Effect of Niobium and Oxygen Contents on Microstructure and Mechanical Properties of α+β-Type Ti–(5–25)Nb–(0.5–1)O (mass%) Alloys for Biomedical Applications

The microstructures, mechanical properties, and biocompatibilities of α+β-type Ti–Nb–O alloys with a wide range of Nb and oxygen contents were investigated. Ingots of Ti–(5–25)Nb–(0.5–1)O (mass%) alloys were prepared by arc melting and hot forged. The forged bars were heat-treated at 873–1373 K for 3.6 ks followed by quenching. The volume fraction of equiaxed α-phase (fα) in the alloys was determined experimentally. The Ti–5Nb–yO and Ti–(15–20)Nb–yO alloys contained α′- and α′′-martensite, respectively, while the Ti–10Nb–yO alloys contained both α′- and α′′-martensite. Therefore, changing the Nb content alters the α′/α′′ ratio. The addition of oxygen increased the distribution coefficient of Nb and accelerated Nb distribution in the β-phase, which increased the boundary temperature for the formation of α′- and α′′-martensite in the Ti–5Nb–yO alloys. The Ti–5Nb–(0.5–0.75)O alloys with fα value of 0.5 had higher elongation and strength and a lower elastic modulus than Ti–6Al–4V alloy. Ion elution from the Ti–5Nb–(0.5–0.75)O alloys into 0.1 M NaCl–0.1 M lactic acid solution was comparable to that of a Ti–6Al–4V extra low interstitial (ELI) alloy. The Ti–5Nb–(0.5–0.75)O alloys did not exhibit cytotoxicity, indicating their excellent biocompatibility. Thus, we propose that Ti–5Nb–(0.5–0.75)O alloys are suitable for use as low-cost α+β-type Ti alloys for biomedical applications.