Effect of severe plastic deformation and subsequent annealing on microstructure, chemical ordering, precipitation behavior, and mechanical properties of the CrMnFeCoNi high-entropy alloy

The influence of high-pressure torsion (HPT) and subsequent annealing on the phase evolution, microstructure, and mechanical properties of the CrMnFeCoNi high-entropy alloy was investigated using synchrotron X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), and microhardness testing. HPT processing at liquid-nitrogen temperature, room temperature, and 473 K resulted in markedly different phase constitutions and defect densities, leading to distinct microstructural evolution and mechanical responses during subsequent annealing. These differences were particularly pronounced in the annealing temperature range of 473–773 K and are attributed to the higher defect density and enhanced atomic mixing introduced by room-temperature and elevated-temperature HPT. In contrast, cryogenic HPT promoted the formation of deformation-induced ε -martensite but resulted in a more heterogeneous microstructure and less effective atomic mixing, leading to distinct phase-transformation and precipitation pathways. Synchrotron X-ray diffraction and HRTEM analyses revealed significant changes in phase composition, grain structure, and precipitation behavior during annealing. These structural evolutions were quantitatively correlated with the corresponding changes in microhardness. The results indicate that the mechanical response is governed primarily by the precipitation of three secondary phases and, at later annealing stages, by grain-size-dependent strengthening associated with both conventional and inverse Hall–Petch mechanisms. The possible contribution of chemical ordering is also discussed as an additional mechanism underlying the pronounced increase in hardness.