Dynamic recrystallization and hot deformation mechanisms of a eutectic Al0.7CoCrFeMnNi high-entropy alloy

Abstract

The deformation mechanisms and microstructural evolution of an Al0.7CoCrFeMnNi high-entropy alloy (HEA) composed of dual phases (FCC phase: 56.6 vol% and BCC phase: 43.4 vol%) have been studied during hot compressive deformation in the temperature range between 1173 and 1373 K and in the strain rate range between 10−3 and 10 s−1 up to a strain of 0.8. Among the AlxCoCrFeMnNi HEAs (with x = 0, 0.5, 0.7 and 1.0) from earlier studies and in the present study, the Al0.7CoCrFeMnNi alloy produced the finest grain size (1–46 µm) and the highest fraction of dynamically recrystallized grains (39–99%) after hot deformation, implying that the most effective grain refinement can be achieved from a eutectic microstructure. Continuous dynamic recrystallization (CDRX) was the main DRX mechanism in both the FCC and BCC phases, but the kinetics of CDRX was faster in the BCC phase, resulting in formation of a higher fraction of dynamically recrystallized grains in the BCC phase under the same deformation condition. The stress exponent associated with plastic flow at low strain rates was approximately 3. The steady-state constitutive relation linking the flow stress and the strain rate could be well interpreted in terms of either viscous glide creep with antiphase boundary interactions (when the BCC phase is assumed to be the B2 phase at high temperatures) or viscous glide creep with Cottrell-Jaswon interactions (when the BCC phase is assumed to be the disordered BCC (A2) phase at high temperatures).