Composition, mechanical properties and friction behavior of nickel/hydrogenated amorphous carbon composite films

Nickel/hydrogenated amorphous carbon composite films have been deposited on silicon and stainless steel substrates by combining sputter-deposition of metal and microwave plasma-assisted chemical vapor deposition of carbon from argon–methane mixtures of various concentrations. The composition and crystallographic structure of films were investigated as functions of the CH4 concentration by Rutherford backscattering spectroscopy and X-ray diffraction techniques, respectively. The carbide phase, Ni3C, was detected in Ni/C films deposited from a gas phase containing more than 8 vol.% of CH4. The grain size of Ni and Ni3C was determined as a function of the carbon content. The maximum magnitude of the compressive residual stresses was 0.6 GPa for films containing 25 at.% of carbon (Ni3C). At carbon concentrations above 50 at.%, the stress magnitude diminished to 0.2 GPa. The hardness and elastic modulus of films deduced from nanoindentation measurements were studied as functions of the carbon content. The ball-on-disk tribological tests were conducted in room air at the temperature of 20 °C under a load of 1 N with a sliding speed of 50 mm/s. The friction coefficient was determined as a function of the carbon content in the films. The minimum value of 0.25 was obtained from films containing about 75 at.% of carbon.