Significant reduction in intrinsic coercivity of high-entropy alloy FeCoNiAl0.375Si0.375 comprised of supersaturated f.c.c. phase

Abstract

We successfully demonstrated that a significant reduction in intrinsic coercivity (HCI) of high-entropy alloy FeCoNiAl0.375Si0.375 is achievable when the alloy is comprised of supersaturated f.c.c. phase. We further investigate the evolution of magnetic properties of the nanocrystalline high-entropy alloy powder as a function of temperature. The x-ray diffraction (XRD) and transmission electron microscopy (TEM) studies indicated the presence of the f.c.c. phase. At 300 K, HCI, magnetic saturation (MS), and remanent magnetization (MR) of the nanocrystalline FeCoNiAl0.375Si0.375 alloy were approximated as ∼5.1 kAm−1, ∼90.8 Am2kg−1, and ∼3.7 Am2kg−1, respectively. The alloy comprised of predominantly the f.c.c. phase exhibited a significant reduction in HCI (by ∼2 to 3 times) in comparison to the alloys of similar compositions fabricated by various techniques. At cryogenic temperatures, MS increased while HCI and MR displayed negligible effect with a decrease in temperature. At elevated temperatures, both MS and HCI decreased with increment in temperature up to 800 K. The thermal treatment (400–800 K) of the as-fabricated powders resulted in an increase in MS and a decrease in both HCI and MR. While fabrication by various methods results in the formation of two-phases—the b.c.c. phase and the f.c.c. phase, fabrication by mechanical alloying facilitated the formation of predominantly the supersaturated f.c.c. phase, having significantly low HCI and good thermal stability.