Investigation on microstructure, superior tensile property and its mechanism in Al0.3CoCrFeNi high-entropy alloy via thermo-mechanical processing

In this study, the fully annealed Al0.3CoCrFeNi high entropy alloy (HEA) with single-phase face-centered cubic (FCC) was cryo-rolled and isochronal annealed at different temperatures from 1123 K to 1473 K for 1 h. The effects of annealing temperature on microstructure, grain boundary evolution, and mechanical properties, especially the deformation mechanism of cryo-rolled Al0.3CoCrFeNi alloys were systematically investigated using XRD, EBSD, TEM, microhardness, and tensile tests. A partial recrystallization was achieved after annealing in the 1123 K and 1223 K temperature ranges, which was mainly attributed to that the precipitation of B2 phase can effectively improve the nucleation rate of phase boundary and play a barrier role in growth of grain. Addi-tionally, The remarkable combination of strength (yield strength of-911 MPa and ultimate tensile strength of-1146 MPa) and ductility (fracture elongation of-23%) achieved in cryo-rolled Al0.3CoCrFeNi alloy annealed at 1123 K with heterogeneous microstructure was mainly due to the contributions of back stress and grain size. It was noticeable that the FCC -> 9R phase -> twin transformation was found in cryo-rolled Al0.3CoCrFeNi HEA annealed at 1473 K during the tensile deformation, which indicated that twin-induced plasticity and phase transformation induced plasticity were reason for the outstanding ductility and strain hardening ability of this sample. This research are important not only for understanding the strengthening mechanisms of HEAs with various microstructure in general, but also for guiding thermo-mechanical processing of single-phase FCC HEAs.

Automated summary

In this study, the effects of different annealing temperatures on the microstructure, grain boundary evolution, and mechanical properties of cryo-rolled Al0.3CoCrFeNi alloys were systematically investigated. A partial recrystallization was achieved at specific annealing temperatures, contributing to the improvement of nucleation rate and hindrance of grain growth. The cryo-rolled Al0.3CoCrFeNi alloy annealed at 1123 K exhibited a remarkable combination of strength and ductility, mainly due to back stress and grain size contributions. Furthermore, the FCC -> 9R phase -> twin transformation was observed in the cryo-rolled Al0.3CoCrFeNi HEA annealed at 1473 K, which explained its outstanding ductility and strain hardening ability.