High-temperature oxidation of TiN/CrN multilayers reactively sputtered at low temperatures

The high-temperature (600-850 degrees C) oxidation of multilayer hard TiN/CrN coatings was investigated. TiN/CrN multilayer coatings (2.6 mu m thick) with modulation periods in the range 83-425 nm were deposited at low temperatures (150 degrees C) onto polished tool steel discs and polished alumina ceramic substrates (R-a = 25 nm) using the plasma-beam sputtering technique. The oxidation rate was obtained from the weight gain as a function of the oxidation time. The activation energy for oxidation of TiN/CrN multilayers was determined and compared with that for CrN, TiN and CrTiN coatings. The depth profiles of samples oxidized at various temperatures were examined by Auger electron spectrometry (AES) and glow discharge optical spectrometry (GDOS) to determine the thickness and the composition of the oxide layer. The morphology of the oxidized coatings was investigated by scanning electron microscopy (SEM). Continuous in-situ electrical resistivity measurements were performed on the same coatings to detect grain-boundary oxidation. The adhesion and microhardness of the multilayers were also determined. (C) 1998 Elsevier Science S.A.