Study of DLC coating influence on lubrication regime transition

摘要

The purpose of this research work was to understand the friction reduction mechanism brought by a DLC coated surface, using a fully formulated commercial oil. Using a linear alternative configuration, the four combination of uncoated and DLC coated surfaces were tested. The results show that all the cylinder/flat pairs show the same friction coefficient in boundary lubrication. The friction is dominated by the shearing of compounds resulting from the decomposition of antiwear additives present in the oil. The situation changes when the condition (speed or pressure or viscosity) allow entering in the mixed regime. It was observed that the friction coefficient is the highest for steel/steel pair, that DLC/steel pairs have similar coefficient of friction, which is lower than that of steel/steel. The lowest friction coefficient is observed for the DLC/DLC pair. Roughness measurements after test are correlated to the friction level in mixed regime. Hence the friction reduction is mainly due to the chemical inertness of DLC that prevents the adhesion of an antiwear tribo-film, leading to surfaces being more polished with time. The consequence of this is the transition of lubrication regime toward lower speeds.