Enhancement in mechanical properties through an FCC-to-HCP phase transformation in an Fe-17.5Mn-10Co-12.5Cr-5Ni-5Si (in at%) medium-entropy alloy

Abstract

The present work focuses on developing a low-cost medium entropy alloy (MEA) with desirable mechanical properties according to the benchmark CoCrFeMnNi high entropy alloy (MEA). By adjusting the ratio of each component and adding silicon to the system, the Fe50Mn17.5Cr12.5Co10Ni5Si5 MEA with a single face-centered cubic (FCC) phase was developed. After homogenization, hot rolling, cold rolling, and annealing, fully recrystallized MEA specimens with grain sizes ranging from 10 µm to 149 µm were used for tensile tests. The microstructure of the elongated MEAs showed a ɛ-martensite transformation from the FCC phase to the hexagonal close-packed (HCP) phase, indicating the stacking fault energy (SFE) of the MEA was significantly reduced. The room-temperature deformed MEA showed improved mechanical properties in yield strength and tensile strength than the CoCrFeMnNi MEA. Meanwhile, the volume fraction of the HCP phase in cryogenic-deformed MEA is much larger than that in room-temperature deformed MEA; its yield strength was increased by two times, while the tensile strength exceeded the level of 1 GPa.