Solute segregation to near-coincidence site lattice grain boundaries in α-iron

Coincidence site lattice grain-boundaries (CSL-GBs) are commonly observed in steel alloys and play a major role in controlling their mechanical properties. In practice, CSL-GBs do experience deviations from their ideal configurations, where the deviation from the ideal symmetry plane can be modeled as sub-boundary network of misfit dislocations. In this study, segregation energy of hydrogen and carbon atoms to n-ary sumation 3 (111), n-ary sumation 3 (112), and n-ary sumation 5 (310) CSL-GBs and their deviated configurations within Brandon's criterion range in alpha-iron is studied using molecular statics simulations. Thereafter, through utilizing Rice-Wang model the change of the cohesive GB energy is computed and correlated to misfit dislocations structures. The results show significant correlation between the crystallographic aspects of the GBs and the hydrogen/carbon embrittlement/strengthening effect. While the ideal CSL-GBs consistently show the highest resistance to hydrogen enhanced decohesion effect, the deviations from the ideal configurations accompanied by misfit dislocation core structures along the boundaries show high solute carbon strengthening.