Tribological And Antiwear Mechanisms Of Fluorinated Zinc Dialkyl Dithiophosphate In Comparison To Zinc Dialkyl Dithiophosphate In Engine Oils

Abstract

Tribofilms generated in wear tests using lubricants containing fluorinated ZDDP and ZDDP were studied. Fluorinated ZDDP demonstrated superior wear performance compared to ZDDP under tribological conditions even at lower phosphorus levels. Chemical properties and the molecular structure of the fluorinated ZDDP were examined and presented in a previous companion study by Parekh and Aswath [1] using techniques such as NMR and DSC while this study examines the tribological behavior of this compound and the characteristics of the tribofilms formed by it. Ball on cylinder tribological tests were conducted with lubricants containing this new fluorinated thiophosphate compound and compared to lubricants containing ZDDP. The antiwear performance of the two chemistries as well as tribofilms were then analyzed by a variety of techniques such as Scanning electron microscopy of the film as well as measuring the thickness of the film by using focused ion beam (FIB). The tribofilms were also chemically analyzed using auger electron spectroscopy (AES) and X-ray absorption near edge structure (XANES) spectroscopy. A nano-indenter was used to study the mechanical properties of the tribofilms by obtaining modulus as a function of the thickness of the tribofilm. In addition the mechanical strength of the tribofilm was evaluated by conducting nano-scale scanning wear and nano-scratch tests. These different techniques have been used to develop a phenomenological model of the tribofilms generated by fluorinated zinc dialkyl dithiophosphate compounds and ZDDP under the testing conditions of this study.