Probing the Tribochemical Impact on Wear Rate Dynamics of Hydrogenated Amorphous Carbon via Raman-Based Profilometry

Solid-liquid lubricating systems have received significant attention as a promising way for energy saving and emission control. For deeply understanding their tribological behaviors, it is necessary to study interaction mechanisms between solid and liquid lubricants from the tribochemical viewpoint, as tribofilms formed by tribochemical products on contact surfaces critically affect the whole tribological process. Continually or periodically monitoring tribofilm formation and evolution can contribute significantly to clarifying its dominating role in tribological behavior under boundary lubrication. However, detecting tribofilms in situ remains a big challenge for conventional surface analytical approaches, mainly due to their limitations in accessing tribofilms or low signal intensities of thin tribofilms. In this study, highly sensitive Raman-based profilometry with in situ potential has been developed for detecting molybdenum dialkyldithiocarbamate (MoDTC)-derived tribofilms and exploring their effect on a-C:H wear over time. The optical properties of tribochemical products formed on the coating surface in different wear stages could result in extra attenuation of Raman signal intensities in the form of measurement deviations in wear depth. By monitoring the deviations, key information of tribofilm compositions was obtained and a two-stage wear progression mechanism was proposed for the first time to clarify the detrimental effect of MoDTC-derived tribofilms on a-C:H wear by combining detailed structure and composition analyses.