M. Gubisch

Tribological characteristics of WC1-x, W2C and WC tungsten carbide films

Thin film coatings with dominant phases of WC1-x, W2C and WC, were prepared by magnetron sputtering. The microstructures and chemistry of the coatings were characterized by X-ray diffraction (XRD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The surface morphology and mechanical properties were examined by atomic force microscopy (AFM) and nanoindentation techniques. The tribological behaviour of the coatings was assessed by means of a microtribometer. Low hardness and indentation modulus of the W2C coatings were found to be from the high surface roughness. The W2C coatings were not wear resistant and were worn through in less than 15,000 cycles under a normal load of 40 mN. The WC1-X coatings were textured with the (200) plane parallel to the surface of substrate. The hardness and indentation modulus of the WC1-x coatings were ∼19 GPa and ∼600 GPa, respectively. A thick transfer layer was observed at the surface of the sphere employed in the sliding tests of the WC1-x coatings. The build-up and maintaining of this transfer layer was found to be important in determining the friction behaviour of the WC1-X coatings. A maximum hardness of ∼23 GPa and the lowest friction coefficient of 0.19 was obtained from the WC coating. In contrast to the large variation of the friction coefficients in the other coatings, the friction coefficient of WC was stable in the long-time running process.

NiO modified thin films for gas monitoring

In our contribution, we present the results concerning the Pt surface modification of nickel oxide thin films deposited by dc reactive magnetron sputtering. Pt very thin overlayers with a thickness of about 3 and 5 nm have been sputtered on the top of NiO samples. The surface structure and morphology of the samples have been analysed by XRD and by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The electrical responses of the NiO-based sensors towards different H2 concentration (500-5000 ppm) have been also considered. The Pt modified NiO samples showed an enhancement of the response towards H2 as compared to the unmodified NiO sample. The thickness of the Pt thin layers seems also an important parameter in determining the properties of the NiO films as H2 sensors.