Dual-phase (η + L1₂) precipitation strengthening contributes to a good strength-ductility synergy in a novel (Co₂Ni₂Cr)₉₂Ti₄Mo₄ medium-entropy alloy with a heterogeneous microstructure

In this study, combining with JMatPro calculation results, Ti (4.0 at%) and Mo (4.0 at%) elements are added to Co₂Ni₂Cr medium-entropy alloy (MEA). Through appropriate thermomechanical processing (80 % cold rolling followed by annealing at 700 °C for 12 h (designated as CA700-12)), a partially recrystallized microstructure was achieved, along with the formation of dual precipitate phases: lamellar η and near-spherical L1₂ at the macro and micro levels, respectively. The recrystallization (achieving a volume fraction of ∼87.5 %) preferentially occurs within shear bands, resulting in the formation of a heterogeneous microstructure. XRD, TEM, and EDS analyses confirm the coexistence of dual precipitate phases (η and L1₂) with volume fractions of ∼25.3 % and ∼8.3 %, respectively. The (Co₂Ni₂Cr)₉₂Ti₄Mo₄ MEA (CA700-12) exhibits a good strength-ductility balance, with a yield strength of ∼1200 MPa, an ultimate tensile strength of ∼1525 MPa, and a ductility of ∼12.5 %. The strengthening mechanisms are discussed from two distinct perspectives. Firstly, from a heterogeneous structural perspective, the hetero-deformation induced (HDI) stress plays a significant role in material strengthening. Secondly, from a perspective of traditional strengthening mechanism, the dual phase (η and L1₂) precipitation strengthening makes the most important contributions (∼60 %) to the overall strength of the alloy. The primary deformation characteristics are the dislocation slip and the formation of microbands, stacking faults (SFs) and Lomer-Cottrell (L-C) locks. Therefore, it provides a good example for the development of materials with excellent mechanical properties by rationally regulating the macroscopic and microscopic structures of alloys.