Synergistic strengthening of heterogeneous structures and dual-morphology nano-precipitates in Co1.5CrNi1.5Al0.2Ti0.1V0.1 medium-entropy alloy

In this paper, we designed a novel non-equiatomic medium-entropy alloy (MEA) with heterogeneous grain structures (HGS) and dual-morphology L12 nano-precipitates through sever plastic deformation followed by directly annealing at 600 °C for 4 h, which exhibited the ultra-high yield strength of 1750 MPa, the ultimate tensile strength of 1890 MPa and the ductility as high as 23.9%. The research on the reveal that the ultra-high strength mainly results from precipitation strengthening and hetero-deformation induced (HDI) strengthening. The HGS effectively induced the HDI strengthening of over 795 MPa during deformation. And the highly coherent lamellar and spherical L12 nano-precipitates provided the yield strength of 770 MPa. Meanwhile, the low stacking fault energy of FCC matrix could make it easy to form a high-density stacking faults and Lomer-Cottrell locks. The Lomer-Cottrell locks not only play a role as strong obstacles to pin the dislocation motion effectively, but also can be sources for dislocation multiplication, enhancing work hardening capacity continuously and delaying the onset of necking. Our work offers an extremely effective strategy to enhance the strength-ductility of non-equiatomic MEAs.