Achieving exceptional strength-ductility combination in a novel L12 nanoparticles-strengthened high-entropy alloy via conventional casting

Abstract

A novel L12 precipitation-strengthened Co51.3Ni19.5Cr19Al6.4Ti3.4Nb0.4 medium-entropy alloy (MEA) with excellent combination of large ductility and high strength was prepared via direct casting. The coherent ultrafine L12 precipitates particles (∼30 nm) with a volume fraction of 65% formed uniformly in the FCC matrix after heat-treatment, which endows this newly-designed MEA with superior tensile properties, i.e., a yield strength of ∼710 MPa, an ultimate tensile strength of ∼1045 MPa and a uniform elongation of ∼31.3%, respectively. The blocking effect of ultra-fine L12 precipitates significantly contributes to the high strength of the Co51.3Ni19.5Cr19Al6.4Ti3.4Nb0.4 MEA. In addition, deformation-induced nano-spaced stacking-fault networks, nano-twins and high-density Lomer-Cottrell locks facilitate the high work-hardening capacity, leading to excellent tensile ductility. This alloy design strategy can potentially be applied to many other alloys and open new avenues for designing strong yet ductile materials for engineering applications.