A Study on the Phase Formation and Magnetic Properties of FeNiCoCuM (M = Mo, Nb) High-Entropy Alloys Processed Through Powder Metallurgy

Multi-phase FeNiCoCuMo and FeNiCoCuNb high-entropy alloys were successfully synthesized via mechanical alloying and hot pressing. FeNiCoCuNb and FeNiCoCuMo formed a face-centered cubic solid solution for 15 and 30 hours of milling, respectively. At longer milling times, both alloys were constituted by amorphous phases. The samples hot-pressed at 1000 °C exhibited a major face-centered cubic phase and intermetallic phases: C14 Laves phase in FeNiCoCuNb alloy, and σ and µ phases in FeNiCoCuMo alloy. Semi-hard magnetism was found in sintered FeNiCoCuMo and FeNiCoCuNb alloys, associated with an extensive amount of phase boundaries. The FeNiCoCuMo alloy presented a saturation magnetization (M_s) of 62.63 emu g⁻¹ and coercivity (H_c) of 40.69 Oe. By substituting Mo for Nb, the M_s value was reduced to 53.27 emu g⁻¹, while the coercivity was increased up to 53.49 Oe. The presence of hard intermetallic phases and solid-solution strengthening led to high-hardness FeNiCoCu-based high-entropy alloys. Although Nb increased the microhardness and electrical resistivity of the alloy, it also reduced the soft magnetic properties of the alloys. Better magnetic properties were found by the addition of Mo, suggesting that tailoring its content could conduct to obtain an excellent balance between mechanical and soft magnetic properties in the FeNiCo-based high-entropy alloys.