Nb Ta Zr Research Articles

Corrosion behavior of Ti–Nb–Ta–Zr–Fe alloy for biomedical applications in Ringer's solution

The corrosion resistance of Ti–25Nb–10Ta–1Zr–0.2Fe (mass fraction, %) (TNTZF) alloy in Ringer's solution at 37 °C was investigated by potentiodynamic polarization measurement. Ti–6Al–4V ELI (Extra low interstitial) alloy was also investigated to make a comparison. The results show that TNTZF alloy has higher corrosion potential, lower corrosion current density, more stable passive current density and wider passive region compared with Ti–6Al–4V ELI alloy, which indicates that TNTZF alloy has better corrosion resistance. In addition, pitting corrosion is observed on the surface passive film of Ti–6Al–4V ELI alloy but is not found on that of TNTZF alloy. The XPS analysis results reveal that the passive film formed on TNTZF alloy is composed of Nb2O5, NbO2, Ta2O5, ZrO2, TiO and Ti2O3 oxides in the matrix of TiO2, which makes the passive film more stable and protective than that formed on Ti–6Al–4V ELI alloy and contributes much to its superior corrosion resistance.

Color tone and interfacial microstructure of white oxide layer on commercially pure Ti and Ti–Nb–Ta–Zr alloys

In this study, the relationships among oxidation condition, color tone, and the cross-sectional microstructure of the oxide layer on commercially pure (CP) Ti and Ti–36Nb–2Ta–3Zr–0.3O were investigated. “White metals” are ideal metallic materials having a white color with sufficient strength and ductility like a metal. Such materials have long been sought for in dentistry. We have found that the specific biomedical Ti alloys, such as CP Ti, Ti–36Nb–2Ta–3Zr–0.3O, and Ti–29Nb–13Ta–4.6Zr, form a bright yellowish-white oxide layer after a particular oxidation heat treatment. The brightness L* and yellowness +b* of the oxide layer on CP Ti and Ti–36Nb–2Ta–3Zr–0.3O increased with heating time and temperature. Microstructural observations indicated that the oxide layer on Ti–29Nb–13Ta–4.6Zr and Ti–36Nb–2Ta–3Zr–0.3O was dense and firm, whereas a piecrust-like layer was formed on CP Ti. The results obtained in this study suggest that oxide layer coating on Ti–36Nb–2Ta–3Zr–0.3O is an excellent technique for dental applications.

Microstructure and fatigue behaviors of a biomedical Ti–Nb–Ta–Zr alloy with trace CeO 2 additions

Abstract The new β-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 β 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 β 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 CeO2 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.

Magmatic–hydrothermal rare-element mineralization in the Songshugang granite (northeastern Jiangxi, China): Insights from an electron-microprobe study of Nb–Ta–Zr minerals

