The ta-C hardness effect on wear properties under MoDTC contained boundary lubrication

Abstract

Abstract The wear acceleration of hydrogenated amorphous carbon under lubrication with molybdenum dithiocarbamate (MoDTC) is one of the problems to apply it to engine components. It is assumed that using high hardness tetrahedral amorphous carbon (ta-C) can easily solve the wear problem regardless of chemical wear by Mo degradable materials, however, we still do not know the effect of ta-C coating hardness on wear of itself with MoDTC. Because, amount and structure of Mo degradable material is assumed to relate contact pressure. It suggested that even if ta-C coating has high hardness, the wear amount changes with normal load. In this study, we prepared four different hardness ta-C coatings (such as approximately 18.2, 22.1, 46.6, and 53.6 GPa) and conducted friction tests to clarify the effect of ta-C hardness on wear characteristics under boundary lubrication with MoDTC. Eventually, chemical analysis (Raman, EDS and XPS) was conducted to reveal the chemical spices existence of tribofilm for three hardness ta-Cs, especially for 22.1 GPa as a representative low hardness ta-C coating. As a result, the wear suppression was achieved when the contact pressure was higher than 200 MPa regardless of the coating hardness.