Influence of Surface Roughness on the Lubrication Effect of Carbon Nanoparticle-Coated Steel Surfaces

In the present study, a systematic evaluation of the influence of the surface roughness on the lubrication activity of multiwall carbon nanotubes (MWCNT) and onion-like carbon (OLC) is performed. MWCNT and OLC are chosen as they both present an sp2-hybridization of carbon atoms, show a similar layered atomic structure, and exhibit the potential to roll on top of a surface. However, their morphology (size and aspect ratio) clearly differs, allowing for a methodical study of these differences on the lubrication effect on systematically varied surface roughness. Stainless steel platelets with different surface finishing were produced and coated by electrophoretic deposition with OLC or MWCNT. The frictional behavior is recorded using a ball-on-disk tribometer, and the resulting wear tracks are analyzed by scanning electron microscopy in order to reveal the acting tribological mechanisms. It is found that the lubrication mechanism of both types of particles is traced back to a mixture between a rolling motion on the surfaces and particle degradation, including the formation of nanocrystalline graphitic layers. This investigation further highlights that choosing the suitable surface finish for a tribological application is crucial for achieving beneficial tribological effects of carbon nanoparticle lubricated surfaces