Simulation of phase transitions during shock waves in zirconium.*

Under ambient conditions, zirconium adopts the hcp structure, but under high pressure or temperature it can transform to bcc or a more complex omega phase. These transformations are martensitic, so can be expected to occur on the timescale of a shock wave. Simulation of this process has been hindered by the lack of a reliable interatomic potential which correctly describes the phase stability. All three phases are metallic, so a short-ranged model such as the embedded atom method describes the bonding, but the phase stability has proved more challenging to predict.

We present an interatomic force model using machine-learning parameterization of an embedded-atom type model. It correctly reproduces the phase diagram and has sensible behaviour under plastic deformation: in particular basal slip is impeded by a large stacking fault energy. The potential enables us to simulate the martensitic phase transition pathway, and resulting microstructure, from quasistatic transformations between the three phases induced by temperature and pressure. The dynamic shock wave simulations reveal the complex interplay between elastic deformation, plastic deformation via dislocations or twinning, and phase transformations.