Temperature Effects on Mechanical Properties of Zinc Dithiophosphate Tribofilms

Nanoindentation tests were performed at several temperatures (24 to 80degC) on one antiwear zinc dialkyl-dithiophosphate (ZDTP) tribofilm using a Nanoindenter XP (R) entirely set into a climatic chamber. Mechanical properties of the tribofilm were determined using a simple model. AFM observations were conducted to estimate the order of magnitude of the film's thickness. The effect of applied pressure on the elastic properties was demonstrated and taken into account in the present analysis. The use of the F/S^2 parameter, independent of contact geometry, revealed a hardness dependency upon temperature. Furthermore, careful AFM observations of the residual pile-up produced by plastic flow around the indents pointed out the evolution of the film deformation process with temperature.