High-temperature and high-dose irradiation study on the NbMoTaW high-entropy alloy coatings

Due to its excellent high-temperature stability and radiation resistance, high-entropy alloys (HEAs) have attracted wide attention as candidate materials for advanced nuclear reactor systems recently. To understand their microstructure evolution and mechanical performance at high irradiation temperatures, NbMoTaW coatings were irradiated with 2.7 MeV Si²⁺ ions to a high peak damage dose of 50 displacements per atom at 450, 550 and 600 °C. Transmission Electron Microscopy and nanoindentation were used to characterize the defects and irradiation-induced hardening. No voids were observed and the grain structure kept stable after irradiated. As the temperature increases, dislocation lines become more distorted and harder to slip, contributing to hardening in high-temperature irradiated samples. The average size of dislocation loops increases slightly but remains approximately 9 nm, and the density of dislocation loops exhibits a fluctuating tendency. The pre-existed microcracks near grain boundaries became narrower with the elevation of temperature and disappeared at 600 °C. It can be attributed to the larger swelling at higher temperature, where the invisible vacancies could squeeze these microcracks. These vacancies should be one of the key factor leading to the highest irradiation-induced hardening occurred at 600 °C. In addition, irradiation segregations were observed at grain boundaries at 600 °C.