Simulation of mechanical effects of hydrogen in bicrystalline Cu using DFT and bond order potentials

Hydrogen embrittlement is a prime cause of several degradation effects in metals. Since grain boundaries (GBs) act efficiently as sinks for hydrogen atoms, H is thought to segregate in these regions, affecting the local formation of dislocations. However, it remains unclear at which concentrations H begins to play any role in the mechanical properties of Cu. In the current study, we use density functional theory (DFT) to assess the accuracy of a bond order potential (BOP) in simulating the segregation of H in Cu S5 GB. BOP accurately predicts the most favorable segregation sites of H in Cu GB, along with the induced lattice relaxation effects. H is found to weaken the crystal by reducing the GB separation energy. Classical molecular dynamics (MD) simulations using BOP are performed to evaluate the concentration of H in bicrystalline Cu required to substantially impact the crystal's mechanical strength. For concentrations higher than 10 mass ppm, H significantly reduces the yield strength of bicrystalline Cu samples during uniaxial tensile strain application. This effect was attributed to the fact that H interstitials within the GB promoted the formation of partial dislocations.