Type Titanium Alloy Research Articles

Recent Research and Development in Metallic Materials for Biomedical, Dental and Healthcare Products Applications

Non-toxic allergy free alloying elements are mostly selected for preparing metallic biomaterials. Currently, functionalities such as low modulus, shape memory, super elasticity, etc. are required for the metallic biomaterials, especially for β type titanium alloys. The harmonization of metallic, ceramic, and polymer biomaterials is needed for advanced biomaterials in the future. Titanium and its alloys are attracting considerable attention with regard to applications not only in the biomedical field, but also for dental and healthcare products. In dentistry, titanium and its alloys are applied to dental products such as crowns, inlays, bridges, etc., as well as dental implants. For fabricating dental products, the dental precision casting process is important. A new dental precision casting process using calcia is currently being developed. Noble alloys such as gold base or silver base alloys are widely applied for the precision casting of dental products. Allergy-free elements, particularly Pd-free low- noble dental alloys are required.

Alloy Design and Properties of New α+β Titanium Alloy with Excellent Cold Workability, Superplasticity and Cytocompatibility

Alloy designing and evaluation of various properties of new α+β type titanium alloy with excellent cold workability, superplasticity, and cytocompatibility were conducted. Alloy designing was performed by investigations of the effects of O, Al, Mo, Fe, and Nb contents on cold workability of the alloy with a basic composition of Ti–4.5%Al–4.5%Nb–2%Fe–2%Mo. Use of β stabilizing elements such as V, Ni, or Cu was avoided for biocompatibility. Cold workability was evaluated on the basis of a critical rolling reduction for onset of cracking, hardness under as solution treated condition and hardness variations with a cold rolling reduction. Excellent cold workability was obtained by enhanced thermal and mechanical stabilities of β phase and by lowered hardness of α phase in the α+β two-phase microstructure. Newly developed alloy Ti–4.5%Al–6%Nb–2%Fe–2Mo showed the β transus of 1156 K, a critical rolling reduction over 60%, and yield strength in recrystallization annealing of 910 MPa. An extremely fine α+β two-phase microstructure with α grain size of approximately 1 μm was evolved by annealing at 1048 to 1073 K, and a superplastic elongation value of around 3000% was obtained by tensile testing at these temperatures. New alloy showed an excellent cytocompatibility in a cell culture test using L929 cells, yielding a higher value of cell viability over Ti–6%Al–4%V and Ti–6%Al–7%Nb alloys.

Surface Hardening Treatment in Use of CO Gas and Post-Heat Treatment in C.P. Titanium and Titanium Alloys

Surface hardening treatment of titanium materials in use of CO gas was studied including investigation of post heat treatment under vacuum. C.P. titanium, α+β type SP-700 alloy with Ti-4.5%Al-3%V-2%Mo-2%Fe and β type alloy with Ti-15%Mo-5%Zr-3%Al were used. Surface hardening was conducted by heating these materials at 1073K for 21.6ks in Ar-5%CO gas. Subsequently, specimens subjected to surface hardening were heated at 1073k for various time periods under vacuum. While the maximum surface hardness value was the largest in C.P. titanium and the least in SP-700 alloy, hardening layer thickness was the thickest in β type alloy and the thinnest in C.P. titanium. Surface hardening in C.P. titanium was brought about by solid solution hardening due to oxygen and carbon. Enrichment of these elements in the surface layer of both titanium alloys caused continuous variations of the microstructure such as β to α+β, or their volume fractions in the surface hardening layer. Post heat treatment at 1073K increased the maximum surface hardness and hardening layer thickness with an extension of the heating time in C.P. titanium, but the surface maximum hardness decreased continuously in β type titanium alloy. Post heat treatment could remove the thin oxide layer formed by surface hardening treatment.

Fatigue strength of an (α + β)-type titanium alloy Ti-6Al-4V produced by the electron-beam physical vapor deposition method

The fatigue test results are presented for an (α + β )-type titanium alloy Ti-6Al-4V in the form of two-layered smooth specimens (the first layer is a condensate prepared by the electron-beam physical vapor deposition method, the second one is a substrate from a standard sheet material of the same type) and condensate specimens. It has been found that the presence in the condensate of deposition defects such as droplets lowers the fatigue limit of the material by approximately 1.5 times as compared to that of the condensate which is free of defects. It is shown that in the absence of droplets, the fatigue limit of the condensate is no lower than that of the substrate material. The microstructure, texture and fracture surfaces of the materials under study are analyzed, on the basis of which the fatigue limits of the defectless condensate and substrate material are calculated using approaches of linear fracture mechanics. Good agreement has been obtained between calculated and experimental data.

