A geometrically invariant description of extreme pressure solid-solid phase transitions

Modern-day dynamic compression experimental platforms are enabling exploration of a new regime of loading rates for extreme-scale materials science experiments. Under these extraordinary conditions, the timescales of the experiment are comparable to the timescales of phase transitions that may occur as the materials are compressed. An important consequence of this fact is that the kinetic processes governing the phase transition have macroscopic consequences for experimental observables. Thus, we need physically motivated macroscopic kinetics models to capture this phenomenon to aid interpretation of experiments and ultimately gain insight into material behavior.

Many models successfully applied thus far rely on an assumption of isotropic daughter phase growth. Recent experiments suggest that for some materials, particularly in the case of solid—solid transitions, this assumption needs to be relaxed allowing for anisotropic growth. Moreover, the precise kinetics of phase-boundary motion may be tied to a lattice defect process known as a disconnection. Herein, we propose a simple, yet representative, model to explore this idea based on a hierarchy of symmetry breaking defects. Phase boundary interfaces are viewed as 2D defects breaking translational symmetry of the solid. Their motion is mediated by 1D line defects (called disconnections) that move within the 2D interfacial manifold. The motion of 1D line defects is mediated by 0D kink events which move within the 1D line defect. We track populations of these defects and study their interactions.

We describe the formulation and implementation of the model and use it to study dynamic compression experiments.