has been developed and extensively researched to achieve highly desirable mechanical properties such as a high strength while maintaining a low Young's modulus that is close to that of bone, as an alternative candidate for conventional titanium metallic biomaterials such as Ti-6Al-4V ELI. Therefore, strengthening by grain refinement and increasing dislocation density is expected to provide TNTZ high mechanical strength while keeping a low Young's modulus because they keep the original β phase. In this case, severe plastic deformation, such as high-pressure torsion (HPT) processing, is a potential treatment for obtaining these properties. Furthermore, HPT processing is effective for producing ultrafine-grained TNTZ having high dislocation density in single β structure. The obtained promising results, which are a tensile strength of around 1100 MPa and a Young's modulus of around 60 GPa, motivated that the above mentioned mechanical properties can be achieved by microstructural refinement through HPT processing However, the mechanism of microstructural refinement is unclear for TNTZ during HPT processing. Therefore, the aim of this study is to investigate microstructural changes of TNTZ through HPT processing by X-ray diffraction analysis and transmission electron microscopy. The microstructures of TNTZ subjected to cold rolling (TNTZCR) and HPT processing (TNTZHPT) comprised single β grains however, the intense β {110} peak reveals that the preferred orientation is β {110} for TNTZHPT. While the microstructure of TNTZCR shows a comparatively high dislocation density (2.3 x 1016 m-2), HPT processing leads to a drastic accumulation of dislocations (5.3 x 1016 m-2 in dislocation density). Dislocations in the microstructures of TNTZHPT are well arranged for the cell wall and/or subgrain boundaries, with a stronger dipole character than random distribution. The dislocation density, arrangement parameter and crystallite diameter (around 11 nm) of TNTZHPT saturate from the center to the peripheral region of a coin shaped specimen at N = 20. Therefore, such a microstructural saturation in a specific strain inducing, N = 20, suggests a threshold for further investigation of β-type titanium alloys. Copyright. © 2014 VBRI press.

Some newly developed β-type titanium alloys for biomedical applications exhibit distinctive heterogeneous structures. The formation mechanisms for these structures have not been completely revealed however, understanding these mechanisms could lead to improving their properties. In this study, the heterogeneous structures of a Ti-29Nb-13Ta-4.6Zr alloy (TNTZ), which is a candidate for next-generation metallic biomaterials, were analyzed. Furthermore, the effects of such heterogeneous structures on the mechanical strength of this alloy, including fatigue strength, were revealed by comparing its strength to that of homogenous TNTZ. The heterogeneous structures were characterized micro-, submicro- and nano-scale wave-like structures. The formation mechanisms of these wave-like structures are found to be different from each other even though their morphologies are similar. It is revealed that the micro-, submicro- and nano-scale wave-like structures are caused by elemental segregation, crystal distortion related to kink band and phase separation into β and β', respectively. However, these structures have no significant effect on both tensile properties and fatigue strength comparison with homogeneous structure in this study. © 2013 Elsevier Ltd.

In order to reduce the anisotropy of mechanical properties of a coilable thin sheet of (alpha + beta)-type titanium alloy, Ti-4.5Al-2Mo-1.6V-0.5Fe-0.3Si-0.03C (Ti9), for use in aircraft applications, duplex heat treatments were examined. In each duplex heat treatment, the first heat treatment controls the volume fraction of the primary alpha phase and orientation of the acicular alpha phase in (alpha + beta) two-phase area between the primary alpha grains, whereas the second heat treatment stabilizes the alpha and beta phases. The microstructure of the Ti9 sheet after the duplex heat treatment was analyzed by optical microscopy, pole-figure measurement through X-ray diffraction, and electron backscatter diffraction. The mechanical properties of the duplex heat-treated Ti9 sheet were evaluated by tensile tests. The Ti9 sheet was heat treated to obtain two different types of microstructures. A microstructure consisting of acicular alpha phase in the beta grains was obtained by a first heat treatment above the beta transus (1273 K) followed by water quenching and a second heat treatment at 973 K. A microstructure consisting of equiaxed primary alpha grains and an (acicular alpha + beta) two-phase area between the primary alpha grains was obtained by heating below the beta transus (1123-1223 K) followed by water quenching and a second heat treatment at 973 K. The volume fraction of the primary is grains decreased and the volume fraction of the acicular alpha phase with 12 variants increased instead of increasing first heat-treatment temperature, suppressing the alignment of the c axis of the alpha lattice parallel to the transverse direction within the rolling plane (T-texture formation) as a result. Anisotropy of the tensile properties can be decreased by increasing the first heat-treatment temperature because the T texture was decreased. (C) 2013 Elsevier B.V. All rights reserved.

Tensile properties, Young's modulus and microstructures of (beta-type Ti-10Mn and Ti-14Mn that were fabricated using a metal injection molding method were investigated as a function of sintering temperature. To investigate the biocompatibility of these Ti-Mn alloys, the metallic ions released in a simulated body fluid from Ti-10Mn and Ti-14Mn that were fabricated using a cold crucible levitation melting method were evaluated by immersion tests. The tensile strengths of the sintered Ti-10Mn and Ti-14Mn achieve maximum values of 860 and 886 MPa, respectively. The Ti-14Mn sintered at 1273 K shows the lowest Young's modulus (76 GPa) among all the sintered Ti-10Mn and Ti-14Mn. The tensile strengths of the Ti-Mn alloys are equal to that of (alpha + beta)-type Ti-6Al-4V ELI (Ti64 ELI); further, their Young's moduli were lower than that of Ti-64 ELI. The Ti ions released in a 1% lactic acid solution from the Ti-10Mn and Ti-14Mn is the same levels as that from pure Ti. The Mn ions released into 1% lactic acid solution from the Ti-10Mn and Ti-14Mn does not show a significant increase with increasing Mn content of the Ti-Mn alloys. The ratio of the amount of the Mn ion released to the amount of the (Ti + Mn) ion released in the 1% lactic acid solution corresponds to the Mn content of the Ti-Mn alloys. These results indicated that the ion-release behaviors of the Ti-Mn alloys in the 1% lactic acid solution are the same as that of pure Ti.

To investigate methods of improving the tensile and fatigue properties of a solutionized Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy without increasing its Young' modulus, two types of TNTZ alloys having oxygen contents of 0.06 and 0.14 mass% (TNTZ-0.06O and TNTZ-0.14O), respectively, were subjected to cold swaging and a subsequent heat-treatment. The effects of the grain refinement caused by the cold swaging and the subsequent heat-treatment as well as those of oxygen addition on the microstructures, Young's moduli and tensile and fatigue properties of the two alloys were investigated. The grain diameters of the TNTZ-0.06O and TNTZ-0.14O decrease from 27 mu m (as-received) to 1.7 mu m and from 33 mu m (as-received) to 1.0 mu m, respectively, after subjected to cold swaging and the subsequent heat-treatment. These results suggest that cold swaging, followed by heat treatment, is effective in refining the grains of TNTZ alloys. However, a beta (110) texture develops in the alloys as a result of the cold swaging. Young's moduli of as-cold swaged and heat-treated TNTZ-0.06O and TNTZ-0.14O are within the range of 61-68 GPa and as low as those of solutionized TNTZ-0.06O and TNTZ-0.14O. The tensile strengths and elongations of the as-cold swaged, heat-treated and solutionized TNTZ-0.14O are approximately 30% higher and 20% lower, respectively, than those of the corresponding TNTZ-0.06O. Moreover, the 0.2% proof stresses of the heat-treated TNTZ-0.14O are approximately 110% higher than that of the corresponding TNTZ-0.06O. On the other hand, the values of the Hall-Petch constant (k) for the TNTZ-0.06O (k(TNTZ-0.06O) = 0.02) and TNTZ-0.14O (k(TNTZ-0.14O) = 0.005) are much smaller than those for pure Ti and another beta-type Ti alloy (Ti-15.2Mo). These results indicate that the addition of oxygen can improve the tensile properties of TNTZ alloys. However, the grain refinement caused by cold swaging and a subsequent heat-treatment does not have a significant effect on the tensile properties of TNTZ. The fatigue limit of the heat-treated TNTZ-0.14O (540 MPa) is much higher than those of the heat-treated and solutionized TNTZ-0.06O (290 and 230 MPa) and solutionized TNTZ-0.14O (330 MPa). These results indicated that it is possible to improve the fatigue properties of solutionized TNTZ using grain refinement, which can be induced by cold swaging and a subsequent heat-treatment and by the addition of oxygen.

This work presents a study on the relationship between the alloying elements such as niobium (Nb), tantalum (Ta) or zirconium (Zr) and the hydroxyapatite (HAp) formability on the surfaces of titanium (Ti) alloys subjected to alkali treatment process that is developed to form a HAp layer. The HAp formability on the surfaces of pure Ti, Ti Nb alloys, Ti Ta alloys, Ti Zr alloys, pure Nb, pure Ta and pure Zr subjected to alkali treatment in 1 mol/L NaOH solution at 363 K for 259.2 ks was investigated. The pure Ti, Ti-10Nb alloy and Ti-10Zr alloy have a good HAp formability because sodium titanate is formed on the surface after the alkali treatment. However, the HAp formability is decreased with increasing Nb and Zr contents. A layer including sodium titanate and sodium tantalate is formed on the surfaces of Ti Ta alloys after the alkali treatment Therefore, the Ti-10Ta, Ti-20Ta, Ti-30Ta and Ti-40Ta alloys have a good HAp formability. On the other hand, a sodium niobate layer and a thick crystalline sodium tantalate layer are formed on the surfaces of pure Nb and pure Ta, respectively, after the alkali treatment Moreover, there is no component change on the surface of pure Zr after the alkali treatment. Therefore, the HAp formability on the surfaces of pure Nb, pure Ta and pure Zr is significantly low after they are soaked in a simulated body fluid for 1 week.

For spinal-fixation applications, implants should have a high Young's modulus to reduce springback during operations, though a low Young's modulus is required to prevent stress shielding for patients after surgeries. In the present study, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) with a low Young's modulus was modified by adding Cr to obtain a higher deformation-induced Young's modulus in order to satisfy these contradictory requirements. Two newly designed alloys, TNTZ-8Ti-2Cr and TNTZ-16Ti-4Cr, possess more stable beta phases than TNTZ. These alloys consist of single beta phases and exhibit relatively low Young's moduli of <65 GPa after solution treatment. However, after cold rolling, they exhibit higher Young's moduli owing to a deformation-induced omega-phase transformation. These modified TNTZ alloys show significantly less springback than the original TNTZ alloy based on tensile and bending loading-unloading tests. Thus, the Cr-added TNTZ alloys are beneficial for spinal-fixation applications. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In order to improve the mechanical properties of Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy without increasing Young's modulus for application in bone prostheses, dispersion strengthening of TNTZ using yttrium oxide (Y2O3) particles was studied. The formation of well-dispersed Y2O3 particles inside grains of Y-added TNTZ is achieved through the reaction of added Y with the oxygen contained in TNTZ. The size and its standard deviation of obtained Y2O3 particles increased at Y concentrations of 0.2 and 0.5 mass%. The addition of Y led to a decrease in the grain size in Y-added TNTZ. Low Young's modulus was retained in the Y-added TNTZ subjected to cold rolling. The tensile strength and 0.2% proof stress slightly increased in Y-added TNTZ with Y concentrations below 0.1 mass%, whereas they decreased significantly in Y-added TNTZ with Y concentrations of 0.2 and 0.5 mass%. Large Y2O3 particles that formed in Y-added TNTZ with Y concentrations of 0.2 and 0.5 mass% worked as sources for the formation of voids during fracture, which resulted in a decrease in the tensile strength and 0.2% proof stress. Elongation tended to decrease in the Y-added TNTZ as compared to that of TNTZ without any Y addition. As a result, it is found that Y-added TNTZ with improved mechanical properties was obtained at a Y concentration of 0.05 mass% in this experiment. The fatigue strength of Y-added TNTZ was also improved at the Y concentration of 0.05 mass%.

The effect of high-pressure torsion (HPT) processing on the microstructure and mechanical biocompatibility includes Young's modulus, tensile strength, ductility, fatigue life, fretting fatigue, wear properties and other functionalities such as super elasticity and shape memory effect, etc. at levels suitable for structural biomaterials used in implants that replace hard tissue in the broad sense (Sumitomo et al., 2008 [4]). In particular, in this study, the mechanical biocompatibility implies a combination of great hardness and high strength with an adequate ductility while keeping low Young's modulus of a novel Ti-29Nb-13Ta-4.6Zr (TNTZ) for biomedical applications at rotation numbers (N) ranging from 1 to 60 under a pressure of 1.25 GPa at room temperature was systematically investigated in order to increase its mechanical strength with maintaining low Young's modulus and an adequate ductility. TNTZ subjected to HPT processing (TNTZ(HPT)) at low N exhibits a heterogeneous microstructure in micro-scale and nano-scale consisting of a matrix and a non-etched band, which has nanosized equiaxed and elongated single beta grains, along its cross section. The grains exhibit high dislocation densities, consequently non-equilibrium grain boundaries, and non-uniform subgrains distorted by severe deformation. At high N which is N>20, TNTZ(HPT) has a more homogeneous microstructure in nano-scale with increasing equivalent strain, cm Therefore, TNTZ(HPT) at high N exhibits a more homogenous hardness distribution. The tensile strength and 0.2% proof stress of TNTZ(HPT) increase significantly with N over the range of 0 <= N <= 5, and then become saturated at around 1100 MPa and 800 MPa at N >= 10. However, the ductility of TNTZ(HPT) shows a reverse trend and a low-level elongation, at around 7%. And, Young's modulus of TNTZ(HPT) decreases slightly to 60 GPa with increasing N and then becomes saturated at N >= 10. These obtained results confirm that the mechanical strength of TNTZ can be improved while maintaining a low Young's modulus in single beta grain structures through severe plastic deformation. (C) 2013 Elsevier B.V. All rights reserved.

The number of hydroxyl groups on a Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy surface was controlled through H2O2 treatment for further improvement of the adhesive strength and durability against water of TNTZ/silane layers (SILs)/segmented polyurethane (SPU) composites. The effect of the terminal functional groups on the adhesive strength of SPU on TNTZ, and the adhesiveness of SPU on TNTZ against water was investigated. Three types of silane-coupling agents were used to bind TNTZ and SPU: methacryloxypropyltrimethoxysilane (γ-MPTS), aminopropyltriethoxysilane (APS), and mercaptopropyltrimethoxysilane (γ-MPS). The adhesive strength of each composite was evaluated by shear bonding tests. The number of hydroxyl groups increases with an increase in treatment time at a H2O 2 concentration of 5% (v/v). On the other hand, an increase from 5% (v/v) to 30% (v/v) in H2O2 concentration leads to a decrease in the number of hydroxyl groups on the TNTZ surface because at higher H2O2 concentrations, the reaction that consumes the hydroxyl groups is dominant. The shear bonding strength is doubled compared with the untreated TNTZ/SIL/SPU interface. Although the shear bonding strength decreases after immersion in water for 30 days when APS and γ-MPS are used, TNTZ/γ-MPTS/SPU composites exhibit good durability to water and maintain an equivalent shear bonding strength before immersion in water. © 2013 Wiley Periodicals, Inc.

Background and Aim A current drawback of endoscopic submucosal dissection (ESD) for early-stage gastrointestinal tumors is the lack of instruments that can safely assist with this procedure. We have developed a pulsed jet device that can be incorporated into a gastrointestinal endoscope. Here, we investigated the mechanical profile of the pulsed jet device and demonstrated the usefulness of this instrument in esophageal ESD in swine. Methods The device comprises a 5-Fr catheter, a 14-mm long stainless steel tube for generating the pulsed water jet, a nozzle and an optical quartz fiber. The pulsed water jet was generated at pulse rates of 3Hz by irradiating the physiological saline (4 degrees C) within the stainless steel tube with an holmium-doped yttrium-aluminum-garnet (Ho:YAG) laser at 1.1J/pulse. Mechanical characteristics were evaluated using a force meter. The device was used only for the part of submucosal dissection in the swine ESD model. Tissues removed using the pulsed jet device and a conventional electrocautery device, and the esophagus, were histologically examined to assess thermal damage. Results The peak impact force was observed at a stand-off distance of 40mm (1.1J/pulse). ESD using the pulsed jet device was successful, as the tissue specimens showed precise dissection of the submucosal layer. The extent of thermal injury was significantly lower in the dissected bed using the pulsed jet device. Conclusion The results showed that the present endoscopic pulsed jet system is a useful alternative for a safe ESD with minimum tissue injury.

The effects of various heat treatments on the microstructure and mechanical properties of an (alpha + beta)-type titanium alloy, Ti-4.5Al-2Mo-1.6V-0.5Fe-0.3Si-0.03C (KS Ti-9), were investigated systematically for possible use in next-generation aircraft applications. The as-received KS Ti-9 shows strong anisotropy of mechanical strength derived from the intense texture (T-texture) of the primary alpha phase. This anisotropy continues to be observed in KS Ti-9 annealed at a temperature below beta transus followed by air cooling, but the anisotropy drastically decreases in KS Ti-9 when subjected to a duplex heat treatment, that is, when the as-received material of KS Ti-9 is sequentially heated to a temperature slightly below beta transus followed by water quenching and then annealed followed by air cooling. It is considered that the reduction in the anisotropy in KS Ti-9 subjected to this duplex heat treatment is associated with the difference in the orientation of the precipitated acicular alpha phase.

