Molecular dynamics simulation of effects of Al on the evolution of displacement cascades in AlxCoCrFeNi high entropy alloys

This work studied the evolution of displacement cascades in AlxCoCrFeNi high entropy alloys (HEAs) with different Al contents by molecular dynamics (MD) simulation to reveal the effects of Al and its-induced microstructural variations on the primary structure damage of HEAs exposed to energetic particle irradiations. Both the amount of peak Frenkel pairs and recombination efficiency of Frenkel pairs in the displacement cascades are increased with Al content, which are induced by the decrease of atomic displacement energies and prolonged thermal spike, respectively. The amount of surviving defects depends on the competition between the two effects. When the PKA energies are 5 and 10 keV, both effects are comparable, resulting in that the amount of surviving defects first decreases and then increases with Al content. The minimum amount of surviving defects is present for Al content of 5 at. %. When the PKA energy is further increased to 20 keV, the increase of peak Frenkel pairs becomes dominant, resulting in the amount of surviving defects increases monotonically with Al content. Moreover, the vacancy clustering is restrained but the interstitial clustering is promoted with increasing Al content. The current results indicate that the addition of oversized alloying elements could introduce two opposite effects in the primary damage stage of HEAs, which should be considered in the design of novel HEAs with higher irradiation resistances.