The Effect of Small Amounts of Yttrium Addition on Static and under Superplastic Deformation Grain Growth in Newly Developed α+β Type, Ti-4.5Al-6Nb-2Mo-2Fe Alloy

New α+β type titanium alloy with Ti-4.5Al-6Nb-2Mo-2Fe was developed on the basis of using biocompatible elements and eliminating the cytotoxic ones such as Vanadium, while achieving the desirable mechanical properties such as appropriate strength, cold workability and low superplastic forming (SPF) temperature. The present study was conducted to investigate the effect of yttrium addition of less than 0.05% into this alloy on static and under superplastic deformation grain growth behavior. The new alloy bar manufactured by α+β processing and annealed at 1073K yielded extremely fine two-phase microstructure with α grain size around 2μm. Specimens were heated at temperatures of 1048, 1073 and 1098K and kept for times between 3.6 to 172.8KS. Yttrium forms in-situ Y2O3 particles, and the presence of these particles yield finer two phase microstructure due to their retardation effect on β phase grain growth. Grain growth behavior during hot deformation was investigated by hot compression test in use of a hot working simulator of THERMEC-Master Z. Strain rate was varied from 2×10-2 to 2×10-4S-1 and strain was 0.69. Grain size of both α and β phases increased with a reduction of strain rate, and Y2O3 particle was also effective to retard grain growth under hot deformation. It was confirmed from comparison of grain growth during isothermal heating with and without hot deformation that grain growth was much accelerated by deformation. All of these results were discussed based on grain growth mechanism or model for two-phase microstructures as well as superplastic deformation mechanism.

Alloy Design and Property Evaluation of New .BETA. Type Titanium Alloy with Excellent Cold Workability and Biocompatibility

Alloy designing of new β type titanium alloy with excellent cold workability and biocompatibility was conducted by using total heat numbers of 38 titanium alloys containing Nb, Fe, Ta or Zr in basic compositions of Ti–10%Mo–2%Fe and Ti–14%Mo. Cold workability was evaluated based on hardness values obtained by solution treating and after cold rolling with a rolling reduction ratio up to 90% as well as a critical rolling reduction ratio for onset of cracking. Excellent cold workability in β type titanium alloy was obtained by enhanced thermal and mechanical stability of β phase through optimum addition of β stabilizing elements in Ti–14%Mo base alloy and a reduction of β transus below 1 000 K. Newly developed alloy of Ti–14%Mo–3%Nb–1.5%Zr yields Vickers hardness values of 240 and 284 in as solution treating and after a cold rolling reduction ratio of 90%, respectively, and no cracking occurs in rolling reduction ratio up to 90%. New titanium alloy shows the almost similar level of non-toxicity to other implant titanium materials in the cell culture test using L929 cells, although a slightly increased passive current density is observed by anodic polarization test in both solutions of saline and 1 mass% lactic acid. New austenitic stainless steel of Fe–6%Mn–22%Cr–10%Ni–2%Mo–0.4%N used as one of comparative materials for evaluation of biocompatibility results in the same level of non-toxicity with new titanium alloy, while relatively poor non-toxicity of the Type 316L steel is observed by cell culture test.