Hydroxyapatite (HAp) films were deposited on a beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), by metal organic chemical vapor deposition (MOCVD) in order to improve its hard-tissue compatibility. The surface morphologies of TNTZ substrates were changed by acid treatments and mechanical polishing prior to the HAp film deposition. The adhesive strength of the HAp films formed on TNTZ substrates treated with an HF solution increased to twice that of the HAp film deposited on a TNTZ substrate with a mirror-like finish. Complex microstructures with deeply etched grain boundaries, formed on the TNTZ substrates after immersion in the HF solution, were responsible for the increase in the adhesive strength of the HAp film caused by an interlocking effect. The HAp films on TNTZ substrates treated with a H2SO4 solution exhibited lower adhesive strength than HAp films on TNTZ substrates treated with HF solution, regardless of the surface roughness of the substrates. Additionally, acid treatments using HNO3 and H2O2 solutions did not change the surface morphologies of the TNTZ substrates. The complex microstructures with deeply etched grain boundaries and nanosized asperities formed on the TNTZ substrates are important factors in the improvement of the adhesive strengths of HAp films deposited on TNTZ substrates. (C) 2012 Elsevier Ltd. All rights reserved.

Titanium and its alloys are widely utilized for biomedical applications because of their high specific strength, corrosion resistance, and biocompatibility. In the past two decades, many researchers gave an effort to achieve a low Young's modulus for such the titanium alloys. However, Young's modulus of the metallic spinal rod that is one of the main components of spinal fixation devices should be not only low to prevent stress shielding effect for patients but also high to suppress springback for surgeons. Therefore, a novel function of biomedical titanium alloys, which is self-adjustment of Young's modulus, has been proposed recently by the authors. Deformation-induced phase transformation was introduced into beta-type titanium alloys to control the Young's modulus at only deformed parts, while the Young's modulus at the non-deformed parts would remain low. In this case, the Young's modulus at the deformed parts depends on the type of deformation-induced phase. Therefore, the Young's modulus change due to deformation was investigated using several types of beta-type titanium alloys. After deformation, the Young's modulus could be increased successfully by deformation-induced omega phase transformation, but was not increased by deformation-induced alpha' phase transformation.

The tensile strengths of TNTZ after solution treatment (TNTZ(ST)) or after cold rolling (TNTZ(CR)) decrease with an increase in the aging temperature, although the elongation shows the reverse trend. The fatigue limits of TNTZ(CR) subjected to aging at 673 K and 723 K are nearly equal to that of Ti-6Al-4V ELI, which has around 800 MPa. The tensile strength of TNTZ(CR) is improved drastically through high pressure torsion (HPT), which is one of severe deformation processes (SDP), and shows more than 1 GPa, although the fatigue strength is not improved by HPT because of the work-softening during the cyclic deformation.

Welding is an important technology for using titanium alloy plates in aerospace applications. However, pores (welding defects) are introduced into the welded zone during welding, including during the melting process, leading to a decrease in the fatigue strength of the welded titanium alloy joint. Friction stir welding (FSW) seems to be effective for avoiding the deterioration of fatigue strength because it is difficult for pores to form in the welded zone during FSW, which does not include a melting process. Therefore, the microstructure and mechanical properties, including the fatigue properties, of an (alpha+beta)-type titanium alloy, Ti-4.5Al-2.5Cr-1.2Fe-0.1C alloy (Ti-531C), subjected to FSW were investigated. In this study, FSW was conducted from both sides of the plates (double-sided FSW) to ensure that the samples were subjected to the same experimental conditions (plate thickness, specimen geometry, etc.) used in our previous study on laser-welded Ti-531C plates for comparison. No pores are observed on the fractured surfaces of Ti-531C subjected to double-sided FSW. Consequently, higher fatigue strength is obtained for Ti-531C subjected to double-sided FSW compared with the samples subjected to double-sided laser welding. However, an acicular secondary alpha phase and a grain-boundary alpha phase in the first welded zone are coarsened by heating in the second welded zone, leading to a difference in hardness in the direction of the loading axis for the fatigue test. As a result, the boundary between these two regions became a stress-concentration site that deteriorates the fatigue strength of Ti-531C subjected to double-sided FSW.

The microstructures and mechanical properties of the TNTZ added with Y or Y2O3 have been investigated. The results indicate that TNTZ added with Y or 2O3 are found to be composed of β phase and the small amount of 2O3. The grain size of TNTZ added with Y or 2O3 is smaller than that of TNTZ. The Young's modulus of TNTZ added with Y or 2O3 are maintained at a low level, and Young's modulus of TNTZ added with Y is smaller than that of TNTZ added with 2O3. The mechanical properties are both improved by adding Y or 2O3, while the tensile strength of TNTZ added with 2O3 is slightly higher than that of TNTZ added with Y. The high cycle fatigue limit of the alloys added with Y or 2O3 are similar, while the low cycle fatigue strength of TNTZ added with Y is higher than that of TNTZ with 2O3. The improving of mechanical properties ascribes to the microstructure refinement and the pining effect of 2O3 particles. On the other hand, Y elements form 2O3 with the oxygen elements in the matrix, thus lead to the weakening of the oxygen solution effect. © (2013) Trans Tech Publications, Switzerland.

The objective of this study was to evaluate the corrosion behavior of Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) with immersion in an acidic saline solution containing fluoride by investigating change in color and the surface structure of the oxide film. With immersion in fluoride-containing solution, TNTZ showed a less marked change in color than commercially pure titanium (TI), and a smaller decrease in glossiness. The outermost surface was covered with oxides from its constituent elements at before and after immersion in solution with or without fluoride. When immersed in fluoride-containing solution, the film consisted of larger niobium and tantalum oxides than that before or after immersion in solution without fluoride. In summary, TNTZ showed superior resistance to discoloration to TI after immersion in fluoride-containing solution. The results suggest that the subsequent increase in niobium and tantalum fractions in the oxide film in TNTZ improves resistance to corrosion.

beta-type titanium alloys comprising low cost elements such as Fe, Mn, Cr, Sn, Al, O and N and having low Young's modulus are currently being developed. Examples of such alloys include Ti-10Cr-Al, Ti-Mn, Ti-Mn-Fe, Ti-Mn-Al, Ti-Cr-Al, Ti-Sn-Cr, Ti-Cr-Sn-Zr, Ti-(Cr, Mn)-Sn, and Ti-12Cr. Ti-5Fe-3Nb-3Zr belongs to that class of titanium alloys in which rare metals such as Nb, Ta, and Zr have been reduced using Fe. Ti-5Fe-3Nb-3Zr has a Young's modulus of around 76 GPa and has greater strength than that of Ti-6Al-4V ELI for biomedical applications. The characteristics of Ti-5Fe-3Nb-3Zr and other low-cost beta-type titanium alloys with low Young's moduli are discussed from the viewpoint of biomedical applications.

The effects of interstitial carbon solute and titanium carbide on the tensile and fatigue properties of an (alpha+beta)-type titanium alloy, Ti-4.5Al-2.5Cr-1.2Fe-0.1C (KS Ti-531C), with bimodal and Widmanstatten alpha structures were investigated. In order to control the microstructures, this alloy was subjected to annealing at temperatures just below and just above the beta-transus (531C-alpha+beta annealed and 531C-beta annealed, respectively). The microstructure of 531C-alpha+beta annealed shows a bimodal structure and any titanium carbide is not observed, whereas that of 531C-beta annealed shows a Widmanstatten alpha structure and some titanium carbides, which are considered to be Ti2C, are observed. The tensile strength and elongation of 531C-alpha+beta annealed and 531C-beta annealed are similar, but 0.2% proof stress is higher and further the reduction of area is much larger for 531C-alpha+beta annealed than 531C-beta annealed. Their tensile properties depend mainly on the type of microstructure and interstitial element partitioning because the titanium carbide is not observed on the fractured surfaces of both the alloys after tensile tests. Also, the fatigue properties of 531C-alpha+beta annealed are better than those of 531C-beta annealed. The titanium carbide is observed on the fractured surface of 531C-beta annealed, but not observed on that of 531C-alpha+beta annealed, after fatigue tests. Therefore, titanium carbide is considered to cause deterioration in the fatigue properties of 531C-beta annealed compared to those of 531C-alpha+beta annealed.

TiFeCu alloys with higher Young's modulus, hardness and compressive mechanical properties than those of the existing Ti alloys were developed using a d-electrons alloy design method in order to improve Young's modulus, hardness and compressive properties of Ti and existing Ti alloys for use as metallic stents. Their microstructures, Young's modulus, hardness and compressive mechanical properties were investigated both before (as-cast) and after heat-treatments performed under a high-purity argon atmosphere at 1173K for 21.6 and 86.4 ks. The studied TiFeCu alloys consist of the β-Ti phase and dendritic TiFe intermetallic phase. Moreover, the area fraction of the TiFe intermetallic phase increases with increasing atom ratio (Fe + Cu)/Ti of the alloys and with the heat-treatment time. The Young's modulus of the studied TiFeCu alloys increases from 110 GPa (Ti78Fe18Cu 4 alloy) to 145 GPa (Ti68Fe30Cu2 alloy) with increasing atom ratio (Fe + Cu)/Ti of the alloys and the area fraction of the TiFe intermetallic phase. However, the Young's modulus is saturated or slightly decreased when the area fraction of the TiFe intermetallic phase is more than 34%. The Vickers hardness of the as-cast alloys increases from 490HV (Ti78Fe18Cu4 alloy to 550HV (Ti 63.4Fe30Cu6.6 alloy with increasing atom ratio (Fe + Cu)/Ti of the alloys and area fraction of the TiFe intermetallic phase. On the other hand, the Vickers hardness of the heat-treated alloys is lower than that of the as-cast alloys, despite the increase in the area fraction of the TiFe intermetallic phase after the heat-treatment. The heat-treated alloys have better compressive properties than those of the as-cast alloys and the reported TiFeCu alloys. The compressive strength and strain of the heat-treated Ti67Fe27Cu6 alloys reach to 2131MPa and 24.5%, respectively. © 2013 The Japan Institute of Metals.

Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy has excellent mechanical properties and bone conductivity. For dental application, TNTZ surfaces were converted to white oxidized layer by a simple heat treatment in air to achieve the formation of aesthetic surfaces. The oxidized layer formed by the heat treatment at 1000 degrees C for 0.5 or 1 hr was whiter and joined to TNTZ substrate more strongly than that formed by the treatment at 900 degrees C. The layer consisted of TiO2 (rutile), TiNb2O7, and TiTa2O7 and possessed similar to 30 mu m in thickness for the sample heat-treated at 1000 degrees C and similar to 10 mu m for that heat-treated at 900 degrees C. The surface average roughness and the wettability increased after the heat treatment. The spreading and proliferation level of mouse osteoblast-like cell (MC3T3-E1 cell) on the heat-treated sample were almost the same as those on as-prepared one. The cell spreading on TNTZ was better than those on pure titanium (CP Ti) regardless of the heat treatment for the samples. There was no deterioration in the in vitro cell compatibility of TNTZ after the oxidized layer coating by the heat treatment.

Micro-arc oxidation (MAO) was performed on a beta-type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) in this study to improve its bioactivity in a body fluid and its hard-tissue compatibility. The surface oxide layer formed on TNTZ by MAO treatment in a mixture of calcium glycerophosphate and magnesium acetate was characterized using various surface analyses. The oxide layer was mainly composed of two types of TiO2 (rutile and anatase), and it also contained Ca, P, and Mg, which were incorporated from the electrolyte during the treatment. The calcium phosphate formation on the surface of the specimens after immersion in Hanks' solution was evaluated to determine the bioactivity of TNTZ with and without MAO treatment. As a result, thick calcium phosphate layers formed on the TNTZ specimen that underwent MAO treatment, whereas only a small amount of precipitate was observed on TNTZ without treatment. Thus, the MAO treatment is a promising method to improve the bioactivity and hard-tissue compatibility of TNTZ. (c) 2012 Elsevier B.V. All rights reserved.

For implant rods as spinal fixation system, low Young's modulus, easy bending to an intended shape (low spring-back), and retaining initial bended shape during a long implantation (low aging-back) are essential properties. The rods were fabricated using a biomedical beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ), and their above-mentioned properties were evaluated in comparison with conventional biomaterials, commercially pure titanium, Ti-6Al-4V ELI, and SUS316L stainless steel. In the results of an animal experiment using implant rods made by TNTZ subjected to solution treatment with low Young's modulus, no negative effects are seen in the radiographs, and no inflammatory cells are observed in histological observation. In spite of low Young's modulus, the spring-back of TNTZ subjected to solution treatment is comparable to that of Ti-6Al-4V ELI. Further, its aging-back is quite small among the other materials. (C) 2012 Elsevier B.V. All rights reserved.

New low modulus beta-type titanium alloys for biomedical applications are still currently being developed. Strong and enduring p-type titanium alloy with a low Young's modulus are being investigated. A low modulus has been proved to be effective in inhibiting bone atrophy, leading to good bone remodeling in a bone fracture model in the rabbit tibia. Very recently beta-type titanium alloys with a self-tunable modulus have been proposed for the construction of removable implants. Nickel-free low modulus beta-type titanium alloys showing shape memory and super elastic behavior are also currently being developed. Nickel-free stainless steel and cobalt-chromium alloys for biomedical applications are receiving attention as well. Newly developed zirconium-based alloys for biomedical applications are proving very interesting. Magnesium-based or iron-based biodegradable biomaterials are under development. Further, tantalum, and niobium and its alloys are being investigated for biomedical applications. The development of new metallic alloys for biomedical applications is described in this paper. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A series of metastable beta-type binary Ti-(18-22)V alloys were prepared to investigate the effect of deformation-induced products (deformation-induced omega phase transformation and mechanical twinning) on the mechanical properties of metastable beta-type titanium alloys. The microstructures, Young's moduli, and tensile properties of the alloys were systemically examined. Ti-(18-20)V alloys subjected to solution treatment comprise a beta phase and a small amount of athermal omega phase, while Ti-22V alloy subjected to solution treatment consists of a single beta phase. Ti-(18-20)V alloys subjected to solution treatment exhibit relatively low Young's moduli and low tensile strengths as compared to cold-rolled specimens. Both deformation-induced omega phase transformation and {332}(beta)< 113 >(beta) mechanical twinning occur in all of the alloys during cold rolling. The occurrences of {332}(beta)(113)(beta) mechanical twinning and deformation-induced omega phase transformation are dependent on the beta stability of the alloys. After cold rolling, all of the alloys comprise a beta phase and an omega phase. The Young's moduli of Ti-(18-22)V alloys increase because of the formation of a deformation-induced omega phase during cold rolling. The significant increase in tensile strength is attributed to the combined effect of the deformation-induced omega phase transformation and work-hardening during cold rolling. [doi: 10.2320/matertrans.M2012116]

Metallic implant rods used in spinal fixtures should have a Young's modulus that is sufficiently low to prevent stress shielding for the patient and sufficiently high to suppress springback for the surgeon. Therefore, we propose a new concept: novel biomedical titanium alloys with a changeable Young's modulus via deformation-induced to phase transformation. In this study, the Cr content in the range of 10-14 mass% was optimized to produce deformation-induced omega phase transformation, resulting in a large increase in the Young's modulus of binary Ti-Cr alloys. The springback and cytotoxicity of the optimized alloys were also examined. Ti-(10-12)Cr alloys exhibit an increase in Young's modulus owing to deformation-induced omega phase transformation. In this case, such deformation-induced omega phase transformation occurs along with {332}(beta) mechanical twinning, resulting in the maintenance of acceptable ductility with relatively high strength. Among the examined alloys, the lowest Young's modulus and largest increase in Young's modulus are obtained from the Ti-12Cr alloy. This alloy exhibits smaller springback than and comparable cytocompatibility to the biomedical Ti alloy Ti-29Nb-13Ta-4.6Zr. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The complex microstructure of a high hot-workable alpha + beta-type titanium alloy, Ti-4.5Al-2.5Cr-1.2Fe-0.1C with a continuously varying alpha phase in terms of its size, distribution, morphology, and crystal orientation from the welded zone to the matrix, including a trace amount of welding defect, was investigated by several microstructural and crystallographical analysis techniques such as optical microscopy, scanning electron microscopy, and X-ray diffraction to elucidate the crucial factors determining its mechanical properties such as tensile properties and fatigue etc. The alloy was processed with laser welding to prepare parts for use in next-generation aircraft. The tensile properties of welded samples exhibit a strength-ductility balance similar to that of non-welded sample. All the failures in these samples occur at their matrices because the hardness values of welded zone on the cross section perpendicular to loading direction of the welded samples are higher than that on the same plane of non-welded sample, which is related to crystal texture of alpha phase. However, the fatigue strengths of welded samples are lower than that of non-welded sample. Such the decrease in fatigue strength of welded samples is caused by the presence of pores formed during welding. (c) 2012 Elsevier B.V. All rights reserved.

