Simultaneous deformation twinning and martensitic transformation in CoCrFeMnNi high entropy alloy at high temperatures

Severe plastic deformation (SPD) leads to substantial strengthening in materials via grain refinement, however, the main drawback of the materials processed using known SPD techniques is the lack of uniform plastic deformation due to low strain hardening capability. In this study, equal channel angular pressing (ECAP) at high temperatures was utilized to activate simultaneous twinning-induced (TWIP) and transformation-induced plasticity (TRIP) in the CoCrFeMnNi high entropy alloy (HEA), which are anomalous at high temperatures and reported for the first time. Transmission electron microscopy and electron backscattered diffraction analysis were performed to reveal microstructural features. The presence of the transformed and twinned regions as well as grain refinement in this alloy yielded a high strength level (around 1 GPa) with uniform plastic deformation ability in room temperature tension experiments. The observation of TWIP/TRIP was attributed to high strength levels applied via ECAP and relatively low stacking fault energy of the present HEA.