Crystallisation progress in Si-rich ultra-soft nanocomposite alloy fabricated by melt spinning

The crystallisation process and the ultras-soft magnetic properties of amorphous/nanocomposite alloy Fe_73.5 Si_17.5 B₅ Nb₃ Cu₁ fabricated by conventional melt-spinning technique are systematically investigated in terms of thermal analysis and in-situ measurement of magnetisation dynamics. The thermal analysis using differential scanning calorimetry showed that crystallisation from Fe-based amorphous state to α-Fe(Si) started at 535 ^{{ring operator}} C. Further heating the sample leads to a transformation from the α-Fe(Si) to Fe-B phases at 670 ^{{ring operator}} C. Crystallisation activation energies were determined using two models: Kissinger and John-Mehl-Avrami (JMA), which were consistent to each other with a value of 2.81 ± 0.03 eV. High resolution transmission electron microscopy investigation revealed an ultrafine structure of α-Fe(Si) nanocrystallite with mean size of 12.5 nm embedded in an amorphous matrix. At a volume fraction of 86% of α-Fe(Si) phase, optimum soft magnetic properties were obtained with very high permeability of 110,000 and a very low coercivity of 0.015 Oe by annealing the amorphous alloy at 530 ^{{ring operator}} C in 40 min. Crown