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The origin of the low Young’s modulus of cold worked Ti–36Nb–2Ta–3Zr–xO mass% polycrystals with a body-centered cubic (β-phase) structure, referred to as gum metal, was investigated with a focus on the roles of oxygen concentration, the electron–atom (e/a) ratio, and the cold working process. Analysis of the temperature dependence of the microstructures and elastic properties of single crystals at x = 0.09, 0.36, 0.51% O using transmission electron microscopy and an electromagnetic acoustic resonance method, respectively, revealed that the shear moduli c′ and c44 of the 0.36 and 0.51% O alloys softened upon cooling near room temperature (RT) and exhibited low values at RT. This was because suppression of the α″ martensitic transformation by oxygen addition led to retention of the low stability single β-phase state at RT. The Hill approximation indicated that the low c′ and c44 values caused by softening gave rise to the low Young’s modulus, which is common to some Ti–Nb-based alloys with an e/a ratio of ∼4.24. Analysis of the microstructures and elastic properties of solution-treated and cold worked x = 0.06, 0.30, 0.47% O alloy polycrystals at RT revealed that the Young’s modulus increased upon 90% cold working due to formation of the α″ martensite phase (0.09% O) and ω phase (0.09, 0.30, and 0.47% O) with a high elastic modulus in the β-phase matrix. However, increasing the oxygen concentration suppresses the increase in Young’s modulus because oxygen addition decreases the amount of α″ and ω phases formed while retaining the low stability β phase. Therefore, cold working combined with oxygen addition produces a low Young’s modulus compatible with high strength.

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.

The improvement in fatigue strength, with maintenance of a low Young’s modulus, in a biomedical β-type titanium alloy, Ti–29Nb–13Ta–4.6Zr (TNTZ), by thermomechanical treatment was investigated. A short aging time at an ω-phase-forming temperature combined with severe cold rolling was employed. A fine ω phase is observed in TNTZ subjected to this thermomechanical treatment. Because the rolling texture of β phase is formed by cold rolling, such as the ω 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 °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.

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 β phase and small athermal ω 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 ω 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 β-type titanium alloy expected to be useful in spinal fixation applications. Thus, 3Cr3Mo is a potential candidate for spinal fixation applications.

TiB2 was added to β-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 TiB2. TNTZ with 0.05–0.50 mass%B consists of a β-phase with a small amount of TiB. 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.

Plastic deformation behavior and its relation to tensile properties were investigated in an attractive β-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.

The cost of titanium (Ti) and its alloys is still much higher than the costs of steels and aluminum alloys; this has inhibited their widespread usage. It is necessary to reduce their cost in order to make Ti and its alloys common metallic materials, namely, ubiquitous titanium and its alloys for their widespread usage. One of the main reasons for their high cost is that they contain a large amount of high-cost rare metals. Therefore, it is imperative to conduct research and development for producing Ti alloys that utilize low-cost common metal elements such as Si, Al, Fe, Cu, and Sn and interstitial elements such as O, N, H, and C. In this paper, the effects of ubiquitous alloying elements such as interstitial elements, O, N, C, and H, and substitutional elements, Fe and Si, which have been generally treated as impurities on functionalities of titanium alloys are discussed.

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 forβ-type titanium alloys used in biomedical applications. Then, the advantage of low Young's modulus ofβ-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 ofβ-type titanium alloys with a self-adjusting Young's modulus for use in removable implants.

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 (AOP) 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.

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 α′, ω, and β phases while the microstructure of Zr-30 mass%Nb alloy subjected to ST consists of almost all single β 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 ω 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.

The composition and temperature dependence of the elastic properties and phase stability of quaternary Ti–Nb–Ta–Zr β-phase alloys with a body-centered cubic structure, developed for biomedical applications, were investigated using their single crystals, in order to clarify the origin of the low Young’s modulus in polycrystals. Transmission electron microscopy observations clarified that α ″ martensitic transformation occurred in a temperature range that depended on the β-phase stability below room temperature. Electromagnetic acoustic resonance measurements clarified that the shear moduli c ′ and c 44 of single crystals softened upon cooling from room temperature and became rather low near the martensitic transformation start temperature, i.e. the lower limit of β-phase stability. An analysis by the Hill approximation indicates that low c ′ and c 44 caused the low Young’s modulus, and thus it is probable that the softening in c ′ and c 44 is the origin of the low Young’s modulus.

A limited number of reports exist regarding the systematic investigation or comparison of the fatigue strength of titanium alloys for medical devices, including plain, fretting and notch fatigue, for improvement through various treatments and processes, with respect to related microstructures. This article focuses on the changes and improvements in fatigue strength of newly developed beta-type and practically used alpha + beta-titanium alloys for medical devices through heat treatments, thermomechanical treatments and surface modifications.

