High-Strength State and Hardening Mechanisms in High-Entropy CoCrFeMnNi Alloy Subjected to High-Pressure Torsion

In the present work, the microstructural evolution and mechanical properties of the high-entropy alloy CoCrFeMnNi were investigated after severe plastic deformation by high-pressure torsion (HPT) at 20 and 300°C, as well as after additional post-deformation annealing at 300°C for 1 h. It was established that HPT at 20°C leads to the formation of an ultrafine-grained structure with an average grain size of ~40 nm and a high defect density, which results in an increase in microhardness up to 600 HV and in tensile strength up to 1820 MPa, accompanied by a reduction in ductility to ~3%. Increasing the HPT temperature to 300°C causes the average grain size to grow to ~400 nm due to the activation of dynamic recrystallization processes. At the same time, the precipitation of nanoscale particles is observed, which provides dispersion strengthening and contributes to an increase in ductility up to 12% while maintaining a high strength of ~1486 MPa. Additional post-deformation annealing at 300°C for 1 h leads to partial relaxation of the defect structure and stabilization of equilibrium grains, accompanied by a reduction in strength to ~1000 MPa and an increase in ductility up to 20%. Thus, it has been shown that adjusting the parameters of thermomechanical treatment enables targeted control over the contributions of different strengthening mechanisms (grain boundary, dislocation, and dispersion) and allows achieving the desired balance of strength and ductility in the CoCrFeMnNi alloy. The results demonstrate the feasibility of tailoring the strength–ductility balance of the CoCrFeMnNi alloy through optimization of thermomechanical processing parameters.