Characterization of oxide layers developed on ZrCuAl-based bulk metallic glasses during gaseous thermochemical treatment

The current study addresses an investigation of low-temperature oxidizing treatment (case formed in the metallic glassy substrate was further investigated with in-situ ion beam channeling. The results demonstrate that after conducting the oxidizing treatment in the atmosphere containing high oxygen partial pressure, an outer oxidation layer and an inner oxide zone develop. In the gas with a low oxygen partial pressure only the inner oxidation zone results. Interestingly, four oxide regions with different chemical composition, which mainly consist of ZrO₂ (with two different lattice structures; tetragonal and monoclinic) and Al₂O₃ are present in the inner layer where the oxygen is distributed through the substrate. Furthermore, the outer oxide layer is enriched in copper which has diffused out of the BMG. Cracks have developed adjacent to the surface, which is ascribed to the stresses resulting from oxide formation in the inner oxidation zone. Some of the cracks are filled out with copper. This phenomenon was also observed in Ag-containing BMG, where both copper and silver enrich at the surface.