Heterogeneous Microstructure Evolution and Mechanical Properties of a CrCoNiAl1Ti2 Medium-Entropy Alloy by Thermo-Mechanical Treatment

Combining high strength and good ductility is a long-standing and challenging goal for metallic materials in modern engineering applications. Recently developed single-phase high and medium-entropy alloys, particularly those featuring heterogeneous microstructures, demonstrate superior strength-ductility synergy. Here, a single-phase CrCoNi-based medium-entropy alloy (MEA) with heterogeneous microstructures is introduced through suitable thermo-mechanical treatment. The analysis systematically examines the development of heterogeneous microstructures and their corresponding mechanical properties. The tailored CrCoNi-based MEA demonstrated an exceptional balance between strength and ductility, with a yield stress of approximately 1160 MPa and fracture elongation of 29.3% at annealing 800 ℃ for 1 h. The analysis reveals heterogeneous microstructures consisting of variously sized deformed grains, recovery substructure, recrystallized grains, and annealing twins. These features are primarily influenced by the initial grain size, deformation texture, cold-rolling reduction, and annealing temperature. Elevated annealing temperatures enhance the transformation trend of the microbands, introduced by cold rolling, into recrystallized grains. These findings not only provide a fundamental understanding of the formation mechanisms of the heterogeneous microstructure but also useful guidance for developing methods to tailor microstructures in high and medium-entropy alloys.

Graphical Abstract