Synergistic effects of MoDTC and ZDTP on frictional behaviour of tribofilms at the nanometer scale

Sandrine Bec (1) , André Tonck (1) , Jean-Marie Georges (1) , Glyn W. Roper (2)

1 LTDS - Laboratoire de Tribologie et Dynamique des Systèmes
2 SHELL - Lubricants Technology Dept.

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 MoS2 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.

Mots clés: ZDTP; MoDTC; tribofilm structure; nanoindentation; mechanical properties; nanofriction; low friction

Domaines: Science des matériaux [cond-mat.mtrl-sci]; Mécanique [physics.med-ph]; Mécanique des matériaux [physics.class-ph]; Mécanique des matériaux [physics.class-ph]

Sandrine Bec, André Tonck, Jean-Marie Georges, Glyn W. Roper. Synergistic effects of MoDTC and ZDTP on frictional behaviour of tribofilms at the nanometer scale. Tribology Letters, 2004, 4, pp.797-809. ⟨10.1007/s11249-004-8088-7⟩. ⟨hal-00125233⟩