Soft magnetic Fe-Co-based amorphous alloys with extremely high saturation magnetization exceeding 1.9 T and low coercivity of 2 A/m

Extremely high saturated magnetization (Bs) of 1.92 T in conjunction with low coercivity (Hc) of 2 A/m was found to be achieved for (Fe0.8Co0.2)85B14Si1 amorphous alloy. The high Bs above 1.9 T was the first evidence for amorphous alloys. The slight increase of B to 15%B reduces Bs to 1.88 T. The high Bs of 1.92 T is much higher than that (1.63 T) for the new commercial Fe-B-Si-C amorphous alloy and comparable to commercial Fe-Si steels. The excellent soft magnetic properties, which cannot be obtained for all soft magnetic alloys including amorphous, nanocrystalline and crystalline alloys reported to date, were obtained by annealing the as-spun amorphous alloy ribbon for 600 s at 593 K in a magnetic field of 15.9 kA/m. The high Bs above 1.9 T was obtained in a rather wide annealing conditions of 543–603 K and 300–1200 s, indicating the ease of achieving the excellent soft magnetic properties. No appreciable crystalline phase is recognized in the annealed ribbon even by HRTEM and electron diffraction pattern. The effective permeability at 1 kHz also exhibits high values above 20000 and the Curie temperature also shows high values above the onset temperature of crystallization corresponding to high thermal stability of soft magnetic properties. Besides, the (Fe0.8Co0.2)84B15Si1 and (Fe0.8Co0.2)85B14Si1 amorphous alloys exhibit good bending ductility even in the optimal annealed state. The corrosion resistance in 3.5 mass% NaCl aqueous solution is better than that for the commercial Fe-Si-B-C amorphous alloy. The first synthesis of the Fe-based amorphous alloy having simultaneously high Bs above 1.9 T, low Hc of about 2 A/m, high effective permeability, high Tc and good bending ductility is promising for future extension of amorphous alloys as engineering soft magnetic materials.