Effect of Mo addition on the microstructure and high-specific tensile strength of Fe–Mn–Al–Ni–C ferrous medium-entropy alloy

Abstract

Molybdenum (Mo) is known to play various roles in ferrous materials, including promoting lattice distortion and forming different types of precipitates. In this study, Mo was added to the Fe–Mn–Al–Ni–C lightweight medium-entropy alloy system, and its effects on microstructure and tensile properties were investigated in comparison to the Mo-free counterpart. The addition of Mo retarded the kinetics of recrystallization and led to the precipitation of M6C-type carbides. In terms of tensile properties, the addition of Mo improved the strength of the alloy by enhancing solid solution strengthening and precipitation strengthening. In particular, the Mo-added alloy, annealed at 800 °C for 7.5 min, exhibited a yield strength of 1274 MPa and an ultimate tensile strength of 1550 MPa. This corresponds to a specific ultimate tensile strength of approximately 218 MPa g−1 cm3, along with a uniform elongation of ∼8.5 %. The Mo content in the solid solution and the presence of Mo-rich M6C-type carbides also contributed to high back stress hardening, which enhanced the alloy's ability for strain hardening and resulted in reasonable uniform elongation.