MoDTC lubrication of DLC-involving contacts. Impact of MoDTC degradation

Recently Diamond-Like Carbon (DLC) coatings have attracted considerable attention due to their low friction, high hardness, good wear and corrosion resistance, and high thermal and chemical stability. Although considerable research has been conducted on the effect of molybdenum-based additives, e.g., molybdenum dithiocarbamate (MoDTC), on the boundary lubrication of DLC coatings, the wear mechanisms leading to the coating removal are not fully understood to date. Moreover, the impact of the degradation of the MoDTC-containing base oil on the tribological properties of DLC coatings has not been investigated. This study could help to elucidate the mechanisms by which the coating is worn out in presence of MoDTC-containing base oil.

In this work, the friction and wear performances of DLC coatings with different hydrogen contents and doping elements have been investigated in the presence of MoDTC-containing base oil. To enable the correlation between these changes and the modification of the contact surface chemistry, tribofilms generated during friction were investigated by SEM combined with Energy Dispersive X-ray Spectrometry (EDX) and X-ray Photoelectron Spectroscopy (XPS). A new mechanism explaining the severe wear experienced by DLC coatings when lubricated with a MoDTC-containing base oil is proposed.