Double heterogeneous structures induced excellent strength–ductility synergy in Ni40Co30Cr20Al5Ti5 medium-entropy alloy

Abstract

The application of single-phase face-centered cubic (FCC) medium entropy alloys (MEAs) in the engineering industry is often hindered by the challenge of insufficient strength. In this study, a novel non-equiatomic ratio Ni40Co30Cr20Al5Ti5 MEA was successfully fabricated. Through the well-designed mechanical heat treatment processing, we introduced a heterogeneous grain structure comprising 67.4% fine grain and 32.6% coarse grain. Additionally, heterogeneous size L12 phases consisting of 18.7% submicron precipitates and 11.7% nano-sized precipitates, were incorporated into the alloy. Tensile tests conducted at room temperature revealed that the double heterogeneous structure alloy demonstrated remarkable strength–ductility synergy. It exhibited a yield strength of 1200 MPa, an ultimate tensile strength of 1560 MPa and a total elongation of 33.6%. The exceptional strength of the alloy can be primarily attributed to heterogeneous deformation induced strengthening, grain boundary strengthening and precipitation strengthening. The excellent ductility is mainly attributed to the high-density stacking faults and Lomer–Cottrell locks. This study not only contributes to the clarification of the strengthening and deformation mechanism of double heterogeneous structure alloys but also provides an effective strategy for the development of high-performance alloys with high strength and ductility.