Tribological behavior of Dy-sialon ceramics sliding against Si₃N₄ under lubrication of fluorine-containing oils

The friction and wear behavior of dysprosium (Dy)-sialon ceramics sliding against Si₃N₄ under lubrication of perfluoropolyethers (PFPE), phosphazene (X-1P) and ionic liquid (1-methyl-3-octylimidazolium tetrafluoroborate, coded as L108) was investigated at room temperature and 150°C. The morphology of the worn sialon surface was analyzed with a scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS). It was found that the anti-wear and friction-reducing properties of the three fluorine-containing lubricants for sialon ceramic at 20 °C can be ranked as L108 > X-1P > PFPE. Under the load of 0.5-60 N and at the temperature of 20 or 150°C, X-1P and L108 are effective lubricants for Dy-sialon, and show superior tribological properties to PFPE and glycerol. The decreased friction coefficient and wear volume of Dy-sialon ceramics under lubrication of the three fluorine-containing lubricants are attributed to the tribochemical products mainly consisting of organic oxyfluoride or carbonfluoride species and silicon fluoride, while the degradation of PFPE during friction might account for the higher wear volume therewith. The lowest friction coefficient 0.065 was recorded for L108 under load of 20-80 N. This is dependent on the formation of B₂O₃ and BN on the worn surface.