Surface modifications induced by the friction of graphites against steel

Graphite is a well-known, multipurpose material used in many applications including tribology, electrochemistry and metallurgy. In this study, we focused our attention on the modifications of the surfaces of graphite pins, one natural and two synthetic, in dynamic contact against steel. Specifically, we explored the effect of the normal load applied to the contact, on the friction behaviour of graphites. The results of the series of tests under “low” loads indicated that the friction coefficient and the transfer film forming tendency increased with increasing load, due to the modification of the morphology of the contact area. Whereas experiments under “high” loads revealed the existence of a critical load at which a sudden decrease of both the coefficient of friction and the transfer film forming tendency is observed. The reorientation of the graphitic planes is supposed to be at the origin of this phenomenon.