A novel beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), has been developed as a candidate for biomedical applications. TNTZ exhibits non-toxicity and a low Young's modulus close to that of bone (10-30 GPa). Such a low Young's modulus of this alloy is achieved by comprising a single metastable beta phase. Greater mechanical biocompatibility, which implies higher mechanical strength and hardness while maintaining a low Young's modulus, has been aimed for TNTZ. Therefore, strengthening by grain refinement and increasing dislocation density is expected to provide TNTZ high mechanical strength while keeping a low Young's modulus because they keep the original beta phase. In this case, high-pressure torsion (HPT) processing is one of the effective ways to obtain these properties simultaneously in TNTZ. Thus, in this study, the effect of HPT processing on the microstructure and mechanical hardness of TNTZ was systematically investigated at rotation numbers (N) of 1 to 20 under a pressure of around 1.25 GPa at room temperature. On the cross sections of TNTZ subjected to HPT processing (TNTZ(HPT)) after cold rolling (TNTZ(CR)) at any rotation number, a heterogeneous microstructure consisting of a matrix and a non-etched band, which is not corroded by etching solution, can be observed. The thickness of non-etched band increases as rotation number and distance from specimen center increase. Both matrix and non-etched band comprise a single beta phase, but their grain geometries are different each other. Equiaxed grains and elongated grains are observed in the matrix and the non-etched band, respectively. The equiaxed grain diameter, which is ranged from 155 nm to 44 nm, in the matrix decreases with increasing rotation number. Contrastingly, the elongated grains with a length of around 300 nm and a width of 30 nm, which are nearly constant with rotation number, are observed in the non-etched band. The mechanical hardness of TNTZ(HPT) is consistently much higher than that of TNTZ(CR). The mechanical hardness distribution on the surface of TNTZ(HPT) is heterogeneous in the radial and depth directions, while that of TNTZ(CR) is homogeneous; the mechanical hardness is higher in the peripheral region than in the central region on the surfaces of TNTZ(HPT) at all N. Further, the mechanical hardness distribution on the cross sections of TNTZ(HPT) at all N is also heterogeneous in depth direction; the mechanical hardness is higher in the peripheral region than in the central region. The heterogeneous mechanical hardness distribution depending on the position on the surface and cross section of TNTZ(HPT) is considered to be related to grain refinement and imposed strain due to HPT processing. (C) 2012 Elsevier Ltd. All rights reserved.

To develop a novel biomedical titanium alloy with a changeable Young's modulus via deformation-induced omega phase transformation for the spinal rods in spinal fixation devices, a series of metastable beta type binary Ti-(15-18)Mo alloys were prepared. In this study, the microstructures, Young's moduli and tensile properties of the alloys were systemically examined to investigate the effects of deformation-induced omega phase transformation on their mechanical properties. The springback of the optimal alloy was also examined. Ti-(15-18)Mo alloys subjected to solution treatment comprise a beta phase and a small amount of athermal omega phase, and they have low Young's moduli. All the alloys investigated in this study show an increase in the Young's modulus owing to deformation-induced omega phase transformation during cold rolling. The deformation-induced omega phase transformation is accompanied with {332}(beta) mechanical twinning. This resulted in the maintenance of acceptable ductility with relatively high strength. Among the examined alloys, the Ti-17Mo alloy shows the lowest Young's modulus and the largest increase in the Young's modulus. This alloy exhibits small springback and could be easily bent to the required shape during operation. Thus, Ti-17Mo alloy is considered to be a potential candidate for the spinal rods in spinal fixation devices. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The mechanical strength of a beta titanium alloy such as Ti-Nb-Ta-Zr alloy (TNTZ) can be improved significantly by thermo-mechanical treatment. In this study, TNTZ was subjected to solution treatment, cold caliber rolling, and cold swaging before aging treatment to form a rod for spinal fixation. The {110}(beta) are aligned parallel to the cross-section with two strong peaks approximately 180 degrees apart, facing one another, in the TNTZ rods subjected to cold caliber rolling and six strong peaks at approximately 60 degrees intervals, facing one another, in the TNTZ rods subjected to cold swaging. Therefore, the TNTZ rods subjected to cold swaging have a more uniform structure than those subjected to cold caliber rolling. The orientation relationship between the alpha and beta phases is different. A |110|(beta)/|121|(alpha), (112)beta//(210)alpha orientation relationship is observed in the TNTZ rods subjected to aging treatment at 723 K after solution treatment and cold caliber rolling. On the other hand, a |110|(beta)//|001|(alpha), (112)(beta)//(200)(alpha) orientation relationship is observed in TNTZ rod subjected to aging treatment at 723 K after cold swaging. A high 0.2% proof stress of about 1200 MPa, high elongation of 18%, and high fatigue strength of 950 MPa indicate that aging treatment at 723 K after cold swaging is the optimal thermo-mechanical process for a TNTZ rod. (C) 2012 Elsevier Ltd. All rights reserved.

The objective of this research was to investigate the effect of constitutional phases on the unique hardening behavior of as-solutionized dental Ag-Pd-Au-Cu alloy fabricated by cold rolling. The commercial dental Ag-Pd-Au-Cu alloy fabricated by cold rolling consists of Cu-rich alpha(1), Ag-rich alpha(2), and beta phases. On the other hand, the Ag-Pd-Au-Cu alloy fabricated by the liquid rapid solidification (LRS) method consists of single alpha phase. They were subjected to various heat treatments, respectively. The microstructures were observed by scanning electron microscope, transmission electron microscope and X-ray diffraction. The hardness was evaluated by a Vickers micro-hardness tester. In the Ag-Pd-Au-Cu alloy fabricated by cold rolling, the fine L1(0)-type-ordered beta' phase is precipitated and the coarse beta phase is remained after solution treatment at 1123 K. The hardness increases drastically. On the other hand, in the Ag-Pd-Au-Cu alloy fabricated by LRS method, the single alpha phase was decomposed into the alpha(1) phase and the alpha(2) phase after solution treatment at 1023 K and its hardness change was small. However, after aging treatment at 673 K, the fine beta phase is precipitated in the alpha phase and the hardness increases greatly even in the Ag-Pd-Au-Cu alloy fabricated by LRS method. It is considered that the precipitation of the fine L1(0)type-ordered beta' phase may contribute strongly to the unique hardening in the as-solutionized dental Ag-Pd-Au-Cu alloy fabricated by cold rolling. (C) 2011 Elsevier B. V. All rights reserved.

Improvement in fatigue strength in spite of maintaining low Young's modulus was achieved in Ti-29Nb-13Ta-4.6Zr (TNTZ) by hard-particles dispersion. A certain amount of Y2O3 additions was added into TNTZ. TNTZ with 0.05-1.00mass%Y consists of a beta-phase with a small amount of Y2O3. Young's moduli of TNTZ with 0.05-1.00mass%Y are maintained low, and are almost similar to that of TNTZ without Y2O3. The tensile strength of TNTZ with 0.05-1.00mass%Y is slightly improved and the elongation does not deteriorate by Y2O3 additions. However, the 0.2% proof stress decreases with the increase in Y concentration. Although tensile properties are not changed drastically, the fatigue strength is significantly improved by Y2O3 additions. The dispersion of Y2O3 particle increases the resistance to fatigue initiation. However. Y2O3 with too large diameter at the surface of the specimen works harmfully as the fatigue initiation site. The Y2O3 diameter and volume fraction increase with the increase in Y concentration. As a result, the fatigue limit of the alloys with 0.05-1.00mass%Y firstly increases and then decreases with the increase in Y concentration. TNTZ with 0.1mass% Y exhibits the best combination of higher fatigue strength and low Young's modulus. (C) 2011 Elsevier B.V. All rights reserved.

The relationship between the microstrucutural changes of L1(0)-type ordered beta' phase and hardening behavior in as-solutionized dental Ag-Pd-Au-Cu alloys was investigated by changing the cooling rate and the solution treatment temperature. Additionally, the formation process of the beta' phase in as-solutionized Ag-Pd-Au-Cu alloy was attempted to clarify. The microstructural changes were observed by X-ray diffraction (XRD) method and transmission electron microscopy (TEM). The hardness was evaluated using a Vickers microhardness tester. The beta' phase is precipitated regardless of the cooling rate, after solution treatment at 1123 K. TEM dark field images show that the size of the beta' phase decreases and the number of beta' phase increases with an increase in the cooling rate. The Vickers hardness value increases with an increase in cooling rate. TEM dark field images show that the microstructure of beta' phase is similar when the solution treatment temperature increases from 1123 K to 1173 K. However, the Vickers hardness increases with an increase of solution treatment temperature. It is of great significance to reveal that the beta' phase precipitated in as-solutionized Ag-Pd-Au-Cu alloy is formed during cooling after high-temperature solution treatment and that the growth of the beta' phase is diffusion controlled. (C) 2011 Elsevier B.V. All rights reserved.

Composite materials that consisted of a biomedical beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) with low Young's modulus and segment polyurethane (SPU) have been fabricated for application in biomedical devices. The effects of different kinds of terminal functional groups and the thickness of the silane layers (SIL) on the adhesive strength between TNTZ and SPU were investigated by means of shear bonding tests. The following silane coupling agents were employed in this study: 3-methacryloxypropyltrimethoxysilane (gamma-MPTS), aminopropyltriethoxysilane CAPS), and 3-mercaptopropyltrimethoxysilane (gamma-MPS). Furthermore, the shear bonding strength of the TNTZ/SIL/SPU interface was also characterized after immersion in water for 30 d. Silane coupling treatment produces a ten-fold increase in the shear bonding strength, independent of the type of terminal functional groups and the thickness of the silane layers. Scanning electron microscopic evaluation of the fracture surfaces of the TNTZ/SIL/SPU composites after the shear bonding tests coupled with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the TNTZ/SIL/SPU composites are partially fractured at the interfaces of the TNTZ/SIL while the rest of the fracture occurs at the interfaces of the SIL/SPU in single sample. The shear bonding strength decreases after immersion in water for 30 d when APS and gamma-MPS are used as the silane coupling agents, because stable chemical bonding is not achieved between the silane layer and SPU, whereas the bonding of the gamma-MPTS composite is not affected by exposure to water. (C) 2012 Elsevier B.V. All rights reserved.

beta-Type titanium alloys with composition of Ti-24 at% Nb-(0, 2, 4) at% Zr were prepared and subjected to aging treatment for different durations. The addition of Zr suppressed the formation and growth of isothermal omega phase during aging treatment, and therefore the investigated Ti-Nb-Zr alloys with different Zr content performed various deformation mechanisms, mechanical properties and super-elastic effects with the changes of aging time. The isothermal omega phase exerted inhibitory effects on twinning and stress-induced martensitic transformation. Desirable properties were obtained in Ti-Nb-Zr alloy by adding suitable Zr content and processing short time aging treatment. Ti-24 at% Nb-2 at% Zr alloy subjected to aging treatment at 573 K for 7.2 ks exhibited an ultimate tensile strength of 710 MPa, an elongation of 13%, a Young's modulus of 64 GPa, and a super-elastic recovery strain of 4.3%. Ti-24 at% Nb-4 at% Zr alloy subjected to aging treatment at 573 K for 1.8 ks, 3.6 ks, and 7.2 ks performed a low Young's modulus of 62 GPa and ultimate tensile strength around 600 MPa. (C) 2012 Elsevier B.V. All rights reserved.

Nowadays, biomaterials that are used to design spinal fixtures cannot meet the requirements of both surgeons and patients; surgeons require the material to have a high Young's modulus to suppress springback during the operation, whereas patients require the material to have a low Young's modulus to prevent the stress-shielding effect. Therefore, new titanium alloys with good biocompatibility and a changeable Young's modulus require to be developed. The,, phase significantly influences the mechanical properties of titanium alloys. According to reports, the as phase can be introduced by deformation at room temperature in p-type Ti-Cr alloys. The effects of deformation-induced phases on the mechanical properties of a metastable beta-type Ti-12Cr alloy were investigated. The experimental results indicate that the Young's modulus, tensile strength, and Vickers hardness of the Ti-12Cr alloy increase remarkably by cold rolling. The transmission electron microscopy (TEM) observation of a Ti-12Cr alloy shows that deformation-induced as phase transformation occurs in the Ti-12Cr alloy during cold rolling. Therefore, the increase in the Young's modulus of the alloy after cold rolling is ascribable to the deformation-induced as phase, which is formed in the alloy during cold rolling at room temperature.

This research focused on development of new titanium alloys with changeable Young's modulus for spinal fixation applications by taking advantage of deformation-induced phase transformation. The microstructures, Young's moduli, and tensile properties of metastable Ti-30Zr-x(Cr, Mo) alloys subjected to solution treatment (ST) and cold rolling (CR) were investigated. During cold rolling, deformation-induced phase transformation occurs in all these alloys. The change in Young's modulus after cold rolling is highly dependent on the type of deformation-induced phase. The decrease in Young's modulus after cold rolling is attributed to the deformation-induced alpha' phase, while the increase in Young's modulus after cold rolling is attributed to the deformation-induced omega phase in {332} mechanical twinning. Ti-30Zr-3Cr-3Mo alloy exhibiting excellent tensile properties and a changeable Young's modulus is a promising candidate for spinal fixation applications.

Ternary beta-type Ti-10Cr-(V, Fe, Mo) alloys with self-tunable Young's moduli were subjected to solution treatment and cold rolling, and their microstructures and mechanical properties were investigated. During cold rolling, a band-like structure, which is considered to be {332},(beta)< 113 >(beta) mechanical twin, and deformation-induced omega phase are formed in alloys with certain chemical compositions. The number of bands increases with an increase in the cold-rolling reduction ratio and V content as well as with a decrease in Mo content. On the other land, the Young's modulus increases during cold rolling, and the increase in Young's modulus is considered to be caused by the deformation-induced omega phase transformation. Furthermore, the tensile strength decreases slightly and the elongation tends to increase with an increase in the alloying element contents, while the effect of the V and Mo contents on the trend in changing the number of mechanical twin is opposite. These tensile properties are derived from the complicated factors among the plastic deformation mode, the type of mechanical twinning, and deformation-induced omega phase transformation, depending on the beta stability and the kind of alloying element.

本研究では,液体急冷凝固法(LRS法)を用い,β相の析出を抑制した本合金に対して再度溶解し,その後の凝固条件すなわち水冷および空冷凝固させた場合,および両凝固後,高温溶体化処理を施した場合におけるβ相の析出挙動から,ミクロ組織と硬さとの関係を検討した.その結果,次のような結論を得た.1.β相の存在しない試料を溶解し,水冷凝固させた組織は等軸晶状組織を呈し,凝固過程でβ相は析出しなかった.高温溶体化処理でもβ相は析出せず,硬さは低下した.空冷凝固の場合はβ相が析出し,高温溶体化処理で硬さは向上した.2.β相の存在するas-received材を溶解・水冷凝固した凝固組織はデンドライト組織を呈し,β相は消失せず存在した.すなわち,1323Kの溶解温度ではβ相は溶解できず,母相に固溶しなかった.さらに,その後の高温溶体化処理でもβ相は消失せず,硬さは向上した.

Strengthening by grain refinement and increasing dislocation density through high-pressure torsion (HPT), which is an attractive technique to fabricate ultrafine grained and nanostructured metallic materials, is expected to provide beta-type Ti-29Nb-13Ta-4.6Zr (TNTZ) higher mechanical strength while maintaining low Young's modulus because they keep the original beta phase. However, the ductility shows reverse trend. Greater strength with enhanced ductility can be achieved by controlling precipitated phases through HPT processing after aging treatment. Aged TNTZ subjected to HPT processing at high N exhibits a homogeneous microstructure with ultrafine elongated grains having a high dislocation density and consequently non-equilibrium boundaries and distorted subgrains with non-uniform shapes and nanostructured intergranular precipitates of alpha phases. Therefore, the effect of HPT processing on the microstructure and mechanical hardness of TNTZ after aging treatment was systematically investigated in this study. TNTZ, which was subjected to aging treatment at 723 K for 259.2 ks in vacuum followed by water quenching, subjected to HPT processing at rotation numbers (N) of 1 to 20 under a pressure of around 1.25 GPa at room temperature. The microstructure of TNTZ(AT) consisted of precipitated needle-like omega phases in beta grains. However, TNTZ(AHPT) at N >= 10 comprises very fine alpha and small amount omega phases in ultrafine beta grains. Furthermore, the hardness of every TNTZ(AHPT) was totally much greater than that of TNTZ(AT). The hardness increased from the center to peripheral region of TNTZ(AHPT). In addition, the tensile strength of every TNTZ(AHPT) was greater than that of TNTZ(AT). The tensile strength of TNIZ(AHPT) increased, but the elongation decreased with increasing N and then both of them saturated at N >= 10.

Change in the microstructure of the L1(0)-type ordered beta' phase precipitated in Ag-20Pd-12Au-14.5Cu alloy (mass%) subjected to solution treatment with varying solution treatment time was investigated. The size of the IT phase is found to decrease with increasing solution treatment time and the Vickers hardness of the alloy after solution treatment decreases. Experimental observations show that the microstructural change of the beta' phase strongly contributes to the change in Vickers hardness. In addition, the formation and growth of the beta' phase are concluded to be affected by the distribution of elements through solution treatment.

In the present study, the effects of the microstructural morphologies of a Ti-6Al-4V (Ti-64) alloy on its fatigue behavior were investigated. Ti-64 bars were Subjected to two different thermo-mechanical processing methods. The first sample, referred to as Material-A, had a forged microstructure with the average primary alpha volume fraction of 44%. The second one, referred to as Material-B, had a hot-rolled microstructure with the average primary alpha volume fraction of 43%. Fatigue tests were performed on each sample to obtain S-N curves. The microstructure of each sample was observed using an optical microscopy in order to measure the grain sizes of the primary alpha and secondary alpha phases. The results of the fatigue tests indicated that Material-B demonstrates better fatigue strength than Material-A. The microstructure of the longitudinal section of each material was also observed to analyze the results of the fatigue tests. The measured diameters and volume fractions of the primary alpha phases of the two types of materials are similar. On the other hand, the secondary alpha width of each material is different. It is found that fatigue strength is related to the width of the secondary alpha phase.

Presently metallic rods that are used for spinal fixtures cannot meet the requirements of both surgeons and patients; surgeons require the material to have a high Young's modulus to suppress springback during the operation, whereas patients require the material to have a low Young's modulus to prevent the stress-shielding effect. In order to develop a novel biomedical titanium alloy with a changeable Young's modulus for spinal fixation applications via deformation-induced omega phase transformation. The effects of deformation-induced phases on the mechanical properties of metastable beta-type Ti-xCr alloys were investigated. The experimental results indicate that the Young's moduli, tensile strength, and Vickers hardness of the Ti-(10-12)Cr alloys increase remarkably by cold rolling. The results of the microstructural observations of Ti-12Cr alloys using a transmission electron microscopy (TEM) show that deformation-induced co phase transformation occurs during cold rolling. Therefore, the increase in Young's modulus of the alloys is attributed to the deformation-induced w phase, which is formed in the alloy during cold rolling at room temperature.

