Microstructural origins of impact resistance of AlCoCrFeNi2.1 eutectic high-entropy alloy

In this work, the mechanical properties and related deformation mechanisms of AlCoCrFeNi2.1 eutectic highentropy alloy (EHEA) under dynamic loading were systematically investigated at a medium strain rate range from 500 to 1500 s-1. The EHEA presents significant strain rate hardening and continuous strain hardening without any adiabatic shear bands. The yield strength increases from 803.8 MPa at 500 s-1 to 1006.8 MPa at 1500 s-1. The strain rate sensitivity and strain hardening exponent were evaluated to be 0.198 and 0.567-0.683, respectively, responding for the superior capability to withstand dynamic loading. Post-deformation microstructural analysis reveals that increased strain rate induces higher dislocation density. In the FCC phase, dislocation planar slip at {111} planes dominates at 500 and 1000 s-1, while high dense dislocation walls (HDDWs) form at 1500 s-1 from coplanar slip along {111} planes. In the BCC phase, high dense nanoprecipitates result in a significant precipitate-strengthening effect, featured by arrow-shaped dislocations, dislocation loops and dislocation tangles.