Enhancing strength-ductility trade-off in a NiFeCoAl0.21Ti0.21W0.04 high-entropy alloy by introducing γ′ precipitation

In this study, we successfully prepared NiFeCoAl0.21Ti0.21W0.04 high-entropy alloy using vacuum arc melting technique and systematically investigated the mechanical properties, microstructure, and phase composition of the alloy using an electronic universal testing machine, EBSD, SEM, EDS, and TEM technologies. The results showed that the alloy can retain good ductility (~ 38%) while having high yield strength (~ 850 MPa). The alloy presented an FCC + L12 dual-phase structure, and the L12 precipitates are a nanoscale with an average size of ~ 63 nm and are highly coherent with the FCC matrix, which ensured excellent precipitation strengthening effect and thus high strength. We have calculated the contribution of the strengthening mechanisms present in the alloy to the strength of the alloy, and the results show that precipitation strengthening dominates among all strengthening mechanisms. At the same time, the formation of annealed twins acts as a barrier to grain growth during heat treatment, which also ensures good fine-grain strengthening. In conclusion, we have obtained an excellent strength-ductility trade-off relationship by introducing a nano-precipitation phase in the alloy that is coherent with the matrix, which is expected to guide the development of higher entropy alloys with superior properties.