Twinning initiation from edge dislocations pinned by hydrogen atoms in bcc iron: A molecular dynamics study

Understanding how hydrogen affects the slip and twinning behaviors in metals is paramount for ensuring safe material use in a hydrogen environment and contributing to the development of hydrogen-resistant structural metals. Despite recent reports highlighting an increase in hydrogen-induced twinning in metals under applied deformations, the root case remains elusive. Here, we use molecular dynamics simulations to investigate how high hydrogen concentrations and shear direction affect edge-dislocation behavior in bcc iron. Our findings reveal that the pinning effect increases with hydrogen density along the dislocation line. This effect becomes more pronounced when shear is applied along the twinning direction. We demonstrate the nucleation of micro-twinning, characterized by a three atomic-layer thickness, originating from the dislocation under these conditions. The growth mechanism of this phenomenon aligns with Mahajan's model. Our findings identify the high shear stress as the primary driver for twinning, owing to the hydrogen's strong pinning effect.