A novel Fe-rich non-equiatomic medium-entropy alloy with superior mechanical properties

Abstract

A cost-effective iron-rich non-equiatomic Fe50Mn20Al15Ni10Co5 medium entropy alloy (MEA) was synthe-sized by vacuum induction melting. The as-cast alloy exhibits a multiphase microstructure with the ordered B2 (a= 2.90 +/- 0.01 angstrom), disordered body-centred cubic (BCC) (a= 2.89 +/- 0.01 angstrom) and face-centred cubic (FCC) (a= 3.61 +/- 0.02 angstrom) phases. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to confirm the structure of the evolved phases. The columnar dendrites having a width in the range of 120-300 gm were observed in the as-cast structure. The formation of Ni-Al rich B2 precipitates in the BCC matrix was confirmed based on detailed microstructural characterization using scanning electron micro-scope (SEM) and TEM. The phase separation in the form of modulated structure of ordered B2 and dis-ordered BCC phase was related to the spinodal decomposition. The formation of the FCC phase at and near the grain boundaries is linked to simultaneous nucleation and growth mechanisms, which occur during the solidification. The as-cast alloy has shown an average compressive yield strength of similar to 1250 MPa and ulti-mate strength of similar to 1675 MPa, along with a compressive strain of similar to 42%. The optimum balance of strength and ductility is achieved due to the formation of the hard (B2, BCC) and soft (FCC) phases and their interplay during the deformation process. These encouraging results of the alloy in the as-cast state have provided the direction to design and develop such economically viable alloys, which could be produced at industrial scale.(c) 2023 Elsevier B.V. All rights reserved.