The Songshugang granite, hidden in the Sinian metasedimentary stratum, is a highly evolved rare-element granite in northeastern Jiangxi province, South China. The samples were systematically taken from the CK-102 drill hole at the depth of 171–423m. Four types of rocks were divided from the bottom upwards: topaz albite granite as the main body, greisen nodules, topaz K-feldspar granite and pegmatite layer. Electron-microprobe study reveals that the rare-element minerals of the Songshugang granite are very different from those of other rare-element granites. Mn# [Mn/(Fe+Mn)] and Ta# [Ta/(Nb+Ta)] of columbite-group minerals and Hf# [Hf/(Zr+Hf)] of zircon are nearly constant within each type of rocks. However, back-scattered electron imaging revealed that Nb–Ta oxides and zircon of the Songshugang granite, especially those of topaz albite granite, topaz K-feldspar granite and greisen, are commonly characterized by a specific two-stage texture on the crystal scale. The early-stage Nb–Ta oxide is simply subhedral-shaped columbite-(Fe) (CGM-I) with low Mn# (0.16–0.37) and Ta# (0.05–0.29). Columbite-(Fe) is penetrated by the later-stage tantalite veinlets (CGM-II) or surrounded by complex Nb–Ta–Sn–W mineral assemblages, including tantalite-(Fe), wodginite (sl), cassiterite, and ferberite. Tantalite has wide range of Mn# values (0.15–0.88) from Fe-dominance to Mn-dominance. Wodginite with Ta>Nb has large variable concentrations of W, Sn and Ti. Cassiterite and ferberite are all enriched in Nb and Ta (Nb2O5+Ta2O5 up to 20.12wt.% and 31.42wt.%, respectively), with high Ta# (>0.5). Similar to Nb–Ta oxides and Nb–Ta–Sn–W mineral assemblages, the early-stage zircon is commonly included by the later-stage zircon with sharply boundary. They have contrasting Hf contents, and HfO2 of the later-stage zircon is up to 28.13wt.%. Petrographic features indicate that the early-stage of columbite and zircon were formed in magmatic environment. However, the later-stage of rare-element minerals were influenced by fluxes-enriched fluids. Tantalite, together with wodginite, cassiterite, and ferberite implies a Ta-dominant media. An interstitial fluid-rich melt enriched in Ta and flux at the magmatic–hydrothermal transitional stage is currently a favored model for explaining the later-stage of rare-element mineralization.

Petrology, geochemistry and geochronology of the magmatic suite from the Jianzha Complex, central China: Petrogenesis and geodynamic implications

The intermediate–mafic–ultramafic rocks in the Jianzha Complex (JZC) at the northern margin of the West Qinling Orogenic Belt have been interpreted to be a part of an ophiolite suite. In this study, we present new geochronological, petrological, geochemical and Sr–Nd–Hf isotopic data and provide a different interpretation. The JZC is composed of dunite, wehrlite, olivine clinopyroxenite, olivine gabbro, gabbro, and pyroxene diorite. The suite shows characteristics of Alaskan-type complexes, including (1) the low CaO concentrations in olivine; (2) evidence of crystal accumulation; (3) high calcic composition of clinopyroxene; and (4) negative correlation between FeOtot and Cr2O3 of spinels. Hornblende and phlogopite are ubiquitous in the wehrlites, but minor orthopyroxene is also present. Hornblende and biotite are abundant late crystallized phases in the gabbros and diorites. The two pyroxene-bearing diorite samples from JZC yield zircon U–Pb ages of 245.7±1.3Ma and 241.8±1.3Ma. The mafic and ultramafic rocks display slightly enriched LREE patterns. The wehrlites display moderate to weak negative Eu anomalies (0.74–0.94), whereas the olivine gabbros and gabbros have pronounced positive Eu anomalies. Diorites show slight LREE enrichment, with (La/Yb)N ratios ranging from 4.42 to 7.79, and moderate to weak negative Eu anomalies (Eu/Eu∗=0.64–0.86). The mafic and ultramafic rocks from this suite are characterized by negative Nb–Ta–Zr anomalies as well as positive Pb anomalies. Diorites show pronounced negative Ba, Nb–Ta and Ti spikes, and typical Th–U, K and Pb peaks. Combined with petrographic observations and chemical variations, we suggest that the magmatism was dominantly controlled by fractional crystallization and crystal accumulation, with limited crustal contamination. The arc-affinity signature and weekly negative to moderately positive εNd(t) values (−2.3 to 1.2) suggest that these rocks may have been generated by partial melting of the juvenile sub-continental lithospheric mantle that was metasomatized previously by slab-derived fluids. The lithologies in the JZC are related in space and time and originated from a common parental magma. Geochemical modeling suggests that their primitive parental magma had a basaltic composition. The ultramafic rocks were generated through olivine accumulation, and variable degrees of fractional crystallization with minor crustal contamination produced the diorites. The data presented here suggest that the subduction in West Qinling did not cease before the early stage of the Middle Triassic (∼242Ma), a back-arc developed in the northern part of West Qinling during this period, and the JZC formed within the incipient back-arc.

