Hot Deformation Behavior and Hardness of a CoCrFeMnNi High-Entropy Alloy with High Content of Carbon

A CoCrFeMnNi high-entropy alloy with a high content of carbon was synthesized, and its hot deformation behavior was studied at the temperatures 800-1000 °C at the strain rates ranging from 0.001 to 0.1 s^-1. As-prepared alloy is a face-centered cubic-structured solid solution, with a large amount of carbides residing at grain boundaries. True stress-strain curves were employed to develop the constitutive equation of apparent activation energy. The apparent activation energy (Q) was found to be 423 kJ mol^-1, indicating a dynamic flow softening behavior. The size of dynamic recrystallized (DRXed) grains increases with increasing the temperature or decreasing the strain rate. A processing map was sketched on the basis of the flow stress. The temperature range of 900-1000 °C and 10^-3-10^-2.6 s^-1 strain rate were found to be the optimum hot-forging parameter. With increasing temperature or decreasing strain rate, the volume fraction of fine carbides (≤?1 μm) increases. A lot of coarse carbides can be found in the matrix after deformation at 800 °C, which leads to a high hardness value of 345 HV. The carbides after deformation at 1000 °C are mainly nano-sized M₇C₃ and M₂₃C₆, which can promote the nucleation of DRX.