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A newly developed high entropy alloy was thermomechanically processed to achieve diverse microstructures holding various initial grain size and substructure characteristics. The thermomechanical processing (TMP) cycles were applied through rolling the as-received material down to a total reduction of 60% at different temperatures of 1250, 1000 and 800 °C. The results indicated that the corresponding microstructure of the deformed matrix at 800 °C could be preserved at room temperature; this was consisted of a banded substructure aligned with the {111} slip traces. These preferentially oriented substructures brought a high density of geometrically necessary dislocations and therefore could provide potential nucleation sites for HCP-e formation. Consequently, the subsequent room temperature mechanical properties (i.e. strength and ductility) were highly improved due to the enhanced capability of the material to exhibit the transformation induced plasticity effect. On the contrary, uniform and nearly equiaxed substructures were developed in the microstructure of the rolled specimens at 1000 and 1250 °C. This, in fact, could lead to the formation of large-scale areas within the grains which were free of geometrically necessary dislocations. Therefore, the HCP phase formation during room temperature (RT) straining was effectively retarded. However, the reduced grain size could regulate the corresponding phase transformation in the material during RT deformation.

The high temperature deformation behavior of a duplex ferrite based low density steel was investigated and the governing restoration mechanisms were determined. Toward this end, the isothermal hot compression tests in the temperature range of 800–1000 °C under the strain rate of 0.001–0.1 s−1 were executed. Interestingly, an appreciable ferrite grain refinement was achieved through thermomechanical processing and the ferrite phase was dynamically recrystallized through continuous mechanism at various temperature and strain rates. The ferrite grain size decreases from ∼900 μm (initial microstructure) down to ∼35 and 50 μm for the microstructure deformed at 800 °C/0.001s−1 and 1000 °C/0.001s−1, respectively. The occurrence of grain refinement within the austenite was also observed which increased the stability of austenite against thermally induced martensitic transformation during quenching. The deformation induced transformation of the austenite to ferrite was also characterized as one of the involved refinement mechanisms which was intensified under the higher strain rates at lower temperature of 800 °C. Considering the portion of the fine ferrite grain resulted from strain induced transformation, the grain size under the lower strain rate of 0.001s−1 decreases down to the ∼14 μm. Finally, the room temperature mechanical properties of the thermomechanically processed specimens was assessed through miniaturized shear punch testing method. It was found that the workability of deformed specimens was significantly improved owning to the simultaneous occurrence of dynamic recrystallization and deformation induced transformation.

The recrystallization behavior of a well-known non-equiatomic high entropy alloy by the nominal chemical composition of Fe–27Mn–10Cr–10Co, at.% was investigated. The compression tests were performed in the temperature range of 400–1000 °C by the interval of 200 °C under the strain rate of 0.001 s−1. Initial microstructure consist of face centered cubic and hexagonal phases by the average grain size of 90, and 11 μm, respectively. Interestingly, the occurrence of dynamic recrystallization was observed during compression testing at warm temperature regime (400 and 600 °C). The appreciable grain refinement, the corresponding flow curve softening, and the detailed analysis of the hardening curves according to the Poliak and Jonas method, verified the occurrence of dynamic recrystallization at such warm temperature regime. The required stored energy was provided through the shear reversion of thermally induced martensite before any straining. In contrast, the softening mechanisms was not strong enough to compensate the strain hardening of the single phase microstructure. This further approved the significant role of the martensite phase to trigger the occurrence of dynamic recrystallization. The intensified substructure development and the random microtexture of the recrystallized grains well indicate the contribution of continuous recrystallization mechanism. The microstructure was also considerably refined (by the mean grain size of ∼1.7 μm) through compressive deformation at 1000 °C. In fact, the deformation temperature was high enough to compensate the inhibitory effects of sluggish diffusion and severe lattice distortion.