Fabrication And Magnetic Properties Of FINEMET Alloy Powder Cores

In the21st century, modern electronic devices become more and more miniaturized. In recent years, the Fe73.5Cu1Nb3Si13.5B9(FINEMET) ribbons have been widely used for its excellent soft magnetic properties. Amorphous ribbons of about25-30μm in thickness were prepared by the melt spinning method. After annealing the ribbons at823-860K for1h, nanocrystalline grain a-Fe(Si) of10-20nm dispersed in a residual amorphous matrix and show a good property. But the shape of these alloys is limited to ribbons and wires due to process of rapidly solidification, show insufficient in middle and high frequency applications. To solve these problems, the FINEMET powders are prepared by ball milling and compacted into toroidal cores after mixed with passivator and binder. The toroidal powder cores were annealed to relieve the stress and to crystallize the amorphous structure in a optimal temperature under a nitrogen atmosphere.Comparing with the ribbons, FINEMET powder cores are suitable for compaction and densification in various shapes,and can be previously insulated to increase their electrical resistivity, leading to a higher using frequency.In this paper, melt-spun amorphous Fe73.5Cu1Nb3Si13.5B9(at.%) ribbons were ball-milled to obtain powders. The powders were sieved and passivated in0.2-1.0wt%Phosphoric acid solution to form a well-coated passivator layer, followed by cold compaction under the pressure of1.64-1.96GPa to prepare toroidal magnetic cores. The powder cores were annealed at400-600℃to relief the internal stress and to optimize the crystalline grain size. After annealed at500℃for1h, a-Fe(Si) crystallites with an average grain size of14.3nm were embedded in the amorphous matrix. Combined with the insulation of each powder and the two-phase structure, the powder core exhibits excellent magnetic properties.