Relationship between grain boundary segregation and grain boundary diffusion in Cu-Ag alloys

TL;DR

This study uses atomistic simulations to explore how grain boundary segregation affects diffusion in Cu-Ag alloys, revealing complex dependencies influenced by site interactions and disordering effects.

Contribution

It introduces a simulation methodology combining Monte Carlo and molecular dynamics to analyze the impact of segregation on grain boundary diffusion in alloys.

Findings

Diffusivities depend non-trivially on composition.

Site blocking and competition influence diffusion.

Premelting effects induce grain boundary disordering.

Abstract

While it is known that alloy components can segregate to grain boundaries (GBs), and that the atomic mobility in GBs greatly exceeds the atomic mobility in the lattice, little is known about the effect of GB segregation on GB diffusion. Atomistic computer simulations offer a means of gaining insights into the segregation-diffusion relationship by computing the GB diffusion coefficients of the alloy components as a function of their segregated amounts. In such simulations, thermodynamically equilibrium GB segregation is prepared by a semi-grand canonical Monte Carlo method, followed by calculation of the diffusion coefficients of all alloy components by molecular dynamics. As a demonstration, the proposed methodology is applied to a GB is the Cu-Ag system. The GB diffusivities obtained exhibit non-trivial composition dependencies that can be explained by site blocking, site competition, and the onset of GB disordering due to the premelting effect.