Microstructure and properties of a novel cost-effective FeNi-based eutectic high entropy alloys

Eutectic high-entropy alloys (EHEAs) are becoming a new research focus in the field of metal materials due to the outstanding casting properties, high fracture strength and high tensile ductility. In present study, a series of [FeNi]75-xCr15Mn10Nbx (x = 0, 3, 6, 9, 10, 12, 15, x value in molar ratio) Co-free high entropy alloys were fabricated and evaluated to investigate the alloying effect of Nb on microstructure and compression properties. With the addition of Nb, the microstructure changes from monophase to divorced eutectic with primary FCC phase and then to the hypoeutectic. With the further addition of Nb, the microstructure is almost eutectic (irregular eutectic + regular eutectic), and then transformed into hypereutectic with primary Laves phase. The compressive fracture strength of [FeNi]75-xCr15Mn10Nbx first increases and then decreases accompanied by the degradation of compressibility as the addition of Nb. The eutectic alloy [FeNi]65Cr15Mn10Nb10 exhibited comprehensive mechanical properties with compressive fracture strength 1638 MPa and fracture strain 22%. The strengthening mechanism of the HEAs is mainly fine grain strengthening (Hall-Petch) and Laves phase strengthening, supplemented by FCC solid solution strengthening. The microstructure formation is explained by Md criterion, when Md is less than or equal to 0.89, the microstructure is composed of single FCC phase; when Md is greater than 0.89, the microstructures are composed of FCC + Laves phases.