A novel biomedical titanium alloy with the ability to undergo self adjustment in its Young's modulus was developed. In spinal fixation devices, the Young's modulus of the metallic implant rod should be sufficiently high to suppress springback for the surgeon, but should also be sufficiently low to prevent stress shielding for the patient. Therefore, deformation-induced omega phase transformation was introduced into beta-type titanium alloys so that the Young's modulus of only the deformed part would increase during operation, while that of the non-deformed part would remain low. The increase in the Young's modulus due to cold rolling was investigated for a binary Ti-12Cr alloy (mass%). Microstructural observation and Young's modulus measurement reveal that the Ti-12Cr alloy undergoes deformation-induced omega phase transformation and exhibits the increase in the Young's modulus by deformation.

Oxygen enhances the strength of titanium alloys in general; however, excess oxygen can make titanium alloys brittle. On the other hand, oxygen enhances the precipitation of the alpha phase and suppresses the formation of the omega phase. Thus, using the optimal amount of oxygen is important to improve the mechanical properties of titanium alloys. The role of oxygen in titanium alloys is still not well understood. The effect of oxygen on the mechanical behavior of a beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (referred to as TNTZ), which is used for biomedical applications, was investigated in this study. Oxygen was found to stabilize the omega phase in TNTZ. This behavior of oxygen is unusual considering the known behavior of oxygen in titanium alloys: oxygen is known to suppress the formation of the omega phase in titanium alloys. A small amount of oxygen increases the tensile strength but decreases the ductility of TNTZ. On the other hand, a large amount of oxygen, of around 0.7 mass%, increases both the tensile strength and the ductility of TNTZ. This phenomenon is unexpected.

The improvement in fatigue strength, with maintenance of a low Young's modulus, in a biomedical beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), by thermomechanical treatment was investigated. A short aging time at an omega-phase-forming temperature combined with severe cold rolling was employed. A fine omega phase is observed in TNTZ subjected to this thermomechanical treatment. Because the rolling texture of beta phase is formed by cold rolling, such as the omega phase may be preferentially oriented to a direction that is effective for inhibiting the increase in Young's modulus. The samples aged at 573 K (300 A degrees C) for 3.6 ks and 10.8 ks after cold rolling exhibit a good balance between a high tensile strength and low Young's modulus. In the case of the sample aged for 3.6 ks, the tensile strength is improved, although the fatigue strength is not improved significantly. Both the tensile strength and the fatigue strength of the sample aged for 10.8 ks are improved. This fatigue strength is the highest among the TNTZ samples used in the current and in previous studies with Young's moduli less than 80 GPa.

Nowadays, there is a significant research focus on the development of bio-implant materials that have not only a low Young's modulus but also other unique characteristics such as a changeable Young's modulus and the ability to prevent calcium phosphate formation. Taking advantage of deformation-induced phases is an effective way to obtain the changeable Young's modulus. This study investigated the relationship between the various deformation-induced products and the mechanical properties - including Young's modulus, microstructure, and tensile properties - of Ti-30Zr-(5,6,7)mass%Mo alloys subjected to solution treatment (ST) and cold-rolling (CR). After ST, each alloy is composed of a beta phase and a small amount of athermally formed omega phase, and exhibits a low Young's modulus. During CR, deformation-induced phase transformation occurs in all the alloys. The change in Young's modulus due to CR is highly dependent on the types of deformation-induced products. The decrease in Young's modulus due to CR is related to the deformation-induced alpha' phase transformation accompanying with the disappearance of athermal omega phase, and the increase in Young's modulus is attributed to the deformation-induced omega phase, which mainly exists in {332}(beta) mechanical twins. (C) 2011 Elsevier Ltd. All rights reserved.

This research focuses on the development of new titanium (Ti) alloys with a low Young's modulus for use in removable implants. In this study. Ti-30Zr alloy was selected as the base alloy, and the effect of Mo addition on the microstructures, Young's moduli, and tensile properties of Ti-30Zr-(0-8 wt.% Mo) alloys was investigated in this study to assess the mechanical compatibility of these alloys for biomedical applications. Further, the cytocompatibility of a part of the designed alloys was examined. The experimental results indicate that both the microstructures and the mechanical properties of the designed alloys are strongly affected by the Mo contents. The Ti-30Zr-(6, 7 wt.%) Mo alloys, located near the boundary of (beta+omega)/beta with a metastable structure, show a good combination of a low Young's modulus, high tensile strength, fairly large elongation. In addition, Ti-30Zr-7Mo alloy is highly cytocompatible. (C) 2011 Elsevier B.V. All rights reserved.

Porous titanium (pTi) can possess a low Young's modulus equal to that of human bone, depending on its porosity. However, the mechanical strength of pTi deteriorates greatly with increasing porosity. On the other hand, certain medical polymers exhibit biofunctionalities, which are not possessed intrinsically by metallic materials. Therefore, a biodegradable medical polymer, poly-L-lactic acid (PLLA), was used to fill in the pTi pores using a modified in-situ polymerization technique. The mechanical and biodegradable properties of pTi filled with PLLA (pTi/PLLA) as fabricated by this technique and the effects of the PLLA filling were evaluated in this study. The pTi pores are almost completely filled with PLLA by the developed process (i.e., technique). The tensile strength and tensile Young's modulus of pTi barely changes with the PLLA filling. However, the PLLA filling improves the compressive 0.2% proof stress of pTi having any porosity and increases the compressive Young's modulus of pTi having relatively high porosity. This difference between the tensile and compressive properties of pTi/PLLA is considered to be caused by the differing resistances of PLLA in the pores to tensile and compressive deformations. The PLLA filled into the pTi pores degrades during immersion in Hanks' solution at 310 K. The weight loss due to PLLA degradation increases with increasing immersion time. However, the rate of weight loss of pTi/PLLA during immersion decreases with increasing immersion time. Hydroxyapatite formation is observed on the surface of pTi/PLLA after immersion for >= 8 weeks. The decrease in the weight-loss rate may be caused by weight gain due to hydroxyapatite formation and/or the decrease in contact area with Hanks' solution caused by its formation on the surface of pTi/PLLA. (C) 2011 Elsevier Ltd. All rights reserved.

The superelasticity and deformation behaviors of beta-type TiNb24Zr2 subjected to aging treatment were investigated in this study. As the aging time increased, the precipitation of isothermal omega phase was found to restrain the formations of twinning and stress-induced alpha aEuro(3) martensite. The superelastic recovery of the sample first improves and then deteriorates with extended aging times. A maximum and stable superelastic recovery of 4.3 pct is obtained for an aging time of 7.2 ks.

In order to develop a novel alloy with a changeable Young's modulus for spinal fixation applications, we investigated the microstructures, Young's moduli, and tensile properties of metastable Ti-30Zr-(Cr, Mo) alloys subjected to solution treatment (ST) and cold rolling (CR). All the alloys comprise a beta phase and small athermal omega phase, and they exhibit low Young's moduli after ST. During CR, deformation-induced phase transformation occurs in all the alloys. The change in Young's modulus after CR is highly dependent on the type of deformation-induced phase. The increase in Young's modulus after CR is attributed to the deformation-induced omega phase on {3 3 2} mechanical twinning. Ti-30Zr-3Cr-3Mo (3Cr3Mo), which exhibits excellent tensile properties and a changeable Young's modulus, shows a smaller springback than Ti-29Nb-13Ta-4.6Zr, a beta-type titanium alloy expected to be useful in spinal fixation applications. Thus, 3Cr3Mo is a potential candidate for spinal fixation applications. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The microstructures, mechanical properties, and biocompatibilities of as-solutionized Zr-Nb system alloys with different Nb contents for biomedical applications were investigated. The microstructures of Zr-5 mass%Nb, Zr-10 mass%Nb, and Zr-20 mass%Nb alloys subjected to solution treatment (ST) consist of a, α, ω and β phases while the microstructure of Zr-30 mass%Nb alloy subjected to ST consists of almost all single ß phase. Young's modulus of Zr-20 mass%Nb alloy shows the lowest value of 63 GPa among the others alloys although the tensile strength and 0.2% proof stress decrease because of decrease in volume fraction of m phase while Zr-10 mass%Nb alloy with a large amount of ω phase shows the highest values of Young's modulus, tensile strength, and 0.2% proof stress. The elongations of Zr-20 mass%Nb and Zr-30 mass%Nb alloys show relatively high values of 22% and 24%, respectively. The cell viability and bone-bonding characteristics of Zr-Nb system alloys are improved with increasing Nb content. Therefore, it is considered that Zr-Nb alloys have relatively high biocompatibility and belong to bio-inert metallic biomaterial. © 2011 The Japan Institute of Metals.

The frictional wear characteristics, mechanical properties, and biocompatibilities of biomedical Zr-20 mass%Nb alloy (Zr-20Nb) subjected to solution treatment (ST) and air-oxidizing process (ACP) were investigated. Vickers hardness of the specimen surface of Zr-20Nb subjected to AOP at 973 K, 1073 K, and 1123 K are approximately 4.5 times larger than that of Zr-20Nb subjected to ST. Young's modulus of Zr-20Nb subjected to AOP increases with increasing AOP temperature up to 1073 K. 0.2% proof stress, tensile strength, and elongation of Zr-20Nb subjected to each AOP decrease proportionally with increasing AOP temperature, and is inferior to those of Zr-20Nb subjected to ST because of the growth of oxide layer with a large amount of micro-cracks and the diffusion of oxygen into the subsurface. Frictional wear loss of Zr-20Nb subjected to each AOP decreases drastically as compared to that of Zr-20Nb subjected to ST. Bone-compatibility of Zr-20Nb subjected to AOP at 973 K is better than that of AOP at 1073 K because of the existence of some cracks and partial exfoliation of oxide layer.

Plastic deformation behavior and its relation to tensile properties were investigated in an attractive beta-type titanium alloy (Ti-29Nb-13Ta-4.6Zr) with the oxygen content of 0.1-0.7 mass% subjected to hot rolling and solution treatment after hot rolling. Hereafter, Ti-29Nb-13Ta-4.6Zr is abbreviated to TNTZ. With the increase of oxygen content, the tensile strength and 0.2% proof stress of all the samples increase, however, their elongation indicates special change, which is contradictory to that reported conventionally. The elongation firstly decreases and then increases with the increase in the oxygen content. Therefore, TNTZ with high strength and high ductility due to the addition of high oxygen content (0.7 mass%) is obtained. Remarkable yielding phenomenon and strain hardening are observed in TNTZ, which can be explained by the interaction between oxygen atoms and a lot of screw and edge dislocations leading to the easy activation of the multiple slip systems. The deformation behavior changes with the addition of oxygen in TNTZ. The plastic deformation mode changes from the deformation-induced martensite transformation to slip mechanism. It is realized that there is a specific compositional area of oxygen in which the TNTZ exhibits strain hardening and high strength, and appropriate Young's modulus value. (C) 2011 Elsevier B.V. All rights reserved.

TiB(2) was added to beta-type Ti-29Nb-13Ta-4.6Zr (TNTZ) to enhance its mechanical properties and lower its Young's modulus, and the microstructures and mechanical properties of TNTZ with 0.05-0.50 mass%B were investigated. The B concentration of TNTZ was controlled by varying the amount of added TiB(2) TNTZ with 0.05-0.50 mass%B consists of a beta-phase with a small amount ofTiB. As the B concentration increases, these TiB precipitates become increasingly efficient at preventing texture movement. The microstructure of TNTZ is refined by TiB, and the TNTZ grain size decreases as the B concentration increases. Moreover, the Young's moduli of TNTZ with 0.05-0.50 mass%B remain below 70 GPa, and are almost similar to that of TNTZ without TiB. The tensile strength of TNTZ with 0.05-0.50 mass%B is slightly improved, and the optimum tensile strength is enhanced by approximately 8%. TNTZ with 0.10 mass%B exhibits a good balance between tensile strength and the elongation. The results of this study are expected to contribute to the creation of a TNTZ-based material with improved mechanical properties and maintained Young's modulus that can be used as dental and orthopedic biomaterials. (C) 2011 Elsevier B.V. All rights reserved.

Microstructural evolution accompanying mechanical properties change by aging treatment at 723 K in cold-swaged Ti-29Nb-13Ta-4.6Zr were investigated in order to obtain an optimized aging condition for getting excellent mechanical properties. The precipitate free zone exists in Ti-29Nb-13Ta-4.6Zr after aging treatment for various time periods. Such the precipitate free zone corresponds to Nb and Ta-enriched region according to the result of element distribution analysis. With the increase in aging time, the area of the precipitate free zone decreases. Two types of alpha phase, acicular and ellipsoidal ones, are observed in Ti-29Nb-13Ta-4.6Zr after aging treatment for various time periods. The acicular alpha phase is precipitated in the Ti- and Zr-enriched region. While the size increases, the area fraction barely changes with aging time for acicular alpha phase, On the other hand, the ellipsoidal alpha phase precipitates at beta grain boundary and its subgrain boundary. Both the size and area fraction increase with the increase in aging time for the ellipsoidal alpha phase. The lattice correspondence between acicular alpha phase and beta matrix is [ (1) over bar 10](beta)//[12 (1) over bar](alpha), (112)(beta)//((2) over bar 10)(alpha), and [ (1) over bar 10]beta//[00 (1) over bar](alpha), (112)(beta)//(200)(alpha) until 86.4 ks of aging time. However, the lattice correspondence of [ (1) over bar 10](beta)//[12 (1) over bar](alpha), (112)(beta)//((2) over bar 10)(alpha) disappear over 259.2 ks of aging time. Tensile strength of Ti-29Nb-13Ta-4.6Zr subjected to aging treatment after cold swaging is around 1200 GPa, regardless of aging time. On the other hand, elongation of those are decreased by the aging treatment up to 86.4 ks, increased at ones over 259.2 ks.

In spinal fixation devices, the Young's modulus of the metallic implant rod should be not only sufficiently low to prevent stress shielding for the patient but also sufficiently high to suppress springback for the surgeon. This paper proposes a novel function of biomedical titanium alloys self-adjustment of Young's modulus. Deformation-induced omega phase transformation was introduced into beta-type titanium alloys so that the Young's modulus of only the deformed part would increase during operation, while that of the non-deformed part would remain low. The Young's modulus increase by deformation was investigated for a binary Ti-12Cr alloy. This alloy successfully underwent deformation-induced to phase transformation and exhibited the increase in the Young's modulus by deformation. (C) 2010 Elsevier B.V. All rights reserved.

A hydroxyapatite(HAp)film was fabricated on the surface of Ti-29Nb-13Ta-4.6Zr(TNTZ)using a metal-organic chemical vapor deposition(MOCVD)technique, and the mechanical biocompatibility and HAp formability of HApcoated TNTZ were evaluated and discussed in this study. HAp film is fabricated on the surface of TNTZ by controlling the heating temperature of the source bis-dipivaloylmethanatocalcium((Ca(dpm)2)and(C 6H5O)3PO). An α-phase precipitates in the TNTZ matrix after heating the substrate, and the mechanical properties and Young's modulus of HApcoated TNTZ are improved. HAp-coated TNTZ maintains excellent mechanical biocompatibility. The formability of HAp on HAp-coated TNTZ in Hank's balanced salt solution is better than that of HAp on non-coated TNTZ.

The effects of microstructures on the mechanical properties of Ti-4.5Al-2Mo-1.6V-0.5Fe-0.3Si-0.03C(KS Ti-9)were systematically investigated by conducting several heat treatments for next-generation aircraft applications. The mechanical strength of as-received KS Ti-9 exhibits high anisotropy that is derived from the intense texture(T-texture)of the primary α phase. Such high anisotropy is observed in KS Ti-9 annealed at temperatures slightly below β -transus, but it is drastically decreased in KS Ti-9 subjected to an anisotropy controlling treatment. The reduction in the anisotropy for KS Ti-9 is related to the differences in the orientations of the precipitated acicular α phase.

The relationship between microstructures and mechanical properties such as tensile and fatigue properties were systematically investigated by conducting several heat treatments on Ti-4.5Al-4Cr-0.5Fe-0.2C(KS EL-F)and Ti-4.5Al-2Cr-1Fe-0.1(KS EL-F mod)for next-generation aircraft applications. TiC and TiCr2 are formed in KS EL-F and KS EL-F mod annealed at temperatures higher than β -transus and aged at 773 K, respectively. However, the precipitation trends of TiC and TiCr2 are considerably higher in the case of KS EL-F because the amounts of both these precipitates are drastically suppressed in KS EL-F mod even when the heat treatments are identical. As-received KS EL-F and KS EL-Fmod exhibit excellent fatigue strength as compared with annealed Ti-6Al-4V. Although the presence of TiCr2 tends to decrease the fatigue strength, the aged KS EL-F mod exhibits higher fatigue strength than the as-received KS EL-F mod with very low TiCr 2 amounts. Therefore, the aging treatment for KS EL-F mod can be effective in improving the fatigue strength.

本研究の目的は,市販歯科用金銀パラジウム合金の凝固組織中のβ相の有無が1123Kの温度で溶体化処理した場合の硬さにおよぼす影響の検討である.凝固組織にβ相が存在する試料は通常の遠心鋳造法で,β相が存在しない試料は液体急冷凝固法(LRS)で作製した.遠心鋳造材は溶体化処理によってXRDからα相およびβ相,そしてTEM像からβ'相が観察された.一方,液体急冷凝固材は,溶体化処理によりXRDからα相と微量のα₂相が観察されたが,TEM像ではα単相であった.凝固組織中にβ相が存在すると,その後の熱処理によりL1₀型のβ'相の規則化が促進されることで,硬さは向上する.また,673Kの温度で時効処理した場合,凝固組織におけるβ相の有無に係わらず,β相およびβ'相の析出によって硬さは向上した.本実験結果から,1123Kでの溶体化熱処理における硬さの向上は,凝固組織中にβ相が存在する場合のみに出現する.

