Microstructure and mechanical properties of Co-free Ni2FeCrWx medium-entropy alloys reinforced by coherent precipitates

Abstract

In the present work, novel Co-free Ni2FeCrWx medium-entropy alloys (MEAs) are designed by equiatomically replacing Co with Ni in the CoCrFeNi high-entropy alloys (HEAs). The effects of W addition coupled with subsequent heat treatment on microstructure evolution and mechanical properties were systematically investigated and analyzed. The W-addition is conducive to the formation of μ phase in Ni2FeCrWx MEAs, while the annealing treatment promotes the precipitation of submicron-sized BCC particles and the spheroidization of μ phase. The orientation relationship (OR) of 1¯21¯0μ phase // [011]FCC and 303¯0μ phase // 111¯FCC and the coherent interface is formed between μ phase and FCC matrix in as-cast alloys, and the orientation relationship of the interfaces between BCC precipitate and FCC matrix have been clarified as the Kurdjumov-Sachs (KS) interfaces presenting [011]FCC //1¯11BCC and 1¯1¯1FCC // 011¯BCC. The annealed Ni2FeCrW0.5 MEA exhibited outstanding strength-ductility synergy, combining a high ultimate tensile strength of ∼982 MPa and an excellent ductility of ∼29%. Strengthening mechanisms were estimated and compared with experimental measurements, revealing that the coherent BCC/μ precipitates bring out effective precipitation strengthening.