Low core losses and magnetic properties of Fe_85-86Si _1-2B₈P₄Cu₁ nanocrystalline alloys with high B for power applications (invited)

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 (H_c) and high magnetic flux density (B). Fe-rich Fe _85-86Si_1-2B₈P₄Cu₁ (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 -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 H_c 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 μδm) 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.