Friction and Wear Properties of Tetrahedral Si-Containing Hydrogenated Diamond-Like Carbon Coating under Lubricated Condition with Engine-Oil Containing ZnDTP and MoDTC

Abstract

In this study, we investigated tribological properties of “tetrahedral” Si-containing hydrogenated DLC coating (TMS coating) during sliding against steel or cast-iron lubricated with engine-oil containing MoDTC and ZnDTP additives. TMS coatings derived from only tetramethylsilane were prepared using PACVD with high-bias process. TMS coating had the highly carbon sp3 bonded structure induced by Si (over 20 at.%) with high hydrogen content (30 at.%). TOF-SIMS analysis showed that TMS coating could form the additive-derived tribofilm on both of the non-ferrous coating surface and the ferrous counter surface to promote Mo-sulfide formation effectively, leading a low friction coefficient. The tribo-chemical reactions were related not only to Mo-sulfides formation, but also reduction of Mo-oxides. Mo-oxides could react with DLC material and induce hydrogen evolution and transformation into further weak carbon structure, causing an increasing wear of hydrogenated DLCs. TMS coating showed no significant wear in spite of plenty hydrogen content. Si induced sp3 bond and could act so as not to induce clustering of the sp2 phase. This could inhibit increasing wear of the DLC in the presence of MoDTC. The effectiveness of TMS coating in friction and wear behavior was shown to depend on tribo-chemical reactions and transformation of carbon bond structure.

Keywords

• diamond-like carbon
• tribochemistry
• lubricant additives
• engine-oil