The enhancement of transformation induced plasticity effect through preferentially oriented substructure development in a high entropy alloy

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 degrees C. The results indicated that the corresponding microstructure of the deformed matrix at 800 degrees 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-epsilon 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 degrees 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.