A metastable, single-phase, polycrystalline Ti0.46Al0.54N film was deposited on a HSS substrate by reactive magnetron sputtering ion plating and oxidized in synthetic air at 800 degrees C. The build-up of the oxidic overlayer formed during 1 h of oxidation was analyzed with the following results : Scanning electron microscopy (SEM) micrographs taken at the inner profile of a crater sputtered through the oxide overlayer showed a glassy morphology of the near surface region and, between the near surface region and the nitridic film, a sublayer consisting of crystals embedded irt a glassy matrix. Electron probe microanalysis (EPMA) cl ater edge linescan analysis revealed that the oxide overlayer consists of two sublayers, which differ significantly in the Al and Ti content. At the surface and in the near surface toplayer the composition corresponds to Al2O3,. whereas with increasing depth a composition conforming with Al2O3, and TiO2, was detected. The binding states of the components Al, Ti, O, and N were determined with increasing depth by high resolution Auger electron spectroscopy (AES) multipoint analysis at the inner profile of the crater. Evaluation of the spectra revealed that oxygen is present in two binding states. In the toplayer, oxygen is bonded to AI in Al2O3, and in the underlying layer, to Al in Al2O3 and to Ti in TiO2-x. Transmission electron microscopy (TEM) and high energy electron diffraction (HEED) analyses revealed that the Al2O3 rich toplayer is present in an amorphous state. With structure analysis by thin film X-ray diffraction (XRD), two modifications of TiO2, : namely anatase and rutile, were detected.