Void suppression during vacancy aggregation in concentrated solid solution alloys using self-adaptive accelerated molecular dynamics

Irradiation-induced void swelling is a major cause of microstructural degradation in structural materials for nuclear applications. Although Ni-based concentrated solid solution alloys (CSAs) exhibit superior swelling resistance, the vacancy-mediated mechanisms by which chemical complexity alters long-term evolution and suppresses the emergence of void-like structures remain unclear. Here, we employ self-adaptive accelerated molecular dynamics for the first time to capture vacancy diffusion, aggregation, cluster dissociation, and structural transformation at experimentally relevant times. Simulations on pure Ni and five Ni-based CSAs reveal strongly element-dependent suppression mechanisms. Specifically, Co limits the void growth by reducing vacancy-cluster mobility and diffusion range. By contrast, Fe, Cr, and Mn lower migration barriers and generate rapid diffusion pathways, promoting aggregation while destabilizing small clusters and driving larger clusters toward faulted defect structures, including Frank loops and stacking fault tetrahedra. These chemically regulated pathways explain the exceptional swelling resistance of CSAs and provide a mechanistic basis for designing radiation-tolerant structural materials.