Metal oxide tribofilms: Relating antiwear additive synergy with mechanical properties.

A reduction in gear and engine oil viscosity is a potential solution in the quest for a higher efficiency transportation sector, but lower viscosity oil requires advanced antiwear additives. Zirconia nanocrystals form tribofilms that inhibit wear and scuffing while behaving cooperatively with commercial antiwear additives, suggesting that the antiwear additives may be integrated in the tribofilm, affecting its properties. This work investigates the mechanical properties of zirconia tribofilms formed with various concentrations of a phosphorus-based additive. Phosphorus integration is determined by spatially resolved compositional characterization, and nanoindentation is used to determine the mechanical properties of the formed tribofilms. We report that phosphorus can be integrated in the tribofilm bulk without influencing the hardness or elastic modulus of the tribofilm. [ABSTRACT FROM AUTHOR]