Microfrictional properties of diamond-like carbon films sliding against silicon, sapphire and steel

The low contact pressure characteristic of the microtribological regime relative to macro and nanosystems is suited for testing the microfrictional properties of different types of thin films. Motivated by macro as well as microsystem applications, this study investigates the microfrictional properties of different types of diamond-like carbon (DLC) films, prepared using low- and high-frequency plasma-assisted chemical vapor deposition (HF-PACVD) and the vacuum arc method. Testing was performed with a reciprocating precision microtribometer. Silicon, sapphire and steel balls were used as counterbodies. Friction-load curves suggest that, for applied forces in the μN to mN regime, two properties have a strong influence on the microfriction: first, the chemical composition plays a dominant role and second, the film roughness. With silicon and steel balls, the microfriction of hydrogen-free DLC films was greater than the hydrogen-containing films. With sapphire counterbodies, the results indicate that microfriction is inversely proportional to the film roughness. Also, for the films tested, microfriction was determined to be independent of the sliding velocity. For the force (pressure) regimes tested, mild wear was observed on silicon and some steel counterbodies, while no wear could be detected on any of the DLC films. These results illustrate the utility of implementing microtribological testing in comparative coating studies.