Heterogeneous precipitates facilitate excellent mechanical properties in non-equiatomic medium-entropy alloy

In this work, a novel non-equiamotic Ni_47.5Cr_23.75Co_23.75Ti₅ medium-entropy alloy strengthened by heterogeneous precipitates was successfully fabricated. Our results demonstrate heterogeneous precipitation behaviors, i.e. nanosized spherical particles with L1₂ superlattice in inner grains plus nano-lamellar precipitates with long-period stacking ordered structure nearby grain boundaries, could bring out outstanding strength-ductility synergy properties. This heterogeneous precipitation-strengthened medium-entropy alloy exhibits high yield strength and ultimate tensile strength of ~840 MPa and ~1220 MPa, respectively, and remains an excellent ductility of ~34.8%. Further analyses indicate this heterogeneous precipitation result in effective precipitation-strengthening enhancement (~603 MPa), stacking-faults activated in spherical precipitates region and deformation nanotwins induced in lamellar precipitates region synergy contribute to high work-hardening capacity and ductility. Our work provides not only a useful insight of precipitation behaviors caused by Ti element addition in non-equiatomic high/medium-entropy alloys, but also a further understanding of precipitation-strengthening in high/medium-entropy alloys.