Friction behaviour of solid oxide lubricants as second phase in alpha-Al2O3 and stabilised ZrO2 composites

The influence of metal oxide additives within alumina (?-Al2O3) and yttria-stabilised tetragonal zirconia (Y-TZP) matrices was studied with respect to the tribological behaviour of the composites. The solid lubricants CuO, ZnO, MgO, MnO2 and B2O3 were added in sufficiently small quantities (1 or 5 wt.%) to preserve the mechanical properties of the matrix phase without increasing the specific wear rate. The additives selected were an attempt to provide the materials with a self-lubricating mechanism and therefore decrease the coefficient of dry-friction. The ceramics were prepared by means of wet-ball milling powders, compaction by isostatic pressing and densification by sintering. Near-full densities (98?99%) were obtained for all ceramics except that containing CuO (92%). Tribological behaviour of the various composite compositions was tested on a pin-on-disk assembly using both ?-Al2O3 and ZrO2 as counter surface. Friction reductions of almost 40% for the CuO composite was obtained while the influence of the other oxide additives were less pronounced.