Dislocation evolution and hardening of CoCrFeMnNi high entropy alloy under Fe ion irradiation at room temperature and 500 °C

Abstract

Recently, high entropy alloy (HEA) has become a research hotspot as a new candidate structural material in nuclear reactors due to its good irradiation resistance in swelling and hardening. Focusing on the temperature effect of irradiation damage, this work investigated the influence of irradiation temperature on dislocation evolution and irradiation hardening of HEAs. CoCrFeMnNi HEA was irradiated by high-energy Fe ions at room temperature and 500 °C. It was found that dense small dislocations were produced in the damage attenuation region (i.e., the tail of the ion range) of HEAs after irradiation at room temperature, whereas the irradiation-induced dislocations could not be observed in the damage attenuation region when the irradiation temperature was increased to 500 °C. For the small-sized dislocations, dissociation may occur more easily than long-range migration in HEAs (such as CoCrFeNi systems) due to the inhibition of defect migration and the decrease in defect binding energy, and this order is reversed in pure metals (such as Ni, W). Therefore, at 500 °C irradiation, small dislocations in the damage attenuation region of CoCrFeMnNi HEAs were dissociated before migrating to deeper regions, thereby resulting in the depth of dislocation distribution smaller than the stopping and range of ions in matter-calculated damage stopping depth, unlike the phenomenon in pure metals where dislocations migrated to regions exceeding the calculated depth. In addition, the dislocation density of CoCrFeMnNi HEAs decreased significantly due to the promotion of dissociation and merging of dislocations by elevated temperatures, and the hardening after 500 °C irradiation was less than that after room temperature irradiation.