First-principles characterization of reversible martensitic transformations
A. Ferrari, D. G. Sangiovanni, J. Rogal, R. Drautz.
Physical Review B, 99, 094107, (2019)
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.
Keyword(s): ferroelasticity; first order phase transitions; martensitic phase transition; shape memory effect; solid-solid transformations; structural order parameter; actuating materials; disordered alloys; shape-memory materials; transition-metal alloys; density fu