Ultrafine-grained Ti–Nb–Ta–Zr alloy produced by ECAP at room temperature

To ascertain the influence of severe plastic deformation (SPD) on a Ti–Nb–Ta–Zr (TNTZ) alloy, we studied the room temperature mechanical behavior and microstructural evolution of an ultrafine-grained (UFG) Ti–36Nb–2Ta–3Zr (wt%) alloy prepared via equal-channel angular pressing (ECAP) of the as-hot-extruded alloy. The tensile behavior, phase composition, grain size, preferred orientation, and dislocation density of the UFG alloy, processed under different conditions, were analyzed and discussed. Compared to the as-hot-extruded alloy, the ECAP-processed TNTZ alloy (3 passes) exhibited approximately 40 and 88 % increase in average ultimate strength and yield strength, respectively. Moreover, as the number of ECAP passes increased from 3 to 6, the TNTZ alloy exhibited not only the expected increase in ultimate and yield strength values, but also a slight increase in elongation. Our results suggest that the deformation mechanisms that govern the behavior of the as-hot-extruded coarse grained (CG) TNTZ alloy during ECAP involve a combination of stress-induced martensitic transformation and dislocation activity. In the case of the ECAP-processed UFG TNTZ alloy, the deformation mechanism is proposed to involve two components: first, dislocation activity induced by the strain field imposed during ECAP; and second, the formation of α″ martensite phase during the early stages of ECAP which eventually transforms into β phase during continued deformation. We propose that the deformation mechanism governing the room temperature behavior of the TNTZ alloy strongly depends on the grain size of the β phase.

MRI compatible Nb–Ta–Zr alloys used for vascular stents: Optimization for mechanical properties

With the increased usage of magnetic resonance imaging (MRI) as a diagnostic tool in clinic, the currently-used metals for vascular stents, such as 316L stainless steel (SS), Co–Cr alloys and Ni–Ti alloys, are challenged by their unsatisfactory MRI compatibility, due to their constituents containing ferromagnetic elements. To provide more MRI compatible vascular stents, the Nb–xTa–2Zr (30≤x≤70) series alloys were selected in the current work. Several key properties of these alloys were optimized in terms of stent requirements, including magnetic susceptibility, elastic modulus and tensile properties. In the as-cast state, a single-phase solid solution with bcc structure was formed in the alloys. The volume magnetic susceptibility (χv) and Young's modulus (E) of the alloys scaled linearly with the Ta content. Increasing the Ta content gave rise to the decreased χv and the increased E, together with the elevated yield strength but less-changed elongation. From multiple requirements for the stents, the Nb–60Ta–2Zr alloy exhibits an optimal properties, including the χv of about 3% of the 316L SS, the E of 142GPa superior to pure niobium, high mass density of 12.03g/cm3 favored to the X-ray visibility, yield strength of ~330MPa comparable to the 316L SS and a elongation of ~24%. These remarkable advantages make it quite promising as a new candidate of stent metals.

Genesis of the 1.21 Ga Marnda Moorn large igneous province by plume–lithosphere interaction

