Modelling Friction Reduction Based on Molybdenum Disulphide Tribofilm Formation and Removal in Boundary Lubrication

Molybdenum dialkyldithiocarbamate is a highly effective friction modifier lubricant additive in boundary lubrication, owing to the formation of a MoS₂ nanosheet lattice structure that significantly reduces friction. The friction reduction behaviour is linked to the MoS₂ amount and coverage buildup at the contacting interface, however, accurately predicting friction reduction based on a semi-deterministic model incorporating Mo₂ formation and removal remains challenging. In this study, a Raman map collection methodology was developed for accurate quantitative analysis of MoS₂ tribofilms. The growth rate of MoS₂ tribofilms was determined by coupling tribochemical experimental data with sophisticated numerical models. A full numerical procedure was implemented under rubbing of two rough surfaces at different temperatures. The results demonstrated localised MoS₂ tribofilms buildup. The friction coefficients show a close agreement with the measurements. The developed model can be adapted to diverse experimental setups and surface geometries.