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

In this work, a novel non-equiamotic Ni47.5Cr23.75Co23.75Ti5 medium-entropy alloy strengthened by heterogeneous precipitates was successfully fabricated. Our results demonstrate heterogeneous precipitation behaviors, i. e. nanosized spherical particles with LI2 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 (similar to 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.