The 1.21Ga Marnda Moorn large igneous province (LIP) of the Yilgarn Craton is important for understanding the final breakup of the Nuna (Columbia) supercontinent. However, its petrogenesis is poorly understood owing to the lack of geochemical data. We conducted geochemical analyses of the Gnowangerup–Fraser Dyke Suite, a major part of the Marnda Moorn LIP, and report the first geochemical and Nd isotope data for this LIP. Results of a complementary paleomagnetic study of these dykes will be published elsewhere. Most of the studied dykes consist of predominately tholeiitic and OIB-like dolerite (Group 1) and one arc-like and more felsic dyke (Group 2). Group 1 samples have incompatible trace element compositions similar to those of tholeiitic Hawaiian plume-induced OIB and typical asthenospheric mantle-derived Nd isotopes with ɛNd(t) varying from +3.7 to +7.5, produced mainly within the spinel stability field (<75km depth). Their source region most likely contains recycled oceanic crust. Samples from the Group 2 dyke are characterized by extremely unradiogenic Nd isotopes with ɛNd(t) of about −12, strong depletion of Nb–Ta–Zr–Hf–Ti, chondritic Nb/Ta ratios (20–18), oversaturated silica, and strong deficiencies in CaO, FeOt, TiO2, and Ni. This implies that the dyke was produced by partial melting of enriched sub-continental lithospheric mantle. The coexistence of OIB- and arc-like end-members but mainly Hawaiian OIB-like tholeiitic mafic dykes, interpreted large-scale asthenosphere upwelling in a very short time, and the large volume of mafic magma, favour a plume origin for the Marnda Moorn LIP. The geochemical and emplacement characteristics are attributed to relief of the lithosphere–asthenosphere boundary across the Yilgarn craton and a complex interplay between the plume, heated lithosphere, normal asthenosphere, and recycled components. We propose a two-stage melting model to explain the geochemical composition and emplacement of the Marnda Moorn LIP. Our plume-lithosphere interaction model is consistent with the occurrence of synchronous ultrahigh-temperature events in the Musgrave Province of central Australia.

Microstructural evolution and final properties of a cold-swaged multifunctional Ti–Nb–Ta–Zr–O alloy produced by a powder metallurgy route

Body centred cubic (BCC) β-phase multifunctional titanium alloys have been developed with a very unique combination of thermal and mechanical properties. In this investigation, a very low porosity Ti–36.8–Nb–2.7Zr–2.0Ta–0.44O (wt%) alloy was produced by powder sintering, hot forging, solution treatment and cold swaging. X-ray diffraction and transmission electron microscopy (TEM) of the solution treated alloy revealed the presence of a small amount of ω-phase in a predominantly BCC β-phase matrix. Electron backscatter diffraction (EBSD) of the swaged alloy revealed a highly elongated and fragmented microstructure, and a strong 〈110〉 fibre texture. TEM also revealed the existence of stress-induced twin lamella, dislocations and ω-phase. Consistent with previous studies on these types of alloys, the swaged alloy exhibited non-linear elasticity during tensile straining, low elastic modulus (45.4GPa), high elastic limit (2.3%), high elongation to failure (8.1%), and a high yield strength (880MPa) and tensile strength (940MPa). The coefficient of thermal expansion was also low (∼5×10−6K−1 between 50 and 300°C) in this alloy.

ω Transformation in cold-worked Ti–Nb–Ta–Zr–O alloys with low body-centered cubic phase stability and its correlation with their elastic properties

The ω transformation and its correlation with elastic properties were investigated in cold-worked Ti–36Nb–2Ta–3Zr–xO mass% alloys with low body-centered cubic (β) phase stability, known as gum metal. Analysis of the temperature dependence of the ω (hexagonal) phase formation using transmission electron microscopy and of the elastic properties of solution-treated and cold-worked alloys using resonant ultrasound spectroscopy revealed that in the solution-treated 0.36% and 0.51% O alloys, the high concentration of oxygen suppressed ω-phase formation from room temperature to a fairly low temperature of ∼13K. However, the ω phase was formed by cold working at room temperature in the 0.30% and 0.47% O alloys. Importantly, the fraction of the ω phase clearly increased upon cooling, which indicates that the formation of the ω phase is thermodynamically favorable near and below room temperature in the cold-worked 0.30% and 0.47% O alloys. This formation of the ω phase and the low stability of the β phase related to the low electron/atom (e/a) ratio were the dominant factors determining the elastic properties near and below room temperature in the cold-worked Ti–Nb–Ta–Zr–O alloys.

