Phase evolution, structure, and magnetic characterization of mechanosynthesized Co40Fe30Ni30 medium-entropy alloy

Abstract

We demonstrate Co40Fe30Ni30 medium-entropy alloy is a suitable Co-rich ternary CoxFeyNiz (x ≥ y ≥ z) alloy precursor for designing high-entropy magnetic alloys having superior semi-hard magnetic properties. Mechanical alloying of the constituent metal powders 40 at.% Co, 30 at.% Fe, and 30 at.% Ni for 12 h resulted in a nanocrystalline Co40Fe30Ni30 alloy comprised of the γ phase. The alloy exhibited semi-hard magnetic behavior at ambient temperature; the intrinsic coercivity (HCI) and saturation magnetization (MS) was ~4.35 kA/m and ~141 Am2/kg, respectively. At sub-ambient temperatures, the alloy maintained semi-hard magnetic behavior; both HCI and MS increased by ~1.4 times and ~4%, respectively, from 300 K to 60 K. The estimated μH (the maximum magnetic moment per atom) was ~1.51 μB. At elevated temperatures, up to T ≤ ~570 K, the as-prepared alloy powder maintained the γ phase, and after that α phase precipitated out. Thermal-treatment increased MS by ~13% and decreased HCI by ~31%, yet the alloy retained semi-hard magnetic behavior. At cryogenic temperatures, the thermally-treated alloy powders exhibited magnetic behavior similar to that of as-prepared alloy powder, i.e., both HCI and MS increased with the decrease in T. Grey relational analysis proposed Co40Fe30Ni30 as a suitable medium-entropy alloy precursor for designing novel high-entropy magnetic alloys having superior semi-hard magnetic properties.