Atomistic Simulations of H-Cu Vacancy Cosegregation and H Diffusion in Cu Grain Boundary

TL;DR

This study uses atomistic simulations combining DFT and BOP to elucidate hydrogen behavior at copper grain boundaries, revealing pathways for adsorption, diffusion, and vacancy interactions that contribute to hydrogen embrittlement.

Contribution

It introduces a detailed atomistic mechanism for hydrogen segregation and diffusion at Cu grain boundaries, highlighting the role of vacancies and low migration barriers.

Findings

Hydrogen preferentially adsorbs at undercoordinated regions like GBs and vacancies.

Hydrogen-vacancy complexes in Cu are energetically favorable with up to -0.8 eV.

Hydrogen diffusion barriers in GBs are as low as 0.2 eV, facilitating rapid migration.

Abstract

Hydrogen embrittlement remains a critical challenge in structural and electronic applications of copper (Cu) but its mechanism is still not fully understood. In this study, we combine density functional theory (DFT) and bond-order potential (BOP) simulations to determine the atomistic pathways for hydrogen adsorption/incorporation and fast interfacial diffusion at Cu grain boundaries (GBs), including its interaction with vacancies. Undercoordinated regions, such as surfaces and GBs, serve as preferential adsorption/incorporation sites for atomic hydrogen, especially in the presence of Cu vacancies. The presence of hydrogen in GB further enhances the segregation of Cu vacancies, leading to the formation of stable H-$V_\mathrm{Cu}$ complexes with cosegregation energy gains of up to $-0.8$ eV. Furthermore, our simulations reveal that the migration barriers for hydrogen within the GB networks are as low as $0.2$ eV and significantly lower than in bulk Cu ($0.42$ eV). The results presented in this paper suggest an atomistic mechanism that links $H_2$ exposure to H accumulation in GBs, providing information on the early stages of hydrogen-induced degradation.