Atomistic Insight into Radiation-Induced Hardening Mechanism of Equiatomic FeNiCrCoCu High-Entropy Alloy by Molecular Dynamics Simulation

Radiation-induced hardening (RIH) severely degrades the mechanical performance and service stability of metallic nuclear structural materials. High-entropy alloys (HEAs) have emerged as promising radiation-tolerant candidates owing to their unique lattice distortion effect and excellent mechanical properties, yet they are still susceptible to RIH under irradiation environments. In this work, molecular dynamics simulations were performed to reveal the atomic-scale RIH mechanism of the equiatomic FeNiCrCoCu HEA. The threshold displacement energy was calculated, and weaker anisotropy was observed compared with medium-entropy alloys and pure Ni, due to severe lattice distortion of the HEA. Overlapping radiation cascade simulations further demonstrated continuous defect generation and aggregation with increasing irradiation dose up to 0.09 dpa. Comparative nanoindentation simulations were conducted on pristine and irradiated HEAs to clarify the coupled evolution of defects and dislocations during plastic deformation. Different from the conventional hardening mechanism, irradiation-induced defects serve as stress concentrators to facilitate initial dislocation nucleation, leading to earlier pop-in behavior at lower indentation loads in irradiated samples. During loading, radiation-induced defects interact with geometrically necessary dislocations and form dense, stable entangled dislocation networks. Upon unloading, residual defects exert strong pinning forces that prevent dislocation network contraction and preserve permanent dislocation substructures. The synergistic effects of defect-induced dislocation pinning and constrained dislocation propagation dominate the RIH behavior of FeNiCrCoCu HEA. This work clarifies the intrinsic atomic-scale mechanism of irradiation hardening in HEAs, providing theoretical guidance for the design and optimization of advanced radiation-resistant nuclear structural materials.