Impact of Tribofilm on the Anti-Wear and Friction-Reduction Properties of Interfaces

Abstract Zinc Dialkyl Dithiophosphate (ZDDP) is widely used in internal combustion engine lubricating oil, which forms tribofilm and effectively blocks the direct contact of the material interface. Tribofilm plays an important role in wear resistance and lubrication performance. This study analyses ZDDP additive lubricant performance and the tribofilm distribution under different concentrations and loads. Tribofilm formation and wear mechanism is characterized by Scanning electron microscope (SEM) and Energy dispersive x-ray spectrometer (EDS), and the lubrication performance is further explained by the Atomic Force Microscope (AFM). This study explored the anti-wear and friction-reducing properties of ZDDP tribofilm respectively, revealing that ZDDP tribofilm distribution plays a pivotal role in reducing wear, the wear amount can be reduced by 50%, but has a slight effect on friction-reducing, only 5.7%. In addition, the concentrations and loads significantly affect the growth of the tribofilm, and change the wear and lubrication characteristics. The tribofilm acts as a significant barrier, effectively protecting the surface from wear. However, excessive pressure may lead to the failure of the tribofilm, resulting in the loss of protection and subsequent severe wear of the surface. Furthermore, the mechanisms of lubrication are explained, wherein the tribofilm serves as micro-texture, reducing direct contact between asperities and thereby lowering the friction coefficient.