β-type titanium alloys with low Young's modulus are required to inhibit bone atrophy and enhance bone remodeling for implants used to substitute failed hard tissue. At the same time, these titanium alloys are required to have high static and dynamic strength. On the other hand, metallic biomaterials with variable Young's modulus are required to satisfy the needs of both patients and surgeons, namely, low and high Young's moduli, respectively. In this paper, we have discussed effective methods to improve the static and dynamic strength while maintaining low Young's modulus for β-type titanium alloys used in biomedical applications. Then, the advantage of low Young's modulus of β-type titanium alloys in biomedical applications has been discussed from the perspective of inhibiting bone atrophy and enhancing bone remodeling. Further, we have discussed the development of β-type titanium alloys with a self-adjusting Young's modulus for use in removable implants. © 2011 M. Niinomi and M. Nakai.

A hydroxyapatite (HAp) film was fabricated on the surface of Ti-29Nb-13Ta-4.6Zr (TNTZ) using a metal-organic chemical vapor deposition (MOCVD) technique, and the mechanical biocompatibility and HAp formability of HAp-coated TNTZ were evaluated and discussed in this study. HAp film is fabricated on the surface of TNTZ by controlling the heating temperature of the source (bis-dipivaloylmethanatocalcium (Ca(dpm)(2)) and (C6H5O)(3)PO). An alpha-phase precipitates in the TNTZ matrix after heating the substrate, and the mechanical properties and Young's modulus of HAp-coated TNTZ are improved. HAp-coated TNTZ maintains excellent mechanical biocompatibility. The formability of HAp on HAp-coated TNTZ in Hank's balanced salt solution is better than that of HAp on non-coated TNTZ. [doi:10.2320/matertrans.L-M2010821]

The purpose in this study is to investigate the effect of microstructure on the unique hardening behavior of dental silver alloy, Ag-20Pd-14.5Cu-12Au (mass%), fabricated by hot rolling process (AS material), which is in as-received condition, and liquid rapid solidification (LRS) process (LRS material). The following results were obtained. The microstructure of AS material is consisted of α1, α, and β phases. The microstructure of AS material changes to α, β, and β' phases through a solution treatment (ST). The microstructure of LRS material is consisted of α, α1, and α2 phases without β phase. The microstructure of LRS material becomes single α phase through ST. Relatively large β phases with the diameter of tens of μm on AS material coarsen according to increasing the ST time, while the small those with the diameter of a few μm are solid-soluted into the matrix. On the other hand, the coherent participation of β' phases with long and short axes of around 100 nm and 10 nm, respectively, also occurs during ST although the amount of β' phase decreases with increasing the ST time. The hard-ness and tensile strength of LRS material and LRS material subjected to ST are relatively smaller than those of AS material and AS material subjected to the same treatment. From this results, the effect of solid solution hardening of α, α1 and α2 phases is lower than that of precipitation hardening of β' phases. In a case of the unique hardening seems to occur because the precipitation of β' phases are enhanced during ST. © 2010 The Japan Institute of Metals.

The applicability of a calcia mold to casting a β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), was evaluated with focusing on the dimensional accuracy of the casting in this study. Pure zirconium particles were added to a calcia mold to take advantage of the expansion of oxidized zirconium during the baking process in order to compensate for the solidification shrinkage of TNTZ. The morphological characteristics of the casting surface, such as the roughness and dimensional accuracy, of the cast TNTZ were investigated. The dilation ratio of the calcia mold is found to increase with increasing the number of pure zirconium particles. The addition of 12 mass % or 14 mass % pure zirconium particles compensates for not only the solidification of TNTZ but also the occurrence of shrinkage of the calcia mold. In addition, the formation of a surface reaction layer in TNTZ is restrained to a larger extent by casting into a calcia mold than into a magnesia mold, which is the conventional investment mold for titanium casting. Furthermore, the volume fraction and number of casting defects are also restrained to a larger extent by casting into a calcia mold than into a magnesia mold. The results of this study should lead to enhancements in the creation of cast TNTZ for dental products.

A calcia mold, which is stable at high temperatures for dental precision casting of β-type titanium alloys such as Ti-29mass%Nb-13mass%Ta-4.6mass%Zr alloy (TNTZ) with high melting point, has been developed. The applicability of the calcia mold to casting TNTZ was evaluated with focusing on the mechanical properties of the casting in this study. The molten TNTZ was cast into the calcia mold of which dimensional accuracy was controlled by adding pure zirconium particles. The tensile and fatigue properties of TNTZ cast into the calcia mold were examined with comparing those of TNTZ cast into the magnesia mold, which is the conventional one for casting titanium alloys. The tensile properties of TNTZ cast into the calcia and the magnesia molds are not markedly different The fatigue strength of TNTZ cast into the calcia mold in the low- and high-cycle fatigue life regions is slightly higher than that of TNTZ cast into the magnesia mold. Therefore, the calcia mold is expected to be applicable to the dental precision casting of TNTZ.

Negative thermal expansion, i.e. a type of shrinkage that occurs during heating, was observed in cold-rolled Ti-29Nb-13Ta-4.6Zr alloy (mass%) (TNTZ). The reduction ratio of cold rolling was systematically changed, and then the thermal expansion rate was measured using a dilatometer. The cyclicity of thermal expansion was also examined for the cold-rolled TNTZ. Further, the effect of oxygen content on the thermal expansion behavior of the cold rolled TNTZ was examined. With an increase in the reduction ratio of cold rolling, the thermal expansion rate of TNTZ cold-rolled parallel to the rolling direction (RD) decreases, but it increases in TNTZ cold-rolled parallel to the transverse direction (TD). The cyclicity of above-mentioned anomalous thermal expansion is observed in a temperature range below 473 K, but it is not observed when the specimen is heated to above 573 K in the first cycle. The oxygen suppresses the negative thermal expansion behavior of TNTZ.

A new β-type Ti alloy composed of non-toxic and allergy-free elements like Nb, Ta, and Zr, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) proposed by present authors, has been developed in order to achieve relatively low Young's modulus and excellent mechanical performance. On the other hand, Zr has been also paid attention as metallic biomaterial for the next generation because of good biocompatibility nearly equal to Ti or a few GPa smaller Young's modulus as compared to one. In this study, mechanical performances such as tensile properties and Young's modulus of TNTZ subjected to thermo-mechanical treatments or severe deformation, and the mechanical properties and biocompatibility of Zr-Nb system alloys were investigated in order to judge their potential for biomedical applications. Young's modulus of as-solutionized TNTZ, which is around 63 GPa, is pretty similar to that of as-cold-rolled TNTZ. The Young's moduli of hot-rolled Ti-6Al-4V ELI alloy are respective around 110 GPa. The Young's moduli of as-solutionized and as-cold-rolled TNTZ are around a half of those, and are twice as large as that of the cortical bone. The tensile strengths of TNTZ aged after solution treatment and those aged after cold rolling decrease with an increase in the aging temperature, although the elongation shows the reverse trend. The tensile strength of as-cold-rolled TNTZ is improved drastically through severe deformation such as high pressure torsion and shows more than 1000 MPa. Zr-XNb system alloy (X: 5-30mass%) shows the smallest value of Young's modulus (around 58 GPa) at Nb content of 20mass%. In the case of implantation of the bars made of Zr-XNb system alloys into the lateral femoral condyles of Japanese white rabbits, the tendency of contact between the cancellous bone and the bar becomes remarkably at 24 weeks after the implantation according to increasing with Nb content. © (2010) Trans Tech Publications.

Implanting a spinal fixture using metallic rods is one of the effective treatments for spinal diseases. Because cyclic bending stress is loaded on the implant rods when patients move their upper bodies in daily life, bending fatigue properties are important for the implant rod. Further, the implant rods are bended plastically into a curved shape of spine by hand in a surgical operation. In that case, keeping shape is important, namely bending spring back properties are important factors. On the other hand, a biomedical beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (mass %) alloy (TNTZ), has been developed by the authors. Currently, this alloy are investigated to be applied to the above mentioned implant rod practically. Therefore, four-point bending fatigue and three point-bending spring back properties of TNTZ subjected various heat treatments were examined in this study. TNTZ rods were subjected to solution treatment, and then some of them were subjected to aging treatment at 673 K or 723 K for 259.2 ks, followed by water quenching. Then, four-point bending fatigue and three-point bending spring back tests were carried out on TNTZ rods subjected to the various heat treatments mentioned above. The bending fatigue strength at 2.5 million cycles in the high cycle fatigue region are not much different among any TNTZ rod. However, the bending fatigue strength of the Ti-6Al-4V ELI (Ti64) rod exceeds the fatigue strengths of every TNTZ rods in both low and high cycle fatigue regions. On the other hand, the lower spring back, which is a favorable property, was obtained for some TNTZ rod than Ti64 rod.

The applicability of a calcia mold to casting a beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ). was evaluated with focusing on the dimensional accuracy of the casting ill this study. Pure zirconium particles were added to a calcia mold to take advantage of the expansion of oxidized zirconium during the baking process in order to compensate for the solidification shrinkage of TNTZ. The morphological characteristics of the casting surface. such as the roughness and dimensional accuracy. of the cast TNTZ were investigated. The dilation ratio of the calcia mold is found to met ease with increasing the number of pure zirconium particles. The addition of 12 mass% or 14 mass% pure zirconium particles compensates for not only the solidification of TNTZ but also the occurrence of shrinkage of the calcia mold. In additions the formation of a surface reaction layer in TNTZ is restrained to a larger extent by casting into a calcia mold than into a magnesia mold, which is the conventional investment mold for titanium casting. Furthermore, the volume fraction and number of casting defects are also restrained to a larger extent by casting into a calcia mold that into a magnesia mold. The results Of this study should lead to enhancements in the creation of cast TNTZ for dental products. [doi:10.2320/matertrans.L-M2009827]

A calcia mold which is stable at high temperatures for dental precision casting of beta-type titanium alloys such as Ti-29Nb-13Ta-4.6Zr (TNTZ) with high inching point, has been developed. The applicability of the calcia mold to casting TNTZ was evaluated with focusing oil the mechanical properties of the casting in this study. The molten TNTZ was cast into the calcia mold of which dimensional accuracy was controlled by adding pure zirconium particles. The tensile and fatigue properties of TNTZ cast into the calcia mold were examined with comparing those of TNTZ cast into the magnesia mold, which is the conventional one for casting titanium alloys. The tensile properties of TNTZ cast into the calcia and the magnesia molds are not markedly different. The fatigue strength of TNTZ cast into the calcia mold in the low- and high-cycle fatigue life regions is slightly higher than that of TNTZ cast into the magnesia mold. Therefore, the calcia mold is expected to he applicable to the dental precision casting, of TNTZ. [doi:10.2320/matertrans.L-M2009828]

Ti–30Nb–10Ta–5Zr–0.3O (TNTZO) alloy, which is simplified chemical composition similar to that of biomedical Ti–29Nb–13Ta–4.6Zr alloy, and the same system alloys of TNTZO with different oxygen (O) and niobium (Nb) contents such as Ti–30Nb–10Ta–5Zr–0.5O, Ti–30Nb–10Ta–5Zr–0.6O alloys, and Ti–27Nb–10Ta–5Zr–0.3O, Ti–28Nb–10Ta–5Zr–0.3O and Ti–29Nb–10Ta–5Zr–0.3O alloys are fabricated by powder metallurgy processing, in which it undergoes severe deformation during swaging. Changes in the deformation behaviors of these alloys caused by small changes in the O and Nb contents are investigated in this study. The stress–strain curve of TNTZO changes nonlinearly with the strain and is characterized by a small stress hysteresis, indicating that TNTZO shows a nonlinear recovery behavior during unloading. This deformation in the alloy is a result of a typical elastic deformation as well as stress-induced martensitic transformation. However, with an increase in the O content, as in the case of alloys with 0.5O and 0.6O, the stress–strain curves change almost linearly with the strain and exhibit a linear recovery behavior during unloading without stress hysteresis. In such alloys, deformation is mainly caused by the typical elastic deformation. On the other hand, with a decrease in the Nb content, the stress–strain curves show two steps with an increase in the strain, and deformation is accompanied by stress hysteresis during both loading and unloading. This deformation is mainly caused by stress-induced martensitic transformation and reverse transformation.

Mechanical properties of beta-type biomedical Ti-29Nb-13Ta-4.6Zr (mass %) (TNTZ), which exhibits non-toxicity and a low modulus similar to that of cortical bone, is improved by thermomechanical treatments, including severe cold swaging. Simultaneously, the biocompatibility of a TNTZ spinal implant rod with living tissue is evaluated using ovines, and TNTZ is proved to show good biocompatibility with bovine tissue.

A peculiar effect of oxygen on co-phase stability, i.e., the enhancement of the isothermal co-phase formation during aging due to oxygen addition was observed in the Ti-29Nb-13Ta-4.6Zr; this effect is contradictory to that reported conventionally. The effect was analyzed from the viewpoint of distribution of alloying elements. Oxygen and/or zirconium may dissolve in the omega phase during aging, resulting in the stabilization of the omega phase in this alloy.

Y2O3 was added to beta-type Ti-29Nb-13Ta-4.6Zr (TNTZ) in order to achieve excellent mechanical performance and low Young's modulus. TNTZ specimens with 0.05%-1.0% Y are all found to be composed of a beta phase. Young's moduli of TNTZ with 0.05-1.0% Y are all maintained low, and are almost the same as that of TNTZ without Y2O3. The grain size of TNTZ with 0.05%-1.0% Y is smaller than that of TNTZ without Y2O3. Moreover, Y2O3 precipitates can prevent the texture movement, and this effect becomes more obvious with an increase in the Y concentration. The tensile strength of TNTZ is successfully improved by adding Y2O3. TNTZ specimens with 0.2% and 1.0% Y exhibit good balance between the tensile strength and the elongation.

Hardness of Ag-20Pd-12Au-14.5Cu (mass%) subjected to a solution treatment (ST) at a temperature over 1073 K followed by water quenching increases drastically. This unique hardening behavior is not clarified becasue of their complex microsturucures. In this study, the relationship between the unique hardening behaviour and the microstructure of dental Ag-20Pd-12Au-xCu subjected to ST with different Cu/Ag ratios was investigated. The Vickers hardness of Ag-20Pd-12Au-14.5Cu increases remarkably from 192 to 286 Hv after ST whereas that of Ag-20Pd-12Au-6.5Cu decreases and that of Ag-20Pd-12Au-20Cu increases slightly after ST, respectively. The spotty regions are observed in only certain areas of Ag-20Pd-12Au-14.5Cu subject to ST. It is considered that the appearance of the spotty regions affects mainly to the unique hardening behaviour in Ag-20Pd-12Au-xCu.

Oxygen plays very important roles in titanium and its alloys. Solute oxygen in titanium alloys leads to solid solution strengthening, suppressing the precipitation of the athermal omega or orthorhombic martensite phase, enhancing the formation of the alpha-case, etc. The proper using oxygen is effective to improve the mechanical functionalities of titanium alloys. However, the role of oxygen in titanium alloys is still not well understood. Therefore, the effect of oxygen on the mechanical functionalities such as strength-ductility balance, hardness, and Young's modulus in Ti-29nb-13Ta-4.6Zr was investigated.

Porous metallic materials can have a low Young's modulus, which is approximately equal to that of human bone, by controlling the porosity. On the other hand, certain medical polymers exhibit biofunctionalities that are not intrinsically present in metallic materials. Therefore, a composite consisting of these materials is expected to possess both these advantages for biomedical applications. However, in the case of using porous metallic materials, the deterioration of mechanical properties should of concern because a stress concentration may be induced near the pores.In this study, for the fabrication of the abovementioned composite, a versatile process for filling a medical polymer into a porous metallic material has been developed using porous pure titanium (pTi) and polymethylmethacrylate (PMMA). Then, the tensile strength and Young's modulus of pTi filled with PMMA (pTi/PMMA) fabricated using this process are systematically investigated.The tensile strength of pTi can be improved by the PMMA filling, Particularly, the improvement in the tensile strength of pTi pretreated using a silane coupling agent before PMMA filling is greater than that of the non-pretreated pTi because the stress concentration near the pores may be reduced by the improvement in the interfacial adhesiveness between the titanium particles and the PMMA. in contrast, the effect of the PMMA filling on the Young's modulus of pTi is smaller than that on the tensile strength because the Young's modulus of PMMA is considerably lower than that of pTi. Further, tensile strengths and Young's moduli comparable to the tensile strength and Young's modulus of the human bone are successfully obtained in the case of some pTi/PMMA samples. (C) 2009 Elsevier Ltd. All rights reserved.

