Microstructural Evolution and Mechanical Properties of Al0.5CoCrFeNi High-Entropy Alloy after Cold Rolling and Annealing Treatments

The present study investigated the microstructure and mechanical properties of as-cast, homogenized, cold-rolled, and annealed Al0.5CoCrFeNi high-entropy alloy. The microstructure is characterized by optical microscopy, XRD, and scanning electron microscopy (SEM) equipped with energy-dispersive x-ray spectroscopy (EDS). Besides, hardness is acquired by Vickers hardness testing, and tensile testing is performed at room temperature for all samples. Results indicate that the matrix and droplet-shaped phases are present in all states. However, the needle-shaped and wall-shaped phases present after homogenization. In all samples, the matrix consists primarily of Fe, Cr, Co, and Ni, while droplet-shaped phases comprise mainly Al-Ni. Moreover, needle-shaped phases are replete with Cr, Ni, Co, Al, and Fe, whereas wall-shaped phases are rich in Cr, Co, and Fe and depleted in Al-Ni. The hardness of the Al0.5CoCrFeNi HEA increases after homogenizing and culminates at cold-rolled to 425 H-v due to the emerging of the needle and wall-shaped phases and consequently lattice distortion. The yield strength (YS), the ultimate tensile strength (UTS), and the ductility (epsilon(f)) of the cold-rolled specimen are about 545 MPa, 834 MPa, and 26%, respectively. The noticeable improvement in hardness and strength in cold-rolled condition demonstrates a remarkable work-hardening effect without sacrificing much ductility.