Comparison testing of diamond-like a-C:H coatings prepared in plasma cathode-based gas discharge and ta-C coatings deposited by vacuum arc

The method of amorphous carbon coating deposition based on decomposition of acetylene in a non-self-sustained hollow cathode pulsed-DC discharge is investigated. The discharge is maintained by the electron emission of a grid-stabilized plasma cathode based on a DC glow discharge. The method allows the gas pressure in the discharge gap and the non-self-sustained discharge parameters to be varied in a wide range. It makes it possible to optimize the properties of the deposited coating and to perform in situ the preliminary ion cleaning of sample surface and the plasma immersion ion implantation to form an interface and to improve the coating's adhesion. The 0.1–10-μm-thick a-C:H films were deposited on tungsten carbide and stainless steel substrates at a deposition rate of 0.5–8 μm/h. The coatings were investigated using the methods of atomic-force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy. The arithmetic average surface roughness (9–34 nm), the friction coefficients (0.01–0.3), the density (2.2–2.4 g/cm3), the microhardness (16–75 GPa) and the internal stresses in the films (3–7 GPa) were measured. Comparison was made between the properties of the resulted a-C:H coating with the properties of the ta-C coating obtained by cathodic vacuum arc deposition.