Insights into irradiation-induced defect evolution and segregation in metastable high-entropy alloys: Effects of high-density incoherent planar defects and temperature

Strong and ductile metastable high-entropy alloys (HEAs) have potential to achieve excellent irradiation resistance with the presence of multiple principal elements. In this work, irradiation behavior of a prototype metastable HEA composed of face-centered cubic matrix and dispersed σ precipitates was systematically studied with the focus on revealing the effects of temperature and high-density planar defects (e.g., grain boundaries and incoherent phase boundaries) on the defect evolution and segregation behavior. Transmission electron microscopy analysis shows that dislocation-denuded zones (DDZs) are formed in the vicinities of grain boundaries and σ phase boundaries after irradiation at room temperature (RT), whereas dislocation-enriched zones (DEZs, mainly faulted loops) are developed near these interfaces upon irradiation at 500 °C. This is mainly attributed to the temperature-dependent defect mobility. Upon irradiation at 500 °C, Co and Ni tend to be enriched, but Fe, Cr and Mn prefer to be depleted around dislocation loops and interfaces, which follows the inverse Kirkendall mechanism and has been verified by first-principles calculations. Moreover, grain refinement and precipitation lead to increased volume fraction of DDZs at RT, whereas the absorption of defects at 500 °C can be promoted due to enhanced defect mobility, enabling a more prominent irradiation hardening resistance at various temperatures. The work rationalizes the enhanced irradiation resistance in fine-grained metastable HEAs with dispersive precipitates and provides important insights for developing irradiation-resistant alloys with excellent mechanical properties.