Abnormal interactions between high-speed edge dislocation and microvoid in BCC metals

Abstract

The interaction between a high speed edge dislocation and a microvoid has been investigated by molecular dynamics (MD) simulations in BCC crystals of Ta, Fe, V and W in the present work. The focus is placed on the dynamic effect on the dislocation-microvoid interaction. Three interaction scenarios different from static cases, i.e., repeated dislocation oscillations around microvoids, dislocation depinning from microvoid like releasing an elastic slingshot, and formation of abnormal “pull forward” dislocation configuration, have been found for the first time. The “repeated oscillations” can be attributed to the dislocation line tension and dynamic effect, which is analogous to under-damped mechanical oscillator system. For the “releasing slingshot” case, the dislocation first bows out after breaking away from the microvoid, and then a stable “drag backward” dislocation configuration is formed. When further increasing the applied shear stress, the dislocation can accelerate to subsonic speed of roughly0.7CT, with CT being the transverse sound speed, leading to a stable “pull forward” configuration. These different dislocation configurations are closely related to the formation of superjog driven by the dislocation-microvoid interaction. By careful analysis, it is found that the variation of relative mobility between the original edge dislocation on the (110) plane and the superjog segments on the (112) plane with shear stresses perfectly coincides with the above three dislocation configurations. In fact, when the applied shear stress is high enough and the dislocation speed is subsonic, the friction stress on the superjog segments turns to be smaller than that of the original edge dislocation, resulting in the formation of abnormal “pull forward” configuration.