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

摘要

Grain boundary complexions have been observed to affect the mechanicalbehavior of nanocrystalline metals, improving both strength and ductility.While an explanation for the improved ductility exists, the observed effect onstrength remains unexplained. In this work, we use atomistic simulations toexplore the influence of ordered and disordered complexions on two deformationmechanisms which are essential for nanocrystalline plasticity, namelydislocation emission and propagation. Both ordered and disordered grainboundary complexions in Cu-Zr are characterized by excess free volume andpromote dislocation emission by reducing the critical emission stress.Alternatively, these complexions are characterized by strong dislocationpinning regions that increase the flow stress required for dislocationpropagation. Such pinning regions are caused by ledges and solute atoms at thegrain-complexion interfaces and may be dependent on the complexion state aswell as the atomic size mismatch between the matrix and solute elements. Thetrends observed in our simulations of dislocation propagation align with theavailable experimental data, suggesting that dislocation propagation is therate-limiting mechanism behind plasticity in nanocrystalline Cu-Zr alloys.