Uncovering the influence of common nonmetal impurities on the stability and strength of a $\Sigma$5 (310) grain boundary in Cu

TL;DR

This study uses first-principles simulations to analyze how common nonmetal impurities affect the stability and mechanical strength of a Cu $\ ext{\Sigma}$5 (310) grain boundary, revealing impurity-specific effects on energetics and strength.

Contribution

It provides a comprehensive first-principles analysis of how various nonmetal impurities influence grain boundary stability and strength in copper, highlighting impurity-specific mechanisms.

Findings

B impurities enhance grain boundary strength via charge density increase.

O impurities weaken the boundary by reducing charge density.

Impurity effects correlate with covalent radii and electronegativity.

Abstract

Impurities are often driven to segregate to grain boundaries, which can significantly alter a material's thermal stability and mechanical behavior. To provide a comprehensive picture of this issue, the influence of a wide variety of common nonmetal impurities (H, B, C, N, O, Si, P and S) incorporated during service or materials processing are studied using first-principles simulations, with a focus on identifying changes to the energetics and mechanical strength of a Cu $\Sigma$5 (310) grain boundary. Changes to the grain boundary energy are found to be closely correlated with the covalent radii of the impurities and the volumetric deformations of polyhedra at the interface. The strengthening energies of each impurity are evaluated as a function of covalent radius and electronegativity, followed by first-principles-based tensile tests on selected impurities. The strengthening of a B-doped grain boundary comes from an enhancement of the charge density among the adjacent Cu atoms, which improves the connection between the two grains. Alternatively, the detrimental effect of O results from the reduction of charge density between the Cu atoms. This work deepens the understanding of the possible beneficial and harmful effects of impurities on grain boundaries, providing a guide for materials processing studies.