Influence Of Oxygen Content On Microstructure And Mechanical Properties Of Ti-Nb-Ta-Zr Alloy

Beta-titanium alloys are highly attractive metallic material for biomedical applications due to their high specific strength, high corrosion resistance and excellent biocompatibility, including low elastic modulus. Recently, Satio et al. developed a new multi-functionalβ-titanium alloy. It is based onβ-type Ti-Nb-Ta-Zr alloy and manifested high strength, low Young's modulus and excellent cold workability when oxygen content higher than 0.7% (at.%). A dislocation-free plastic deformation mechanism is supposed to explain the origin of the multifunctional properties, but it has been challenged by resent studies, in which conventional deformation mechanisms were found in Gum Metal. As Gum Metal maintains properties different to Ti-Ni-Ta-Zr alloy, the influence of oxygen is taken into consideration as one of the possible reasons for the"superproperties".In this paper, Ti-22.5Nb-0.7Ta-2Zr (at.%) was prepared, and oxygen was added in the form of TiO2, ranging from 0.5-2.5%. The influence of oxygen content on microstructures and mechanical properties of Ti-Nb-Ta-Zr alloy was investigated. The results showed that the grains were refined with the increase of oxygen content when it is lower than 2.0%. The ultimate tensile strength (UTS) increased and elongation decreased. But at the content of 1.0%, the elongation was close to that of the original alloy (about 16%). The elastic modulus remained comparatively low (<65GPa) when oxygen content is lower than 1.5%, and then increased dramatically. There existed a best oxygen content-1.0%, at which refined grains, UTS of 750MPa, elongation of 16% and elastic modulus of 65GPa were obtained. The Ti-22.5Nb-0.7Ta-2Zr-1.0O alloy maintained superelasticity and ductile fracture characteristics ofβ-Ti alloy.To further improve the properties, Ti-22.5Nb-0.7Ta-2Zr-1O alloy was aging-treated under different temperatures. The highest tensile strength (821.44MPa) and elongation (around 6.3%), as well as the lowest elastic modulus (55.29GPa) and micro-hardness value (235HV) were obtained at the temperature of 450℃, as well as ductile fracture characteristics, indicating it was the appropriate temperature for heat treatment.The biocompatibility of this alloy is investigated compared with commercially pure titanium and Ti-6Al-4V. The results showed that Ti-35Nb-2Ta-3Zr had no cytytoxicity and cells could grow on it. After proper surface modification, the surface morphology can be improved significantly, making the materials promising biomedical material for clinical implants.