Restrained diffusional transformation in high entropy (TiZrVNbTa)2AlC ceramic under He ions irradiation

The high-entropy (HE) effect has been reported to be able to improve the structural stability of materials under irradiation. However, whether the HE strategy is also effective for MAX phases having specific metal-carbide intercalating structures and suffering from serious diffusional transformation under irradiation remains unknown. In this study, Nb2AlC and high-entropy (TiZrVNbTa)2AlC were prepared and irradiated by 540 keV He ions with the fluence of 1 × 1017 /cm2. The structural evolution were characterized and compared in detail by transmission electron microscopes. Generation of anti-site defects and hex‑cubic diffusional transformation were both observed in Nb2AlC, whereas the latter was absent in (TiZrVNbTa)2AlC. The larger formation energy of C-related trimer defects as-revealed by ab initio calculation, dispersed diffusion of atoms under non-uniform stress field, and more intrinsic Al vacancies with lower migration barrier are considered to be the main reasons for the enhanced irradiation resistance in (TiZrVNbTa)2AlC.