Effects of He-ion irradiation on the microstructures and mechanical properties of the novel Co-free VxCrFeMnNiy high-entropy alloys

Abstract

High-entropy alloys (HEAs), as a promising candidate structural material for advanced nuclear energy system, have been widely studied recently due to the combination of the outstanding irradiation tolerance and enhanced mechanical properties at elevated temperatures. In this study, an FCC-structured CrFeMnNi2 HEA and a BCC-structured VCrFeMn HEA without Co element were designed and prepared. The effects of He-ion irradiation on the microstructures and mechanical properties were investigated, so as to preliminarily evaluate the irradiation tolerance of the novel Co-free HEAs. At fluences of 3 × 1016 and 6 × 1016 ions/cm2, the CrFeMnNi2 and VCrFeMn HEAs showed good structural stability at 1023 K; the transmission electron microscope results revealed no amorphization/precipitations. The average sizes and number densities of He bubbles increased as the fluence improved for the two alloys. At each fluence, the average size of the He bubbles in the VCrFeMn HEA was larger than that in the CrFeMnNi2 HEA, while the number density and volume fraction were lower. The CrFeMnNi2 HEA possessed a higher hardening fraction (77%), and an irradiation-induced hardening saturation was observed in the VCrFeMn HEA with a lower hardening fraction of 33%. The experimental results indicated that the novel low-activation VCrFeMn HEA might be a competitive candidate structural material for advanced reactors. The mechanisms of the irradiation tolerance of Co-free HEAs were also discussed.