Direct control of medium range order in a Ni modified Finemet-type alloy

Using continuous-heating differential scanning calorimetry (DSC) and X-ray diffraction, the planar-flow casted Fe54Ni20Cu1Nb3Si13B9 amorphous ribbons have been investigated. In the as-prepared alloy, a heating rate dependence of the crystallization kinetics differs from that of other finemet alloys. Namely, the ordered Fe3 Si and Fe3NiSi1.5 phases crystallize simultaneously in one crystallization step via a viscous flow mechanism at heating rates, w>25 K min−1. However, in the same material, the crystallization proceeds as a two-step transformation either after a >20-min isothermal anneal at 663 K (which is 100 K less than the onset of the main transformation) or when applying a smaller heating rate, w<20 K min−1. Then, the same phases crystallize separately in the first and second crystallization steps. The interpretation is based on the correlation between the change of both atomic transport mechanism and kinetics of the formation of two alternative crystalline phases and the topological Fe–Ni ordering in the sample during the stage prior to the nucleation.