.BETA. Grain Refinement due to Small Amounts of Yttrium Addition in .ALPHA.+.BETA. Type Titanium Alloy, SP-700

The effect of small amounts of yttrium addition on refinement of β grain size and grain growth behavior in SP-700 alloy with Ti-4.5%Al-3%V-2%Fe-2% Mo was investigated in the temperature region from 1 223 to 1 573 K. Yttrium and oxygen contents in yttrium-added alloys were varied from 0.007 to 0.070 % and 0.017 to 0.086 %, respectively. Such a small amount of yttrium addition as 0.007 % resulted in marked β grain refinement. Variation of β grain size with the heating temperature exhibited rapid grain growth at the particular temperature, which became higher with the increase of yttrium or oxygen content in alloys. It was confirmed that β grain refinement and grain growth behavior with the heating temperature in yttrium-added alloys were brought about by fine precipitates of yttria and dissolution of these precipitates into the p matrix at the higher temperature. TEM and SEM observations of yttrium-added alloys revealed the cubic shape of yttria precipitates with the size of 0.1 to 0.2 μm, and this range of the precipitate's size was well fitted to results analyzed by modified Zener' model for pinning of grain boundary due to a fine particle. Based on assumption that the onset temperature of rapid grain growth corresponds to the re-dissolution temperature of yttria into the β phase, solubility product of Y 2 O 3 in reaction of 2Y+30⇆Y 2 O 3 was obtained in use of data of variation of the onset temperature of rapid grain growth with yttrium and oxygen contents in alloys. It was also confirmed that yttria powder could be used as an alloying additive of yttrium in melting of yttrium-added alloys.

Biocompatibility of Ti-8Ta-3Nb alloy with fetal rat calvarial cells

Titanium is the material of choice for oral implantology. The superiority of titanium comes from its mechanical, physicochemical, and biological properties, particularly immunotolerance and cytocompatibility1,2). However because of needs to improve its mechanical properties, titanium alloys such as Ti-6Al-4V, Ti-6Al-7Nb, have also been used for dental and orthopedic material3-5).1) Although titanium alloys are still widely used in medicine, some concern has been expressed over its use since it appears that small amounts of both vanadium and aluminum, released in the human body, induce possible cytotoxic effect and neurological disorders, respectively6-8). In terms of mechanical properties, Ti-6Al-4V alloy belongs to α+β type titanium alloy family. The rigidity of α+β type titanium alloy is much higher (about 120 GPa) than that of the cortical bone (Max 30 GPa)9). Such a strong rigidity (a large modulus of elasticity) causes insufficient loading of the bone adjacent to the implant. This is often referred to as the stress-shielding phenomenon and can lead to potential bone resorption and eventual failure of the implant10). Consequently the recent trend in research and development of titanium alloys for biomedical application is to develop low rigidity titanium alloys composed of non-toxic and non-allergenic elements with excellent mechanical properties and workability9,10). The most promising materials are the β-type titanium alloys because their elastic moduli are smaller than that of αor α+β type titanium family. Therefore new β-type titanium alloys which are composed of non-toxic elements like Tantalum (Ta), Niobium (Nb), Zirconium (Zr),

Microstructural Change of Beta Type Titanium Alloy by Intense Plastic Deformation

Usual static recrystallization treatment and a method to provide intense plastic deformation, ARB namely Accumulative Roll-Bonding, have been applied to two beta type titanium alloys, i.e. Ti-29Nb-13Ta-4.6Zr and Ti-15V-3Cr-3Sn-3Al. Microstructural change as well as work-hardening behavior was examined as a function of plastic strain. Both the work-hardening rate and the hardness at the initial as-hot-rolled state were smaller in the Ti-Nb-Ta-Zr alloy than in the Ti-V-Cr-Sn-Al alloy. Recrystallized grains of 14μm in size were obtained by the usual static recrystallization treatment, which was significantly smaller than that of the starting as-hot-rolled plate of 38μm. No significant change other than flattening and elongating of the original grains was found in the optical microscopic scale. It was revealed, however, from a TEM observation combined with selected area diffraction technique that geometric dynamic recrystallization occurred in the Ti-Nb-Ta-Zr alloy deformed at room temperature by a true strain of 5, resulting in an ultra-fine-grained microstructure where the grain size was roughly estimated to be about 100nm.

