Atomistic analysis of nano He bubble evolution in Al: considering stress triaxiality and Lode parameter effects

The He bubble is of utmost importance for understanding the dynamics and evaluating the performance of irradiated metals. This work systematically investigates the effect of the stress triaxiality and Lode parameter on the evolution of He bubble in Al via molecular dynamic simulations. Numerical results show that implanting He atoms into the cavity reduces the yield strength but boosts the ductility of the material, with this effect becoming more pronounced as both the stress triaxiality and Lode parameter decrease. One important discovery is the He bubble fragmentation under low stress triaxiality, and the underlying mechanism mediated by dislocation slip and surface diffusion is clearly revealed. Conversely, the He bubble tends to coalesce under high stress triaxiality, and the coalescence strain increases with the increasing He concentration. Additionally, the heuristic applications of coalescence onset criteria for He bubble are explored. The extended Thomason criterion, considering the hardening effect, provides qualitatively acceptable predictions.