METHOD FOR SUPPRESSING SURFACE CRYSTALLIZATION IN FE-BASE AMORPHOUS ALLOY RIBBONS CONTAINING AL

The magnetic properties of amorphous Fe-Si-B alloys are greatly deteri orated if a small amount of Al is present in the master alloy. This de gradation is caused by thin crystalline layers formed on the surface o f the ribbon during casting, as reported. We studied methods for avoid ing the occurrence of surface crystallization and found that adding Sn to the master alloys was effective. The effect of Sn is to prevent Al from being enriched on the surface, which is believed to nucleate the crystalline layer through the formation of oxides. Sn also enhances t he concentration of Si as a solute in the layer 150-300 angstrom deep, so causing a high resistance to surface crystallization.