Influence of High Concentration Vacancy-Type Defects on the Mobility of Edge Dislocation in <i>α</i>-Iron: An Atomistic Investigation

Abstract

Many vacancy-type defects (vacancy, vacancy clusters, and hydrogen-vacancy complexes) are generated in metals by plastic deformation in hydrogen environments. In this study, we use extensive molecular dynamics calculations based on a highly accurate interatomic potential to examine how vacancy-type defects affect the mobilities of edge dislocations in α-iron at a temperature range of 300–500 K and a dislocation speed 𝑉d range of 0.1–10 m/s. Under all conditions, the edge dislocation absorbs the vacancies along the slip plane and causes them to migrate with the edge dislocation. Although the necessary shear stress to glide edge dislocation in α-iron containing vacancy increases with dislocation speed, the effect is small compared to the hydrogen effects. The dislocation absorbs the hydrogen-vacancy complex along the slip plane and causes the hydrogen and the jog to migrate with the edge dislocation at low dislocation velocity regimes (𝑉d ≤ 0.1 m/s). Therefore, the hydrogen-vacancy complex exerts a continuous drag effect on the dislocation. At higher dislocation speeds (𝑉𝑑 ≥ 1 m/s), hydrogen does not migrate with the dislocation, resulting in the formation of isolated hydrogen detached from the dislocation and diffused into the material; only vacancy is absorbed. When multiple hydrogen-vacancy complexes are arranged along the slip plane, the dislocation absorbs them if they interact with dislocation at different points rather than at a single point to avoid the formation of a large jog at the colliding segment, and the required shear stress increases as the hydrogen atoms in the dislocation core increase.