Ta-doping induces heterogeneous microstructures in CoCrNi medium-entropy alloy to achieve excellent strength-ductility combination

Face-centered cubic high-entropy alloys and medium-entropy alloys (MEAs) are limited by their mediocre yield strength. This work proposes a simple yet efficacious strategy that capitalizes on the advantages of heterogeneous structure and doping large-size atoms. Using this strategy, various types of heterogeneous structures can be introduced simultaneously into Ta-doped CoCrNi MEAs, resulting in significant enhancements in their mechanical properties. After annealing at 800 °C, the (CoCrNi)100-xTax (x = 1, 2, and 3) MEAs show heterogeneous, dual heterogenous, and partially recrystallized structures, respectively. Notably, compared to the CoCrNi MEA (546 MPa) processed under the same conditions, the yield strength of these alloys is increased to 696 MPa, 1180 MPa, and 1470 MPa, respectively, which indicates increases of 27%, 116%, and 169%. Precipitation morphology and distribution significantly impact the formation of heterogeneous structures. During recrystallization, primary coarse precipitation and secondary fine precipitation give rise to the particle-stimulated nucleation and Zener pinning effects, respectively, inducing the refinement of surrounding grains. Furthermore, a detailed investigation was conducted to elucidate the effect of Ta doping on grain growth kinetics and deformation mechanisms in the (CoCrNi)98Ta2 alloy. •Combining the advantages of heterogeneous structure and doping large-size atoms.•Thermo-mechanical processing introduces various types of heterogeneous structures.•Precipitate is crucial for the formation of heterogeneous structures.