Formation of Voids or Stacking-Fault Tetrahedra Induced by Local Chemical Variations in Face-Centered-Cubic Complex Concentrated Alloys

Understanding how elemental variations influence defect cluster formation is a longstanding challenge in materials science. By combining defect rates-based long-time dynamics with molecular dynamics and irradiation experiments, we identify a distinct, cluster-mediated mechanism-governed by element-specific interactions-as the dominant driver of vacancy cluster evolution into voids or stacking-fault tetrahedra in irradiated complex concentrated alloys, specifically NiCoCr, Fe_{50}Mn_{30}Co_{10}Cr_{10}, and Ni at elevated temperatures. Unlike conventional models that focus on point defect behaviors, the proposed mechanism highlights a critical two-step process-vacancy-tetrahedron formation and annihilation-that governs the bifurcation of vacancy clusters. Ni and Co promote void formation by favoring annihilation over formation, leading to Ni/Co segregation, whereas larger atoms such as Cr, Fe, and Mn resist annihilation, thus favoring stacking-fault tetrahedra formation. These findings offer new insights into how local chemical environments influence defect evolution and provide strategies for tailoring materials to perform better under extreme conditions.