An interplay between a hydrogen atmosphere and dislocation characteristics in BCC Fe from time-averaged molecular dynamics

C Nowak and XW Zhou, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 25, 8369-8375 (2023).

DOI: 10.1039/d2cp05024b

The interplay between hydrogen and dislocations (e.g., core and elastic energies, and dislocation-dislocation interactions) has implications on hydrogen embrittlement but is poorly understood. Continuum models of hydrogen enhanced local plasticity have not considered the effect of hydrogen on dislocation core energies. Energy minimization atomistic simulations can only resolve dislocation core energies in hydrogen-free systems because hydrogen motion is omitted so hydrogen atmosphere formation can't occur. Additionally, previous studies focused more on face-centered-cubic than body-centered-cubic metals. Discrete dislocation dynamics studies of hydrogen-dislocation interactions assume isotropic elasticity, but the validity of this assumption isn't understood. We perform time-averaged molecular dynamics simulations to study the effect of hydrogen on dislocation energies in body-centered- cubic iron for several dislocation character angles. We see atmosphere formation and highly converged dislocation energies. We find that hydrogen reduces dislocation core energies but can increase or decrease elastic energies of isolated dislocations and dislocation-dislocation interaction energies depending on character angle. We also find that isotropic elasticity can be well fitted to dislocation energies obtained from simulations if the isotropic elastic constants are not constrained to their anisotropic counterparts. These results are relevant to ongoing efforts in understanding hydrogen embrittlement and provide a foundation for future work in this field.

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