Surface Reactions of Extreme Pressure Additive on Steel Surface in Ceramics-Steel Couples

Abstract

The behavior of zinc dithiophosphate (ZnDTP) is investigated for the antiwear properties in SiC-steel and Si3N4-steel sliding contact systems under boundary lubrication. Reaction products formed on the steel surfaces under the sliding contact differ in the chemical compositions and the thickness between these couples. These differences are specifically related to the physical properties of mating materials such as heat conductivity and friction coefficient. The reaction products are analyzed by SEM (scanning electron microscope), EPMA (electron probe microanalysis), AES (Auger electron spectroscope), and PAS (photoacoustic spectroscopy), and it is confirmed that iron phosphate for SiC-steel and iron phosphate and zinc sulfide (or some complex compound containing equal amounts of Zn and S in atomic ratio) for Si3N4-steel couple exist on the steel surface, respectively. An examination is conducted on steel-steel couple in comparison with ceramics-steel couples, and the atomic ratio (Zn:P:S) of the constituent elements of the reaction products coincides fairly with that of SiC-steel couple.