Magnetic Crystalline Transition Metal Ribbons Prepared by Melt-Spinning and Reactive Annealing

Abstract

Transition metal alloys are often difficult to be prepared as amorphous ribbons by conventional methods. If boron is added to these alloys, amorphous ribbons may be prepared by melt spinning. These amorphous ribbons have a better workability than the crystalline ones. However, their composition is different from the target composition. Upon annealing treatments in flowing hydrogen the boron may be extracted and the ribbon crystallizes. Thermodynamically, the extraction of boron proceeds by the reaction of hydrogen with the borides formed during the crystallization of the ribbons. In order to investigate this extraction in more detail Fe80B20 amorphous ribbons were used. Thermogravimetric measurements were performed at three different heating rates, which permitted to develop a thermokinetic description of the extraction process. It is controlled by chemical reactions and diffusion. The description allows to calculate the degree of boron extraction for various annealing procedures. After the extraction of boron the ribbon becomes a single phase. Various soft magnetic alloys can be prepared by this method. For Fe15Co10Si, the coercivity is 36 A/m and the saturation polarization is 1.45 T. Core losses in sinusoidal magnetic field measured at 50 Hz to 500 Hz at 1 T are 1.36 W/kg to 18 W/kg.