Creep or tensile stress induced anisotropy in FINEMET-type ribbons?

Continuous stress annealing can be performed on FINEMET-type (Fe73.5Cu1Nb3Si15.5B7) ribbons. Here we report experiments conducted in a cheap open tubular furnace as a function of pulling velocity (v). We achieved up to v=120 m/min that is almost 100 times higher than previously reported for this kind of equipments. In this report we show for the first time how the properties are depending on the pulling velocity. While the achieved relative permeability µr remained constant without changing any other parameter than v, the elongation of the ribbon and the contraction of the ribbon width were monotonically changing as v was increased. The results support that the creep is not determined exclusively by the applied stress, but it is determined by the details of the amorphous-nanocrystalline transformation, which is influenced by the pulling velocity. The bigger the pulling velocity is, the higher the onset temperature of the amorphous-nanocrystalline transformation is, and the wider the associated exothermic peak is, resulting in increased elongation of the ribbon due to a short time formation of undercooled liquid state.