Morphology and magnetic properties of rapidly quenched Fe-B alloys

Abstract

Crystallization kinetics and the effect of annealing on the microstructure, morphology and magnetic properties of rapidly quenched Fe-B alloys are studied in this paper. Fe-B ribbons with different boron content were prepared ranging from 12 to 25 at%, covering the extended glass formability limit in hypoeutectic compositions to hypereutectic limit. Fe-B alloys were prepared by planar flow casting in the form of ribbons approximately 20 µm thick and 6 mm wide. The chemical compositions are Fe75B25, Fe80B20, Fe83B17, Fe86B14 and Fe88B12. Resistivity measurements were taken place at different heating rates, illustrating the phase transformations, aiding in the calculation of Avrami and Kissinger parameters. Soft magnetic properties of the Fe-B alloys were investigated by hysteresis loop measurements before and after annealing. XRD, DSC, TGA and TEM measurements illustrated the mechanisms of the crystallization process. The crystallization of Fe100-xBx amorphous alloys containing <17 at% Boron occurs by two stages of reaction. In this work, the crystallization process and Curie temperature for Fe100-xBx (12 < x < 25) are studied. Ribbons with boron content above 12 at% were found to be fully amorphous; small amount of quenched-in nano-crystallinity was present in the as-cast alloy with 12 at% B. Each composition has been annealed to achieve 5 %, 50 % and 95 % of crystallinity. In the first stage of crystallization, α-Fe phase with bcc structure crystallizes from amorphous matrix.