Effect of Oxygen on the Microstructure and Mechanical Properties of α+β-type Ti-5Nb Alloys for Biomedical Applications

Oxygen is the primary impurity in titanium (Ti); thus, utilizing oxygen as an alloying element may effectively lower the production costs of Ti alloys. In this study, the microstructure and mechanical properties of the Ti-Nb-O alloy system were studied to develop low-cost α+β-type Ti alloy. Ti-5Nb-(0.2, 0.5, 0.7)O (mass%) alloys were prepared by arc melting, and the ingots were hot-forged and heat-treated at 973–1323 K for 3.6 ks in an argon (Ar) atmosphere. The alloys consisted of α and α' phases under the heat-treatment condition of the α-phase fraction (f_α) of 0.3, independent of the oxygen content. The elastic modulus of the Ti-5Nb-xO alloys was approximately 95 GPa, independent of the oxygen content, which is lower than that of the Ti-6Al-4V (Gr. 5) alloy. The indentation hardness of the α phase is higher than that of the α' phase because of the distribution of oxygen in the α phase. The critical cold rolling reduction (CCR) of the Ti5Nb-xO alloys decreased with increasing the oxygen content. The CCR of Ti-5Nb-(0.2 and 0.5)O alloys was higher than that of Ti-6Al4V alloy. Thus, in conclusion, the Ti-5Nb-0.5O alloy is a promising low-cost α+β-type Ti alloy for biomedical applications. It has a low elastic modulus and good tensile properties, with toughness and cold workability comparable to those of Ti-6Al-4V alloy.