Effects of molybdenum on hot deformation behavior and microstructural evolution of Fe40Mn40Co10Cr10C0.5 high entropy alloys.

The remarkable properties of high-entropy alloys (HEAs) have resulted in their increased research interest and prompted the use of various strategies to enhance their mechanical properties. In this study, the effects of Mo on the hot compressive deformation behavior of carbon-containing FeMn₄₀Co₁₀Cr₁₀ HEAs in the temperature range of 800-1000°C and strain rate of 0.001-0.1 s^-1 was investigated. The microstructural evolutilon and phase structure were characterized by X-ray diffraction and electron backscattered diffraction. The effects of strain, strain rate, and deformation temperature on the thermally activated deformation restoration process of the Fe_39.5Mn₄₀Co₁₀Cr₁₀C_0.5 and Fe_38.3Mn₄₀Co₁₀Cr₁₀C_0.5Mo_1.7 HEAs during hot compression were represented by the Zener-Hollomon parameter. Dynamic recrystallization was initiated at 800°C with the strain rate of 0.001-0.1 s^-1. The precipitation of the M₂₃C₆ carbide along the grain boundaries and within the matrix exerted a strong pinning effect on the grain/subgrain boundaries and promoted dynamic recrystallization through the particle-stimulated nucleation of recrystallization. Moreover, the addition of Mo to the Fe_39.5Mn₄₀Co₁₀Cr₁₀C_0.5 HEA changed the dynamic recrystallization mechanism by reducing the stacking fault energy and enhancing the reverse $fcc\leftrightarrow hcp$ phase transformation. The heterogeneous microstructure composed of ultrafine, fine, and larger grains in the Fe_38.3Mn₄₀Co₁₀Cr₁₀C_0.5Mo_1.7 HEA could be obtained by the nucleation of new recrystallized grains at large deformed grain boundaries adjacent to the first necklace structures and shear bands.