Crystalline layer on the surface of Zr-based bulk metallic glasses

The structure, stability and microstructure Of Zr65Cu17.5Ni10Al7.5 and Zr50 Cu18Ni17Ti5Al10 bulk amorphous alloys was studied by X-ray diffraction, dif ferential scanning calorimetry, and scanning electron microscopy. A thin cr ystalline surface layer was observed on both bulk metallic glasses. This la yer consists of zirconium carbide and some crystalline phases. The thicknes s of the layer varies between 5 and 10 mum, it depends on the location in t he sample. The origin of the formation of the crystalline layer is discusse d. The formation of the crystalline layer is connected with carbon depositi on on the sample surface during the production of the metallic glass, and w ith select carbide formation. The resulting change of the concentration of the alloy components near the surface due to the carbide formation leads to a shift of the alloy composition from the amorphization region and results in further crystallization of near surface regions. (C) 2001 Elsevier Scie nce B.V. All rights reserved.