Ti-29Nb-13Ta-4.6Zr Research Articles

Influence of load and sliding distance on the micro-scale abrasive wear behavior of TZNT alloy

The micro-scale abrasive wear behavior of TiZrNbTa (TZNT) alloy in Hank’s solution and distilled water was studied using the TE66 machine. The effect of load and sliding distance was considered. The results of experiments show that the wear volume of the TZNT alloy is increased with increasing distance because of the greater damage, but the wear volume is not present the same regularity as the increase of load due to the effect of several factors. Only three-body abrasive wear is present at the lower load, while the mixed wear mechanism includes three-body and two-body abrasive wears at the higher load. Through observation, the wear appears under the same sliding distance at various simulated body fluids. The wear appearance is related to the wear mechanism. For wastage map, under the conditions of this paper, the majority of the area is medium wastage, the rest is low wastage, and there is no high wastage. The wastage map is related to the wear volume of the alloy under different conditions.

Newly developed Ti–Nb–Zr–Ta–Si–Fe biomedical beta titanium alloys with increased strength and enhanced biocompatibility

Beta titanium alloys are promising materials for load-bearing orthopaedic implants due to their excellent corrosion resistance and biocompatibility, low elastic modulus and moderate strength. Metastable beta-Ti alloys can be hardened via precipitation of the alpha phase; however, this has an adverse effect on the elastic modulus. Small amounts of Fe (0–2wt.%) and Si (0–1wt.%) were added to Ti–35Nb–7Zr–6Ta (TNZT) biocompatible alloy to increase its strength in beta solution treated condition. Fe and Si additions were shown to cause a significant increase in tensile strength and also in the elastic modulus (from 65GPa to 85GPa). However, the elastic modulus of TNZT alloy with Fe and Si additions is still much lower than that of widely used Ti–6Al–4V alloy (115GPa), and thus closer to that of the bone (10–30GPa). Si decreases the elongation to failure, whereas Fe increases the uniform elongation thanks to increased work hardening. Primary human osteoblasts cultivated for 21days on TNZT with 0.5Si+2Fe (wt.%) reached a significantly higher cell population density and significantly higher collagen I production than cells cultured on the standard Ti–6Al–4V alloy. In conclusion, the Ti–35Nb–7Zr–6Ta–2Fe–0.5Si alloy proves to be the best combination of elastic modulus, strength and also biological properties, which makes it a viable candidate for use in load-bearing implants.

Elastic-modulus enhancement during room-temperature aging and its suppression in metastable Ti–Nb-Based alloys with low body-centered cubic phase stability

Changes in the elastic properties during room-temperature aging (RT aging) of metastable Ti–Nb-based alloy single crystals with low body-centered cubic (bcc)-phase stability were investigated. The elastic stiffness components of Ti–Nb–Ta–Zr alloys with different Nb concentrations were measured by resonant ultrasound spectroscopy during RT aging; the results revealed that shear moduli c′ and c44 were increased by RT aging. In the alloy with the lowest Nb concentration, i.e., with the lowest bcc phase stability, shear moduli c′ and c44 were enhanced by the largest amount. The increase rates were ∼5% for 1.1 × 107 s (127 days), whereas the bulk modulus was hardly changed by aging. In Ti–Nb–Ta–Zr–O alloys with different oxygen concentrations, shear moduli c′ and c44 of the alloy with the lowest oxygen concentration increased most significantly. Moreover, the electrical resistivity of Ti–Nb–Ta–Zr and Ti–Nb–Ta–Zr–O alloys was increased by RT aging. Importantly, the enhancements of shear moduli and electrical resistivity were suppressed by increases in the bcc-phase stability (i.e., increase in the Nb concentration) and oxygen concentration; these factors are known to suppress ω (hexagonal) phase formation. However, transmission electron microscopy (TEM) observations revealed that only a diffuse ω structure—an ω-like lattice distortion—was formed after RT aging. On the basis of alloying element effects, TEM observations, and analysis of the changes in elastic properties by using a micromechanics model, it was deduced that the enhancements of shear moduli and electrical resistivity were possibly caused by the formation of a diffuse ω structure.