Ti-29Nb-13Ta-4.6Zr has been recently developed as a biomaterial showing most potential. The study here was conducted to investigate the high temperature deformation behavior under uniaxial tensile stress at various temperatures (i.e., 700°C, 800°C and 900°C) with different initial strain rates at atmospheric condition. Results of the high temperature tensile tests show a significant improved elongation-to-failure of this novel biomaterial at elevated temperatures compared to open literature, and hence its formability potential.

The superelastic behaviour of Ti-30Nb-10Ta-5Zr and Ti-30Nb-8Ta-5Zr (wt.%) biomedical alloys was investigated by tensile testing and in situ synchrotron X-ray diffraction. The phenomenological theory of martensite crystallography and texture prediction based on the Schmid law indicate that alpha '' in Ti-30Nb-10Ta-5Zr forms in untwinned variants. Measurement of single-crystal elastic constants using an Eshelby-Kroener-Kneer self-consistent model shows that the 10-Ta alloy has a C' modulus 3 GPa higher than that of the 8-Ta alloy. That it nevertheless has a proof stress 35 MPa lower can be qualitatively explained by the differences in martensite crystallography. The results suggest that high tensile strength can be maintained for low modulus beta-Ti in spite of martensitic transformation by optimizing transformation strains. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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.

Titanium exhibits many attractive properties. It is considered to be ubiquitous since it has the 9th-highest Clarke number of all the elements. However, the principal beta-stabilizing elements for titanium can be very expensive, making many titanium alloys expensive. Manganese is a beta stabilizer for titanium alloys and it is also considered to be ubiquitous since it has the 11th-highest Clarke number of all the elements. The behavior of Ti-Mn alloys during heat treatment has been investigated and it was found that in some alloys the isothermal omega phase is precipitated. Because this phase can lead to brittleness, it is very important to suppress its precipitation. Since it is well-known that aluminum suppresses isothermal omega precipitation, we investigated the effect of adding aluminum using Ti-7mass% Mn-0, 1.5, 3.0 and 4.5mass% Al alloys by performing electrical resistivity, Vickers hardness, and X-ray diffraction measurements. In solution-treated and water-quenched 0 and 1.5 alloys, only beta phase was identified, while hcp martensite and bate phase were identified in 3.0 and 4.5Al alloys. The resistivities at room and liquid-nitrogen temperatures were found to increase monotonically with increasing Al content. Isothermal  precipitation was suppressed by aluminum addition, while alpha precipitation was accelerated by Al addition.

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.

A peculiar effect of oxygen on ω-phase stability, i.e., the enhancement of the isothermal ω-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 ω phase during aging, resulting in the stabilization of the ω phase in this alloy.

Y2O3 was added to β-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 β 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.

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 -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.

Simulated Body Fluid (SBF) has served as a useful standard to check the bioactivity of implant materials for years. However, it is not perfectly able to imitate human serum; sometimes disparities between the SBF test and animal test were confirmed. Therefore, to ensure the reliability of the results of the SBF test obtained from our previous study, an animal study was performed to check osteoconductivity of surface modified implant materials. Three types of solution processes, hydrothermal (H), electrochemical (E), and hydrothermal-electrochemical (HE), were performed on the Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) to improve its bioactivity, and their bioactivities were measured in vivo using bone-implant contacts (BICs). BICs of the HE- and H-treated samples were significantly higher than that of the control. Metal ion diffusion towards the bone was also evaluated to examine the adverse effect of metal ions. No metal ion diffusion was observed, indicating the safety of our solution processed implant materials.

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 (C 6 H 5 0) 3 PO). An α-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.

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 hardness 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.

