Studying crack propagation along symmetric tilt grain boundary with H segregation in Ni by MD simulation

Hydrogen ingression in metals generally causes catastrophic failure. The H-induced fracture surface mostly exhibits intergranular feature, suggesting that grain boundary (GB) is the dominant crack propagation path. In this paper, the grand canonical Monte Carlo method was first performed to obtain equilibrated H distribution around various symmetric tilt grain boundaries (STGBs) in nickel. Then, atomistic simulations were conducted to study the influence of H segregation on the Mode I crack propagation behavior. In the absence of hydrogen, significant crack tip blunting and transgranular fracture are observed, implying a tendency toward ductile transgranular fracture. However, in the case of H segregation, it is found that dislocation emission from the crack tip is enhanced but the crack tip still remains highly sharp. Moreover, crack propagation is dominated by alternate GB dislocation emission and GB cleavage, implying a tendency of ductile–brittle alternating intergranular fracture behavior. The H-inhibited GB migration and H-enhanced GB dislocation emission are believed to be the key mechanisms governing the H-assisted crack propagation along the GB.