A Multi Technique Study of the Tribological Behavior and the Tribofilms Generated From Fluorinated Thiophosphate Compounds in Comparison to Normal ZDDP

Tribofilms generated in wear tests using lubricants containing a new fluorinated compound and Zinc Dialkyl Dithiophosphates (ZDDP) were studied. This compound has demonstrated superior wear performance compared to ZDDP under tribological conditions even at lower phosphorus levels which partly addresses the current environmental concerns and regulations calling for further reductions in the phosphorus content of commercial engine oils. Chemical properties and the molecular structure of the Fluorinated Thiophosphate Compound were examined and presented in a companion study by Parekh and Aswath [1] using techniques such as NMR and DSC while this study examines the tribological behavior of this compound. Ball on cylinder tribological tests were conducted with lubricants containing this new fluorinated thiophosphate compound and compared to lubricants containing ZDDP. The anti wear performance of the two chemistries as well as tribofilms were then analyzed by a variety of techniques such as scanning electron microscopy (SEM) 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). 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 tribowear and nano scratch tests. These different techniques have helped establish the mechanism of why the Fluorinated Thiophosphate Compounds are better antiwear compounds in comparison to ZDDP.