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The layered structure and the rheological properties of anti-wear films generated in a rolling/sliding contact from lubricants containing zinc dialkyldithiophosphate (ZDTP) and/or molybdenum dialkyldithiocarbamate (MoDTC) additives have been studied by dynamic nanoindentation experiments coupled with a simple modelling of the stiffness measurements. Local nano-friction experiments were conducted with the same device in order to determine the evolution of the friction coefficient as a function of the applied pressure for the different lubricant formulations. For the MoDTC film, the applied pressure in the friction test remains low (<0.5 GPa) and the apparent friction coefficient is high (µ>0.4). For the tribofilms containing MoDTC together with ZDTP, which permits the applied pressure to increase up to a few GPa through some accommodation process, a very low friction domain appears (0.01<µ<0.05), located a few nanometers below the surface of the tribofilm. This low friction coefficient is attributed to the presence of MoS 2 planes sliding over each other in a favourable configuration obtained when the pressure is sufficiently high, which is made possible by the presence of ZDTP.

Silicon oxide-doped hydrogenated amorphous carbons (a-C:H:Si:O) are amorphous thin films used as solid lubricants in a range of commercial applications, thanks to its increased stability in extreme environments, relative to amorphous hydrogenated carbons

International audienceSeveral models have been developed to extract the intrinsic elastic modulus of thin films from the composite film/substrate modulus value obtained from indentation tests on coated systems. Either analytical, semi-analytical or empirical, they generally propose an expression of the composite modulus as a function of the film and substrate elastic moduli and of the film thickness. When the substrate's properties and the film's thickness are known, the expression without adjustable parameter contains only the film elastic modulus as unknown parameter, which can thus be deduced. In this paper, some models from the litterature are briefly described and compared with the easy-to-use model we have developed. Based on experimental results obtained with various film/substrate systems, this paper also aims to demonstrate that the error induced by the uncertainty in the knowledge of the substrate's Young modulus value and in the film's thickness value is often as large as the difference resulting from the choice of the model

Nanoindentation tests were performed at several temperatures (24 to 80°C) on one antiwear zinc dialkyl-dithiophosphate (ZDTP) tribofilm using a Nanoindenter XP ® 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 ( ) 2 F S 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.