High Friction Mechanism of ZDDP Tribofilm Based on in situ AFM Observation of Nano-Friction and Adhesion Properties
Kaisei Sato, Seiya Watanabe, Shinya Sasaki
Abstract
Abstract Zinc dialkyl dithiophosphate (ZDDP) is a typical anti-wear additive that forms tribofilm on sliding surfaces and prevents adhesion wear but increases the friction force. In this study, the nano-friction and adhesion properties of ZDDP tribofilms were investigated by performing in situ observations by atomic force microscopy to explore the relationship between the formation process and physical properties of ZDDP tribofilm. The results showed that the nano-friction force increased with the formation of the ZDDP tribofilm. In addition, the adhesion force on the ZDDP tribofilm increased with the friction force. It was confirmed that the Young's modulus and nanoindentation hardness of the ZDDP tribofilms were lower than those of steel. However, the contact areas calculated using the Derjaguin–Muller–Toporov (DMT) contact theory were similar. In addition, the shear strengths calculated using the DMT model of the ZDDP tribofilm were substantially higher than those of steel.