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.

Automated summary

The mechanism of austenite-martensite interface migration plays a key role in understanding phase transformations and hysteresis in shape memory alloys. Molecular dynamics simulations have the potential to study these transformations in detail, but the timescales involved prevent the observation of interface formation near the transformation temperature. To overcome this challenge, a simulation methodology is presented where steady-state austenite-martensite interfaces are allowed to form close to equilibrium. These interfaces contain well-defined structures that can be perturbed to study their migration. In NiTi alloys, the interfaces are semicoherent and composed of terrace planes separated by structural disconnections. Interface migration occurs through the movement of disconnections, providing an atomic-scale mechanism. The methodology and results presented here lay a foundation for utilizing molecular dynamics simulations to further understand how the atomic-scale structure of austenite-martensite interfaces influences macroscopic properties like hysteresis in shape memory alloys.