Energetically favorable dislocation/nanobubble bypass mechanism in irradiation conditions

With exposure to high-energy particle irradiation, structural metals develop a number of nanoscale defects, one of which is the nano-sized He bubble. Formed throughout the material, these bubbles can directly impair the movement of dislocations and dramatically alter mechanical performance. Propagating edge dislocations in face-centered cubic metals, driven under sufficient mechanical forces, are expected to cut through He bubbles, due to the higher energetic expense. Here, using atomistic simulations for a model Cu material, we find that when the He-vacancy ratio and bubble diameter become sufficiently large and the ratio of the bubble spacing to the diameter is reduced below a threshold, an extended edge dislocation engages in a multi-step-bypass (MSB) maneuver to change its glide plane and overcome the bubble at room temperature. This unanticipated MSB mechanism provides a more energetically favorable pathway compared to conventional bypass mechanisms under these severe conditions.