Hot deformation behavior of CoCrFeMnNi FCC high entropy alloy

Abstract

Hot deformation behavior of an equiatomic CoCrFeMnNi high entropy alloy was investigated. Hot compression tests were carried out at various temperatures ranging from 800 °C to 1000 °C at different strain rates from 0.001s−1 to 1s−1. Stress-strain curves indicated softening due to dynamic recrystallization (DRX) under most conditions. Flow stress analysis was carried out by using Arrhenius type hyperbolic-sine relationship, and a linear dependence of flow stress on Zener-Hollomon parameter (Z) was found. Based on the flow stress analysis, a constitutive equation was formulated for describing interdependency between deformation temperature, strain rate, flow stress and strain. The estimated apparent activation energy (Q) ∼350 kJmol-1 for the hot deformation was approximately similar to the activation energy for diffusion of the slowest diffusing element Ni in this alloy. Microstructural observations were carried out by electron backscatter diffraction (EBSD). The EBSD analysis indicated that the DRX grains nucleated along initial grain boundaries resulting in necklace like structures. The fraction and size of DRX grains showed a strong dependence on Z. Textures of deformed and DRX grains were found to be similar to each other, but rather weak. This feature could be attributed to the nucleation of dynamic recrystallization without any preferential orientation selection.