Effect of lubricant contamination with water on friction modifier properties

Friction and wear are unavoidable in mechanical systems with moving parts; however, their impact can be mitigated with the appropriate use of chemical additives in lubricants. Under severe conditions, these additives undergo tribochemical reactions, creating a low-shear strength tribofilm that reduces friction and wear. However, the tribofilm's growth and effectiveness can be adversely affected by the presence of water in the lubricant. This study proposes a new method for in-situ analysis of the effect of water on tribofilm chemical composition and growth, and its impact on friction and wear. A fully formulated oil containing Molybdenum dialkyldithiocarbamate (MoDTC) inorganic friction modifier has been tested using a bespoke pin-on-disc tribometer integrated with Raman spectroscopy. A cross-sectional analysis of in-situ grown tribofilm was carried out using Focused Ion Beam (FIB) and TEM-EDS to obtain the chemical information and thickness of the tribofilm. The results indicate that the presence of water not only negatively affects the tribological performance of MoDTC but also hampers the growth of MoDTC-derived low-friction tribofilm.