Helium irradiated cavity formation and defect energetics in Ni-based binary single-phase concentrated solid solution alloys

Binary single-phase concentrated solid solution alloys (SP–CSAs), including Ni₈₀Co₂₀, Ni₈₀Fe₂₀, Ni₈₀Cr₂₀, Ni₈₀Pd₂₀, and Ni₈₀Mn₂₀ (in atomic percentage), were irradiated with 200 keV He⁺ ions at 500 °C. He cavity size and density distribution were systematically investigated using transmission electron microscope. Here we show that alloying elements have a clear impact on He cavity formation. Cavity size is the smallest in Ni₈₀Mn₂₀ but the largest in Ni₈₀Co₂₀. Alloying elements could also substantially affect cavity density profile. In-depth examination of cavities at peak damage region (∼500 nm) and at low damage region (∼300 nm) demonstrates that cavity size is depth (damage) dependent. Competition between consumption and production of vacancies and He atoms could lead to varied cavity size. Density functional theory (DFT) calculations were performed to obtain the formation and migration energies of interstitials and vacancies. Combined experimental and simulation results show that smaller energy gap between interstitial and vacancy migration energies may lead to smaller cavity size and narrower size distribution observed in Ni₈₀Mn₂₀, comparing with Ni₈₀Co₂₀. The results of this study call attention to alloying effects of specific element on cavity formation and defect energetics in SP–CSAs, and could provide fundamental understanding to predict radiation effects in more complexed SP–CSAs, such as high entropy alloys.