Effect of Processing and Heat Treatment on the Phase Kinetics, Microstructure, and Hardness Behavior of CoCrFeMnNi High Entropy Alloy

Abstract

In this study, an equiatomic CoCrFeMnNi high entropy alloy (HEA) was prepared by powder metallurgy (PM) and casting methods. Both processed HEAs exhibited face-centered cubic (FCC) and Cr-rich sigma (σ) phases. To mitigate the presence of undesirable Cr-rich σ phase, heat treatment was performed at 800 °C, 1000 °C, and 1200 °C for 5 hours. The effects of heat treatment (HT) temperature on phase, microstructure, and hardness properties of HEAs were investigated. The PM-processed HEA exhibited superior microhardness (~408 ± 10 HV), nanohardness (~6.54 GPa), and elastic modulus (~254.29 GPa) compared to the as-cast HEA due to its fine-grained and uniform microstructure. However, increasing heat treatment temperatures caused a reduction in hardness and elastic modulus in both processed HEAs, due to grain coarsening and reduced fraction of the Cr-rich σ phase. The present study highlights the critical role of heat treatment in optimizing the phase, microstructure, and hardness behavior of HEAs produced by PM and casting techniques.