Proton irradiation-induced microstructure changes in a CrFeMnNi high entropy alloy

High entropy alloys have demonstrated superior radiation tolerance compared to pure metals and some conventional alloys. However, the stability of high entropy solid solution microstructure within a cascade-involved irradiation environment at elevated temperatures has not been well understood. In this study, we examined the microstructural evolution of a CrFeMnNi high entropy alloy (HEA) subjected to irradiation with 2 MeV protons under three different conditions: 2.8 dpa at 400 °C, 2.8 dpa at 600 °C, and 16.8 dpa at 400 °C. The irradiation-induced microstructural changes were characterized using (scanning) transmission electron microscopy ((S)TEM) combined with energy dispersive x-ray spectrometry (EDS) and electron energy loss spectroscopy (EELS). Irradiation-induced Frank loops in the damage plateau areas were statistically characterized. The samples irradiated to 2.8 dpa at 400 °C exhibited the highest density of Frank loops, whereas the largest average size of Frank loops was observed in the sample irradiated at 600 °C. Spinodal decomposition and L10-type NiMn ordering were observed in the irradiated samples, with the extent of decomposition increasing with irradiation temperature. Additionally, segregation of Ni and Fe and depletion of Mn were observed around Frank loops. Voids were observed only within the Cr precipitates in the 600 °C sample, which is attributed to the excess vacancies associated with Cr precipitation.