Microstructural Evolution and Tensile Properties of AlCoCrFeNi High-Entropy Alloy Associated with B2 Precipitates.

The room-temperature strength of AlCoCrFeNi high-entropy alloys (HEAs) is relatively low owing to its intrinsic fcc structure. In the present study, the as-cast HEAs were subjected to cold rolling and subsequent annealing treatment (800, 900, and 1000 °C) to adjust the microstructures and tensile properties. This treatment process resulted in the partial recrystallization, full recrystallization, and grain coarsening with increasing the annealing temperature. It was found that the large and spherical B2 precipitates were generated in the recrystallized grain boundaries of three annealing states, while the small and elongated B2 precipitates were aligned along the deformation twins in the non-recrystallized region of the 800 °C-annealing state. The former B2 precipitates assisted in refining the recrystallized grains to quasi ultra-fine grain and fine grain regimes (with the grain sizes of ~0.9, ~2.2, and ~7.2 μm). The tensile results indicated that the decreased annealing temperature induced the gradual strengthening of this alloy but also maintained the ductility at the high levels. The yield strength and ultimate tensile strength in 800 °C-annealed specimen were raised as high as ~870 and ~1060 MPa and the ductility was maintained at ~26%. The strengthening behavior derived from the heterogeneous microstructures consisting of quasi ultra-fine recrystallized grains, non-recrystallized grains, deformation twins, dislocations, and B2 precipitates. Current findings offer the guidance for designing the HEAs with good strength and ductility.