The effect of oxygen content on the microstructure and mechanical properties of the Ti-29 mass%Nb-13 mass%Ta-4.6 mass%Zr (TNTZ) alloy was investigated in this study. The microstructural observation of TNTZ alloys, containing 0.1-0.4 mass% oxygen, subjected to solution treatment shows the presence of a single phase. With an increase in oxygen content, the hardness, tensile strength, and Young's modulus of TNTZ alloy increase, but its elongation decreases. Further, the a phase precipitates in TNTZ alloys subjected to aging treatment at 723 K for 259.2 ks. The results of transmission electron microscopy and X-ray diffraction analysis indicate that the size and volume fraction of the a phase increase with oxygen content. Corresponding to the changes in the microstructure. the mechanical properties of TNTZ alloy subjected to aging treatment at 723 K change with oxygen content. The increase in oxygen content leads to enhancement of the age hardening of TNTZ alloy, thereby increasing both tensile strength and Young's modulus of TNTZ alloy, but its elongation decreases due to the a-phase precipitation. The mechanical properties of TNTZ alloy (Young's modulus: around 60-100 GPa, tensile strength: around 600-1400 MPa, and elongation: around 5-25%) vary significantly depending on oxygen content and heat treatment. [doi: 10.2320/matertrans.MA200904]

The objective of this study is to develop a dental precision casting process for a beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy which has been developed for biomedical applications, using a mold made by electrically fused calcia particles. The effect of a combination of different sizes of calcia particles on the surface condition of the mold was investigated. In addition, to obtain a smooth surface, a cast TNTZ was made using a mold made using a mixture of calcia particles with a wax pattern conducted with calcia Slurry coatings. Furthermore, surface reaction layer of the cast TNTZ was evaluated using an optical microscopy. a Vickers' hardness test and a X-ray diffractometry. The surface of the mold fabricated with a mixture of fine (diameter < 0.3 mm) and coarse (diameter = 1-3 mm) calcia particles is smooth and showed no cracks or defects. In addition, the Surfaces of the cast TNTZ made using the duplex-coated wax pattern with the fine pure calcia slurry and crushed silica fiber-rein forced fine calcia slurry are very line. Furthermore, the formation of the surface reaction layer on the cast TNTZ is remarkably inhibited. The results of this study should lead to enhancements in the creation of cast TNTZ for dental products. [doi: 10.2320/matertrans.M2009139]

There is a possibility for beta-type Ti-29Nb-13Ta-4.6Zr(TNTZ) to exhibit super-elastic characteristics, which is advantageous for biomedical applications such as orthodontic wires. Thermomechanical treatments are expected to induce super-elastic characteristics in beta-type titanium alloys. Therefore, TNTZ specimens were subjected to various thermomechanical treatments, including solution treatments and severe cold rolling, wherein the second solution treatment temperature, second solution treatment time, and reduction ratio of cold rolling were varied in order to investigate the elastic deformation characteristics. One of the thermomechanical treatments induces super-elastic characteristics in a TNTZ specimen. In particular, a highest total pseudoelastic strain of 2.8% is measured in the TNTZ specimen subjected to the thermomechanical treatment at a cold rolling reduction ratio of 95%, second solution treatment temperature of 1073 K, and second solution treatment time of 0.3 ks. Tensile loading and unloading stress-strain curves of the TNTZ specimens subjected to various thermomechanical treatments indicate a high total pseudoelastic strain and exhibit three step deformation process. An alpha '' martensite phase is formed in the TNTZ specimen subjected to the thermomechanical treatment carried out under the above mentioned conditions. [doi:10.2320/matertrans.MF200922]

Negative thermal expansion, i.e. a type of shrinkage that occurs during heating, was observed in cold-rolled Ti-29Nb-13Ta-4.6Zr alloy (mass%) (TNTZ). The reduction ratio of cold rolling and the angle of the longitudinal axis of specimens with respect to the cold-rolling direction were systematically changed, and then the thermal expansion rate was measured using a dilatometer. Further, the cyclicity of thermal expansion was examined for the cold-rolled TNTZ. From the results, it is observed that with an increase in the reduction ratio of cold rolling, the thermal expansion rate of TNTZ cold-rolled parallel to the rolling direction (RD) decreases, but it increases in TNTZ cold-rolled parallel to the transverse direction (TD). With regard to the anisotropy of thermal expansion, the thermal expansion rate increases with the angle between the longitudinal axis of the specimens and RD. Further, the cyclicity of the above-mentioned anomalous thermal expansion is observed in a temperature range below 473 K, but it is not observed when the specimen is heated above 573 K in the first cycle. [doi: 10.2320/matertrans.MRP2008380]

Currently, β-type Ti-Nb-Ta-Zr alloys are gaining attention owing to their feasibility for use as biomedical materials. However, the deformation behaviors of these alloys have not yet been clarified. In this study, the Nb content of the Ti-30Nb-10Ta-5Zr (TNTZ) alloy was altered between 1.0 and 3.0 mass% from 30 mass%, and the corresponding changes in the superelasticity and shape-memory characteristics were investigated by tensile loading-unloading tests, X-ray diffraction (XRD) analysis, and microstructural analysis using a transmission electron microscopy (TEM). When the Nb content is less than approximately 29 mass%, the loading-unloading stress-strain curves show two-step gradients and are similar to those of common shape-memory alloys such as Ti-Ni alloys; these gradients result from stress-induced martensitic transformation and its reversion. When the Nb content is approximately 30 mass%, the tensile loading-unloading curves show a nonlinear gradient corresponding to superelastic behavior, which can not be explained by XRD and TEM microstructural analyses on stress-induced martensitic transformation and its reversion in the present state. When the Nb content is approximately 31 mass%, the tensile loading-unloading curves show a single gradient. The elastic deformation is mainly caused by the elastic strain in the lattice. Changes in the chemical content of Nb in TNTZ within a very narrow range are found to alter the superelastic behavior of this alloy.

Metallic biomaterials with a higher Young's modulus than that of a bone adversely affect bone healing and remodeling. Therefore, it is important to develop the metallic biomaterials having a low Young's modulus. Porous materials are advantageous from this viewpoint because the Young's modulus decreases with increasing porosity. However, with an increase in porosity, the other mechanical properties start deteriorating simultaneously. In comparison with metallic biomaterials, polymers exhibit lower Young's moduli; therefore, a polymer filling is a possible option to improve the mechanical properties of porous materials by preventing the stress concentration at the pores without increasing the Young's modulus. Furthermore, certain polymers exhibit intrinsic biofunctionalities. Thus, a polymer filling is expected to prevent an increase in the Young's modulus and impart biofunctionalities to porous materials without deteriorating their mechanical properties. In this study, porous pure titanium (pTi) with a porosity of 22%-50% and filled with a medical polymer (polymethylmethacrylate: PMMA) (pTi/PMMMA) was firstly fabricated. The effects of the PMMA filling on the tensile strength of pTi were then investigated. However, the deterioration of mechanical properties was not satisfactorily prevented because of the poor interfacial adhesiveness between the titanium particles and the medical polymer. Therefore, in the present study, silane-coupling treatment was employed in order to improve the interfacial adhesiveness, and silane-coupling-treated (Si-treated) pTi filled with PMMA (Si-treated pTi/PMMA) was fabricated. The effect of the silane-coupling treatment on the mechanical properties of pTi/PMMA was investigated.It is found that the PMMA filling improves the tensile strength of pTi that has a porosity of over 40%. The tensile strengths of Si-treated pTi/PMMA are greater than those of pTi and pTi/PMMA. In the fractographs of pTi/PMMA obtained after the tensile test, the detachment of titanium particles from PMMA is observed; this occurs because of poor interfacial adhesiveness between titanium particles and PMMA. However, in the case of Si-treated pTi/PMMA, the interfacial adhesiveness between titanium particles and PMMA is improved by the silane-coupling treatment. This leads to the dispersion of the stress concentration at the necks between particles, resulting in an improvement in the tensile strength of pTi. On the other hand, the PMMA filling hardly affects the Young's modulus of pTi because the Young's modulus of PMMA is lower than that of pTi.

Implanting a spinal fixture by using implant rods is one of the effective treatments for spinal diseases. Most of the implant rods are made of the Ti-6Al-4V ELI alloy (Ti64). However, some problems regarding using Ti64 rods have been pointed out; these rods contain vanadium, which is highly toxic to the human body, and exhibit a considerably higher Young's modulus than the cortical bone. The Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) developed by the authors exhibits good biocompatibility due to its nontoxic- and nonallergic- components. Further, TNTZ has a lower Young's modulus as compared to Ti64. It is expected that implant rods made of TNTZ exhibiting low Young's modulus will prevent the accelerated degeneration of the segment adjacent to a fusion. The mechanical properties of TNTZ rods subjected various heat treatments are comprehensively evaluated through tensile tests, Young's modulus measurement, and four-point bending fatigue tests based on the ASTM F2193 standard and compared with those of Ti64 rods. Among the TNTZ rods used in this study, the TNTZ rod aged at 673 K (Rod(673) (K)) exhibits the highest tensile strength because of the precipitation of the isothermal omega-phase and alpha-phase in it. The tensile strength of Rod(673) (K) exceeds that of Ti64, while the increase in Young's modulus of the former is suppressed below that of the latter. With regards to four-point bending fatigue strength, no advantages are obtained from every TNTZ rods in comparison with Ti64 rod.

The effect of oxygen content on the microstructure and mechanical properties of Ti-29Nb-13Ta-4.6Zr (TNTZ) solutionized and aged at 723 K was investigated. The microstructure of solutionized TNTZ consists of a single,6 phase, and addition of oxygen leads to the increase in the hardness and tensile strength because of solid solution hardening, and the increase in Young's modulus, and the decrease in the elongation. On the other hand, the alpha phase precipitates in the aged TNTZ. The results of transmission electron microscopy and X-ray diffraction imply that the size and volume fraction of the alpha phase increase with the oxygen content in the aged TNTZ. The mechanical properties of the aged TNTZ change with the oxygen content. Age hardening in aged TNTZ is enhanced by an increase in the oxygen content. Further, with an increase in the oxygen content, both the tensile strength and Young's modulus increase, while elongation decreases due to the precipitation of the alpha phase. TNTZ with different mechanical properties (Young's modulus: around 60-100 GPa, tensile strength: around 600-1400 MPa, elongation: around 5-25%) can be obtained depending on the oxygen content and the heat treatment technique.

Binary titanium alloys containing Nb or Ta, which are allergy-free and non-toxicity elements, were fabricated, and then the possibility of their application to various music instruments made of brass was investigated by the evaluation of corrosion characteristics, elastic modulus-density ratio (E/ρ), resonance frequency (f) and internal friction (Q -1). The practical models of the mouthpieces of the trumpets made of the binary titanium alloys were also fabricated by precision casting method in order to compare directly with the sound characteristics of those made of brass and commercially pure Ti. The critical current density for the passivation of the Ti-Nb and Ti-Ta system alloys is approximately 40% lower than that of brass and nearly equal to or a little higher than that of commercially pure Ti. The Q -1 of the Ti-Nb and Ti-Ta system alloys with α″ phase drastically increase. The E/ρ and f of the Ti-Nb and Ti-Ta system alloys exhibit a positive relationship. The sound characteristics of practical mouthpieces of trumpets for a bass instrument can be controlled by changing the E/ρ and/of the alloys.

As a new type of metallic biomaterial, porous pure titanium filled with a medical polymer has been developed for obtaining a low Young's modulus similar to that of bone. This type of biomaterials will inhibit the deterioration of mechanical properties due to the presence of pores, and provide biofunctionalities that are intrinsically possessed in certain polymers. However, the inhibition of the deterioration of mechanical properties is not satisfactory because of the poor interfacial adhesiveness between the titanium particles and the medical polymer. Therefore, in the present study, silane coupling treatment is employed in order to improve the interfacial adhesiveness, and silane-coupling-treated (Si-treated) porous pure titanium (pTi) filled with polymethylmethacrylate (PMMA) is fabricated. Subsequently, the effect of the silane coupling treatment on the mechanical properties of the pTi filled with PMMA is investigated.The tensile strengths of the Si-treated pTi filled with PMMA are higher than those of pTi and non-Si-treated pTi filled with PMMA. In the fractographs of non-Si-treated pTi filled with PMMA obtained after the tensile test, the detachment of titanium particles from PMMA is observed; this occurs because of poor interfacial adhesiveness between titanium particles and PMMA. However, in the case of the Si-treated pTi filled with PMMA, the interfacial adhesiveness between titanium particles and PMMA is improved by the silane coupling treatment. This leads to the dispersion of the stress concentration at necks between particles, resulting in an improvement in the tensile strength of pTi. On the other hand, PMMA filling hardly affects Young's modulus of pTi because Young's modulus of PMMA is lower than that of pTi.

Installing a spinal fixture using implant rods is one of the effective operations for spinal diseases. Most of the implant rods are made of Ti-6Al-4V ELI alloy (Ti64). However, some problems regarding the Ti64 rod have been pointed out; it contains vanadium, which is considerably toxic to the human body, and exhibits a much higher Young's modulus than that of the cortical bone. Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) developed by the authors exhibits good biocompatibility due to its nontoxic- and allergy- free elements, and has a lower Young's modulus than that of Ti64. In addition, the mechanical properties of TNTZ can be changed drastically according to various heat treatments. The mechanical properties of TNTZ rods subjected to various heat treatments have been investigated in this study. The as-solutionized TNTZ rod consists of a single beta phase. Isothermal omega phase and alpha phase precipitate in the beta phase of the TNTZ rod aged at 673 K for 259.2 ks. Only alpha phase precipitates in the beta phase of the TNTZ rod aged at 723 K for 259.2 ks. Tensile strength and 0.2% proof stress become larger in order of as-solutionized TNTZ rod, TNTZ rod aged at 723 K for 259.2 ks and TNTZ rod aged at 673 K for 259.2 ks, while elongation is smaller in order of as-solutionized TNTZ rod, TNTZ rod aged at 723 K for 259.2 ks and TNTZ rod aged at 673 K for 259.2 ks. Young's modulus become larger in order of as-solutionized TNTZ rod, TNTZ rod aged at 723 K for 259.2 ks and TNTZ rod aged at 673 K for 259.2 ks.

Relationships between fatigue properties and microstructures of hot-forged Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) in under aged, peak aged, and over aged conditions at aging temperatures of 673K and 723K are investigated. The changes in the fatigue properties of TNTZ subjected to thermomechanical treatments, which includes an aging treatment at 673K or 723K for 259.2ks after a severe deformation process by cold rolling, are also investigated. At an aging temperature of 673K, ω phase precipitates at the early stage of aging, but α phase precipitates at relatively longer aging time. The precipitation site of α phase changes from intra-grain to grain boundary at around peak aging time when TNTZ is aged at 673K and 723K. The elastic modulus of TNTZ increases simply with increasing aging time at both 673K and 723K The fatigue strength of TNTZ increases considerably when α phase precipitates compared with when ω+α phases co-exist. The fatigue strength of TNTZ decreases slightly due to the coarsening of α phase precipitated in β grain and its grain boundary. TNTZ aged at 723K for 259.2ks after cold rolling exhibits the highest fatigue strength in both the low- and high-cycle fatigue life regions. Furthermore, the fatigue limitof about 770MPa (fatigue raito : 0.71) is nearly equal to that of hot-forged Ti-6Al-4V ELI alloy subjected to aging after solution treatment with equiaxed α structure. © 2008 The Society of Materials Science.

The surface oxide film on a Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) was precisely characterized using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) to understand the composition and chemical state of the surface oxide film of TNTZ. For comparison, the component metals, titanium, niobium, tantalum, and zirconium, were also characterized to consider the effect of those on the formation of the surface oxide film on their alloy. The characterization of the surface oxide films on TNTZ and its component revealed the following issues. The surface oxide film on TNTZ consists of a composite oxide that contains titanium, niobium, tantalum, and zirconium but forms continuous layer and is very thin, ca. 3.7 nm. The oxide film is not completely oxidized because it contains various valences of cations. In particular, the oxidation of tantalum is inhibited in the oxide. Tantalum is enriched in the substrate in TNTZ just under the surface oxide because of this inhibition in the oxidation. The formation of the surface oxide film in TNTZ is predominantly governed by titanium. The preferential oxidation of an element is not always dependent on the initial oxidation potential of that element, the relationship between the oxidation energy from a smaller valence to a larger valence, and the dehydration process. In other words, a complicated competition governs the resultant composition of surface oxide. (C) 2008 Elsevier Ltd. All rights reserved.

The microstructure and hardness near the surface of a biomedical titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), subjected to gas nitriding at 1023-1223 K was investigated in comparison with the conventional biomedical Ti-6Al-4V ELI (Ti64). After gas nitriding, the microstructure near the specimen surface was observed by optical microscopy, X-ray diffraction (XRD), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). In both alloys, two types of titanium nitrides (TiN and Ti(2)N) are formed and the a phase is precipitated by gas nitriding. Furthermore, the oxygen impurity in the gas nitriding atmosphere reacts with the titanium nitrides; thus, TiO(2) is formed at the outermost titanium nitride layer. The surface hardening was also evaluated by Vickers hardness measurement. The Vickers hardness near the surface of TNTZ and Ti64 increases significantly by gas nitriding. (c) 2007 Published by Elsevier B.V.

High Young's modulus of metallic biomaterials in comparison with that of bone affects harmfully on bone healing and remodeling. Therefore, it is important to decrease Young's modulus of the metallic biomaterials. In that case, porous materials are advantageous from the viewpoint of obtaining a lower Young's modulus, because Young's modulus decreases with increasing porosity of the porous materials. However, with an increase in porosity, the other mechanical properties start deteriorating simultaneously. This deterioration of the mechanical properties is probably derived from the stress concentration at the pores of the porous materials. In comparison with metallic biomaterials, polymers exhibit lower Young's moduli thus a polymer filling is a likely option to improve the mechanical properties of porous materials by preventing the stress concentration at the pores without increasing the Young's modulus. Furthermore, certain polymers exhibit intrinsic biofunctionalities, Thus, polymer filling is expected to improve the mechanical properties and impart biofunctionalities to porous materials without an increase in its Young's modulus. In this study, the pores of porous pure titanium (pTi) with the porosity of 22-50% were filled with a medical polymer (polymethylmethacrylate: PMMA). The effects of PMMA filling on the tensile strength and Young's modulus of pTi were then investigated. As a result, it is found that the PMMA filling improves the tensile strength of pTi with the porosity over 40%, although not significantly affecting the Young's modulus of pTi.

