TOF-SIMS analysis of friction surfaces of hard coatings tested in engine oil

This report describes the results of TOF-SIMS analysis of friction surfaces of hard coatings such as CrN and TiN tested in model engine oil containing typical engine oil additives, i.e., polyisobutenyl succinimide, Ca-sulfonate, Zn-dithiophosphate, and Mo-dithiocarbamate, as a real-world lubrication system used in the automobile industry. As model engine oils, two types of lubrication systems containing the above additives were prepared. For the aim of analysis of friction surfaces of engine oil lubrication systems, the friction surfaces tested with each additive were analyzed before the analysis for the engine oil systems. By TOF-SIMS analysis of friction surfaces tested in each additive, secondary ions originating from adsorbed components were detected for each additive. From this result, the friction surfaces for model engine oil were analyzed by TOF-SIMS. The differences in adsorbing behavior of additives between different engine oil components and between different substrates were clarified, and the causes of difference in friction coefficient among the engine oil lubrication systems were partly explained with the adsorbing behavior of Mo-dithiocarbamate. These results demonstrate that TOF-SIMS analysis of friction surfaces is useful for the analysis of real-world lubrication phenomena.