Cyclic degradation mechanisms of Al_0.3CoCrFeNi high-entropy alloy under different loading rates

The effect of loading rate on the cyclic degradation behavior of Al0.3CoCrFeNi high-entropy alloy (HEA) was investigated through nanoindentation experiments and molecular dynamics simulations. The evolution of mechanical properties and microstructure characteristics under different loading rates, as well as the mechanisms of cyclic degradation, were revealed. It is found that the increase of the loading rate induces higher hardness and smaller nanoindentation depth of the Al0.3CoCrFeNi HEA, which gradually increases with the cyclic loading of nanoindentation, resulting in a larger difference in characteristic nanoindentation depth among different loading rates. What's more, a larger loading rate is inclined for nanoindentation depth to reach a steady state. Slip lines and pile-ups are formed around the nanoindentation region at higher loading rates indicating the occurrence of a more localized plastic deformation, while an amorphous transformation occurs at different loading rates after cyclic nanoindentation. Cyclic loading results in the gradual accumulation of residual stress, nanoindentation depth and amorphous structures within the material, and a localized plastic deformation. In summary, cyclic degradation of the Al0.3CoCrFeNi HEA is featured by cyclic softening due to dislocation slipping and the accumulation of amorphous phases.