Effect of niobium addition upon microstructure and tensile properties of CrMnFeCoNix high entropy alloys

Nb-doped CrMnFeCoNix (x = 0.2, 0.4, 0.6, 0.8 and 1) high entropy alloys were prepared by vacuum induction melting. The effects of Ni and Nb content on the microstructure evolution and tensile properties of the alloys were investigated. With increasing Ni content, the CrMnFeCoNix alloy changed its structure from a combination of face-centered cubic phase and a phase to a single face-centered cubic phase. The yield strength, ultimate tensile strength and ductility of CrMnFeCoNix alloys first increased and then decreased with the increase of Ni content. Compared with other CrMnFeCoNix alloys, CrMnFeCoNi0.8 HEA has shown superior mechanical properties, exhibiting a high yield strength (240.9 MPa), ultimate tensile strength (527.5 MPa) and an impressive elongation-to-failure (62.5%). The addition of Nb significantly increased the volume fraction of Laves phase in the CrMnFeCoNi0.8 alloy, which further enhanced the tensile properties of CrMnFeCoNi0.8 high entropy alloys. The yield strength and ultimate tensile strength of the CrMnFeCoNi0.8Nb0.2 alloy were determined to be 406.9 MPa and 662.8 MPa, representing a 68.9% and 25.6% increase over CrMnFeCoNi0.8 alloy.