Although titanium is considered to be a ubiquitous element since it has the tenth highest Clarke number of all elements, it is classified as a rare metal because the current refinement process is more environmentally damaging than the processes used to refine iron and aluminum. Furthermore, the beta stabilizing elements of titanium alloys (e.g., V, Mo, Nb, and Ta) are very expensive due to their low crustal abundances. Manganese is also considered to be a ubiquitous element, since it has the 12th highest Clarke number of all elements. Therefore, manganese is a promising alloying element for titanium, especially as a beta-stabilizer. In order to develop beta titanium alloys as ubiquitous metallic materials, it is very important to investigate the properties of Ti-Mn alloys. In this study, the phase constitution of and the effect of heat treatment on Ti-3.3 to 8.7 mass% Mn alloys were investigated by electrical resistivity and Vickers hardness (HV) measurements and by X-ray diffraction (XRD) analysis and optical microscopy. In 3.3, 5.1, and 6.0 mass% Mn alloys quenched from 1173 K, ’ martensite and  phase were identified by XRD, whereas in the 8.7 mass% alloy, only the  phase was detected. The resistivities at both temperatures increased with increasing Mn content up to 6.0 mass% Mn and the positive temperature dependence of resistivity became negative at 6.0 mass% Mn. LN increased gradually with increasing Mn content up to 8.7 mass% Mn, whereasRT decreased considerably at a Mn content of 8.7 mass% Mn. HV increased with increasing Mn content up to 5.1 mass%, after which it began to decrease. In Ti-3.3 mass%Mn and 5.1 mass%Mn alloys, the resistivity and the resistivity ratio decreased with increasing temperature of isochronal heat treatment because of decomposition of ’ martensite. In 6.0Mn and 8.7Mn alloys, the resistivity and the resistivity ratio decreased, while Vickers hardness increased with increasing temperature of isochronal heat treatment because of isothermal  precipitation. Furthermore, the temperature for the onset of precipitation increased with higher Mn content.

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.

The applicability of a calcia mold to casting a � -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. [doi:10.2320/matertrans.L-M2009827]

Beta-Ti-type Ti-30Nb-10Ta-5Zr (TNTZ) wires with high-ductility were developed using the arc-melt-type melt-extraction method. The continuous melt-extracted wire with very smooth surface and small fluctuations in the diameter realizes the high tensile strength and superior bending ductility of TNTZ alloy. The melt-extracted Beta-Ti wire shows the possibility for the use in biomedical applications. The arc-melt-type melt-extraction method is very effective for developing new Beta-Ti-based biomaterials.

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 β-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.

A new -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.

New Ti-based and Zr-based metallic wires for the future application as biomaterials were developed by arc-melting type melt-extraction method. Zr-based metallic glass wire, -Ti type Ti-Zr binary wire and -Ti type Ti-Nb-Ta-Zr (TNTZ) wire show high tensile strength and good vending ductility. Zr-based metallic glass wire shows extremely high tensile strength over 1GPa and large elastic strain limit reached approximately 2%. Ti-Zr binary alloy shows high wire-shape forming tendency during melt-extraction, and high Ti concentration Ti90Zr10 alloy wire was obtained. TNTZ wire shows superior bending ductility and full ductility is achieved.

A calcia mold, which is stable at high temperatures for dental precision casting of � -type titanium alloys such as Ti-29Nb-13Ta-4.6Zr (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. [doi:10.2320/matertrans.L-M2009828]

Ti–Hf alloys with Hf contents of 10, 20, 30, and 40 mass% were prepared by a tri-arc furnace and homogenized at 1273 K for 21.6 ks, and then these alloys were cold rolled into 3-mm-thick plates. The alloy specimens were subjected to a solution treatment in a vacuum at 1223 K for 3.6 ks and then rapidly quenched in ice water before corrosion tests. The corrosion resistance of these alloys was investigated by studying the anodic polarization curves at 310 K in 5% HCl solution to determine the potential use of these alloys in biomedical applications. The passive films formed on the surfaces of the alloys were examined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. The results reveal that all the Ti–Hf alloys exhibit a passive behavior in 5% HCl solution, which is attributed to the passive film formation of a mixture of both HfO 2 and TiO 2 . The corrosion resistance of the Ti–Hf alloys gently increases with the Hf content and the Ti–Hf alloys exhibit better corrosion resistance than commercial pure (CP) Ti—the currently-used metallic biomaterial.

The Ti-6Al-7Nb alloy has been developed for a more suitable biomaterial in place of the Ti-6Al-4V alloy, due to the toxicity of vanadium to the human body. However, the cost of the starting material powder for MIM Ti-6Al-7Nb alloy is understood to be expensive. This study investigates the feasibility of using commercially available powders…

The microstructures, dynamic elastic modulus, and mechanical properties of the Ti–25Ta (mass%) alloy are investigated in this study in order to assess its mechanical compatibility for biomedical applications. The microstructures are examined by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The dynamic elastic modulus is measured by the resonance vibration method and the mechanical properties are determined from uniaxial tensile tests. The experimental results indicate that the Ti–25Ta alloy exhibits an orthorhombic martensite (α″) twinned structure after solution treatment. The Ti–25Ta alloy has the lowest elastic modulus and the highest ratio of strength to modulus among Ti–Ta alloys. Thus, the Ti–25Ta alloy exhibits the best mechanical compatibility among Ti–Ta alloys and is a promising candidate for novel metallic biomaterials.

