Structural Evolution and Mechanical and Magnetic Properties of Nonequiatomic CoFe₂NiMn_0.3Al_x (0.25 ≤ x ≤ 1.00) High-Entropy Alloys

CoFe₂NiMn_0.3Al_x (x = 0.25, 0.50, 0.75, 1.00) alloys were prepared using the arc melting method, and their crystal structure, microstructure, and mechanical properties were systematically studied. The results show that a greater Al content beneficially alters the crystal structure of the alloys from a single FCC phase to a mixture of FCC + BCC phases. With increasing Al content, the volume fraction of the BCC phase increases steadily, whereas the volume fraction of the FCC phase substantially decreases. With increasing Al content, the yield strength and hardness of the CoFe₂NiMn_0.3Al_x alloys increases, whereas their ductility gradually decreases. Among the studied alloys, that with x = 0.75 exhibits both high strength and good ductility and its yield strength, fracture strength, and fracture strain are 1100 MPa, 2335 MPa, and 33.24%, respectively. Measurements of magnetic properties indicated that the saturation magnetization increases from 90 emu g⁻¹ for the Al_0.25 alloy to 148 emu g⁻¹ for the Al_1.00 alloy. The results show that the CoFe₂NiMn_0.3Al_x high-entropy alloys are potential candidates to serve as magnetic materials in industrial applications.