Molecular dynamics simulation on stability and diffusivity of hydrogen around a <111> symmetric tilt grain boundary in bcc-Fe

The effects of the grain boundary (GB) on the stability and diffusivity of hydrogen in bcc-Fe are investigated via a molecular dynamics (MD) simulation focusing on the symmetric tilt Σ19b, <111> 46.8°, {5 -3 -2} GB. MD simulation results show that H atoms are trapped around the GB and the binding energy per H atom is weakly dependent on the hydrogen concentration at the GB. In hydrogen diffusivity, the Σ19b GB induces an anisotropy reflecting its structure, and the diffusion on the GB becomes one-dimensional. For each diffusion direction, the effective hydrogen diffusivity shows a characteristic dependence on the hydrogen concentration in the system, which can be explained by two phenomena: trapping effect by the GB and blocking effect on the GB.