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.

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 β 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 α 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 α 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 α-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.

The microstructures, dynamic elastic modulus, and mechanical properties of Ti-Nd alloys with Nd contents of 1.5, 3, 4.5, and 6 (mass%) were investigated in this study in order to assess whether Nd was an effective alloying element for decreasing the elastic modulus of a Ti alloy and simultaneously increasing its strength for its potential use in biomedical applications. The microstructures were examined by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The dynamic elastic modulus was measured by the vibration resonance method and the mechanical properties were determined from uniaxial tensile tests. Experimental results indicate that all the Ti-Nd alloys exhibit hexagonal structures of both α Ti and α Nd. An increase in the Nd content decreases the elastic modulus of the Ti-Nd alloys by a small amount and gradually increases their strength. The residual stress caused by cold rolling has a slight effect on both the elastic modulus and the mechanical properties of the Ti-Nd alloys. From this investigation, it can be concluded that Nd is not an effective alloying element for decreasing the elastic modulus of Ti alloys and simultaneously increasing their strength for their potential use in biomedical applications.

It has been found that the sintered MIM Ti-6Al-4V alloy compacts were strengthened by addition of fine Mo powder because of the microstructural modification. In this study, the metal injection molding process has been applied to strengthen Ti-6Al-4V compacts by addition of Fe or Cr powders, which are the same beta stabilizing elements as Mo and are more cost effective powders as compared to Mo powder. The effect of Fe or Cr contents and sintering conditions on the mechanical properties, oxygen content and microstructures of the sintered compacts were mainly investigated. The microstructures of sintered compacts were consisted of acicular alpha phase and intergranular beta phase, and the acicular alpha phase showed fine with increasing Cr content. The tensile strength of sintered compacts was increased with increasing Fe or Cr contents, and the effect of Fe addition for strengthening the sintered compacts was larger than Cr or Mo addition. Eventually, the tensile strength of sintered compacts added 2 mass% of Fe was improved to be 1010 MPa with 11.2 % of elongation, and the compacts added 4 mass% of Cr showed the excellent tensile strength of 1040 MPa with 16.1 % of elongation.

Although titanium is considered to be a ubiquitous element as it has the 10th-highest Clarke number of all the elements, it is actually classified as a rare metal because the current refinement process for the metal is more environmentally damaging than the processes used to refine iron and aluminum. Furthermore, the principal alloying elements of titanium alloys are very expensive, owing to their low crustal abundances; this is especially true of the beta-stabilizing elements. Manganese is also considered to be a ubiquitous element as it has the 12th-highest Clarke number of all the elements. Therefore, manganese is promising as an alloying element for titanium, especially as a beta-stabilizing element. In order to develop beta titanium alloys as ubiquitous metallic materials, it is very important to investigate the properties of Ti-Mn alloys. In this study, the phase constitutions and isothermal aging behaviors of Ti-6.0 to 14.8 mass%Mn alloys were investigated by electrical resistivity and Vickers hardness measurements, X-ray diffraction (XRD), and optical microscopy. In 6.0 mass%Mn alloys quenched from 1173 K, both hexagonal close-packed martensite and the beta phase were identified by XRD, whereas only the beta phase was detected in 8.7 and 14.8 mass%Mn alloys. The resistivity at liquid nitrogen temperature was greater than that at room temperature between 6.0 and 14.8 mass%Mn. The Vickers hardness decreased with an increase in the Mn content up to 11.3 mass%Mn and then increased slightly. On aging at 673 K, the isothermal omega phase was precipitated in 6.0 to 11.3 mass%Mn alloys, while it was precipitated by aging at 773 K in 6.0 and 8.7 mass%Mn alloys. The Vickers hardness increased drastically on isothermal omega precipitation, whereas it increased slightly in the case of direct alpha precipitation with no isothermal omega precipitation. [doi:10.2320/matertrans.MA200902]

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-reinforced fine calcia slurry are very fine. 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.

The microstructures and resulting mechanical properties of Ti–50 mass% Ta alloy were investigated for biomedical applications. The microstructures were examined using an X-ray diffraction (XRD) analysis, a scanning electron microscopy (SEM) and a transmission electron microscopy (TEM), the dynamic elastic modulus was measured by the vibration resonance way and the tensile properties by a tensile test. Ti–50 mass% Ta alloy exhibits the orthorhombic martensite (α″) structure after the given solution treatment, and this microstructure is sensitive to both aging temperature and time. The different microstructures precipitate during the subsequent aging treatments, resulting in various mechanical properties. The α + β microstructure obtained by aging at 873 K for 259.2 ks exhibits a lower modulus, better mechanical biocompatibility and moderate elongation to failure, hence it is more suitable than the other microstructures for biomedical applications.

