Deformation mechanisms of the Fe40Mn20Cr20Ni20 high entropy alloy upon dynamic tension

In this study, the Fe40Mn20Cr20Ni20 HEA is successfully prepared, and the deformation mechanism and microstructure evolution upon dynamic tension are investigated. The alloy achieves excellent strength-ductility synergies and extraordinary work-hardening capabilities under conditions of decreasing the temperature or increasing the strain rate. After cold rolling and annealing, the Fe40Mn20Cr20Ni20 HEA exhibited apparent secondary work hardening during dynamic tension (the temperature is 298 K and the strain rate is ∼ 1,400 s-1). The yield strength and ultimate tensile strength increased from ∼ 416 to ∼ 555 MPa and from ∼ 742 to higher than 950 MPa, respectively. At the same time, the plasticity is increased. This improvement is similar to that at cryogenic temperature and quasi-static tension (the temperature is 77 K and the strain rate is ∼ 10-3 s-1). The above two cases have a different deformation mechanism. The activation and evolution of the deformation mechanism under dynamic loading at room temperature with increasing strain are determined through dynamic interruption experiments. Deformation mechanisms such as dislocations, nano-twins, stacking faults & deformation twin networks, precipitated phases, and possibly 9R phases undergo evolutions with increasing plastic deformation. Their extensive interactions are the dominant reasons for the improved mechanical performance, which is rarely identified under quasi-static deformation. The σ phase plays a crucial role during the plastic deformation of the alloy at high strain rates, delaying the onset of necking together with deformation twins.