Sliding behavior of multifunctional composite coatings based on diamond-like carbon

The sliding behavior of several coatings based on non-hydrogenated diamond-like carbon (DLC) is described. Coatings were produced by using a magnetron sputter-assisted pulsed laser deposition process developed at the Air Force Research Laboratory. Results are compared for two types of coatings: DLC with WC nanoparticles and DLC with both WC particles and WS2 (“WCS”). Sliding tests were done in air, nitrogen and vacuum and for alternating periods in different environments, e.g., cycling between air and vacuum conditions. The friction force and the signal from an in situ Kelvin probe were monitored during sliding. Friction coefficients ranging from near 0.01 to 0.6 have been observed. The Kelvin probe detected transients lasting from ten minutes to more than one hour. Post-test characterization included SEM/EDS, Raman and TEM. The role of transfer and mixing is discussed.