Evolution from amorphous to nanocrystalline and corresponding magnetic properties of Fe-Si-B-Cu-Nb alloys by melt spinning and spark plasma sintering

The nanocrystalline Fe-Si-B-Cu-Nb alloys were prepared by firstly melt spinning and then spark plasma sintering process. The microstructure and magnetic properties of the samples obtained were investigated by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The body-centered cubic α-Fe(Si) phase precipitated from the amorphous matrix when the sintering temperature was increased to 800 K. The Fe23B6 phase started to form at the sintering temperature of 950 K. The grain size and densities of the sintered Fe-Si-B-Cu-Nb alloys increased with increasing the sintering temperature. Moreover, the saturation magnetizations of the samples obtained increased first and then decreased as the sintering temperature was increased from 750 K to 1050 K, while the values of coercive force changed in the opposite direction. The Fe-Si-B-Cu-Nb alloys sintered at 900 K exhibited a nanocrystalline structure with a grain size of ∼34 nm. It also displayed excellent soft magnetic properties with saturation magnetization at 137.5 emu/g, coercivity at 5 Oe and remanence at 1.0 emu/g.