Microstructures and wear properties of surface treated Ti–36Nb–2Ta–3Zr–0.35O alloy by electron beam melting (EBM)

Ti–36Nb–2Ta–3Zr–0.35O (wt.%) (TNTZO, also called gum metal) alloy was surface treated by electron beam melting (EBM), in order to improve wear properties. The microstructures and phase constitutions of the treated surface were characterized by optical microscopy (OM), scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXD) and electron backscattered diffraction (EBSD). The results showed that the martensitic phase and dendrites were formed from the β phase alloy after the EBM treatment, and microstructures in the surface changed with the processing parameters. Compared with the untreated TNTZO alloy, the surface modified TNTZO alloys exhibited higher nano-hardness, 8.0GPa, and the wear loss was also decreased apparently. The samples treated at a scanning speed of 0.5m/s exhibited the highest wear resistance due to the fast cooling rate and the precipitation of acicular α″ phase. The relationship between the wear property and the surface microstructure of TNTZO alloy was discussed.

Effects of oxygen concentration and phase stability on nano-domain structure and thermal expansion behavior of Ti–Nb–Zr–Ta–O alloys

Abstract In this study, in order to fully elucidate the origin of nano-domain structure and abnormal thermal expansion behavior of Gum metals, the effects of oxygen concentration, β phase stability and cold rolling on the microstructure and thermal expansion properties were investigated in (Ti–xNb–2Zr–0.7Ta)–yO (at.%) (x = 21–25; y = 0.3–1.8) alloys. Normal thermal expansion behaviors with positive linear thermal expansion coefficients were observed in all the annealed alloys irrespective of oxygen and Nb concentrations. The thermal expansion behavior of as-rolled alloys was strongly affected by the concentration of oxygen and Nb. A negative thermal expansion coefficient was observed in the as-rolled alloys with lower oxygen and Nb concentrations. The thermal expansion coefficient increased with increasing oxygen and Nb concentrations. The amount of nano-domains increased with increasing oxygen concentration while decreased with increasing Nb concentration. The growth of a preferential nano-domain variant was observed in as-rolled alloys and became more prominent with decreasing oxygen and Nb concentrations. The reverse transformation from the nano-domain structure to the β phase occurred with increasing temperature. Thermal expansion behavior of as-rolled alloys resulted from a competing relationship between the contribution of lattice distortion of nano-domain structure and the contribution of lattice vibration of the β phase.

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.

Biocompatibility evaluation of novel β-type titanium alloy (Ti–35Nb–7Zr–5Ta)98Si2in vitro

Cell proliferation, osteoblast adhesion, morphology, differentiation, inflammatory response, apoptosis and biomineralization were investigated to evaluate the biocompatibility of (Ti–35Nb–7Zr–5Ta)98Si2 alloy.

Phase transformation and its effect on mechanical characteristics in warm-deformed Ti-29Nb-13Ta-4.6Zr alloy

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

S0410101 パルス通電焼結によるTi-Nb-Ta-Zr(TNTZ)合金の作製とその特性

In this research, the fabrication conditions of Ti-29Nb-13Ta-4.6Zr(TNTZ) alloy by pulse-current sintering and the properties of the alloy were investigated experimentally. The sintering was performed at various temperatures in a vacuum, and then the solution treatment was carried out in Ar gas atmosphere. As a result, the alloy sintered at 1273 K was showed almost full density. The microstructure of the as-sintered alloy became β-phase by solution treatment. The tensile strength and elongation of the solution-treated alloy were 539 MPa and 12.3 %, respectively. The Young's modulus was around 60 GPa and was similar to that of the wrought alloy.

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.

