Atomistic simulations of effect of hydrogen on kink-pair energetics of screw dislocations in bcc iron

Atomistic simulations are conducted on the hydrogen-affected kinking process of a screw dislocation in iron by the nudged elastic band method. We find that when a kink pair nucleates at hydrogen, the activation energy is decreased by the transition of hydrogen to a stronger binding site, while it is increased by the transition to a weaker binding site. When a kink pair meets hydrogen during expanding, the sideward motion of the kink pair is impeded by hydrogen. The simulation provides an insight into the complex atomistic process of hydrogen-induced softening and hardening.