Unraveling mechanical performances and underlying deformation mechanisms in Ni2CoFeV0.5Mo0.2 medium-entropy alloy under extreme strain rate conditions

In the present work, we systematically surveyed mechanical behaviors and associated deformation mechanisms of a face-centered cubic Ni 2 CoFeV 0.5 Mo 0.2 medium-entropy alloy (MEA) at the two extremely high strain rates (8 × 10 3 s -1 and 1 × 10 4 s -1 ). A high strain-rate sensitivity value (m = 0.29) of yield strength was determined for the MEA due to the massive dislocation nucleation and dislocation drag effect. In addition, the true stress increased with the increased strain rate and kept increased along with the increased strain. Specifically, the observation of electron backscatter diffraction maps and transmission electron microscopy images showed that the main deformation mechanism is planar dislocation slip, and dislocation interactions and multiplications result in superb strain hardening in this MEA. Quite interestingly, there is no adiabatic shear band and crack formed at the dynamic deformation regime. It has been found that resistance to thermal softening and a low adiabatic shear band sensitivity factor ( ) value are indicative of plastic stability during dynamic impact. Our findings can provide insight for the development of alloys for impact applications where twinning is not a viable design parameter.