Strength and ductility synergy of Nb-alloyed Ni_0.6CoFe_1.4 alloys

Designing strong, yet ductile, and body-centered cubic (BCC) medium-entropy alloys (MEAs) remains to be a challenge nowadays. In this study, the strength–ductility trade-off of Ni_0.6CoFe_1.4 MEAs was tackled via introducing a BCC + face-centered cubic (FCC) dual-phase microstructure. Ni_0.6CoFe_1.4Nb_x (x = 0, 0.05, 0.08, 0.10, and 0.15, in molar ratio) MEAs were prepared using vacuum induction melting. Results show that the new alloy is composed of BCC plus FCC dual phases featuring a network-like structure, and the BCC phase is the main phase in this alloy system. Moreover, the Nb0.10 MEA shows high strength and respectable tensile ductility, representing the best combination of the strength and fracture elongation among the alloys studied here. The remarkable strength of the Nb0.10 MEA is attributed to the combined effect of the solid solution strengthening, the precipitation hardening effect and the interface strengthening effect.