The lubricated wear of ceramics .2. The wear and friction of silicon nitride and steel in the presence of mineral oil or an ester based lubricant

The influence of the lubricant upon the friction and wear characteristics of the silicon nitride and steel couples investigated in the experiments described in Part I of this paper has been determined for a solvent refined mineral oil and an ester based lubricant. Whereas the ester based lubricant provided greater protection for the ceramic pins than did the mineral oil under modest sliding speeds and identical loads, the reverse was true during the more severe running-in conditions. The relatively high wear factor of 10(-9) mm(3)/Nm recorded for the ester based lubricant during running-in was about an order of magnitude greater than that observed with mineral oil, and appeared to be associated with oxidation and the production of corrosive acids. With the ester based lubricant, steel pins wore at a lower rate throughout the tests than in the mineral oil, probably because of the higher thermal conductivity of the metal and the consequent reduction of both the contact temperatures and the formation of corrosive acids from the ester.