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An amorphous alloy rod of 0.5 mm in diameter was produced for an Fe72.5Si10B12.5Nb4Cu1 alloy by copper mold casting, though the maximum diameter of 1.5 mm for (Fe0.75Si0.1B0.15)96Nb4 alloy decreased by the addition of 1 at%Cu and the decrease in B content. The amorphous alloy rod crystallizes through multi-stage exothermic reactions. The first exothermic peak is due to the precipitation of nanoscale bcc-Fe phase and the following exothermic peaks result from the transition of bcc-Fe+amorphous→bcc-Fe+Fe23B6+Fe2B+Fe3Si+Fe2Nb. The bcc-Fe phase has a particle size of about 10 nm and its volume fraction is approximately 70% after annealing for 300 s at 883 K . The alloy rod consisting of bcc-Fe and amorphous phases exhibits good soft magnetic properties, i.e., high saturated magnetic flux density of 1.21 T, low coercive force of 1.8 A/m and high initial permeability of 32000. The good soft magnetic properties for the nanocrystalline Fe72.5Si10B12.5Nb4Cu1 alloy in a rod form of 0.5 mm in diameter are encouraging for future development as a new type of nanocrystalline soft magnetic bulk material.
Inoue et al. (Tue,) studied this question.