Influence of the Volume Structure on the Tribological Properties of Lamellar Tribofilms

Abstract

It has been shown that friction coefficient of powdered lamellar compounds measured at macroscale undergoes a drastic decrease when the experiments are performed in the presence of a low-viscosity liquid. The effect was attributed to the simultaneous presence of the solid particles and the liquid in the area of contact. However, the friction reduction mechanisms are still not yet fully understood. Recently, it was found by Atomic Force Microscopy that the presence of liquid during graphite tribofilm built-up induced a nanostructuration of the film surface and it has been demonstrated that such structuration has no influence on the tribological properties measured at macroscale. In this work, we report structural and friction analyses of MoS2 tribofilms performed at nano- and macroscales, in comparison with graphite tribofilms. In addition, MoS2 and graphite tribofilm structure are investigated by means of transmission electron microscopy. The results clearly indicate that, at macroscale, friction does not always take place at the surface but could occur inside of the tribofilm depending on its nanostructuration.