Influence of He injection amount on the microstructure of ion irradiated Cr0.8FeMnNi medium entropy alloy compared with 316L stainless steel

• Different He amounts were injected into MEA and 316L to investigate He effect. • Irradiation defects in no He injected MEA has smaller size and higher number density. • The defect evolution under different He amount in MEA and 316L showed different trend. • The binding energy of SIA to He-V varies from He amount and affects the irradiation induced defects. • The enhanced self-healing process in MEA contributes to the difference in the difference between MEA and 316L. In recent years, medium and/or high-entropy alloys (M/HEAs) have attracted attention due to their excellent mechanical properties, positioning them as potential candidates for structural materials in advanced nuclear reactors. This study investigated the effect of He injection amount on the microstructural evolution in Cr 0.8 FeMnNi MEA and 316L stainless steel. Helium atoms were injected, followed by Fe 2+ irradiation. Transmission electron microscopy was used to characterize the irradiation-induced defects. The primary irradiation-induced defects observed across all He injection amounts were black dots; no voids were seen under any irradiation conditions. In He-injected Cr 0.8 FeMnNi, the number density of black dots was significantly lower than in non-He-injected Cr 0.8 FeMnNi, while the average size of black dots increased with higher He injection rates. As the He injection amount increased, the binding energy of the self-interstitial atom (SIA) to the He-V complex decreased. This reduction facilitated the nucleation and growth of numerous SIA clusters within the matrix, consequently increasing the number density of black dots. The change in the number density of black dots in Cr 0.8 FeMnNi was much smaller than that observed in 316L. This could be ascribed to the enhanced self-healing process caused by the diversity of point defects and higher lattice distortion in Cr 0.8 FeMnNi.