Co-free non-equilibrium medium-entropy alloy with outstanding tensile properties

In this work, we report a novel Co-free non-equiatomic Ni52.6Cr19.2Fe19.2Nb4 medium-entropy alloy (MEA) with outstanding tensile properties. We systematically investigate its microstructure, strengthening and deformation mechanisms combined by XRD, EBSD and TEM investigations. Experimental results demonstrate this Co-free MEA strengthened by nanosized coherent D0(22)- (Ni, Cr, Fe)(3)(Nb, Fe)-type precipitate (gamma '' phase) with disk shape. This gamma ''-precipitation strengthened MEA exhibits the outstanding strength-ductility synergy, showing a high yield strength of similar to 960 MPa, tensile strength of similar to 1320 MPa and an excellent ductility of similar to 34%. The nanosized gamma '' phases bought out effective precipitation strengthening in this Co-free MEA, contributing a majority yield strength enhancement of similar to 660 MPa. For this gamma ''-precipitation strengthened MEA, the dominant deformation model was the stacking-faults controlled mode, which resulted in a slight ductility sacrifice, in comparison with the solid solution treated MEA. Our work provides solid foundations for further development of high performance Co-free MEAs/(high-entropy alloys) HEAs. (C) 2020 Elsevier B.V. All rights reserved.