Abstract: The coarsening-grained single-phase face-centered cubic (fcc) medium-entropy alloys (MEAs) normally exhibit insufficient strength for some engineering applications. Here, superior mechanical properties with ultimate tensile strength of 1.6 GPa and fracture strain of 13.1% at ambient temperature have been achieved in a (CoCrNi)₉₄Ti₃Al₃ MEA by carefully architecting the multi-scale heterogeneous structures. Electron microscopy characterization indicates that the superior mechanical properties mainly originated from the favorable heterogeneous fcc matrix (1-40 µm) and the coherent spherical γ' precipitates (10-100 nm), together with a high number density of crystalline defects (2-10 nm), including dislocations, small stacking faults, Lomer-Cottrell locks, and ultrafine deformation twins.

Key words: Medium-entropy alloys, Mechanical properties, Heterogeneous structure, γ' nanoprecipitates, Crystalline defects