Experimental modelling of boundary lubrication using an ultra high vacuum tribometer

Abstract The understanding of boundary additive mechanisms is of primary interest for the development of high-performance lubricants and replacement of environmentally undesirable additives. However, chemical interactions occuring in a boundary lubricated contact under industrial conditions are complex and their study requires a simplified model to boundary lubrication. A new method has been developed, based on in situ friction experiments performed in an analytical ultra-high vacuum tribometer where the contact is lubricated by low molecular weight molecules which simulate the heavy lubricant components by their chemical function. A study of the evolution of the friction coefficient versus molecular pressure and sample temperature allows a clear differentiation of the different compounds. The in situ analytical tools enable the analysis of sample surfaces before the friction process and the understanding of additive tribochemistry. The friction behaviour and wear track morphologies under gaseous feed can be related to those obtained in classical boundary lubricated contacts. Consequently, this method appears capable of accurately modelling the boundary action of molecules and is likely to be a powerful tool in the prediction and the understanding of the action mechanisms of boundary additives.