Role of monodispersed nanoparticles on the tribological behavior of conventional epoxy composites filled with carbon fibers and graphite lubricants

The present work focuses on the role of monodispersed SiO2-nanoparticles, with an average diameter of 20 nm (as introduced via a sol–gel process), on the tribological behavior of conventional epoxy (EP) composites, i.e. EP filled with short carbon fibers and graphite flakes. Moreover, the contribution of these nanoparticles was directly compared to that of sub-micron (TiO2/ZnS) particles (300 nm in diameter). In particular, the tribological performance of the composites when sliding either against a rough stainless steel (Ra=0.30 μm) surface or an initially mirror polished counterface (Ra=0.01 μm) was compared. The monodispersed nanoparticles lead to a significant reduction in the friction and wear rate, and they contribute significantly better to the tribological performance than the sub-micron particles. When sliding took place against the rough surface, the nanoparticles resulted in an extremely thin transfer film, which was created from the initial roughness while its grooves were filled up completely. A rough counterface seems to be an essential precondition for the starting of material transfer. With the polished counterface, significant material transfer starts only after the countertface is scratched. This is true especially for the conventional composite and the hybrid composite reinforced with sub-micron particles. Whereas, the addition of nanoparticles promotes the formation of a homogeneous transfer film before the counterbody is severely scratched.