Low-temperature crystallization of Fe78B13Si9 and Fe81B13.5Si3.5C2 metallic glasses

The low-temperature crystallization behavior of Fe78B13Si9 and Fe81B13.5Si3.5C2 metallic glasses was investigated. Samples of each glass were isothermally annealed in vacuum and in air between 623 and 773 K. X-ray diffraction, optical–electron microscopy and differential scanning calorimetry were employed to follow the crystallization reaction. Crystallization in Fe78B13Si9 below 748 K always starts at the surface of the ribbons and is more prevalent on the wheel-side. Primary α(Fe) dendrites grow in a direction more or less parallel to the surface normal. Further growth of these dendrites is no longer evident, however, once crystallization in the bulk starts. When annealed in air, the air-side of the ribbons have also experienced substantial surface crystallization prior to any crystallization in the bulk. The response of the Fe81B13.5Si3.5C2 metallic glass to low-temperature anneals, on the other hand, is considerably different. Crystallization takes place predominantly in the interior of the ribbons, regardless of the annealing temperature and the atmosphere. Differences in the low-temperature crystallization behavior of these glasses and the underlying mechanisms are discussed.