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 Fe-3 Si and Fe3NiSi1.5 phases crystallize simultaneous
ly in one crystallization step via a viscous flow mechanism at heating rate
s, w > 25 K min(-1). However, in the same material, the crystallization pro
ceeds as a two-step transformation either after a > 20-min isothermal annea
l at 663 K (which is 100 K less than the onset of the main transformation)
or when applying a smaller heating rate, it, < 20 K min(-1). Then, the same
phases crystallize separately in the first and second crystallization step
s. The interpretation is based on the correlation between the change of bot
h atomic transport mechanism and kinetics of the formation of two alternati
ve crystalline phases and the topological Fe-Ni ordering in the sample duri
ng the stage prior to the nucleation. (C) 2001 Elsevier Science B.V. All ri
ghts reserved.