Effect of Nb on microstructural characteristics of Ti-Nb-Ta-Zr alloy for biomedical applications

Abstract

The effects of several commonly used heat treatment schemes on the microstructures of two Ti-Nb-Ta-Zr alloys aimed at biomedical applications were studied in this work using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specimens were water quenched from 790°C and then aged at temperatures between 300°C and 600°C. The experimental results showed that α and ω phase precipitated from the metastable β matrix in Ti-29Nb-13Ta-4.6Zr alloy during isothermal ageing. But for Ti-39Nb-13Ta-4.6Zr, the precipitation reaction was more sluggish than that in Ti-29Nb-13Ta-4.6Zr because of high amount of β stabilizing elements in the former alloy. As a result the α phase was unable to precipitate during short time ageing treatment. After longer time (12 days) ageing treatment at 500°C or 400°C, recognizable α precipitates were observed in the aged samples. It is concluded that Ti-29Nb-13Ta-4.6Zr can be heat treated to obtain different microstructures and is better than Ti-39Nb-13Ta-4.6Zr in terms of age hardenability.