Defect Cluster Evolution under Primary Cascade Damage in TiVTaW High-Entropy Alloy and Its Constituent Elements Investigated by Molecular Dynamics Simulations

High-entropy alloys (HEAs) have attracted attention as promising candidates for nuclear fusion reactor materials owing to their superior mechanical properties and irradiation resistance. In our previous research, we predicted the existence of metastable small vacancy cluster configurations in the TiVTaW HEA, attributed to its chemically heterogeneous atomic environment. In this study, molecular dynamics simulations were conducted on TiVTaW and its constituent pure elements (Ti, V, Ta, W) to investigate the defect behavior under cascade damage conditions. The temporal profiles of Frenkel pair counts showed distinct differences among these material systems, which can be explained by two main factors: element-specific intrinsic properties, such as thermal conductivity and displacement threshold energy, and the thermodynamic stability of defects. Notably, TiVTaW exhibited a prolonged thermal spike and generated a greater number of Frenkel pairs than the average of its constituent elements. Furthermore, the defect clusters in TiVTaW were generally smaller in size compared to those in its individual elements. This small defect cluster size can be attributed to two characteristic features of HEAs: the presence of metastable defect and defect cluster sites, and sluggish defect mobility. These findings enhance the understanding of how HEA composition influences irradiation resistance.