The effects of Al on the soft magnetic properties of nanocrystalline Fe73.5−xAlxCu1Nb3Si13.5B9 alloy ribbons are investigated in the composition range of 0≤x≤1.0. The relative initial permeability at 1 kHz is found to increase by the addition of Al, and reaches the peak value at x=0.1. The coercivity decreases, rather significantly, with the Al content in the whole composition range investigated in the present work, the values of the coercivity being 12.5 mOe at x=0 and 9.3 mOe at x=1.0. The magnetic induction at an applied field of 10 Oe, however, decreases moderately by the introduction of Al, possibly due to the dilution effect. The improvement in the soft magnetic properties is considered to result from the reduction in the grain size of the α Fe-Si solid solution phase of the Al-added alloy ribbons, which has been observed by transmission electron microscopy. Another factor may be due to the decrease in the intrinsic magnetocrystalline anisotropy K1 as Al is added to the alloy.

The effect of Cu and/or Nb addition on crystallization processes and soft magnetic properties for Fe-Si-B alloys has been investigated. For Fe-Si-B, Fe-Cu-Si-B, and Fe-Nb-Si-B alloys annealed at various temperatures, the effective permeabilities were very low and decreased considerably as they crystallized, while for Fe-Cu-Nb-Si-B alloy annealed at a temperature above Tx , a very good soft magnetic property was obtained. From DTA analysis of Fe-Cu-Nb-Si-B alloys, it became clear that the combined addition of Cu and Nb expanded largely the temperature range over 100 °C where a single phase of α-Fe solid solution can exist. Above 580 °C, the second crystalline phase such as Fe2 B and some unidentified phases other than the α-Fe phase precipitated, and soft magnetic properties deteriorated rapidly. It is concluded that the combined addition of Cu and Nb makes the α-Fe single phase stable in a broad temperature range, which is considered to be the necessary condition for the superior soft magnetic properties.

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The magnetostriction of melt-spun ribbons of Dy, (Fe, -,B,,), --x (x =0.2,0.25,0.3; Osy ~0.2) alloys is systematically investigated as a function of the wheel speed during melt quenching. As the wheel speed increases from 10 to 50 m/s, the magnetic softness improves with the wheel speed rather continuously for the alloys with the Dy content x=0.2 and 0.25 but it exhibits a maximum at the wheel speed of 30 or 40 m/s for the alloys with the highest B content (x=0.3). The softness also improves with the B content for a fixed wheel speed. Homogeneous and ultrafine grain structure is observed for the first time even in the as-spun state when the ribbons. of the alloy Dya,a(Fe,,sB,J,, are fabricated at the wheel speed of 30 m/s. The ribbon having the ultraflne grain structure exhibits good magnetic softness together with a high strain.

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