SOFT NANOCRYSTALLINE FERROMAGNETIC-ALLOYS WITH IMPROVED DUCTILITY OBTAINED THROUGH DC JOULE HEATING OF AMORPHOUS RIBBONS

Nanocrystalline ferromagnetic materials of the type Fe-Nb-Cu-B-Si obtained by appropriate furnace annealing of amorphous ribbons display excellent soft magnetic properties but are very brittle. Dc Joule heating in vacuo allows nanocrystallization to occur in these systems well before the atomic rearrangements in the amorphous phase have been completed, thus partially avoiding the processes leading to sample embrittlement. In Fe73.5Cu1Nb3Si13.5B9, the average grain size of Joule-heated samples is significantly lower than in the furnace-annealed alloy. Nanocrystalline strips of this material having very high magnetic permeability and better ductility are therefore obtained. The advantages of this rapid heating technique are highlighted.