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

Abstract

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.