Strength–ductility balance in an ultrafine-grained non-equiatomic Fe50 (CoCrMnNi) 50 medium-entropy alloy with a fully recrystallized microstructure

Abstract

We explored the phase stability and mechanical properties of an ultrafine-grained non-equiatomic Fe50(CoCrMnNi)50 medium-entropy alloy (MEA). The alloy was processed by conventional cold rolling and then annealed at temperatures between 500 °C and 800 °C. X-ray diffraction revealed that this alloy has a single face-centered-cubic structure even below 800 °C, where the equiatomic CoCrFeMnNi mostly forms second phases. The kinetics of recrystallization of this alloy demonstrated that a fully recrystallized microstructure with an ultrafine grain size of 0.97 μm is achieved after annealing at 600 °C. Tensile results further revealed that this alloy overcomes the strength–ductility trade-off experienced in nanocrystalline alloys, showing an excellent combination of strength and ductility. The origin of discontinuous yielding behavior in both partially recrystallized and fully recrystallized ultrafine-grained specimens is discussed.