Limitations on the use of ceramics in unlubricated sliding applications due to transfer layer formation

The tribological mechanisms in contacts with alumina (Al₂O₃), partially stabilized zirconia (PSZ), silicon carbide (SiC) and silicon nitride (Si₃N₄₎ sliding unlubricated on steel and on themselves were studied with a pin-on-disc apparatus at a 10 N normal load and a 0.2 m s⁻¹ sliding velocity. Of the material combinations investigated, only alumina and silicon carbide against themselves and possibly silicon carbide against steel are applicable in continuously operating unlubricated sliding contacts. Strong formation of tribological transfer layers occurred in most of the material combinations studied, the direction of the materials transfer being governed by the thermal, chemical and mechanical conditions in the sliding interface. The transfer direction was material-dependent when ferrous material was transferred from steel to alumina and when silicon-based material was transferred from silicon carbide and silicon nitride to steel. With PSZ and steel the transfer layer formation was geometry-dependent, the material mainstream being from the pin to the disc.