Hot deformation behavior analysis of as-cast CoCrFeNi high entropy alloy using Arrhenius-type and artificial neural network models

An as -cast equiatomic CoCrFeNi high entropy alloy was investigated through hot compression tests conducted at various temperatures ranging from 700 to 1000 degrees C and different strain rates ranging from 0.001 to 0.1 s -1 . The flow stress curves were analyzed and modelled using both Arrhenius-type hyperbolic -sine relationship and artificial neural network (ANN) modeling. While the Arrhenius-type modeling yielded satisfactory results, the ANN modeling exhibited better fit between the experimentally obtained and predicted stress values. Based on the experimental results, the calculated apparent activation energy for the hot deformation process was determined to be 541.6 kJ mol -1 at the strain of 0.8. For the as -cast high entropy alloy with large grain size in comparison to wrought alloy, the electron backscatter diffraction (EBSD) analysis revealed that a small fraction of dynamically recrystallized grains appears primarily along the initial grain boundaries (necklace formation), but only at high deformation temperatures. This phenomenon was attributed to the limited number of nucleation sites arising from the larger grain size, which in turn delays dynamic recrystallization (DRX) to larger strains and/or higher temperatures during thermomechanical processing.