Molecular dynamics simulations of austenite-martensite interface migration in NiTi alloy

The mechanism of austenite-martensite interface migration is a key component in understanding the phase transformations in shape memory alloys. It is also intimately tied to their observed hysteresis. Molecular dynamics simulations offer a unique capability to study phase transformations in detail, however, their associated timescales prevent the observation of interface formation via nucleation and growth near the transformation temperature. To address this challenge, we present a simulation methodology in which steady-state austenite-martensite interfaces are allowed to form close to equilibrium. The resulting structures contain well-defined interfaces which can be perturbed from equilibrium to study their migration. In NiTi specifically, the austenite-martensite interfaces are semicoherent, made up of terrace planes separated by structural disconnections. The disconnections advance via kink pairs and provide an atomic-scale mechanism for interface migration. The methodology and results presented here provide a foundation toward further leveraging molecular dynamics simulations to better understand how the atomic-scale structure of austenite-martensite interfaces impacts macroscopic properties such as hysteresis in shape memory alloys.