Tribological study of hydrogenated amorphous carbon films with tailored microstructure and composition produced by bias-enhanced plasma chemical vapour deposition

We investigated the mechanical and tribological properties of hydrogenated amorphous carbon (a-C:H) films on silicon substrates by nanoindentation, ball-on-disc tribotesting and scratch testing. The a-C:H films were deposited from an argon/methane gas mixture by bias-enhanced electron cyclotron resonance chemical vapour deposition (ECR-CVD). We found that substrate biasing directly influences the hardness, friction and wear resistance of the a-C:H films. An abrupt change in these properties is observed at a substrate bias of about -100 V, which is attributed to the bias-controlled transition from polymer- to fullerenelike carbon coatings. Friction coefficients in the range of 0.28-0.39 and wear rates of about 7 x 10(-5) mm(3)/Nm are derived for the polymeric films when tested against WC-Co balls at atmospheric test conditions. On the other hand, the fullerenelike hydrogenated carbon films produced at ion energies >100 eV display a nanohardness of about 17 GPa, a strong reduction in the friction coefficient (similar to 0.10) and a severe increase in the wear resistance (similar to 1 x 10(-7) mm(3)/Nm). For these films, relative humidity has a detrimental effect on friction but no correlation with the wear rate was found. (C) 2010 Elsevier B.V. All rights reserved. / status: published