Fe-Based Soft Magnetic Alloys Composed of Ultrafine Grain Structure

Abstract

Magnetic properties of Fe–Cu–M–Si–B (M: Nb, Mo, Ta, W, etc.) alloys were investigated for development of new Fe-based soft magnetic alloys. The alloys were first formed into the amorphous ribbons, and then annealed above the crystallization temperature. The annealings gave rise to excellent soft magnetic properties which correspond to those of Co-based amorphous alloys. Especially, the alloys containing Cu and Nb were superior to the alloys containing other elements. These new alloys were composed of ultrafine grain structure. The grains were about 10 nm in diameter and the main crystalline phase was presumed to be a bcc Fe solid solution which contains Si and B. This might be attributed to the nucleation process of the bcc Fe–Si–B solid solution influenced by Cu and the suppression of the grain growth by Nb. The newly developed alloys are suitable for many kinds of magnetic components such as saturable reactors, choke coils and transformers, because of their excellent soft magnetic properties and high saturation flux density.