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 obta ined by appropriate furnace annealing of amorphous ribbons display exc ellent soft magnetic properties but are very brittle. Dc Joule heating in vacuo allows nanocrystallization to occur in these systems well be fore the atomic rearrangements in the amorphous phase have been comple ted, thus partially avoiding the processes leading to sample embrittle ment. In Fe73.5Cu1Nb3Si13.5B9, the average grain size of Joule-heated samples is significantly lower than in the furnace-annealed alloy. Nan ocrystalline strips of this material having very high magnetic permeab ility and better ductility are therefore obtained. The advantages of t his rapid heating technique are highlighted.