First principles characterization of reversible martensitic transformations

TL;DR

This paper introduces an ab initio method to analyze reversible martensitic transformations in alloys, enabling the assessment of phase stability, energy barriers, and conditions for reversibility, exemplified on Ti-Ta shape memory alloy.

Contribution

It develops a fully ab initio approach using Landau expansion parametrized by molecular dynamics data to characterize and evaluate the reversibility of martensitic transformations.

Findings

Small metastability regions in Ti-Ta suggest high reversibility.

Quantified free energy barriers and latent heat for phase transitions.

Method applicable to other shape memory alloys.

Abstract

Reversible martensitic transformations (MTs) are the origin of many fascinating phenomena, including the famous shape memory effect. In this work, we present a fully ab initio procedure to characterize MTs in alloys and to assess their reversibility. Specifically, we employ ab initio molecular dynamics data to parametrize a Landau expansion for the free energy of the MT. This analytical expansion makes it possible to determine the stability of the high- and low-temperature phases, to obtain the Ehrenfest order of the MT, and to quantify its free energy barrier and latent heat. We apply our model to the high-temperature shape memory alloy Ti-Ta, for which we observe remarkably small values for the metastability region (the interval of temperatures in which the high-and low-temperature phases are metastable) and for the barrier: these small values are necessary conditions for the reversibility of MTs and distinguish shape memory alloys from other materials.