Shiyi Wang, Mengye Duan, Xu Shen, Lingbao Hu, Hao Hu, Shayuan Weng, Tao Fu
Multi-principal element alloys (MPEAs) have potential applications as structural materials in advanced nuclear energy systems, but the mechanisms by which internal stacking faults (SFs) affect irradiation defect evolution and post-irradiation mechanical responses remain to be further investigated. Molecular dynamics simulations were performed to investigate the effects of pre-existing SFs on displacement cascade evolution and post-irradiation deformation behavior in CoCrNi medium-entropy alloys with different stacking-fault spacings ( λ ). The results show that densely distributed SFs suppress peak defect accumulation during displacement cascades and promote earlier defect stabilization, leading to reduced peak Frenkel pair (FP) production but enhanced defect survival. These effects become increasingly pronounced with decreasing λ , indicating that SFs strongly modify defect recombination and retention behavior during cascade evolution. Post-irradiation tensile deformation exhibits pronounced loading-direction anisotropy arising from slip-system-dependent SF-dislocation interactions. Irradiation-induced defect clusters facilitate dislocation nucleation and promote yield softening, whereas pre-existing SFs impede dislocation propagation and enhance resistance to plastic flow. Under [11 ]-direction loading, stable intersecting SF networks continuously hinder dislocation glide and promote flow hardening. In contrast, under [ 10]-direction loading, repeated interactions between propagating SFs and pre-existing SFs induce Hirth-lock formation and dissociation, resulting in sustained Shockley partial dislocation emission, progressive SF annihilation, and enhanced planar slip activity, which ultimately lead to flow softening at small λ . The present work provides atomistic insights into the role of planar defects in governing irradiation tolerance and anisotropic mechanical behavior in low-stacking-fault-energy multi-principal-element alloys.