PREPARATION OF W-C-H COATINGS BY REACTIVE MAGNETRON SPUTTERING

The reactive d.c.-magnetron sputter technique in conventional and unba lanced modes was used to prepare tungsten-containing hydrocarbon (W-C: H) coatings which have low friction coefficients and high wear resista nces. Reproducible deposition processes stable over a long time withou t poisoning could be realized using a plasma emission monitor (PEM) co ntrol unit. From investigation of the light emission spectra of the ma gnetron discharge the intensive tungsten line at 401 nm was selected a s most suitable for process control. The dependences of characteristic process parameters such as target voltage, optical emission intensity or deposition rate on the reactive gas flow were quite different from those known for the reactive sputter deposition of TiN or other nitri des and oxides. For both tungsten and WC targets the PEM intensity dec reased monotonically with increasing acetylene flow. However, the depo sition rates on substrates with floating potential increased. An addit ional r.f. excitation of the substrate electrode caused only slight ch anges in rate and metal content in the coatings. it can be concluded t hat the sputter process is dominant for W-C: H growth. The contributio n of direct plasma polymerization at the substrate is small. From X-ra y diffraction investigations it was concluded that the W-C:H coatings contain microcrystallites of the metastable cubic tungsten carbide WC1 -x. The Vickers hardness and Young's modulus depend on the atomic rati o of tungsten to carbon.