Upgrading of superior strength–ductility trade-off of CoCrFeNiMn high-entropy alloy by microstructural engineering

One of the challenging phenomena in the materials science community is the issue of the strength-ductility trade-off. Pre-strain followed by annealing at low temperatures was used as a novel strategy to overcome the strength-ductility trade-off of CoCrFeNiMn high entropy alloy. The proposed process aims to retain the deformation-induced twins after partial recovery. However, the lack of precipitate in the processed alloy bears in mind to consider the effect of precipitation. In this paper, for the first time, we proposed a simple thermomechanical process including light cryogenic rolling (reduction of thickness ∼28%) followed by low-temperature annealing (at 500 °C for 180 min) to obtain a unique microstructure. The microstructure with partial recovery contains retained deformation-induced twins along with bcc Cr-rich precipitates under optimum conditions (size and volume fraction) and no brittle sigma precipitates. This microstructure provides the appropriate balance between deformation and precipitation strengthening. The microstructure exhibits much improved mechanical properties (UTS ∼1.25 GPa and uniform elongation ∼15%). Additionally, a model was introduced for predicting mechanical properties using microstructural parameters. The present results indicated that this thermomechanical processing could be used as an innovative processing strategy for achieving superior strength–ductility trade-off by microstructural engineering. We believe that a similar concept may be applied for optimizing the mechanical properties of other fcc high or medium entropy alloys based on the Co-Cr-Fe-Ni-Mn system.