# Discovery of $\omega$-free high-temperature Ti-Ta-X shape memory alloys from first principles calculations

## TL;DR

This paper uses first principles calculations to discover new Ti-Ta-X shape memory alloys that avoid $ ext{omega}$ phase formation, maintaining high transformation temperatures and functional stability, validated by experiments.

## Contribution

It introduces a computational approach to identify ternary Ti-Ta-X alloys that stabilize shape memory effects without low-temperature degradation, proposing four new promising alloys.

## Key findings

- Ti-Ta-Sc shows no $ ext{omega}$ phase after cycling
- Four new alloys (Ti-Ta-Sb, Ti-Ta-Bi, Ti-Ta-In, Ti-Ta-Sc) predicted to have high-temperature stability
- Validated Ti-Ta-Sc experimentally as a stable shape memory alloy

## Abstract

The rapid degradation of the functional properties of many Ti-based alloys is due to the precipitation of the $\omega$ phase. In the conventional high-temperature shape memory alloy Ti-Ta the formation of this phase compromises completely the shape memory effect and high (>100{\deg}C) transformation temperatures cannot be mantained during cycling. A solution to this problem is the addition of other elements to form Ti-Ta-X alloys, which often modifies the transformation temperatures; due to the largely unexplored space of possible compositions, very few elements are known to stabilize the shape memory effect without decreasing the transformation temperatures below 100{\deg}C. In this study we use transparent descriptors derived from first principles calculations to search for new ternary Ti-Ta-X alloys that combine stability and high temperatures. We suggest four new alloys with these properties, namely Ti-Ta-Sb, Ti-Ta-Bi, Ti-Ta-In, and Ti-Ta-Sc. Our predictions for the most promising of these alloys, Ti-Ta-Sc, are subsequently fully validated by experimental investigations, the new alloy Ti-Ta-Sc showing no traces of $\omega$ phase after cycling. Our computational strategy is immediately transferable to other materials and may contribute to suppress $\omega$ phase formation in a large class of alloys.