CVD of TiCx/a-C-layers under d.c.-pulse discharge

Hard layers consisting of TiCx, and amorphous carbon have been co-deposited from CH4–TiCl4–H2–Ar gas mixtures, by plasma CVD varying the carbon-concentration in a wide range. The layers were characterized with respect to their composition, structure and some properties. The influence of the CH4/TiCl4 ratio and the addition of hydrogen on the layer constitution and behavior were especially investigated. The TEM investigations demonstrated a homogeneous distribution of the TiCx crystallites and a grain size of approximately 4–7 nm. The layers are textureless and with an increasing amorphous carbon content as the surface roughness decreases. The microhardness depends on the excess amount of carbon and the content of dissolved hydrogen. If the deposition process is realized without any additional H2 in the gas phase, the microhardness increases strongly (>4000 HV [0.02]) and a maximum microhardness was observed at 60 at.% carbon in the coating. Stress measurements carried out by XRD and the beam bending method revealed generally that the high compressive stress occuring in stoichiometric TiC layers, significantly decreases in TiCx/a-C layers. Nevertheless, all the composite layers showed a low adhesion on different substrates. An improvement could be achieved by the pre-deposition of suitable interlayers. The low friction coefficient and the favorable surface roughness make PACVD–TiCx/a-C-layers a good candidate for sliding wear applications.