Surface Hardening Treatment for C.P. Titanium and Titanium Alloys in Use of Ar–5%CO Gas

Surface hardening of C.P. (commercially pure) titanium and titanium alloys in use of Ar–5%CO gas was investigated in the temperature range between 973 K and 1 123 K. Titanium materials used were α+β type alloy of Ti–4.5%Al–3%V–2%Mo–2%Fe (SP-700) and β type alloy of Ti–15%V–3%Cr–3%Sn–3%Al (Ti-15-333). Oxidation accompanied with surface hardening in use of Ar–5%CO gas is much reduced compared with that of Ar–20%CO2 gas. Surface hardening was evaluated by both of the maximum surface hardness and hardening layer depth obtained from hardness distribution profiles in the subsurface region. The former is the highest in C.P. titanium and the lowest in Ti-15-333 alloy, and the latter is the deepest in Ti-15-333 alloy and the shallowest in C.P. titanium. Surface hardening in C.P. titanium is caused by solid solution hardening of oxygen and carbon enriched in the subsurface region. Enrichment of these interstitials in the subsurface region of SP-700 or Ti-15-333 alloys causes the increase of α volume fraction in α+β two phases or phase transformation from β to α+β two phases, respectively, and surface hardening is primarily controlled by volume fraction of α phase hardened by interstitials enrichment. The other β type titanium alloy of Ti–15%Mo–5%Zr–3%Al yields much marked surface hardening over Ti-15-333 alloy. All of these results were analyzed and discussed based on oxygen and carbon concentration profiles, which were obtained by EPMA, and were also calculated by uni-dimensional diffusion model.

電気化学処理による新生体用β型チタン合金の生体活性表面修飾

電気化学処理による新生体用β型チタン合金の生体活性表面修飾

Compression Characteristic and Tensile Property in an (Alpha+Beta)-Type Titanium Alloy at High Temperature

Compression Characteristic and Tensile Property in an (Alpha+Beta)-Type Titanium Alloy at High Temperature

Super Elastic Functional β Titanium Alloy with Low Young's Modulus for Biomedical Applications

Abstract The low modulus β type titanium alloy, Ti-29Nb-13Ta-4.6Zr, was designed, and then the practical level ingot of the alloy was successfully fabricated by Levicast method. The mechanical and biological compatibilities, and super elastic behavior of the alloys were investigated in this study. The mechanical performance of tensile properties and fatigue strength of the alloy are equal to or greater than those of conventional biomedical Ti-6Al-4V ELI. Young's modulus of the alloy is much lower than that of Ti-6Al-4V ELI, and increases with the precipitation of α phase or ω phase in the β matrix phase. The compatibility of the alloy with bone is excellent. Low modulus of the alloy is effective to enhance the healing of bone fracture and remodeling of bone. Super elastic behavior is observed in Ti-29Nb-13Ta-4.6Zr conducted with short time solution treatment after heavy cold working. Total elastic strain in that case is around 2.8 %. The mechanism of the super elastic behavior of Ti-29Nb-13Ta-4.6Zr is still unclear.

Improvement in fatigue characteristics of newly developed beta type titanium alloy for biomedical applications by thermo-mechanical treatments

Tensile and plain fatigue properties of β type titanium alloy, Ti–29Nb–13Ta–4.6Zr, which underwent various thermo-mechanical treatments, were investigated in order to judge its potential for biomedical applications. Microstructures of Ti–29Nb–13Ta–4.6Zr (TNTZ) aged directly at 723 K for 259.2 ks after cold rolling and TNTZ aged at 723 K for 259.2 ks after solution treatment are composed of precipitated α phase in β phase. While, microstructures of TNTZ aged directly at 598 K and 673 K for 259.2 ks after cold rolling and aged at 598 K and 673 K for 259.2 ks after solution treatment are composed of precipitated ω phase, and precipitated α and ω phases in β phase, respectively. Tensile strength of aged TNTZ after solution treatment and aged TNTZ after cold rolling decreases with increasing aging temperature although the elongation shows the reverse trend. TNTZ composed of ω phase or ω and α phases in β phase shows the tensile strength of around 1000 MPa or more. Young's moduli of aged TNTZ after solution treatment and aged TNTZ after cold rolling decrease with increasing aging temperature. TNTZ conducted with solution treatment has the lowest Young's modulus of around 60 GPa. Fatigue strengths of aged TNTZ after solution treatment and aged TNTZ after cold rolling increase with increasing aging temperature. In particular, TNTZ aged directly at 723 K after cold rolling shows the greatest fatigue strength in both low cycle fatigue life and high cycle fatigue life regions, and the fatigue limit, which is around 770 MPa, is nearly equal to that of hot-rolled Ti–6Al–4V ELI conducted with aging, which is one of representative α + β type titanium alloys for biomedical applications.

