Flow behavior and microstructures of powder metallurgical CrFeCoNiMo0.2 high entropy alloy during high temperature deformation

Dynamic recrystallization (DRX) refine grains of high entropy alloys (HEAs) and significant improve the mechanical property of HEAs, but the effect of high melting point element molybdenum (Mo) on high temperature deformation behavior has not been fully understood. In the present study, flow behavior and microstructures of powder metallurgical CrFeCoNiMo_0.2 HEA were investigated by hot compression tests performed at temperatures ranging from 700 to 1100 °C with strain rates from 10⁻³ to 1 s⁻¹. The Arrhenius constitutive equation with strain-dependent material constants was used for modeling and prediction of flow stress. It was found that at 700 °C, the dynamic recovery is the dominant softening mechanism, whilst with the increase in compression testing temperature, the DRX becomes the dominant mechanism of softening. In the present HEA, the addition of Mo results in the high activation energy (463 kJ mol⁻¹) and the phase separation during hot deformation. The formation of Mo-rich σ phase particles pins grain boundary migration during DRX, and therefore refines the size of recrystallized grains.