Ti-XNb-10Ta-5Zr (mass %) alloys based on nominal compositions of Ti-35Nb-IM-5Zr,Ti-30Nb-10Ta-5Zr, and Ti-25Nb-10Ta-5Zr were fabricated through powder metallurgy and forging and swaging processes for biomedical applications. The tensile deformation mechanisms of the Ti-25Nb-10Ta-5Zr, Ti-30Nb-10Ta-5Zr, and Ti-35Nb-10Ta-5Zr alloys were investigated in situ by X-ray diffraction analysis under several loading conditions. Under the loading conditions, the X-ray diffraction peaks of all the specimens shifted to higher angles than those obtained under the unloading conditions. For the Ti-30Nb-10Ta-5Zr alloy, the elastic deformation is considered to progress continuously in a different crystal direction although after the elastic strain reaches elastic limit in the crystal direction where the elastic limit is the smallest, slip deformation occurs in that crystal direction. The elastic modulus of this alloy appears to decrease in terms of strain over the proportional limit. Thus, the elastic deformation behavior of the Ti-30Nb-10Ta-5Zr alloy does not obey Hooke's law. (c) 2007 Elsevier B.V. All rights reserved.

Beta-type titanium alloys used in biomedical applications have been developed all over the world. In particular, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) is one of beta-type titanium alloys for biomedical applications that has been developed by the authors in Japan. Although TNTZ is composed of non-toxic elements such as niobium, tantalum, and zirconium, it still lacks bioactivity, which is the ability to form chemical bonds with living bones. The stems that are parts of artificial hip joints, dental implants, etc., which are made of metallic materials, etc. are required to bond strongly with living bones. However, these stems, dental implants etc., cannot form chemical bond with living bones by themselves. The bioactive surface modification of metallic materials by the application of ceramics is effective in improving the biocompatibility of TNTZ. Calcium phosphate ceramics such as hydroxyapatite (Ca-10(PO4)(6)OH2; HAP) and beta-tricalcium phosphate (beta-Ca-3(PO4)(2); beta-TCP) possess bioactivity. In this study, the characteristics and morphology of TNTZ coated with a calcium phosphate invert-glass-ceramic (CPIG) layer by dip-coating treatment or with a sodium titanate layer by alkali solution treatment are investigated before and after soaking it in a simulated body fluid (SBF). The bonding strength between a CPIG layer with a thickness of around 5 mu m and a specimen surface of TNTZ is around 25 MPa. No cracks or exfoliations are observed along the boundary between the CPIG layer and the specimen surface. This is the reason why the difference in the thermal expansion coefficients between CPIG layer and TNTZ reduced due to a compositional gradient zone with a thickness of around 3 mu m in CPIG layer. HAP is formed on the entire surface of the TNTZ specimen after soaking it in the SBF for more than 1728 ks. The fatigue properties of TNTZ coated with a CPIG layer are similar to those of as-solutionized TNTZ. A reticulate structure with a thickness of 400 to 800 nm is formed on the TNTZ specimen surface after soaking it in 3 to 10 kmol/m(3) NaOH solution for 86.4 ks and 172.8 ks. HAP is completely formed on the entire surface of the TNTZ specimen when it is soaked in the SBF for 1209.6 ks after being soaked in 5 kmol/m(3) NaOH solution for 172.8 ks.

From the results obtained in this study, an important guideline for designing new titanium alloys with excellent mechanical properties for medical applications, which have the functionalities: e.g. low Young's modulus and super-elasticity, through thermomechanical treatments can be obtained.

In addition to composing safe elements, with regard to the long-term usage of biomaterials, the following factors are considered to be critical: the mechanical biocompatibilities such as the Young's modulus, the functionalities such as superelasticity and shape memory characteristics, and the mechanical properties including fatigue characteristics, fretting fatigue characteristics, fracture toughness, and wear characteristics. The Young's modulus and the functionalities are very important and have attracted considerable attention.

The Nb content of TNTZ (Ti-29Nb-13Ta4.6Zr) was changed by 1 mass% to 2 mass% below 30 mass%. The change in the behavior of functionalities such as superelasticity and the shape- memory effect was investigated by tensile loading-unloading tests, X-ray analysis and differential scanning calorimetric (DSC) analysis. When the Nb content is below approximately 28 mass%, the tensile loading-unloading stress-stain curve is similar to that representing the general shape-memory behavior, which occurs due to deformation induced martensitic transformation and its reversion. When the Nb content ranges from approximately 29 mass% to 30 mass%, the tensile loading-unloading curve exhibits superelastic behavior that cannot be explained by deformation- induced martensitic transformation and its reversion. A change in the chemical content of Nb in TNTZ within a very narrow range alters the superelastic behavior of this alloy.

Low Young's modulus is an important property for metallic biomaterials. Porous materials are advantageous from the point of view of obtaining a lower Young's modulus. However, with a decrease in Young's modulus, the other mechanical properties start deteriorating simultaneously. In comparison with metallic biomaterials, polymers exhibit lower Young's moduli; and thus a polymer filling is a likely option to improve the mechanical properties of porous materials by preventing the stress concentration at the pores without increasing the Young's modulus. Furthermore, certain polymers exhibit intrinsic biofunctionalities. Thus, polymer filling is expected to prevent an increase in the Young's modulus and impart biofunctionalities to porous materials without the deterioration of its mechanical properties. In this study, the pores of porous pure titanium (pTi) were filled with a medical polymer (polymethylmetbacrylate: PMMA). The effects of PMMA filling on the mechanical properties of pTi were then investigated.

Dental Ag-Pd-Cu-Au-Zn system alloy, which is a semi-precious alloy, is one of the most widely used metallic dental materials in Japan due to its excellent mechanical properties and corrosion resistance and applicability to health insurance. Dental products, e.g., inlays and crowns, fabricated from this alloy are used under cyclic loading conditions including frictional wear, when it comes in contact with the same or other dental materials in the oral cavity or an opposing tooth during mastication. The effects of microstructures of Ag-20 mass%Pd-14.5 mass%Cu-12 mass%Au-2 mass%Zn alloy on the fretting-fatigue properties are, therefore, investigated in this study. The fretting-fatigue strength of the Ag-20 mass%Pd-14.5 mass%Cu-12 mass%Au-2 mass%Zn alloy subjected to solution treatment (ST) and aging treatment (AT) decreases significantly as compared to the fatigue strength without fretting (plain-fatigue strength). Moreover, the fretting-fatigue strength after the AT decreases by approximately 60% as compared to that after the ST, especially in the high-cycle fatigue life region. Several traces of fretting wear are observed to be distributed in the slip region of both materials. These wear traces are generated due to the accumulation of wear debris on the fretting pad or the fretting fatigue specimen. These traces of fretting wear are distributed more closely in the slip region of the AT material. Therefore, the fatigue life decreases significantly because the fretting fatigue crack initiation life and the propagation life decrease in the AT material. © 2008 The Japan Institute of Metals.

Frictional wear resistance is one of the important properties of metallic biomaterials. Surface hardening treatments such as oxidizing, nitriding and ion implantation tend to be applied for improving the wear resistance of titanium and its alloys. The simple gas nitriding process is expected to further improve the wear resistance of newly developed beta-type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) for biomedical applications. However, there is a possibility for the mechanical properties such as tensile and fatigue strength of TNTZ to be degraded through gas nitriding process. Therefore, the gas nitriding process was carried out in this study to improve the wear resistance of TNTZ and alpha+beta-type Ti-6Al-4V ELI alloy (Ti64), which is one of the representative titanium alloys practically applied for biomedical applications, in simulated body fluid (Ringer's solution). Their tensile and fatigue properties and cell viability was also investigated in order to confirm the reliability as biomedical materials. The Vickers hardness near the specimen surface of nitrided TNTZ and Ti64, where TiN and Ti2N forms. increases significantly as compared to that of their matrices. The wear resistances of TNTZ and Ti64 are improved significantly in Ringer's solution by nitriding process as compared to those of as-solutionized TNTZ (TNTZ(ST)) and Ti64 (Ti64(ST)). The tensile strength of nitrided TNTZ increases by around 90 MPa as compared to that of TNTZST. The tensile strength of nitrided Ti64 does not change significantly at all nitriding temperatures. On the other hand, the elongation decreases with increasing the nitriding temperature. The run out (plain fatigue limit) of TNTZ subjected to a nitriding process at 1123 K, which has relatively good balance between wear resistance and tensile properties, is around 300 MPa, and is nearly equal to that of Ti64 subjected to a nitriding process at 1123 K, although the tensile strength of the nitrided TNTZ is around 200 MPa smaller than that of the nitrided Ti64. The cell viabilities of nitrided TNTZ and Ti64 range from 1.4 to 1.6 against that of control (cell disc), and are a little higher than that of TNTZ(ST) and Ti64(ST). The cell viabilities of nitrided TNTZ and Ti64 after removing the oxide layer on their surfaces are similar to that of control and are not significantly degraded.

The frictional wear characteristics of Ti-29Nb-13Ta-4.6Zr alloy subjected to solution treatment ( referred to as TNTZ(ST)) and aged at 598, 673 and 723 K after solution treatment ( referred to as TNTZ(598K), TNTZ(673K) and TNTZ(723K), respectively) were investigated in air and a simulated body environment ( Ringer's solution) as a function of the loading level. Ti-6Al-4V ELI alloy aged at 813 K after solution treatment ( referred to as T64(STA)) was employed as a reference material. Wear weight losses of TNTZST, TNTZ(598K), TNTZ(673K), TNTZ(723K) and Ti64(STA) are lower in Ringer's solution than in air under both low and high loading conditions (1.96 and 29.4 N, respectively). It is considered that the frictional factor decreases because of the lubricating effect of Ringer's solution between the contact surface of the specimen and the zirconia ball - the mating material. Moreover, the wear weight losses of TNTZ(598K), TNTZ(673K) and TNTZ(723K) are lower than that of Ti64(STA) in both air and Ringer's solution under the low loading condition, but are higher under the high loading condition. This result implies that the transition from severe wear to mild wear versus loading level depends on the type of material.

The frictional wear characteristics of heat-treated Ti-29Nb-13Ta-4.6Zr (TNTZ) subjected to solution treatment (TNTZST) or aging treatments at 598, 673, and 723 K, respectively after solution treatment (TNTZ 598 K, TNTZ673 K, and TNTZ 723 K, respectively) and Ti-6Al-4V ELI (Ti64) subjected to aging treatment after solution treatment (T64STA) in air and simulated body environment (Ringer's solution) were investigated as a function of load in this study. Wear weight losses of TNTZST, TNTZ598 K, TNTZ673 K, TNTZ 723 K, and Ti64STA are smaller in Ringer's solution than in air under both low and high loading conditions (1.96 and 29.4N, respectively). This is considered to suggest that the frictional coefficient decreased because of the lubricant effect of Ringer's solution between the contact surfaces of specimen and zirconia ball as mating material. The wear losses of TNTZST, TNTZ598 K, TNTZ673 K, TNTZ723 K, and Ti64STA increase with increasing load in Ringer's solution. The wear losses of TNTZST, TNTZ598 K, TNTZ698 K, and TNTZ723 K at a low loading level are smaller than that of Ti64STA in Ringer's solution. On the other hand, the wear losses of TNTZ598 K and TNTZ673 K at a high loading level are larger than that of Ti64STA in Ringer's solution. This reason is that the transition point from sever wear to mild wear versus load is changed according to the materials. © 2007 The Japan Institute of Metals.

Formation of the reaction product layer on the surface of biomedical titanium alloys, Ti-29Nb-13Ta-4.6Zr (TNTZ) and Ti6A1-4V ELI (Ti64), during gas nitriding was investigated. These alloys were exposed to nitrogen atmosphere at 1023, 1073, 1123 and 1223 K. After the gas nitriding, a reaction product layer was observed on the surface of both alloys, and was analyzed using an X-ray diffraction (XRD), Auger electron spectroscopy (AES) and X-ray Photoelectron spectroscopy (XPS). The layer was comprised of two phases, which were outer oxide layer (mainly TiO2) and inner nitride layer (mainly TiN or Ti2N). In these layers, the thickness of the oxide layer particularly depended on the kinds of alloys. According to the thermodynamics and point defect theory, the growth rate of oxide layer is expected to be increased by the presence of Al in TiO2. Namely, the dissolution of Al into TiO2 may increase the number of oxygen vacancies, resulting in acceleration of oxygen diffusion inward. On the other hand, the elements that accelerate the growth of the oxide layer are not contained in TNTZ. Thus, the oxide layer formed on Ti64 was thicker than that of TNTZ. In a similar way, the elements that accelerate the growth of the nitride layer are not contained in both TNTZ and Ti64. Thus, the nitride layers with similar thicknesses may be formed on TNTZ and Ti64 during gas nitriding.

Biomedical /3-type titanium alloys have been developed or are under development all over the world. In particular, researchers in Japan have been developed Ti-29Nb-13Ta-4.6Zr alloy (TNTZ)-beta-type titanium alloy-for biomedical applications. Bioactive ceramic surface modification is effective for further improvement in the biocompatibility of TNTZ. Calcium phosphate ceramics such as hydroxyapatite (Ca-10(PO4)(6)OH2; HAP), beta-calcium pyrophosphate (beta-CaP2O7; CPP), and P-tricalcium phosphate (beta-Ca-3(PO4)(2); beta-TCP) exhibit bioactivity. In this study, the formability and morphology of HAP on the surface of TNTZ, covered with sodium titanate film by alkali solution treatment were investigated before and after immersion in a simulated body fluid (SBF). A reticulate structure with a considerable number of large cracks and mainly composed of sodium titanate and niobate films having a thickness of 400 nm to 800 nm is formed on the specimen surface of TNTZ after immersing in 3, 5, and 10 kmol(.)m(-3) NaOH solutions for 86.4 and 172.8 ks. As the concentration of the alkali solution and the immersion time are increased, the formability of HAP improves because of the presence of a large amount of oxygen and the sodium in sodium titanate and mobate film. HAP is completely formed on the entire specimen Surface of TNTZ immersed in the SBF for 1209.6ks after immersing in 5 and 10 kmol(.)m(-3) NaOH solutions for 172.8 ks. Alkali treatment at 333 K in 5 kmol(.)m(-3) NaOH solutions for 172.8 ks is proposed to be an excellent condition to rapidly form HAP and fully cover the specimen surface of TNTZ with it. The bonding strength between TNTZ (alkali treatment at 333 K in 5 kmol(.)m(-3) NaOH solutions for 172.8 ks) and HAP is around 2 MPa, which was half or less than half the value required for biomedical applications. The inclusion of a baking treatment after the alkali treatment in order to improve the bonding strength degraded the HAP formability. Furthermore, the formability decreases with an increase in the baking temperature.

Metal injection molding (MIM) is a cost-saving process for fabricating products that have complicated shapes with a very high accuracy of size. It is expected that MIM will be employed as a new process for fabricating orthopedic and dental products with complicated shapes. The mechanical properties of Ti-6Al-4V, particularly its tensile and fatigue properties, fabricated by MIM (Ti64) were investigated to determine their suitability for medical applications. In order to improve the reliability of Ti64 for biomedical applications, the effects of heat treatments, and the addition of an element (Mo) on its mechanical properties were also investigated. The 0.2% proof stress, tensile strength and elongation of Ti64 are approximately 740 MPa, 850 MPa, and 12%, respectively. The volume fraction of the pores is around 1.1%. The tensile strength of Ti64 subjected to heat treatment at 1323 K for 3.6 ks followed by air cooling and hot rolling increases by around 24%. However, it is difficult to improve the strength-elongation balance because the elongation decreases after heat treatment and hot rolling. The strength elongation balance of Ti64 is improved by hot isostatic pressing (HIP): the tensile strength and elongation are around 960 MPa and 13%, respectively. The tensile strength of Mo added Ti64 that contains Mo (Ti-6Al-4V-3Mo) increases by around 15% in comparison with that of Ti64. The elongation of both the alloys is almost the same. The size of the pores of Ti64 is reduced drastically by HIP The fatigue strengths of Ti64 subjected to HIP is the highest in the low- and high-cycle fatigue-life regions. Its fatigue strength is comparable to that of wrought Ti-6Al-4V.

High-temperature oxidation of a pure iron, Fe-2Cr alloy, Fe-10Cr alloys and an Fe-10Cr-0.08C steel was examined in both air and steam at 923 K. In case of pure iron, the thickness of the oxide scale formed in steam at 923 K for 360 ks was comparable to that of the scale formed in air. On the other hand, in case of the Fe-Cr binary alloys and the ternary martensitic steel, the oxide scale was much thicker in steam than in air. The amount of hydrogen dissolved into the pure iron and the steels during exposure to the high-temperature steam was measured with thermal desorption spectroscopy (TDS). It was found that the amount of the dissolved hydrogen in the oxide scale was much larger in both the binary alloys and the ternary ferritic steel than in pure iron, and then it leads to the more accelerated oxidation rate of the binary alloys and the ternary steel in the steam. Furthermore, the martensite structure of the ternary steel exhibited an excellent oxidation resistance in air compared to the ferrite phase in the same steel. This is probably because the martensite phase has a lot of plane defects such as block boundaries for the fast diffusion path of Cr element. © 2007 The Japan Institute of Metals.