In situ nitrided titanium alloys: Microstructural evolution during solidification and wear

Surface and subsurface structural evolution during sliding wear of two in situ nitrided titanium alloys, β Ti–35Nb–7Zr–5Ta (TNZT) and α/β Ti–6Al–4V (Ti64), was studied by cross-sectional transmission electron microscopy coupled with precession electron diffraction. In situ nitriding during the laser engineered net shaping (LENS™) process resulted in the formation of hard and wear-resistant Ti2N+TiN phases and nitrogen-enriched α phase in TNZT and Ti64, respectively. Subsurface structural analyses of the worn nitrided TNZT revealed the tendency of α grains, and to greater extent β grains, to undergo severe plastic deformation, forming a heavily grain-refined nanocrystalline α and β tribolayer. Corresponding precession–orientation imaging phase maps were used to determine the orientation and percentage of α and β-Ti in the worn nitrided TNZT. The maps revealed that the nanocrystalline grains of soft/compliant β are much smaller (10–100nm) than hard/stiff α grains (>100nm). Wear reduction is due to the combination of the above phases and the increase in the alignment of {0002}-textured coarser α grains along the sliding direction in absence of texture in the highly refined β grains. Conversely, nitrided Ti64 exhibited slightly increasing wear, despite higher hardness, due to the change in sliding-induced deformation mechanism where shear bands formed and networked leading to brittle fracture and third body abrasive wear particle generation.

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.

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.

Influence of Heat Treatment on Fatigue Resistance of Sintered Ti 35Nb 7Zr 5Ta β Alloy

Mean stress on fatigue strength of Ti-35Nb-7Zr-5Ta, used in the manufacture of orthopedic prosthesis, was evaluated. Samples of Ti-35Nb-7Zr-5Ta were pressureless sintered and tested using microhardness (Vickers) and four point bending fatigue apparatus. Characterization was carried out using optical microscopy, scanning electron microscopy, EDS analysis, oxygen analysis and density. The density analysis shows almost 98% of density and microscopy reveals some precipitates of α phase and presumably ω phase at the grain and grain boundaries. The bending fatigue resistance limit reached (Se (106) 88 MPa), due to, presumably, the influence of coarse α phase precipitates at grain boundaries as well as the high oxygen content in the material after sintering (0.96 %). In this study, Kwofie model best explains the influence of mean stress on fatigue strength of this alloy.

Mechanical Performance and Biocompatibility of Biomedical Beta-Type Titanium Alloy Subjected to Micro-Shot Peening

Beta-type Ti-29Nb-13Ta-4.6Zr (TNTZ) was recently developed as a representative biomedical Ti alloy. As-solutionized TNTZ has a low Young’s modulus less than 60 GPa close to that of cortical bone along with very low cytotoxicity and good bone biocompatibility. Solution treatment and aging (STA) is a typical heat treatment for improving the mechanical properties of beta-type titanium alloys. However, STA also drastically increases the Young’s modulus. Therefore, this study investigated the effects of surface modification, micro-shot peening, on the mechanical properties of TNTZ subjected to severe thermomechanical treatment in order to maintain a relatively low Young’s modulus. The bone contact characteristics of TNTZ samples subjected to surface modification and cancellous bone were also compared. The Vickers hardness of cold-swaged TNTZ (TNTZSW) subjected to micro-shot peening was significantly increased within 20 mm from the very edge of the specimen surface. The fatigue strength of TNTZSW subjected to micro-shot peening increased especially in the high cycle fatigue life region. The fatigue limit was around 400 MPa. The bone formations on TNTZSW subjected to micro-shot peening and TNTZSW with the mirror surface as comparison material were almost identical to each other. However, the relative bone contact ratio of TNTZSW subjected to micro-shot peening was better than that of TNTZSW with the mirror surface.

Plastic Deformation and Elastic Properties of Ti-Nb-Zr-Ta(-Fe-Si) Biomedical Alloys

Beta titanium alloys are promising biomedical material for their excellent biocompatibility and low elastic modulus. Moderate strength of those materials in beta-annealed condition can be increased by precipitation hardening of alpha phase, but this causes significant increase in elastic modulus. In this study, small additions of Fe and Si are used to increase strength of commercial Ti - 35Nb - 7Zr - 5Ta (TNZT) alloy. Alloys with iron content up to 2% and silicon content up to 1% were manufactured. Elastic properties were investigated by pulse-echo method and flow curves were determined from tensile tests. Modulus of elasticity is increases from initial 60 GPa to 80 GPa due to Fe and Si content. Strength and modulus of elasticity were then related to chemical composition. Yield stress is increased from 450 MPa to 700 MPa thanks to small Fe and Si additions. Fe causes solid solution strengthening exhibited by sharp yield point. (Ti,Zr)5Si3 intermetallic particles further increase strength via precipitation hardening. An alloy containing 0.5% Si and 2% Fe showed improved properties for biomedical use.

