MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Special Issue on Recent Research and Development in the Processing, Microstructure, and Properties of Titanium and Its Alloys
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
Kyosuke UedaMasahito OmiyaKotaro KatoHiroyasu KanetakaTakayuki Narushima
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2023 Volume 64 Issue 1 Pages 138-146

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Abstract

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.

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