Relationships between tensile deformation behavior and microstructure in Ti–Nb–Ta–Zr system alloys

Ti–Nb–Ta–Zr system alloys are receiving more attention for biomedical material component applications. However, the deformation behavior of the Ti–Nb–Ta–Zr system has not been evaluated to date. Therefore, the deformation behavior of Ti–Nb–Ta–Zr alloys with different Nb contents was investigated in this study. The behaviors of loading–unloading stress–strain curves of Ti–20Nb–10Ta–5Zr and Ti–25Nb–10Ta–5Zr air-cooled after final heating of the manufacturing process are similar to that obtained in metastable β type titanium alloys that have the shape memory effect. Therefore, the shape memory effect was expected in Ti–20Nb–10Ta–5Zr and Ti–25Nb–10Ta–5Zr alloys. The elastic deformation of Ti–30Nb–10Ta–5Zr disobeyed Hooke's law. However, stress or strain-induced martensite (SIM) is not observed on the loading–unloading stress–strain curve. The deformation mechanism of Ti–25Nb–10Ta–5Zr changes with varying its microstructure. In Ti–25Nb–10Ta–5Zr air-cooled after final heating, the microstructure consisted of an ω phase in a β phase. The stress for inducing martensite in a β phase, σ M, was nearly equal to the yielding stress, σ y. Therefore, stress-induced martensitic transformation and movement of dislocations occurred together. In Ti–25Nb–10Ta–5Zr water-quenched after final heating of the manufacturing process, the microstructure consisted of a single β phase, where σ M is lower than σ y. Therefore, stress-induced martensitic transformation occurred before yielding.

Mechanical properties and cyto-toxicity of new beta type titanium alloy with low melting points for dental applications

Beta stabilized new alloys such as Ti–29Nb–13Zr–2Cr, Ti–29Nb–15Zr–1.5Fe, Ti–29Nb–10Zr–0.5Si, Ti–29Nb–10Zr–0.5Cr–0.5Fe and Ti–29Nb–18Zr–2Cr–0.5Si have been developed for dental applications. These alloys were designed based on master alloy Ti–29Nb–13Ta–4.6Zr (TNTZ) for biomedical applications. In this research, high melting temperature element Ta was replaced with beta stabilizing elements such as Cr, Fe and Si to lower the melting temperature of the alloy. Their melting points, mechanical properties, surface reaction layers and cyto-toxicity were investigated in this study. Melting points of designed alloys fall by about 50 K to 370 K as compared with that of TNTZ, and Ti–29Nb–13Zr–2Cr has the lowest melting point of around 2050 K. Vickers hardness of the surface of each designed alloy cast into modified magnesia based investment material is in the range of 400 Hv to 500 Hv, which is lower than that of TNTZ (around 560 Hv). Balances of strength and ductility of cast Ti–29Nb–13Zr–2Cr, Ti–29Nb–15Zr–1.5Fe and Ti–29Nb–10Zr–0.5Cr–0.5Fe are nearly equal to that of cast TNTZ. Cell viability of each cast designed alloy is excellent.

Wear Loss and Elution of C.P.Ti and Titanium Alloys in Simulated Body Fluids

Wear behavior of titanium materials such as C.P.Ti, Ti-6Al-4V and Ti-6Al-7Nb, was studied in simulated body fluids by means of the pin-on-disk type wear testing. The mass loss in wear testing increased with increasing the sliding distance. The a+b type titanium alloys, Ti-6Al-4V and Ti-6Al-7Nb, exhibited higher wear resistance than the C.P.Ti. Average size of the wear debris was 4.5 µm and 3.7 µm for C.P.Ti and the a+b type titanium alloys, respectively. The elution of metallic constituents into 1 mass% lactic acid solution was detected after the wear test.

