The influence of ternary and quaternary alloy additions on the superelastic behaviour of metastable Ti-Nb based alloys

Abstract

The superelastic behaviour of Ti-Nb alloys gives rise to properties that are attractive for specific applications in the biomedical and aerospace sectors. However, to date, industrial utilisation of these alloys has been limited due the inability to tailor the transformation conditions or achieve stable cyclic behaviour. Alloying is the primary method for modifying transformation conditions but significant variations exist between the results of different studies within the literature. Here, to try and provide increased clarity, the transformation behaviour of Ti-24Nb-(0-8)Ta and Zr (at.%) have been investigated using in situ synchrotron diffraction to directly assess the transformation behaviour of the alloys in response to both temperature and tensile loads. In contrast to previous reports, no evidence of the αʺ phase was found in any of the alloys when cooled from 350 to -196˚C. In addition, the β to αʺ transformation was observed to be reversible when loaded at both 30˚C and ‑196˚C. These observations suggest that β stability may be far greater than previously thought and requires a review of the current mechanistic understanding.