Metallic glasses (MGs) are a category of materials that are characterized by their amorphous structure and metallic bonds. Owing to their disordered structure, MGs possess unique properties that make them attractive for mechanical and tribological applications. In this work, we study the surface chemistry of Fe40Ni40B20 MGs, which are promising materials fulfilling the requirements for various industrial applications. The surface and bulk structure are investigated by X-Ray Diffraction (XRD), Auger Electron Spectroscopy (AES), X-Ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS). Different XRD geometries, as well as sputter etching during XPS and SIMS experiments were used to study the structural and chemical profile of these glasses. The findings of this study include the segregation of Fe on the MG surface. We found a strong correlation between the concentration of trivalent Fe (oxide form) and the concentration of O, and comparing the [Ni]/[Fe] and [Ni]/[Fe3+] we concluded that the excess of [Fe] on the surface is attributed to preferential surface oxidation. This behavior is reported for the first time for a glass system, and it is similar to the corresponding oxidation behavior of Fe-Ni crystalline alloys. It is worth to emphasize that such oxidation occurs in a glass system, although O diffusion is expected to be limited compared to the Fe-Ni crystalline alloys. Depth profile experiments in combination to exposurre of clean glass surfaces to O-ambient have shown that the oxidation-driven Fe-segregation on the surface is a reversible and repeatable process. XPS has also detected that in the buried layers the concentration of trivalent Fe is higher than it would be expected for the corresponding O concentration. This observation might be attributed to the coordination of Fe in the glass state.

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