Effects of cold deformation on microstructure, texture evolution and mechanical properties of Ti–Nb–Ta–Zr–Fe alloy for biomedical applications

Abstract The effects of cold deformation on the microstructure, texture evolution and mechanical properties of Ti–25Nb–10Ta–1Zr–0.2Fe (TNTZF) alloy during cold rolling (CR) were investigated. The results showed that the dominant deformation mechanisms changed from stress-induced α″ martensitic transformation and dislocation tangles to twinning, shear bands and nanostructuring with the increase of cold reduction. Meanwhile, the transition from {1 1 1}〈1 1 0〉 to {1 1 1}〈1 1 2〉 orientation took place during CR and a dominant {1 1 1}〈1 1 2〉 texture was obtained after 80% cold deformation. The hardness and strength increased with the increase of cold reduction owing to the effects of the increase of dislocation density and the grain refinement caused by cold deformation. The decrease in Young's modulus after CR is mainly attributed to the stress-induced α″ martensitic transformation accompanying with the disappearance of ω phase. The cold deformed TNTZF alloy with reduction of 60% has a great potential to become a new candidate for biomedical applications since it possesses high strength-to-modulus ratio and appropriate plasticity.

Development of thermo-mechanical processing for fabricating highly durable [formula omitted]-type Ti–Nb–Ta–Zr rod for use in spinal fixation devices

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}β are aligned parallel to the cross-section with two strong peaks approximately 180∘ apart, facing one another, in the TNTZ rods subjected to cold caliber rolling and six strong peaks at approximately 60∘ 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 α and β phases is different. A [110]β//[121]α, (112)β//(210)α 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]β//[001]α, (112)β//(200)α 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.

The influence of chemical composition and thermo-mechanical treatment on Ti–Nb–Ta–Zr alloys

Ti–Nb–Ta–Zr quaternary alloying system is very promising for biomedical alloys. It is due to good mechanical properties and corrosion resistance of titanium alloys. Moreover no potentially harmful elements are contained in this system.Mechanical properties were influenced by changing the chemical composition and by various heat-treatment operations. The alloys were prepared by arc melting and then they were hot forged (900–1000°C). After solution treatment 850°C/0.5h/water quenched, cold swaging was carried out with section reduction about 85%. As final heat treatment aging at 450°C/8h/furnace cooling was used.Mechanical properties were measured from tensile tests results at cold swaged and aged specimens. The microstructure was observed by using light microscopy and transmission electron microscopy (TEM)-thin foils method. X-ray diffraction analysis reveals the phase composition. By using these techniques the changes in microstructure caused by precipitation during aging treatment were clarified. After aging, the presence of ω or α phases may occur. Influence of changing Zr and Ta contents on mechanical properties and also on precipitation of secondary phases during aging treatment was observed.

Age-hardening behavior, microstructural evolution and grain growth kinetics of isothermal ω phase of Ti–Nb–Ta–Zr–Fe alloy for biomedical applications

Age-hardening behavior, microstructural evolution and the grain growth kinetics of isothermal ω during aging treatments of Ti–25Nb–10Ta–1Zr–0.2Fe alloy were investigated. The results showed that in addition to martensite α″, a small amount of α and athermal ω was observed in the β matrix after solution treatment. The decomposition of martensite α″ and the transformation from athermal ω (ωath) to isothermal ω (ωiso) occurred at the early stage of aging. ωiso firstly competed to grow with α phase, and then dissolved and transformed into α phase. The growth and dissolution of ωiso was accelerated with increasing aging temperature. Finally, the α + β stable microstructure was obtained after aging for 280, 200, 24 and 2 h at 623, 673, 743 and 773 K, respectively. The alloy showed stronger age-hardening response at intermediate temperatures of 673 and 743 K, while exhibited weaker age-hardening response at lower temperature of 623 K and higher temperature of 773 K. The uniform distribution of dense ωiso and α precipitates in the β matrix with moderate size resulted in the peak micro-hardness values. The grain growth of ωiso obeys an asymptotic law, and the grain-growth exponent, n, was computed to be in the range of 0.23–0.26 at temperatures in the range of 623–743 K. The activation energy for ωiso grain growth, Qg was calculated to be 119.7 kJ/mol.

