Microtribology and Friction-Induced Material Transfer in WS2 Nanoparticle Additives

The tribological behavior of platelet and nested colloidal particles of tungsten disulfide was studied using the surface forces apparatus, atomic force microscopy, lateral force microscopy, and Auger spectroscopy. Shear-induced material transfer from the colloidal particles to the surfaces was shown to be a dominant factor in the tribological behavior observed for both structures. An ultrathin, ordered layer was observed when nested particles were sheared, while WS2 platelets produced a rough and disordered transfer layer, with substantially inferior lubricating properties.