Study on interactions of an edge dislocation with vacancy-H complex by atomistic modelling

Due to trapping of hydrogen atoms to vacancy, vacancy-Hydrogen complex exists dispersively in materials working in hydrogen environment and influences significantly the dislocation mobility, rendering so-called hydrogen embrittlement. The interactions between a moving edge dislocation and vacancy-Hydrogen complexes or clusters in α-Fe are studied carefully in this paper by atomistic modelling. Our results show that vacancy and vacancy cluster are stable and easier to grow due to their lower formation energy and binding energy with the help of trapped H atoms. When approaching a vacancy-H complex, the edge dislocation is first attracted and in most cases pinned by the complex. The pinning strength of a vacancy-H complex or cluster on the edge dislocation increases with the increasing number of hydrogen atoms trapped in vacancy or vacancy cluster. The critical shear stress for an edge dislocation de-pinning from the vacancy-H complex can be described by a de-pinning equilibrium equation. The inherent pinning mechanism mainly originates from the migration of H atoms in vacancy or vacancy cluster when it is cut by the moving edge dislocation. These results will be helpful for further understanding of the hydrogen induced deformation and failure.