Tuning AC magnetic properties of FeCoNi1+xCu1-xAl (0 ≤ x ≤ 1.0) high-entropy alloys by adjusting Ni and Cu content

In this work, the AC magnetic properties and microstructure of FeCoNi1+xCu1-xAl (0 ≤ x ≤ 1.0) high-entropy alloys (HEAs) are studied. The results show that the total loss (Ps), AC coercivity (AC Hc), and AC applied field (AC Hm) are improved by adjusting the amounts of Ni and Cu. When x = 0.1, Ps, AC Hc, and AC Hm of the alloy at 50 Hz decrease by 40 %, 41 %, and 43 %, respectively. When x = 0.7, the alloy has optimised magnetic properties, and Ps, AC Hc, and AC Hm of the alloy at 50 Hz decrease by 77 %, 78 %, and 82 %, respectively. The Ps is divided into hysteresis loss (Ph) and eddy current loss (Pe). When f ≤ 100 Hz, Ph is the dominant contributor to Ps, while when f ≥ 850 Hz, Pe is the dominant contributor. At the same frequency, Ph is closely connected with AC Hc, and AC Hm, and Pe is inversely proportional to ρ. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the alloys consist of a mixture of face-centred cubic (FCC) and body-centred cubic (BCC) phases. As x increases, the elemental distributions of FCC and BCC phases clearly change. Transmission electron microscopy (TEM) shows that there are many Cu-rich nano-precipitates in the BCC phase. Compared with the alloy where x = 0, nano-precipitates of the alloy where x = 0.1 have shorter lengths, lower distribution densities, and more uniform size. Our work provides an effective approach to explore novel soft magnetic materials.