Effect of Mo addition on AC soft magnetic property, hardness and microstructure of FeCoNiMox (0 ≤ x ≤ 0.25) medium entropy alloys

The FeCoNi medium entropy alloy (MEA) has good alternating current (AC) magnetic properties but poor mechanical properties. This limits its application in soft magnetic materials. In this work, the effects of adding a small amount of Mo on the soft magnetic properties, hardness, and microstructure of FeCoNiMox (0 ≤ x ≤ 0.25) MEAs were investigated. The results indicate that a suitable addition of Mo can simultaneously improve the AC soft magnetic properties and hardness of the alloys. When x = 0.15, the total loss (Ps), AC coercivity (AC Hc), and maximum AC applied magnetic field (AC Hm) of the alloy were improved by 41%, 37%, and 38% over those of the x = 0 alloy, respectively. When x = 0.25, the nano-hardness of the alloy is 91% higher than that of the x = 0 alloy. The results of the microstructure analysis show that the appropriate addition of Mo homogenized the microstructure and refined the grains of the alloys. Meanwhile, the addition of Mo also led to the appearance of two FCC phases with alternating distribution and inhibited the formation of dislocation in the alloys. The mechanisms of adding elemental Mo to improve the soft magnetic properties and hardness of the alloys are discussed. Our work provides an effective way to enhance the soft magnetic and mechanical properties of MEA simultaneously.