Mechanical performance of a novel low-cost Fe–25Mn–5Co-12.5Cr–5Ni-2.5Si (in at. %) medium-entropy alloy

This study presents a FCC crystal structure medium entropy alloy (MEA) with a nominal composition of Fe–25Mn–5Co-12.5Cr–5Ni-2.5Si (in at. %). The MEA deformed at room temperature exhibits superior mechanical performance compared to benchmark CoCrFeMnNi high entropy alloys (HEA). The empirical Hall-Petch equation was calculated with a high intrinsic strengthening coefficient of 335 MPa and a grain boundary strengthening coefficient of 634 MPa ∙μm−1/2. The deformed microstructure is comprised of planar and wavy dislocations and deformation twins. Cryogenic deformation results in an increase in mechanical strength, brought about by the complex deformed microstructure involving deformation twins and ε martensite laths. Addition of silicon to the alloy system increases the atomic misfit of the MEA and decreases the alloy's stacking fault energy (SFE) value, thereby activating the deformation mechanism of FCC-to-HCP martensitic phase transformation. Overall, the study concludes that MEA has the potential to be a more cost-effective alternative to expensive high entropy alloys.