Titanium and its alloys have been widely used as biomaterials for hard tissue replacements because of their excellent mechanical properties and biocompatibility. However, the bonding between their surfaces and bone is not enough after implantation. The bioactive surface modification such as a hydroxyapatite (HAp) coating on their surfaces has been investigated. Recently, a simple method for forming HAp layer on the surfaces of titanium and its alloys has been developed. This method is called as alkaline treatment process. In this method, HAp deposits on the surfaces of titanium and its alloys by dipping into simulated body fluid (SBF) after an alkaline solution treatment that is followed by a baking treatment (alkaline treatment). This process is applicable to newly developed beta-type Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) for biomedical applications achieving bioactive HAp modification. In this study, the morphology of the HAp layer formed on the surface of TNTZ was investigated after various alkaline treatments followed by dipping in SBF. The formability of HAp on the surface of TNTZ was then discussed. The formability of HAp on TNTZ is much lower than that of commercially pure Ti, Ti-6Al-4V ELI and Ti-15Mo-5Zr-3Al alloys, which are representative metallic biomaterials, The formability of HAp on TNTZ is improved by increasing the amount of Na in the sodium titanate gels formed during an alkaline solution treatment where the NaOH concentrations and the dipping time are over 5 M and 172.8 ks, respectively. The formability of HAp on TNTZ is considerably improved by dipping in a 5 M NaOH solution for 172.8 ks. This condition for alkaline solution treatment process is the most suitable for TNTZ.

The effect of oxygen content on aging behavior and invar characteristics of Ti-29Nb-13Ta-4.6.Zr (TNTZ) were investigated.The age hardening of TNTZ aged at 573 K and 723 K is enhanced with the oxygen content. The omega phase precipitates and grows from early stage of aging in TNTZ regardless of the oxygen content when aged at 573 K. The lath-like shape alpha phase precipitated in TNTZ aged at 723 K increases in size with the oxygen content. The elastic modulus increases with the oxygen content and aging. The omega phase increase the elastic modulus to a greater extent than the increase due to the alpha phase. The tensile strength increases with the oxygen content and aging, while the elongation decreases. TNTZ with oxygen content of 0.1 mass% exhibits invar-like characteristics through severe cold working. A higher oxygen content suppresses the invar-like characteristics of TNTZ.

The tensile and plain fatigue properties of the P-type titanium alloy, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ), which was subjected to various thermomechanical treatments. and cast TNTZ were investigated in order to judge its potential for biomedical and dental applications. The tensile strengths of TNTZ aged after solution treatment and that aged after cold rolling decrease with an increase in the aging temperature; however, their elongation exhibits an opposite trend. TNTZ composed of the omega phase or the alpha and a phases in the beta phase exhibits a tensile strength of about 1000 MPa or more. The tensile properties of the cast TNTZ with and without a surface reaction layer is are not significantly different, and are almost identcal to those of as-solutionized TNTZ. The plain fatigue strengths of TNTZ aged after solution treatment and those of TNTZ aged after cold rolling increase with the aging temperature. In particular, TNTZ aged at 723 K after cold rolling exhibits the highest fatigue strength in both the low- and high-cycle fatigue life regions. Further, the plain fatigue limit, which is about 770 MPa, is nearly equal to that of hot-rolled Ti-6Al-4V ELI alloy subjected to aging after solution treatment; Ti-6Al-4V ELI alloy is a representative alpha+beta-type titanium alloy for biomedical applications. The plain fatigue strength of cast TNTZ with a Surface reaction layer is considerably less than that of the as-cold-rolled and as-solutionized TNTZ. Consequently, in the low-fatigue life region, the fatigue crack easily Occurs at the surface reaction layer, which is brittle, and in the high-Fatigue life region, the fatigue crack occurs at the sites of casting defects (shrinkage). The fatigue limits range from 180 MPa to 200 MPa.

The surface of Ti-29Nb-13Ta-4.6Zr (TNTZ) subjected to gas nitriding at 1023-1223 K was investigated in comparison with the conventional biomedical titanium alloy, Ti-6Al-4V ELI (Ti64). After gas nitriding, the microstructures near the surface of these alloys were observed by optical microscopy, X-ray diffraction, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. In both alloys, two titanium nitrides (TiN and Ti2N) are formed and the a phase precipitated by gas nitriding. Furthermore, oxygen impurity in the gas nitriding atmosphere reacts with the titanium nitrides; thus, TiO2 is formed at the outermost titanium nitride layer. The surface hardening was also evaluated by Vickers hardness measurement. The Vickers hardness near the surface of TNTZ and Ti64 increases significantly by gas nitriding.

Hydrogen effect on high-temperature steam oxidation resistance was investigated using an Fe10%Cr-0.08%C ternary ferritic steel. In order to suppress hydrogen dissolution during steam oxidation, the steel was pre-oxidized in air at 923 K before exposure to steam. A thin oxide layer formed by the pre-oxidation was identified as Cr2O3 With containing a small amount of Fe2O3. This oxide layer worked to lower the oxidation rate in steam at 923 K. However, such a beneficial pre-oxidation effect disappeared when the specimen was exposed to steam for a long time, and nodular-like oxides were formed on the pre-oxidized specimen. There was a clear resemblance in both the chemical composition and the layer structure between the nodular-like oxides and the oxide scale usually formed during steam oxidation. As hydrogen diffusivity was much higher in such an oxide scale than in Cr2O3, hydrogen could dissolve in the nodular-like oxides readily during steam oxidation. Then, hydrogen-accelerated oxidation progressed even on the pre-oxidized specimen. (c) 2006 Elsevier Ltd. All rights reserved.

Ti-29Nb-13Ta-4.6Zr, referred to as TNTZ, and Ti-6Al-4V ELI were subjected to gas minding or oxidation process as comparison in order to harden their surface and improve their wear resistances. The friction wear tests were carried out on the nitrided or oxidized TNTZ and Ti-6Al-4V ELI in air and a simulated body fluid-Ringer's solution. The wear losses in the minded or oxidized TNTZ and Ti-6Al-4V ELI in Ringer's solution are lower than those in TNTZ and Ti-6Al-4V ELI without mtriding or oxidizing.

The amount of hydrogen dissolved into Fe-10Cr-0.08C-0 similar to 0.03S (mass%) steels during the steam oxidation at 923 K was measured by thermal desorption spectroscopy (TDS). The amount of dissolved hydrogen was found to be dependent largely on the steam oxidation resistance of the steels. In other words, it was much smaller in the sulfur-doped steels with good oxidation resistance than in the sulfur-free steels with poor oxidation resistance. Thus, we suggest that the hydrogen dissolution is one of the most important factors to understand the steam oxidation resistance of the steels.

The high-temperature oxidation in both air and steam was examined experimentally with pure iron and a Fe-10Cr-0.08C (mass%) ternary ferritic steel. In case of pure iron, the thickness of the oxide scale formed in steam at 923 K for 360 ks was comparable to that of the scale formed in air. On the other hand, in case of the ternary ferritic steel, the oxide scale formed was much thicker in steam than in air. Thus, the oxidation rate was nearly independent of the air and the steam atmosphere for pure iron, but was dependent for the ternary ferritic steel. In the present study, this difference was investigated from a viewpoint of the hydrogen dissolution in the oxide scale during the steam oxidation. The amount of dissolved hydrogen was measured using a thermal desorption spectroscopy (TDS). It was found that the amount of the dissolved hydrogen was much larger in the ternary ferritic steel than in pure iron. Also, it was shown that the hydrogen dissolution in the ternary ferritic steel was related to the presence of (Fe,Cr)(3)O-4 in the oxide scale. The defect structure in this chromium-rich oxide was modified by hydrogen dissolution, so that the ionic diffusion could be enhanced in it, resulting in the more accelerated oxidation rate in steam.

The system free energy was estimated for the martensite phase of an Fe-Cr-C ternary alloy. The system free energy of the martensite phase is defined as, G(SYS)=G(0)+E-Str+E-Surf, where G(0) is the chemical free energy, E-Surf is the interfacial energy for the boundaries in the martensite microstructure, and E-str is the elastic strain energy due to the dislocations in the martensite phase. From the experimental results on SEM/EBSD, the interfacial energy was estimated to be 0.05 J/mol for the prior austenite boundary, 0.11 J/mol for the martensite packet boundary and 0.32 J/mol for both the martensite block and the lath boundaries in the asquenched specimen. The total decrement in the interfacial energy accompanying annealing at 873 K for 100 h after quenching was estimated to be about 0.1 J/mol. Also, the elastic strain energy of the asquenched specimen was estimated to be 7.1 J/mol. The total microstructural energy of the martensite phase was about 10J/mol, which operates as a driving force for the microstructure evolution, e.g., recovery of dislocations and the coarsening of the sub-structures such as martensite-packet, -block and -lath.

The presence of sulfur (S) at an impurity level in high chromium (Cr) ferritic steels improves remarkably high-temperature steam oxidation resistance. However. it still remains unknown which S state in the steels gives such a beneficial effect. There are two possible S states in the steels: one is the soluble S state in a solid solution of the steel, and the other is the precipitated S state which occurs through the sulfide formation or the S segregation in grain boundaries. Either state appears depending on the S content and the heat-treatment temperature. In this study in order to elucidate the effective S state, high-temperature steam oxidation resistance was investigated with high Cr ferritic steels, by changing the S states in them by proper heat treatments. As the result, it was found that the precipitated S state operated more effectively to the improvement of steam oxidation resistance, as compared to the soluble S state.

The dependence of steam oxidation resistance on the sulfur content has been investigated systematically in both terrific and austenitic steels. It is found that the presence of impurity S. being considered as a harmful element in the past, improves significantly the steam oxidation resistance of high Cr steels. However, such a beneficial S effect is not so remarkable in low Cr steels, indicating that the S effect is related strongly to the Cr content in the steels. However, in case of high Cr ferritic steels containing more than 0.3%Si. the S effect is still less remarkable. These results are probably caused by the difference in the affinity of S for Cr atom and for Si atom. Since S has a strong affinity for Cr, Cr is enriched in the vicinity of the segregated-Si on the specimen surface even after the steam oxidation test for a short time. The enriched Cr layer obstructs the formation of any island-like Fe oxides on the surface because of the easy formation of the passive Cr2O3 oxide layer on this area. On the other hand, Si segregates onto the iron surface faster than S, but a part of the segregated-Si on the surface is replaced by S. Therefore, it is considered that the formation of SiO2 is difficult in the case when the S content is too higher in the steel. As a result, the S effect does not appear so significantly in the Si-containing steels.

Microalloying effects of sulfur are investigated systematically on the steam oxidation resistance of austenitic steels and ferritic steels. It is found that the presence of S, about 50ppm, in the steels improves remarkably the steam oxidation resistance of both austenitic steels and high Cr ferritic steels. This result indicates that ferritic steels with excellent steam oxidation resistance can be designed and developed by just leaving S at an impurity level in them without detriment to the mechanical strength. However, the S effect is not so remarkable in low Cr ferritic steels as in high Cr ferritic steels. This fact implies that the S effect is related strongly to the stability of Cr2O3 in high temperature steam conditions.

Mass loss occurs in Cr2O3 when it is exposed to steam at 923 K for 0.5 Ms or 1.3 Ms. The presence of Satan impurity I eve I of 23 pp in in the oxide suppresses the mass loss by about a half. For example, for the 0.5 Ms exposure, the mass loss is about 0.055% in pure Cr2O3 but about 0.030% in S-doped Cr2O3. This result is related closely to our previous result that the existence of 50 ppm S in high Cr ferritic steels causes a tremendous improvement in the steam oxidation resistance at 923 K.

Most hydrogen storage compounds consist of hydride forming elements. A, and hydride non-forming elements, B. From the DV-X alpha molecular orbital calculation, it is found that hydrogen interacts more strongly with B elements than A elements in every hydrogen storage compound, despite that there is a larger affinity of A elements for hydrogen than B elements in the binary metal-hydrogen system. Also, it is shown that the A/B compositional ratio of hydrogen storage compounds is understood in terms of a simple parameter, 2 Bo(A-B) / [Bo(A-A)+Bo(B-B)], where the Bo(A-B), Bo(A-A) and the Bo(B-B) are the bond strengths between atoms given in the parentheses. This parameter resembles the ordering energy parameter, Omega(AB) (=V-AB- 1/2(V-AA+V-BB)), which controls the order-disorder phase transformation in alloys.

The 5th International Symposium on Designing, Processing and Properties of Advanced Engineering Materials (ISAEM-2012) & the 3rd International Symposium on Advanced Materials Development and Integration of Novel Structural Metallic and Inorganic Materials (AMDI-3)

本研究課題では、研究実施者らが発見した「レーザー照射による空気中での金属表面窒化現象」の機序解明を通じて、当該技術の産業への応用可能性を探ることを目的としている。この指針に沿い、令和３年度は、レーザー照射に伴う空気中窒化現象の機序解明に重点を置き研究をおこなった。具体的には、種々金属材料表面に、同一条件（プロセス条件）でレーザ照射をおこない、その表面に形成した皮膜を分析して比較することで、皮膜形成に及ぼす金属材料物性の影響を調べた。 金属材料としては、空気中窒化現象がすでに確認できているチタン材料の他に、ジルコニウム、純鉄および銅を選択した。これら表面に、チタン材料で窒化皮膜形成が確認されている条件にてレーザー照射をおこない、その後に形成した表面皮膜を、Ｘ線光電子分光法、走査型電子顕微鏡、Ｘ線回折法にて調べた。加えて、レーザー照射時に発生するプラズマも分光解析した。 チタン材料の他に、ジルコニウム表面にも、膜厚マイクロの窒化皮膜が形成し、この皮膜は窒化ジルコニウムであることが明らかとなった。純鉄表面にも窒化皮膜は形成したが、その皮膜膜厚は１マイクロ以下と薄く、さらに窒素の含有量は数at％程度でありチタンやジルコニウムと比較して著しく低かった。銅の表面には皮膜形成は全く認められず、窒素の侵入は観察できなかった。 電子顕微鏡像およびプラズマ解析結果から考察すると、チタンおよびジルコニウムでは、レーザー照射に伴い高温プラズマが発生し、これにより金属表面が溶融し、窒化物形成に至ったことがわかった。純鉄でも、高温プラズマの発生および溶融の痕跡が見られたが、表面には窒素が放出された痕跡（脱気の跡）が観察され、このことが窒素の低濃度化の要因になったと推察された。また銅については、溶融の痕跡が小さかった。空気中での窒化皮膜形成は、表面の溶融および窒素の取り込みが重要要素であることがわかった。

骨固定用金属製インプラントの剛性は、骨修復中とその後とで適正値が異なり、骨修復中は高剛性、骨修復完了後は低剛性のほうが適切であることが実験的に示唆されている。さらに、この骨修復状況に依存した金属製インプラントの剛性の適正値の変化は力学的負荷方向に依存し、骨修復中は骨のねじり方向、骨修復後は軸方向の剛性が重要であると考えられる。そこで、本研究では、骨のねじり方向に高剛性であり、軸方向に低剛性となるように、意図的に大きな剛性異方性を付与した金属製インプラントの作製を試みる。この実現のため、材質と形状とを同時に制御することが可能な金属積層造形技術を用いる。昨年度、市販の316Lステンレス鋼を供試材として用い、横方向には高ヤング率となり、縦方向には低ヤング率となるように、面内の直交する二方向の結晶方位を制御し、プレートのヤング率を縦方向よりも横方向に高くすることに成功した。今年度は、結晶構造が体心立方格子（BCC）からなる、市販されていないチタン合金製粉末をガスアトマイズ法およびプラズマ回転電極法を用いて試作し、粒度分布や流動性を評価するとともに、粉末内部のミクロ組織を観察・分析した。その結果、粉末製造法に依存して、各粉末のサテライトの付着状況や真球度が異なっていたが、いずれも金属積層造形に用いることが可能であることを確認した。さらに、粉末内部の気孔の存在割合やデンドライト組織形態が粉末製造法に依存して異なることを明らかにした。ただし、元素分布自体は、いずれの粉末内部においても、BCC安定化元素の濃化部とそれ以外の元素の濃化部とに分かれ、濃化の程度は粉末製造法にあまり依存しないことが明らかとなった。

紡錘状脳動脈瘤の臨床例に対して、流体力学解析を行い、動脈瘤の壁におけるストレスデータの標準化を行った。続いて、流体工学的に動脈瘤壁から出血を起こしにくい条件、しかも、動脈瘤から分岐する細血管の開存が維持される条件を算出し、ステントデザインを検討した。さらに、プロトタイプのステントを用いて、ブタ紡錘状動脈瘤モデルに留置した場合に内部を流入する血流データをシミュレーションし、ステントデザイン適正性の検討を行った。

研究代表者らにより開発された弾性率自己調整金属は、変形誘起相変態により変形部の弾性率が上昇し、非変形部は低弾性率を示す。本研究では、この材料の応用として、力学負荷応答性自己強化金属インプラント開発の可能性について検討した。弾性率自己調整金属にひずみ量を系統的に変化させて引張変形を与えたところ、弾性変形領域における変形誘起相変態の発生が認められた。さらに、繰り返し荷重を印加した際の弾性率変化を計測し、一部の試験片では、繰り返し荷重負荷による弾性率の上昇も認められた。これらの実験結果から、力学負荷応答性自己強化金属インプラント開発の可能性が示唆される。

研究期間中に出血性椎骨動脈解離は計15例来院した．全例に脳血管撮影を行い，解離部の解剖学的特徴を検討し，解離周囲からの穿通枝の起始を確認した．血管撮影のデータを基に，computational fluid dynamicsの解析を行い，流体工学的に血流阻害効果の得られる条件を検討し，停滞する流れ環境下においても血流停止が生じず，分枝細血管の開存が維持される条件を検討した．シミュレーションでは新規ステントデザインを作成可能であったが，患者毎の解離部の形状バリエーションが多いこと，穿通枝を血管撮影で視認不可能な場合も多いこと，などから実際に臨床応用可能な新規ステントを開発するには至らなかった．