Abstract: In this work, molecular dynamics modeling was conducted to study hydrogen (H)-induced plastic deformation and cracking of polycrystal α-Fe. Under cyclic loading, the number of vacancies and the stress intensity increase with H atom concentration and the number of loading cycles. However, the effect of cyclic loading on cracking is not as significant as the increment of H concentration. As the H concentration increases, the dislocation generation and emission are enhanced in the {110}<111> slip system, but are inhibited in other slip systems. There is a critical H atom concentration, below which the plastic deformation of α-Fe is facilitated by H atoms. When the critical H concentration is exceeded, the dislocation emission is inhibited by H atoms at grain boundaries, where the H atoms can pin dislocations, causing piling-up of the dislocations to generate a stress concentration.

Key words: Hydrogen atoms, Dislocations, Grain boundary, Cyclic loading, Molecular dynamic modeling