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 degrees 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. (c) 2005 Elsevier B.V. All rights reserved.