Low core losses and magnetic properties of Fe85-86Si1-2B8P4Cu1 nanocrystalline alloys with high B for power applications (invited)

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Abstract
Recently, the energy crisis and the continued growth in electrical power generation strongly demand minimization of wasteful energy dissipation. Magnetic core loss (W) is the main source of energy dissipation in motors and transformers. This requires the development of soft magnetic materials with low coercivity (Hc) and high magnetic flux density (B). Fe-rich Fe85-86Si1-2B8P4Cu1 (at. %) alloy ribbons made from industrial raw materials (containing some impurities) with 6 mm in width have a heteroamorphous structure containing a large number of extremely small Fe grains (less than 3 nm), resulting from the unique effects of P and Cu addition in proper amounts. Crystallization of these alloys by annealing shows a uniform precipitation of α-Fe, leading to a uniform nanocrystallized structure of α-Fe grains, 16–19 nm in size, accompanied by an intergranular amorphous layer about 1 nm in width. The wide ribbons exhibit high B of 1.82–1.85 T (at 800 A/m), almost comparable to commercial oriented Fe–3 mass% Si alloys. Excellent magnetic softness (low Hc of 2.6–5.8 A/m, high permeability of 2.4–2.7 × 104 at 1 kHz and small saturation magnetostriction of 2.3–2.4 × 10−6) along with high electrical resistivity (0.67–0.74 μΩ m) of these alloys result in superior frequency characteristics of core losses and a much lower W at 50 Hz up to the maximum induction of 1.75 T, in comparison to the silicon steels now in practical use for power applications.

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