Triboscopic Investigation of Self-Mated Carbon Coatings in Non-Lubricated Friction Conditions

Tetrahedral amorphous carbon (ta-C) has shown to exhibit exceptionally low friction and wear under dry sliding in the presence of water vapor as well as acceptable low friction and wear in the presence of inert gases. However, it is known that these properties deteriorate rapidly under vacuum conditions with decreasing pressure.
For a better understanding of the wear mechanisms in doped and undoped ta-C coatings under vacuum and dry conditions, more advanced triboscopic imaging methods in regard to these systems were developed. Triboscopy is the imaging of the evolution of a tribosystem via combination of highly-resolved local and spatial information, most often the evolution of friction.
The experimental data of self-mated ta-C contacts in air and vacuum shown in this study was obtained from a custom-built ultra high vacuum tribometer in ball-on-disc configuration. Based on these experiments, the resulting triboscopic images are discussed based on their triboscopic features according to the persistence in both track position and time. The resulting specific triboscopic features are correlated to distinct wear phenomena, demonstrating the increased analytical capabilities when compared to conventional friction curves and wear track images. While in the context of this work the correlations were made after the experiments, the use of these findings for monitoring in-line experiments can strongly enhance the capability of monitoring tribological systems in the future.