Tribochemical investigation of Cr-doped diamond-like carbon with a MoDTC-containing engine oil under boundary lubricated condition

Cr-doped diamond-like carbon (Cr-DLC) coatings were deposited and investigated for their tribological properties. A hybridized deposition technique consisted of a bipolar plasma-based ion implantation and deposition (PBII&D) and magnetron sputtering was used for the deposition. Raman spectra revealed an increase of ID/IG upon the Cr introduction, indicating the embedded CrCx act as catalysts to produce sp2 sites. The coefficients of friction (COF) were effectively reduced once MoDTC was added to the base oil. X-ray photoelectron spectroscopy (XPS) confirmed the presence of MoO3, MoS2, and MoS2−xOx in the MoDTC-derived tribofilm. The contribution of MoS2−xOx decreased with the Cr content, suggesting that the wear particles of CrCx intervenes in the process of MoDTC decomposition by preventing the oxidation of MoS2 sheets.