Ti alloys composed of nontoxic and allergy-free elements and Ni-free stainless steels and Co-Cr alloys are currently being developed. Ni-free Ti alloys exhibiting superelastic behavior, or the shape memory effect, are also being developed. beta-type Ti alloy with a low elastic modulus has proved to be effective for inhibiting bone absorption and enhancing bone remodeling. Simple bioactive surface modifications such as alkali-treatment processes and the calcium phosphate glass-ceramic dip-coating method are applicable to newly developed beta-type Ti alloys such as lowmodulus Ti-29Nb-13Ta-4.6Zr. Blood-compatible polymers such as poly(ethylene glycol) have been successfully fixed on the surface of Ti via chemical bonding by an electrodeposition method. Ti alloys for dental applications have also been recently developed.

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 α 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.

The cause of a low Young’s modulus was investigated in quaternary β-type Ti–Nb–Ta–Zr alloys, as the modulus is decreased to prevent bone absorption and degradation of bone quality when these alloys are implanted into human bones. This investigation was carried out using the alloys′ single crystals. Acoustic measurements and analysis by the Hill approximation revealed that a low Young’s modulus in a polycrystalline form is caused by the low shear modulus c′, related to the low β-phase stability, low c44, and relatively low bulk modulus B compared with those of binary Ti-based alloys. Furthermore, it was found that the single crystals had strong orientation dependence on Young’s modulus, where that in the 〈1 0 0〉-direction E100 is the lowest of all crystallographic orientations. For quaternary Ti–29Nb–13Ta–4.6Zr alloy (mass%), E100 is only ∼35 GPa, which is similar to Young’s modulus of human cortical bones as a result of the low B and c′. These results indicate that decreases in c′, c44 and B are essential for decreasing Young’s modulus of novel β-type Ti alloys which are expected to be developed in the near future.

The effects of Ta and Hf on the dynamic Young's moduli and tensile properties of Ti–Ta and Ti–Hf alloys for biomedical applications are comparatively studied in this paper. It is found that with increasing Hf content, the dynamic Young's modulus of the Ti–Hf alloy gently decreases and its tensile strength keeps on increasing. In contrast, with increasing Ta content, the dynamic Young's modulus of the Ti–Ta alloys first decreases, reaches a minimum value of 69 GPa and then increases. In parallel, the tensile strength first increases, reaches a maximum value of 587 MPa, and then slightly decreases. It is shown that the addition of Hf has a slight influence on the dynamic Young's modulus and a strong influence on the tensile properties of the Ti–Hf alloy, while an increase of Ta content has a strong effect on both the dynamic Young's modulus and tensile properties of the Ti–Ta alloy.

In this work the fatigue and wear behavior of Ti–15Al–33Nb(at.%) and Ti–21Al–29Nb(at.%) was evaluated and compared to that for other titanium-based biomedical implant alloys, in particular Ti–6Al–4V(wt.%). Fatigue stress versus life curves were obtained for tests performed at room temperature in air at a stress ratio of R = 0.1 for maximum stresses between 75%–90% of the ultimate tensile strength. The results indicated that the fatigue strength and lives of the as-processed alloys are comparable to that for Ti–6Al–4V(wt.%). Heat treatment significantly increased the orthorhombic-phase volume fractions in the alloys and resulted in reduced fatigue strength. The wear resistance for the alloys was significantly greater than that for Ti–6Al–4V(wt.%). Based on the current results, it is proposed that titanium–aluminum–niobium alloys will be of considerable future interest for biomedical applications.

Ti–XNb–10Ta–5Zr (mass %) alloys based on nominal compositions of Ti–35Nb–10Ta–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.

In order to investigate bone tissue reaction to the low rigidity titanium alloy of TNTZ in bone plate fixation, animal experiment with rabbit was performed with X-ray follow-up and histological observation. Experimental fractures were made in rabbit tibiae, and fixed by different bone plates of SUS316L, Ti-6Al-4V and TNTZ. Although there was no significant difference in fracture healing, bone atrophy was observed in cortical bone especially under the bone plate, which was different in time course among three materials. The bone atrophy under the bone plate was confirmed as porous or poor bone tissue in histological observation. In addition, the diameter of the tibia bone was increased in TNTZ as the result of bone remodeling with a new cortical bone. It is confirmed that the elastic modulus of the bone plate will naturally influence bone tissue reaction to the bone plate fixation according to the Wolff's law of functional restoration.

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 f of the alloys.