WTC2005-63960 ANTIWEAR CHEMISTRY IN PRESENCE OF ZDDP

ABSTRACT Antiwear chemistry is related to the role of tribochemical reactions in controlling abrasive wear, adhesive wear as well as physical and mechanical properties of tribofilms. In the case of additives in boundary lubrication, three different chemical reactions have been found to be directly connected to mechanical response. First one is the digestion of hard metal oxides in the glassy tribofilm formed from the antiwear additives, thus combating with abrasive wear. Second reaction is the reaction of sulphur species with nascent metal surfaces, reducing adhesive wear between antagonist metal surfaces. The third reaction is an equilibrium one in the stressed tribofilm, leading to a change of mechanical properties of the tribofilm and explaining its smart behavior. INTRODUCTION Since the pioneering work of Heinecke in 1984, tribochemistry is a growing field in tribology and particularly under mixed and boundary lubrication. Zinc dithiophosphate (ZDDP), the classical antiwear additive, is certainly the best model to study tribochemical reactions. Today, one of the reasons to study more and more ZDDP is certainly to better anticipate its replacement in the coming years. Products of tribochemical reactions with ZDDP have been extensively studied in the past 10 years from the point of view of the chemical and mechanical characterization. The use of new analytical tools and especially the synchrotron radiation has allowed focusing on important features in the tribofilm composition. This is described in details in a series of papers by Kasrai et a