Formation, thermal stability and soft magnetic properties of Fe-Co-B-Si amorphous alloys with ultrahigh saturation magnetic induction of 2.0 T

This paper studies the influence of metallic element composition on the formation ability, thermal stability and magnetic properties of melt-spun (Fe 1-x Co x )B 15–19 Si 1 (x =0.2–0.4) amorphous alloy ribbons. The maximum metal concentration at which an amorphous phase is formed during melt spinning has been determined in conjunction with the metal content dependence of crystallization processes and crystallized phases. The amorphous (Fe 0.8 Co 0.2 ) 84 B 15 Si 1 alloy with the highest metal content in an optimally annealed state exhibits an extremely high saturation induction (M S ) of 2.0 T, low coercive force of 7.6 A m −1 , high effective permeability of 13500 at 1 kHz and low core losses of 5.5 W kg −1 at 100 mT and 19.7 W kg −1 at 200 mT at 10 kHz which have not been simultaneously obtained for all kinds of soft magnetic materials up to date. The replacement of Fe with Co significantly increases the Curie temperature of the amorphous phase, resulting in very high thermal stability of the high M S alloys. The combination of excellent soft magnetic properties with ultrahigh M S value makes them candidates for use in highly loaded high-speed electric motors capable of operating at temperatures up to 473 K. • Amorphous FeCoBSi alloy ribbons were studied in as-spun and annealed states. • The boundary of amorphous phase formation was located at the (Fe+Co) content of 84 %. • The increase of metal content changes crystallization process of amorphous phase. • Soft magnetic characteristics of optimally annealed amorphous alloy exceed those for commercial Fe-Si electrical steel.