Molecular dynamics simulation of punched loop detachment during helium bubble growth in nickel

The coarsening of helium (He) bubbles in nickel-based alloys significantly impacts their service performance. Understanding the underlying mechanisms is crucial for ensuring the long-term durability and reliability of these alloys in reactor radiation environments. Molecular dynamics simulations of single bubble growth at temperatures of 300 and 900 K were conducted using the sequential He atom injection method to investigate the He bubble growth and evolution in nickel. A noteworthy phenomenon observed during bubble growth is the detachment of punched prismatic loops. The critical bubble size for punched loop detachment can be reduced by growing the bubble at a slower rate or lower temperature. The reduction is attributed to the additional time available for the punched loop to dissociate or the higher pressure within the bubble pushing it out. Meanwhile, the formation mechanism of bubble-loop complexes is explored through the interaction of punched loops with nearby punched loops or bubbles. In addition, the integration of these simulation results with variations in material mechanical performance yields valuable insights for interpreting material degradation. This study provides a foundation for improving in-reactor service performance, contributing to a broader understanding of the complex interplay between helium bubble coarsening and material behavior.