Suppression of vacancy clustering in nonequiatomic NiFeMnCrAl high-entropy alloys

The investigation of vacancy diffusivity in metallic materials is crucial for advancing predictive models of radiation damage under extreme environmental conditions. In this work, positron annihilation spectroscopy was employed to systematically investigate the formation and diffusion mechanisms of irradiation-induced vacancies in cobalt-free NiFeMnCrAl high-entropy alloys (HEAs) and Ni subjected to 6 MeV proton irradiation. A broad activation energy spectrum for monovacancy migration, from 1.55 to 1.90 eV, is found owing to the lattice distortions and chemical complexity in HEAs. Vacancy clustering, which occurs in pure metals during thermal treatment, is suppressed in the HEAs. A complex energy landscape stems from the chemical diversity, and inherent lattice distortion leads to instability of vacancy clusters, slowing down long-distance defect diffusion – sluggish diffusion – thereby suppressing the formation of large vacancy clusters. This mechanism underpins the pronounced void swelling resistance under irradiation in multiple-component alloy systems.