On the effect of cooling rate during melt spinning of FINEMET ribbons

Abstract

The effect of quenching wheel speed on the structure and Curie temperature of Fe_73.5Si_13.5B₉Nb₃Cu₁ alloy has been investigated using X-ray diffraction, differential scanning calorimetry, transition electron microscopy and a SQUID magnetometer. Ribbons were melt-spun at different wheel speeds and then were annealed to nucleate nano crystals embedded in the amorphous matrix. The results indicated that the thickness of the ribbons was inversely proportional to the wheel speed following the power law of the type t ∝ V_s^−1.231. DSC and XRD results showed that at higher wheel speeds the greater potential energy triggers the formation of Fe (Si) crystallites and thus, increases the crystallinity. TEM observations confirmed the presence of an α-Fe (Si) phase with ∼11 nm crystallite size in the amorphous matrix of annealed ribbons. Special emphasis was placed on the effect of the quenching wheel speed on the Curie temperature during the measurements. To this end, the magnetization variations versus temperature were studied before and after annealing. It was found that increasing the wheel speed results in the reduction of the Curie temperature in as-spun ribbons. Moreover, the Curie temperature of the intergranular amorphous region in the annealed ribbons was at least 80 °C higher than that of corresponding amorphous phase in as-spun ribbons due to exchange interaction penetration of the adjacent Fe (Si) crystallites and relaxation processes.