  Previous studies have shown that the elastic properties of Zinc
Dialkyl-dithiophosphate (ZDTP) tribofilms measured by nanoindentation increase
versus applied pressure (Anvil effect) [1, 2]. The aim of this paper is to
demonstrate that, up to 8 GPa, this increase is a reversible phenomenon. A ZDTP
tribofilm has been produced on "AISI 52100" steel substrate using a
Cameron-Plint tribometer. After its formation, a hydrostatic pressure of about
8 GPa was applied during one minute on the tribofilm using a large radius steel
ball ("Brinell-like" test). Nanoindentation tests were performed with a
Berkovich tip on pads in order to measure and compare the mechanical properties
of the tribofilm inside and outside the macroscopic plastically deformed area.
Careful AFM observations have been carried out on each indent in order to take
into account actual contact area. No difference in elastic properties was
observed between the two areas: tribofilm modulus and pressure sensitivity are
the same inside and outside the residual hemispherical print. This demonstrates
that Anvil effect is a reversible phenomenon in the studied pressure range.
