Microstructure and mechanical properties of medium-entropy alloys with a high-density η-D024 phase

Medium-entropy alloys (MEAs) have attracted considerable research attention because of their excellent mechanical properties. In these, the γ’ phase has been utilized as a strengthening phase. However, the η phase has not been widely investigated. Herein, we explain the precipitation behavior of the η phase in a non-equimolar CoCrNiTi MEA. The MEA adopts a face-centered cubic (FCC) matrix upon Ni3Ti η phase precipitation. Various characterization techniques were used to analyze the microstructure, phase structure, and phase composition of the as-prepared MEA. The grain size and volume fraction of the η phase were ~ 70 nm and ~ 35%, respectively. The FCC-η interface exhibited semi-coherence, adopting an interplanar angle of 23°. Upon precipitation strengthening, the MEA exhibited a yield strength of ~1.7 GPa, an ultimate tensile strength of ~2 GPa, and an elongation of ~2.87%. This work facilitates a novel approach to ultrahigh-strength alloy production. ? 2022 Elsevier Inc.