Establishing processing-microstructure-property paradigm in complex concentrated equiatomic CoCuFeMnNi alloy

Abstract

Hot deformation behavior of equiatomic FCC CoCuFeMnNi complex concentrated alloy has been investigated via isothermal compression tests on Gleeble-3800 thermo-mechanical simulator in the temperature (T) range of 1073–1273 K and strain rate (ε˙) range of 1–10−3 s−1. This has been aided with detailed microstructural analysis using SEM, EBSD and TEM to decipher the deformation micro-mechanisms during hot compression tests. The processing maps have been constructed by superimposition of the instability map with efficiency map and the optimum thermo-mechanical processing conditions were found to be T = 1173 K, ε˙ = 10−3 s−1 and T = 1273 K, ε˙ = 10−2 s−1. Microstructural investigation using SEM and EBSD reveal phase separation between Cu-rich and Cu-lean regions wherein Cu-rich FCC phase at the grain boundaries undergoes discontinuous dynamic recrystallization (DDRX) while the Cu-lean phase undergoes dynamic recovery (DRV). The average activation volume in the range of 44–250 b3 suggest that cross slip is the rate controlling mechanism during the deformation and activation energy of 394 kJ/mol, that is almost twice than that for diffusion in copper, indicate contribution from both mechanical and thermal component to the overall activation energy. It is evident that the diffusion assisted copper segregation aids in obtaining higher efficiency of deformation and easy processability due to a unique microstructure comprising of Cu-lean grains surrounded by soft Cu-rich grains near grain boundaries which undergo DDRX. Numerical simulations using finite element method are able to correctly predict hot deformation behavior, establishing the processing-microstructure-property paradigm in CoCuFeMnNi complex concentrated alloy. © 2019 Elsevier B.V.