Friction and wear mechanisms of tungsten-carbon systems: a comparison of dry and lubricated conditions.

The unfolding of a sheared mechanically mixed third-body (TB) in tungsten/tungsten carbide sliding systems is studied using a combination of experiments and simulations. Experimentally, the topographical evolution and the friction response, for both dry and lubricated sliding, are investigated using an online tribometer. Ex situ X-ray photoelectron spectroscopy, transmission electron microscopy, and cross-sectional focused ion beam analysis of the structural and chemical changes near the surfaces show that dry sliding of tungsten against tungsten carbide results in plastic deformation of the tungsten surface, leading to grain refinement, and the formation of a mechanically mixed layer on the WC counterface. Sliding with hexadecane as a lubricant results in a less pronounced third-body formation due to much lower dissipated frictional power. Molecular dynamics simulations of the sliding couples predict chemical changes near the surface in agreement with the interfacial processes observed experimentally. Finally, online topography measurements demonstrate an excellent correlation between the evolution of the roughness and the frictional resistance during sliding.