Discovery ofω-free high-temperature Ti-Ta-Xshape memory alloys from first-principles calculations

Abstract

The rapid degradation of the functional properties of many Ti-based alloys is due to the precipitation of the ω 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 • 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 • 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 ω phase after cycling. Our computational strategy is immediately transferable to other materials and may contribute to suppress ω phase formation in a large class of alloys.

Discovery of New Ti-Based Alloys Aimed at Avoiding/Minimizing Formation of α” and ω-Phase Using CALPHAD and Artificial Intelligence

“…The author listed as his future work that he will work on the development of models based on first-principle calculations for predicting the α" and ω phase [2] and indicated plans to study the effect of Sn addition in larger amounts in order to study its effect on the stability of the β phase [2]. Another work [16] based on shape memory alloys can also be compared with the present work. In their work [16], the authors performed first-principle calculations for developing ω-phase free Ti-Ta-X systems.…”

“…Another work [16] based on shape memory alloys can also be compared with the present work. In their work [16], the authors performed first-principle calculations for developing ω-phase free Ti-Ta-X systems. Both of these references are thorough works and have included results from first-principle calculations [2,16].…”

“…In their work [16], the authors performed first-principle calculations for developing ω-phase free Ti-Ta-X systems. Both of these references are thorough works and have included results from first-principle calculations [2,16]. Density functional theory (DFT) or first-principle calculations are computationally expensive, and a user needs to have access to supercomputers for performing DFT-based study.…”

“…In titanium alloys, experiments show that ω-phase can be stabilized and has been observed at cryogenic temperatures [15]. From first-principle calculations, researchers have demonstrated the scope of development of ω-phase free Ti-Ta-X shape memory alloys [16].…”

Laboratory-Scale Processing and Performance Assessment of Ti–Ta High-Temperature Shape Memory Spring Actuators

“…The influence of oxidation on the martensitic transformation in the surface region was investigated [27]. Atomistic calculations on the stability of phases, especially the x-phase, were performed [28][29][30]. Special emphasis was placed on the role of the x-phase during functional fatigue of Ti-Ta alloys [31][32][33][34] and it has been shown that by controlling the temperature during heating and cooling one can counteract fast functional degradation by x-phase precipitation.…”