PLASMA-BOOSTER-ASSISTED HYDROGENATED W-C COATINGS

The production of hard amorphous metal carbon films was arranged using two opposing magnetron cathodes which are positioned at a distance of 1 m. This arrangement produces a large volume of highly dense plasma by using a special magnetic guiding of the electrons (plasma booster). In this configuration metal is deposited by the magnetron cathodes by sputtering (physical vapour deposition) and carbon is deposited by decomposition of a hydrocarbon gas (plasma chemical vapour deposition). As magnetrons, interpole target cathodes combined with electromagnetic coils are used. Additionally, on the magnetron cathodes magnetically assisted hollow anodes are installed to extract electrons from the discharge. It was found that for the decomposition of acetylene as hydrocarbon gas the area in front of the cathodes showed the strongest effect. In this region a condensation rate for carbon of 10-15 mu m h(-1) is found. For the production of amorphous metal carbon this is the ideal condition because only in front of the cathode the sputtering process provides the metal to achieve a specific metal-to-carbon ratio. For hydrogenated W-C coatings the metal content of the film was changed from 8% to 70%. The coatings showed a dense microstructure at low deposition temperatures of 200 degrees C or less. The colour of the coatings changed from dark anthracite for the lowest metal content of 8% to light grey for 70% tungsten in the coating. The dense amorphous coating and the high microhardness values of 17 GPa or more (based on the Vickers scale) combined with the low friction coefficient of less than 0.2 (against steel and ceramics) offer ideal conditions for the use of these coatings on components as well as for decorative applications.