Space-time approach to microstructure selection in solid-solid transitions

TL;DR

This paper introduces a space-time dynamical framework to understand microstructure selection during solid-solid transitions, linking particle activity, microstructure, and energy landscape in a unified approach.

Contribution

It develops a novel trajectory-based thermodynamic approach to analyze the nucleation process and microstructure evolution in solid-solid phase transitions.

Findings

Active particle trajectories determine microstructure outcomes.

String-like excitations facilitate twinned martensite formation.

Transition characterized by dynamical action in trajectory space.

Abstract

Nucleation of a solid in solid is initiated by the appearance of distinct dynamical heterogeneities, consisting of `active' particles whose trajectories show an abrupt transition from ballistic to diffusive, coincident with the discontinuous transition in microstructure from a {\it twinned martensite} to {\it ferrite}. The active particles exhibit intermittent jamming and flow. The nature of active particle trajectories decides the fate of the transforming solid -- on suppressing single particle diffusion, the transformation proceeds via rare string-like correlated excitations, giving rise to twinned martensitic nuclei. These string-like excitations flow along ridges in the potential energy topography set up by inactive particles. We characterize this transition using a thermodynamics in the space of trajectories in terms of a dynamical action for the active particles confined by the inactive particles. Our study brings together the physics of glass, jamming, plasticity and solid nucleation.