Temperature-dependent defect accumulation and evolution in Ni-irradiated NiFe concentrated solid-solution alloy

Temperature significantly affects defect migration and evolution in irradiated materials. However, the effects of temperature on defect evolution in concentrated solid-solution alloys (CSAs), including high entropy alloys, are not well understood, despite their potential as structural materials in advanced nuclear reactors. As an important model system of these CSAs, equiatomic Ni ₅₀ Fe ₅₀ (NiFe) was selected to understand the effects of temperature on defect evolution during irradiation and subsequent thermal annealing. Specifically, defect accumulation and evolution in NiFe alloy under Ni-ion irradiation at 150, 300, and 500 K were studied, and the irradiated specimens were subsequently annealed at higher temperatures. Rutherford backscattering spectrometry along the <100> channeling direction was employed to study damage accumulation and evolution before and after each irradiation and annealing experiment. Here we show that more defects survive and accumulate at 150 K, but more importantly defects can migrate to deeper depths at this low irradiation temperature. Irradiation-induced damage at 150 and 300 K does not recover substantially after post-irradiation annealing at 500 K, but dramatic recovery is observed after post-irradiation annealing at 700 K, indicating an onset temperature of defect recovery between 500 and 700 K. The migration of irradiation-induced defects upon annealing is closely related to the mobility and stress state arising from the surviving defects. With the consideration of five stages of defect recovery in conventional dilute alloys, the underlying mechanisms for temperature-dependent defect accumulation and evolution in NiFe CSA are discussed.