EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Cu has been used in a wide variety of applications ranging from power generation and transmission to electronics. Stress-induced voids are amongst the most commonly reported defects in Cu. Since voids are formed by the condensation of vacancies, certain regions within the material like grain boundaries (GBs) have been considered as efficient sinks and thus favorable sites for the void initiation. Once voids are formed in the material, stress is exhibited on its surroundings leading to severe degradation effects.

Voiding growth and nucleation are considered to initiate from the formation, diffusion and accumulation. For that purpose, density functional theory (DFT) simulations were used. As the modelling of purely metallic systems using ab initio methods allows only small scale calculations, interatomic potentials (IPs) have been also tested. The current study provides an overview of the kinetic properties of vacancies under static theoretical simulations by investigating their properties, formation mechanisms, diffusion barriers and how all these properties are influenced by sink effects. The clustering process from single vacancies to the formation of nanovoids has been investigated. The pentavacancy was identified as a crucial step in the clustering process. The diffusion properties of vacancies have been investigated and divacancies were found to have the lowest diffusion barriers using both methods. The segregation of divacancies in the grain boundaries introduces strong relaxation effects and phase transitions, resulting in a 2 eV gain in energy. Such effects significantly increase local stresses which can have detrimental effects on the material’s performance. Since the adsorption of vacancies by the GBs leads to cluster dissociation, the effect of hydrogen on stabilising vacancies and on the migration properties of the grain boundaries has been also investigated using both DFT and IPs.