In Vitro Cytotoxicity of a Ti-35Nb-7Zr-5Ta Alloy Doped with Different Oxygen Contents

Cp-Ti is the most common material used for dental implants, but its elastic modulus is around five times higher than that of bone. Recently, promising alloys that add Nb, Ta, Zr and Mo to Ti have been developed. The mechanical properties of these alloys are directly related to its microstructure and the presence of interstitial elements, such as oxygen, carbon, nitrogen and hydrogen. In this study, the in vitro cytotoxicity of Ti-35Nb-7Zr-5Ta (TNZT) alloys was analyzed in the as-received condition and after being doped with several small quantities of oxygen on a cultured osteogenic cell. The cell’s morphology was also examined by scanning electron microscopy (SEM). The TNZT alloy presented no cytotoxic effects on osteoblastic cells in the studied conditions.

微粒子衝突処理を施した生体用低ヤング率型チタン合金の機械的強度と骨接触性の変化

Beta-type Ti-29Nb-13Ta-4.6Zr (TNTZ), which is a recently developed biomedical titanium alloys, shows a relatively low Young’s modulus of around 60GPa when subjected to a solution treatment. However, our focus in this study was on the practical applications of TNTZ in vivo because its mechanical strength decreases with solution treatment progress. Therefore, we investigated the effect of fine particle bombarding (FPB) on the mechanical properties of TNTZ subjected to a cold-swaging treatment in order to maintain its relatively low Young’s modulus and to improve its mechanical properties. The relative bone contact ratios between the cancellous bones of Japanese white rabbits and column-shaped TNTZ samples subjected to FPB were also evaluated. The microstructure of cold-swaged TNTZ showed a single beta-phase with a marble-like structure. Moreover, its Vickers hardness did not increase remarkably with changes in its diameter, although the average diameter of the beta-grains of solutionized TNTZ ranged from 5.0 to 20 μm, depending on the increase in the holding time of the solution treatment. The Vickers hardness and Young’s modulus of TNTZ subjected to FPB increased at the edge of the specimen surface to be around 70% and 15%, respectively, more than those of cold-swaged TNTZ. Further, the fatigue strength of TNTZ subjected to FPB became significantly higher than that of cold-swaged TNTZ in the high-cycle fatigue life region. Lastly, TNTZ with a rough surface texture (Ra: 0.65μm) showed a relative bone contact ratio of more than 80% after undergoing FPB; this value was significantly higher than that of cold-swaged TNTZ with a very smooth surface texture (Ra: 0.07 μm). [doi:10.2320/matertrans.M2014349]

A review of surface modification of a novel low modulus β-type titanium alloy for biomedical applications

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

Mechanical properties enhancement in Ti–29Nb–13Ta–4.6Zr alloy via heat treatment with no detrimental effect on its biocompatibility

The present investigation deals with the microstructural evolution and mechanical properties optimization of a new titanium based TNTZ (Ti–29Nb–13Ta–4.6Zr) alloy through applying a proper heat treatment strategy. The TNTZ alloy was subjected to solution treatment and cooling procedure via different medias including liquid nitrogen, water, oil, static air and vacuum furnace. The slow cooling in vacuum furnace and static air resulted in precipitation of ω phase. The formation of this phase secures an increase in the strength and hardness value, however stands detrimental to the ductility. The α″ martensite is formed due to accelerated cooling in liquid nitrogen, water and oil. This phase remains neutral to the ductility of the alloy, while its excessive formation increases the hardness and shear strength. This study proposes the liquid nitrogen quenching as a process that optimizes the mechanical properties by rendering the highest strength while preserving the ductility.