Optimum circumstances for heat treatment mechanisms: soft magnetic properties and microstructural evaluation in nanocrystalline FeCuNbSiB alloys

Abstract In the present study the magnetic, magneto-optical, morphological and microstructural properties of the amorphous Fe83Cu1Nb3Si5B8 alloy were thoroughly investigated in accordance with various annealing circumstances. The kinetic nanocrystallization temperatures of certain ribbon were determined at the range of 500–515 °C. Furthermore, optimum heat treatment conditions were sought in the air atmosphere (AA), in vacuum (VA) and in vacuum with the presence of longitudinal magnetic field (LFA) at 70 A/m. This study aimed to put forward a quantitative explanation of the advantages of LFA in terms of several factors such as magnetic properties, microstructural evaluation and magneto-optical effects. The present nanocrystalline Fe83Cu1Nb3Si5B8 alloy has allowed the yielding of ultrafine grain structure correlated with the literature results. Accordingly, average grain size of 5.9 nm, saturation induction of 1.84 T and coercivity of 6.4 A·m−1 and saturation magnetostriction as low as 6 ppm were obtained as a result of LFA implementation. However, the sample subjected to VA under the same circumstances showed relatively lower magnetic and microstructural capability, with an average grain size of 9.8 nm, saturation induction of 1.73 T, coercivity of 14.7 A·m−1 and saturation magnetostriction of 14 ppm, in comparison with LFA. To ensure precise average grain size, both XRD data and TEM micrographs were separately considered. Even though saturation magnetostriction could not be completely eliminated, it was significantly minimized from 52 ppm to 35 ppm, 14 ppm and 6 ppm in the samples subjected to AA, VA and LFA, respectively.