Grain boundary complexions and the strength of nanocrystalline metals: Dislocation emission and propagation

TL;DR

This study uses atomistic simulations to investigate how grain boundary complexions influence dislocation behavior, revealing their dual role in reducing emission stress and increasing propagation resistance, which affects nanocrystalline metal strength.

Contribution

It provides new insights into how ordered and disordered complexions affect dislocation mechanisms, explaining their impact on nanocrystalline metal strength and ductility.

Findings

Ordered and disordered complexions reduce dislocation emission stress.

Complexions increase flow stress for dislocation propagation.

Simulation results align with experimental data on Cu-Zr alloys.

Abstract

Grain boundary complexions have been observed to affect the mechanical behavior of nanocrystalline metals, improving both strength and ductility. While an explanation for the improved ductility exists, the observed effect on strength remains unexplained. In this work, we use atomistic simulations to explore the influence of ordered and disordered complexions on two deformation mechanisms which are essential for nanocrystalline plasticity, namely dislocation emission and propagation. Both ordered and disordered grain boundary complexions in Cu-Zr are characterized by excess free volume and promote dislocation emission by reducing the critical emission stress. Alternatively, these complexions are characterized by strong dislocation pinning regions that increase the flow stress required for dislocation propagation. Such pinning regions are caused by ledges and solute atoms at the grain-complexion interfaces and may be dependent on the complexion state as well as the atomic size mismatch between the matrix and solute elements. The trends observed in our simulations of dislocation propagation align with the available experimental data, suggesting that dislocation propagation is the rate-limiting mechanism behind plasticity in nanocrystalline Cu-Zr alloys.