Molecular dynamics simulation of tensile strain-altered hydrogen behaviour and its effects on local plasticity

Using molecular dynamics simulation, local plasticity of bcc Fe (0 0 1) is studied at different density of Fe–H cluster. H-induced softening and hardening of Fe substrate are observed along with the tensile elongation at low and high density, respectively. The two contradictory phenomena are ascribed to H behaviours-related plastic deformation. At high H partial pressure, initial H aggregation would lead to the formation of many H-enriched clusters similar to hydride. Tensile strain-induced dislocations (TSID) prefer to be generated and grow at the weakening interface of clusters and iron substrate. At low H partial pressure, TSIDs are uniformly distributed in the whole substrate. Owing to the affinity between H and dislocations, the diffusion of H appears to be distinct under different spatial distribution of TSIDs. H aggregation and dispersion can be enhanced and produce nonuniform and uniform plastic deformation during the continuous tensile process at high and low Fe–H cluster density, respectively. The former can stimulate local failures and accelerate the degradation of mechanical property. The results are helpful for better understanding of Fe–H cluster-related hardening and softening considering external strain-altered H behaviours except for the mechanism of H-dislocation interaction.