Micromechanical Behaviour of Amorphous Hydrogenated Silicon Carbide Films
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MICROMECHANICAL BEHAVIOUR OF AMORPHOUS HYDROGENATED SILICON CARBIDE FILMS J. MENEVE, R. JACOBS, F. LOSTAK, L. EERSELS, E. DEKEMPENEER and J. SMEETS Materials Division, Vlaamse Instelling voor Technologisch Onderzoek (VITO), Boeretang 200, B-2400 Mol (Belgium) ABSTRACT Amorphous hydrogenated silicon carbide (a-Si,,C,,:H) films (x = 0.65 to 1) were deposited by radio frequency plasma assisted chemical vapour deposition (RF-PACVD). Their friction and wear properties were investigated by means of a conventional ball-on-disk apparatus. The results were correlated with film mechanical properties. It was found that adding silicon to a-C:H (also called diamond-like carbon (DLC)) films reduces the hardness, elastic modulus and internal stress values by 15 to 30 %. Scratch testing induces film spallation from stainless steel substrates at low loads (1 N). In the low normal load (1 N) ball-on-disk tests under humid N2 conditions, a-Si_.xC.:H films (0.7 < x < 0.9) combine a very low wear rate of both the film and the counterbody with a steady state low friction coefficient below 0.1. For higher loads (5 and 10 N), however, this low friction coefficient only lasts for a relatively short time. In this case, the harder diamond-like carbon films perform tribologically better because of their higher wear resistance, low wear rate of the counterbody and generally low friction coefficients between 0.15 and 0.35 in a humid ambient atmosphere. In a dry N2 atmosphere, pure DLC films perform tribologically better than a-Sil,,C,:H films in all respects. INTRODUCTION The protection of materials by means of hard, wear resistant coatings is now a well established technology and is an extremely versatile means of improving component performance. Most often, a coating material with an acceptable wear resistance and the lowest friction coefficient is preferred over one with a higher wear resistance and friction coefficient. This is so because a lower power dissipation in a friction pair is desirable'. Diamond-like carbon (DLC) films are of large technological interest because of their extreme wear resistance and generally low friction coefficients 2. However, it is well known that the friction coefficient of DLC films increases from about 0.05 in a dry N2 atmosphere or under ultrahigh vacuum UHV conditions, to a value between 0.2 and 0.3 above about 10 % relative humidity (RH)z-3 . Oguri and Arai demonstrated that a-Si11. C1:H films (x = 0.7 to 0.9) grown by DC glow discharge PACVD at 550 *C showed a very low friction coefficient of 0.05 nearly independent of RH, while the wear resistance of their material was slightly lower than that of DLC4"5. In this work, the friction and wear properties of a-Si1 1xC.:H films (x = 0.65 to 1) deposited by RF-PACVD are systematically investigated under dry and humid N2 conditions. The results are correlated with internal stress, hardness, elastic modulus and adhesive strength values. EXPERIMENTAL DETAILS Preparation of films The films were grown in a capacitively coupled parallel plate RF-PACVD reactor descri
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