Grain Boundary Motion Exhibits the Dynamics of Glass-Forming Liquids

TL;DR

This study uses molecular dynamics simulations to reveal that grain boundary dynamics at high temperatures resemble glass-forming liquids, exhibiting collective motion, caging, and non-Arrhenius mobility, offering new insights into polycrystalline material behavior.

Contribution

It demonstrates that grain boundary motion shares key features with glass-forming liquids, providing a novel conceptual model for understanding polycrystalline materials at elevated temperatures.

Findings

GB exhibit string-like collective motion

GB mobility shows non-Arrhenius temperature dependence

Structural frustration causes glass-like behavior in GB

Abstract

Polycrystalline materials can be viewed as composites of crystalline particles or grains separated from one another by thin amorphous grain boundary (GB) regions. While GB have been exhaustively investigated at low temperatures, where these regions resolve into complex ordered structures accessible to measurement, much less is known about them at higher temperatures where the GB can exhibit significant mobility, structural disorder, and where experimental characterization methods are limited. The time and spatial scales accessible to molecular dynamics (MD) simulation make this method appropriate for investigating both the dynamical and structural properties of grain boundaries at elevated temperatures. In the present study, we use MD simulations to determine how the GB dynamics changes with temperature and applied stress. It has long been hypothesized that GB have features in common with glass-forming liquids based on the processing characteristics of polycrystalline materials. We find remarkable support for this suggestion, as evidenced by string-like collective motion, transient caging of atom motion, and non-Arrhenius (Vogel-Fulcher) temperature dependence of GB mobility. Evidently, the frustration caused by the inability of atoms in GB region to simultaneously order with respect to competing grains is responsible for this striking similarity. The paradigm that grains in a polycrystalline material are encapsulated by a frustrated fluid provides a powerful conceptual model of polycrystalline materials, pointing the way to improved control over their material properties.