  Graphene nanoplatelets (GNPs) have emerged as one of the most promising
filler materials for improving the tribological performance of ceramic
composites due to their outstanding solid lubricant properties as well as
mechanical and thermal stability. Yet, the addition of GNPs has so far provided
only a very limited improvement in the tribological properties of ceramics,
particularly concerning the reduction of their friction coefficient. This is
most likely due to the challenges of achieving a lubricating and protecting
tribo-film through a high GNP coverage of the exposed surfaces. Here we show
that this can be achieved by efficiently increasing the exfoliation degree of
GNPs down to the few-layer (FL) range. By employing FL-GNPs as filler material,
the wear resistance of Si3N4 composites can be increased by about twenty times,
the friction coefficient reduced to nearly its half, while the other mechanical
properties are also preserved or improved. Using confocal Raman microscopy, we
were able to demonstrate the formation of a continuous FL- GNP tribo-film,
already at 5wt% FL-GNP content.
