Amorphization of a crystalline solid by plastic deformation

TL;DR

This paper explores how plastic deformation causes a crystalline solid to undergo a transition to an amorphous state, revealing a phase change with complex dynamics and structural heterogeneity.

Contribution

It introduces a novel analogy between amorphization in solids and phase transitions in superconductors, supported by analytical and simulation evidence.

Findings

Identification of a stress Meissner effect during amorphization

Observation of slow ageing dynamics in the transition

Formation of band-like amorphous regions under strain

Abstract

We demonstrate that plastic deformation in solids is associated with a dynamic transition that is reminiscent to the transition from a superconducting to a mixed phase in Type II superconductors. We report analytic calculations, extensive molecular dynamics and sequential umbrella sampling Monte Carlo simulations of a two dimensional triangular crystalline solid undergoing plastic deformation under strain. The solid consists of particles connected by harmonic springs. Non-affine displacement fluctuations of the solid are enhanced using an external field, causing a rich deformation behaviour. The external field leads to a mixed phase, where defect and stress-free crystallites are surrounded by a network of amorphous regions with large local internal stress --- a "stress Meissner" effect. The transition shows slow ageing dynamics caused by the presence of many competing, non-crystalline free-energy minima. Under uniform uniaxial strain, this amorphization transition gives rise to irreversible plastic deformation with the amorphous regions appearing as band-like structures. Our results may be checked by careful experiments on colloidal crystals using holographic optical tweezers.