Grain-Boundary Topological Phase Transitions

TL;DR

This paper reveals that grain boundaries in polycrystalline materials undergo a Kosterlitz-Thouless topological phase transition at finite temperature, significantly affecting their migration, sliding, and roughening behaviors.

Contribution

It demonstrates the existence of a KT-type phase transition in grain boundaries and analyzes its impact on microstructural phenomena using theoretical and simulation methods.

Findings

Identification of a KT phase transition in GBs

Abrupt change in GB migration and sliding behavior

Implications for grain growth and superplasticity

Abstract

The formation and migration of disconnections (line defects constrained to the grain boundary (GB) plane with both dislocation and step character) control many of the kinetic and dynamical properties of GBs and the polycrystalline materials of which they are central constituents. We demonstrate that GBs undergo a finite-temperature topological phase transition of the Kosterlitz-Thouless (KT) type. This phase transition corresponds to the screening of long-range interactions between (and unbinding of) disconnections. This phase transition leads to abrupt change in the behavior of GB migration, GB sliding, and roughening. We analyze this KT transition through mean-field theory, renormalization group theory, and kinetic Monte Carlo simulations, and examine how this transition affects microstructure-scale phenomena such as grain growth stagnation, abnormal grain growth and superplasticity.