The dynamic response of He bubble in bicrystal copper under uniaxial compression and tension

He bubbles can exhibit different behaviors due to their different positions in the nanocrystalline materials. Using molecular dynamics simulations, we study the dynamic response of He bubble in bicrystal Cu under uniaxial compression and tension. The differences between He bubbles in grain interiors and grain boundaries (GBs) are explored, for different loading orientations. Our results reveal that the He bubble-induced dislocations dominate the initial yielding behaviors of the samples, and will induce the earlier dislocations emission from the GB due to the GB-dislocation interaction. Different reductions in yielding stress are observed for different loading directions and He bubble positions, leading to the changes in the compression/tension asymmetry. Particularly, the effect of He bubble positions on the yield stress is more significant under the loading direction that perpendicular to the GB plane than parallel to the GB plane. Three stages of He bubble evolution are interpreted during both compression and tension loading. The GB-bubble distance is found to have little effect on the yielding behavior of the material, but plays an important role in the He bubble evolution at the later stage of tension. Furthermore, the Carnahan-Starling equation of state is used to describe the evolution of He bubble embedded in bicrystal Cu during compression and tension, by fitting the parameters in the Brearley and MacInnes hard-sphere model.