The hot deformation behavior of a FeCoCrNi high-entropy alloy was investigated in this work. The tests were carried out at 900–1100 oC, under strain rates of 0.001–0.1 s-1 and the effect of friction between specimen and tool on flow stress curves under different deformation conditions was analyzed and modified. The experimental results were employed to determine the constitutive equation with strain-dependent material constants for modeling and for prediction of flow stress at different deformation conditions, using the data obtained from the Sellars–Tegart–Garofalo equation. Microstructural studies revealed that dynamic recrystallization was the primary softening mechanism, resulting in significant microstructural reconstitution and fine grains formation. A complete-recrystallized microstructure with a high proportion of annealing twin boundary was obtained in the specimen hot compressed at 1000 oC/0.01 s-1, so that the average grain size was 22 μm, compared to the initial grain size of 42 μm. The increase of the size and fraction of the DRXed grains during hot deformation decrease the alloy hardness. The dynamic recrystallization parameters such as critical, peak, and steady-state stress, and strain were determined using the work hardening rate analysis. Moreover, the activation energy for deformation of the alloy was determined to be 417 kJ mol-1. The results also indicated that the critical stress and strain for initiating dynamic recrystallization were inversely proportionate to deformation temperature and the strain rate. Furthermore, increasing the deformation temperature resulted in grain growth, whereas increasing the strain rate led to grain refinement. The critical stress and strain were dependent on the Zener–Hollomon (Z) parameter via a power relation with exponents of 0.14 and 0.12, respectively.

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