Influence of Process Parameters on Microstructure Evolution During Hot Deformation of a Eutectic High-Entropy Alloy (EHEA)

Abstract

High-entropy alloys (HEAs) have shown unique combinations of strength and ductility along with other properties after optimized thermomechanical processing (TMP). In this study, the hot deformation of an AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) was studied by using a Gleeble 3800® thermomechanical simulator at 800 °C, 1000 °C and 1200 °C deformation temperature under different strain rates of 10−4, 10−2, and 1 s−1. The influence of strain rate and temperature on the evolution of the microstructure was discussed. The apparent activation energy (Q), stress exponent (n) and Zener–Holloman parameter (Z) were determined from the true stress–strain curves to develop the constitutive equation. The activation energy was determined to be 336 kJ/mol, and the stress exponent (n) was 2.5. Microstructures, characterized using electron-backscattered diffraction (EBSD), were analyzed as a function of (Z) values and interpreted in terms of solute diffusion and the interactions between dynamic softening (dynamic recovery and dynamic recrystallization) and hardening (dynamic precipitation) phenomena. It was found that the hot deformation behavior of EHEAs was controlled by pipe diffusion for the selected process parameters. The pipe diffusion coefficient of Ni increased with increasing strain rate at constant deformation temperature, whereas the lattice diffusion coefficient remained constant for all the examined strain rates. Dynamic recovery (DRV) was the dominant softening mechanism at lower temperatures irrespective of strain rates, while dynamic precipitation played a critical role in the inhibition of dynamic recrystallization (DRX) under these conditions. At higher temperatures and for all the strain rates, microstructure evolution was controlled by the DRX mechanism.