Interstitially strengthened metastable FeCoCr-based medium-entropy alloys with both high strength and large ductility

We investigated the effect of interstitial solutes on the phase stability and tensile properties of metastable FeCoCr-based medium-entropy alloys (MEAs). Thermodynamic calculations indicate that the interstitial carbon atom acts as an austenite stabilizer and suppresses the thermally induced martensite formation. With the benefit from interstitial strengthening, carbon-doped FeCoCr-based MEAs have demonstrated an enhanced tensile strength as compared with the undoped counterpart. Originated from the phase metastability and low stacking-fault energy, the martensitic transformation can be activated upon the plastic deformation, leading to the dynamic microstructural refinement. In this way, the significantly improved strength with a maintained tensile ductility can be achieved in the developed MEAs. Our findings have demonstrated that the incorporation of interstitial solutes into metastable alloys contributes to the development of high-performance alloys with a superior strength-ductility synergy.