Ordering of hydrogen atoms at coherent twin boundary and its influence on dislocation emission and cracking of Ni

By enabling a swift redistribution of H with lattice-based particle swarm optimization, this work uses molecular dynamics tensile simulations to elucidate the role of hydrogen arrangement at the coherent twin boundary (CTB) in hydrogen embrittlement. In pristine CTB, we found that external strain drives H atoms to form a short-range ordered (H-SRO) structure at the boundary, arising from H-induced changes in atomic volume and stress state. The short-range ordering influences the local mechanical responses under external loading, eventually prompting the dislocation emission from the edge of the H-SRO structure. In the pre-cracked CTB, the H-SRO structure also forms between the crack and the CTB, promoting plastic activity near the crack tip while blunting the crack.