Improved tensile properties of Al_0.5CoCrFeNi high-entropy alloy by tailoring microstructures

The effect of heat treatment on microstructure and tensile properties of as-cast Al_0.5CoCrFeNi high-entropy alloy was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), and tensile tests. The results show that heat treatment strongly affects the microstructure, particularly the morphology of bcc phases, and improves tensile properties. Microstructure analysis reveals that rod-shaped and elliptoid phases appear in the matrix after heat treatment at 1150 °C. Besides, under 850 °C heat-treated condition, ultimate tensile strength increases by about 60% without sacrificing much plasticity, which can be attributed to the content of bcc phases and fine precipitates dispersed in the dendrites. For other heat-treated conditions, tensile ductility increases by at least 30%, especially 60% for heat treatment at 450 °C, and strength also improves. Fracture analysis indicates that the fracture mode of heat treatment at 850 °C is a mixture of quasi-cleavage and ductile fracture, while the other heat-treated conditions show the mode of ductile fracture.