Atomic modeling of the segregation of vacancies on 111 dislocations in α-iron by diffusive molecular dynamics simulations

Abstract The interaction between dislocations and vacancies at finite temperature is crucial for many physical properties and phenomena in materials, such as vacancy segregation, strengthening effect, dislocation motion, and crystal plasticity. Conventional dislocation-vacancy interaction models use approximations based on elasticity theory and assumption that transition state energy can be deduced from the binding energy of the vacancies. The long-term vacancy diffusion near dislocation and the change of dislocation core induced by vacancy segregation are still difficult to capture. In this paper, we present the theoretical study on diffusion and segregation properties of vacancies near 111 edge or screw dislocation on slip planes of {110}, {112} and {123} in bcc iron. The calculations are performed with the distribution of vacancy concentration and dislocation-vacancy interaction energy as a function of distance from dislocation core using diffusive molecular dynamics (DMD). Meanwhile, the accompanying effects of the interaction on vacancy segregation, dislocation motion, and crystal plasticity are discussed. The vacancy diffusion near dislocation is a process highly anisotropic and inter-correlated towards equilibrium. The interaction of vacancies with the tensile stress field of edge dislocations is numerically stronger than that with the pure shear stress field of screw dislocations. The Peierls stress are calculated to reflect the effect of the vacancy segregation on dislocation motion. The slip planes of 111 dislocations have a significant influence on this interaction. With the slip planes changing from {110} to {123} to {112}, the absorption intensity of dislocation to vacancy and the ranges of the “effective interaction region” of both edge and screw dislocation decrease while the ranges of “absorption region” increases gradually. In addition, vacancy segregation produces a regulatory mechanism for the structure of dislocation core and promotes the transformation of dislocations on different slip planes to a more stable intermediate structure. This study visually presents the evolution of vacancies near dislocation, providing fundamental insights on the vacancy transport mechanisms which are essential for understanding dislocation-vacancy interaction, dislocation motion and plasticity of metallic materials.