Improvement in Fatigue Strength of Biomedical β-type Ti–Nb–Ta–Zr Alloy While Maintaining Low Young’s Modulus Through Optimizing ω-Phase Precipitation

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.

Low Young’s modulus in Ti–Nb–Ta–Zr–O alloys: Cold working and oxygen effects

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 c 44 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 c 44 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.

Hydrogen permeability, thermal stability and hydrogen embrittlement of Ni–Nb–Zr and Ni–Nb–Ta–Zr amorphous alloy membranes

Amorphous alloys are a promising alternative to Pd alloy membranes for hydrogen separation because of their lower cost and comparable hydrogen permeability. A series of amorphous alloy membranes consisting of Ni 60Nb 20Zr 20 (at%), (Ni 0.6Nb 0.4) 100− x Zr x and (Ni 0.6Nb 0.3Ta 0.1) 100− x Zr x (where x = 0, 10, 20 or 30) were prepared by melt spinning and then coating the foil surfaces with a thin (500 nm) layer of Pd using physical vapor deposition (PVD). A (Ni 0.6Nb 0.4) 70Zr 30 membrane exhibited the highest hydrogen permeability (1.4 × 10 −8 mol m −1 s −1 Pa −0.5) of any of the materials, measured in pure hydrogen at 450 °C. Membrane permeability increased with Zr content, but membranes higher in Zr were more susceptible to brittle failure and were more thermally unstable. Decreases in hydrogen permeability were almost always observed during long-term permeability tests at 400 and 450 °C. The addition of Ta slightly increased the thermal stability, but moderately lowered the hydrogen permeability. An AES depth profile of the membrane surface showed that metallic interdiffusion had taken place between the Pd coating and the bulk membrane, which probably accounts for the reduction in hydrogen permeability over time at 400–450 °C.

Characterization of deformation localization in cold-rolled metastable β-Ti–Nb–Ta–Zr alloy

The deformation-induced microstructural variation in the metastable β-type biomedical Ti–35Nb–5Ta–7Zr (wt.%) alloy subjected to multi-pass cold-rolling to 90% reduction has been investigated by a combination of X-ray diffraction, optical microscopy, conventional transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) techniques. Multi-pass cold rolling for the Ti–35Nb–5Ta–7Zr alloy includes various localized deformation processes which can result in dislocation tangle, stress-induced ω-phase transformation and deformation-band formation. Deformation-induced amorphization caused by high-density defect accumulation in deformation bands has been identified. By means of TEM and HRTEM observations, distributional, morphological and structural features for deformation bands have been clearly revealed.

Influence of oxygen content on microstructure and mechanical properties of Ti–Nb–Ta–Zr alloy

The influence of oxygen content on microstructure and mechanical properties of Ti–22.5Nb–0.7Ta–2Zr (at.%) alloy was investigated in this work. According to experiments, the grains were refined apparently when the oxygen content was between 1.5% and 2.0%. The ultimate tensile strength (UTS) increased and elongation decreased with increasing oxygen content. But at the content of 1.0%, the elongation was nearly the same to that of the original alloy (about 16%). The elastic modulus remained comparatively low (<65 GPa) when the content was lower than 1.5%, and then increased dramatically. Therefore, there existed the best oxygen content-1.0%, at which fine grains were obtained, as well as UTS of 750 MPa, elongation of 16% and elastic modulus of 65 GPa. The Ti–22.5Nb–0.7Ta–2Zr–1.0O alloy maintained typical ductile fracture characteristics of beta titanium alloy, and had a little superelasticity.

Low Young’s modulus of Ti–Nb–Ta–Zr alloys caused by softening in shear moduli c′ and c44 near lower limit of body-centered cubic phase stability

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.