Published online by Cambridge University Press: 21 March 2011
Tetrahedral amorphous carbon (ta-C) contains a large percentage of sp3 carbon bonding. However, high internal stresses develop in ta-C films with a high sp3 content, which limits their applications for wear protection. In this study, Al containing ta-C films were produced using Filtered cathodic vacuum arc (FCVA) technique. The structure of films was studied using Micro-Raman spectroscopy in terms of aluminum content. The pure carbon ta-C films generally contained a relatively high residual compressive stress, which was related to its sp3 content, amorphous structure and preparation conditions. For the Al containing ta-C films, the stress reduction is significant with increase of aluminum content in the film. A decrease of the mechanical properties of the ta-C:Al nanocomposite films was noticed with the decrease of the internal stress in the films. The tribological behavior of the films was measured using ball-on-disk tribometer. The wear rate and friction coefficient were determined correspondingly. In the ball-on-disk testing, different loads are applied to the sapphire counterbody. All the tests were performed in ambient air (RH50%) and at room temperature (22°C). It was noted that the friction coefficient of ta-C:Al films increased at the beginning of the testing before reaching a peak value of about 0.25. After the peak, the friction coefficient dropped until reaching a steady state value. The original surface roughness of the counterfaces, surface smoothening due to successive wear, and wear debris produced during the testing are all responsible for the tribological behavior of ta-C:Al films.