Nanoscale Properties of Tribofilms Formed with Zinc Dialkyl Dithiophosphate (ZDDP) Under Extreme Pressure Condition

Nanoscale properties of tribofilms formed at extreme loads under boundary lubrication were examined. The tribofilms were formed in-situ by decomposition of Zinc dialkyl dithiophosphate (ZDDP) in wear tests. Influence of detergents and antioxidants in the base ail on the wear performance was also studied. The results indicate that at lower loads the amount of phosphorus (between 0.05 to 0.1 wt%) does not affect the amount of wear occurring on the surface, on the other hand increased amounts of wear occurred at higher loads in oils with 0.05 wt% P. When detergents and antioxidants were added, relatively higher amounts of wear were observed across the board for different loads that indicate the overall antagonistic effect these additives have on the performance of ZDDP as an anti wear agent. Focused ion beam studies of the wear film indicate that the thickness of the tribofilm is approximately 100 nm and transmission electron microscopy analysis of the wear debris indicates that the tribofilm is constituted of an amorphous film of Zn-O-P-S glass with nanoparticles of Fe3O4 embedded in them.