Making Combinatorial Libraries of Titanium Based Alloys by Direct Metal Deposition Technique

Abstractα/β type titanium alloys, such as Ti-6Al-4V and Ti-6Al-7Nb, have been used for orthopedic implant materials because of their combination of biocompatibility, corrosion resistance and mechanical properties. However, toxicity of alloying elements is a concern.In this project, it is proposed to design the new type of titanium alloys composed of non-toxic elements, such as Ti, Al, and Fe with lower modulus of elasticity and greater corrosion resistance. To find the optimal ratio of components in the Ti-Al-Fe system is important. The composition of the alloy determines its properties. Using combinatorial approach the optimal ratio can be found relatively easily.Direct metal deposition (DMD) is a novel precise manufacturing process for fabricating metal parts directly from Computer Aided Design (CAD) solid models. The DMD process allows making several layers of different composition on one substrate. One sample includes several Ti-xAl-yFe alloys at once. This combinatorial library dramatically reduces the time and cost of the investigation.The structure, mechanical and electrochemical properties of each new composition was studied using scanning electron microscopy (SEM) with energy-dispersive X-ray fluorescence analyzer (EDAX ZAF®), and electrochemical polarization method.

The Effects of the Oxygen-enriched Surface Layer on Mechanical Properties of .ALPHA.+.BETA. Type Titanium Alloys

The effects of heat treating conditions on thickness of the oxygen-enriched layer or α-case in Ti-4.5%Al-3%V-2%Fe-2%Mo alloy were studied in comparison with Ti-6%Al-4%V alloy, and then the effects of these layers on the mechanical properties were investigated. The higher heating temperature and an extended heating time increased oxygen-enriched layer or α-case thickness in Ti-4.5%Al-3%V-2%Fe-2%Mo alloy, and atmospheric heating using high purity argon gas with 99.999% purity could not prevent formation of the oxygen-enriched layer even by heating at such a low temperature as 998 K. The 30 μm thick oxygen-enriched layer without α-case was formed by heat treating at 1048 K for 3.6 ks in use of 99.9% purity argon gas which corresponded to the typical heating conditions adopted in a practical superplastic forming (SPF) operation using Ti-4.5%Al-3%V-2%Fe-2%Mo alloy. The thickness of both surface layers in Ti-6%Al-4%V alloy was much thicker than Ti-4.5%Al-3%V-2%Fe-2%Mo alloy because of its higher heating temperature. Tensile elongation, fatigue strength and bendability were deteriorated with the increase of oxygen-enriched layer or α-case thickness, and removal of these layers by pickling treatment fully recovered these properties to an original level. Deterioration of the mechanical properties was exerted by existence of the surface layer with high hardness, and in particular, the oxygen-enriched layer with α-case decreased fatigue strength more pronouncedly compared with the surface layer without α-case. Existence of brittle surface layer with high hardness and the coarse grain size in α-case appeared to be responsible for accelerated formation of microcrack at the surface of the mechanical testing specimens, resulting in deterioration of various properties.

Fatigue, Fretting Fatigue and Corrosion Characteristics of Biocompatible Beta Type Titanium Alloy Conducted with Various Thermo-Mechanical Treatments

Plain and fretting fatigue properties of β type titanium alloy, Ti-29Nb-13Ta-4.6Zr, underwent various thermo-mechanical treatments were investigated in order to judge its potential for biomedical applications. Ti-29Nb-13Ta-4.6Zr aged directly at 723 K for 259.2 ks after cold rolling shows the greatest fatigue strength in both low cycle fatigue life and high cycle fatigue life regions, and the fatigue limit, which is around 770 MPa, is nearly equal to that of hot-rolled Ti-6Al-4V ELI conducted with aging, which is one of representative α + β type titanium alloys for biomedical applications. Fretting fatigue strength tends in proportion to Young's modulus. Fretting fatigue limits of the forged bar of Ti-29Nb-13Ta-4.6Zr conducted with solution treatment, and aging at 723 K after solution treatment are around two thirds and a half of plain fatigue limits, respectively, and those are around 180 MPa and 285 MPa, respectively. Passive current densities of the plate of Ti-29Nb-13Ta-4.6Zr conducted with a multi-step-thermo-mechanical treatment, where the cold rolling and solution treatment are repeated 4 times, in 0.5%HCl and Ringer's solutions are much smaller than that of Ti-29Nb-13Ta-4.6Zr conducted with general thermo-mechanical treatment, and the values are a little smaller than those of forged Ti-15Mo-5Zr-3Al conducted with annealing and hot rolled Ti-6Al-4V ELI conducted with aging.