Ultrastrong and ductile (CoCrNi)94Ti3Al3 medium-entropy alloys via introducing multi-scale heterogeneous structures

Abstract

• A three-level heterogeneous structure was introduced in CoCrNi alloy. • (CoCrNi) 94 Ti 3 Al 3 delivers ultimate tensile strength of 1.6 GPa and strain of 13.1%. • Heterogeneous matrix, γ’ precipitate and defects led to high strength and ductility. 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) 94 Ti 3 Al 3 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 coherent spherical γ' precipitate (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.