Pierre Ponthiaux

Tribocorrosion: Material Behavior Under Combined Conditions of Corrosion and Mechanical Loading

Oxide particles, referred to as ‘debris”, are released from the contacting materials. Then, the debris can be removed from the contact zone or on the contrary trapped in it. In the case of removal, the debris dissolve chemically or are dragged out by a hydraulic flow along the material surface. In this case, the tribocorrosion mechanism is based on a repeated tearing off of the oxide after each contact and eventually a removal of some of the underlying material depending on the intensity of mechanical stress acting on the contacting materials. The major concern is then to quantify and eventually to model the kinetics of repassivation as accurately as possible. This type of tribocorrosion process can be classified as an oxidative wear mechanism as, for example, the ‘mild oxidative wear model’ (Quinn, 1992). In the case of debris trapping, one has to consider that under appropriate hydrodynamical, chemical, and thermal contact conditions and relative speed of the two contacting bodies, the debris will remain temporarily in the contact zone mainly as colloids with a diameter usually in the range of a few hundred nanometers. Two cases may then be distinguished: (a) the debris accelerates the wear in comparison to the case of debris-free contacts is accelerated by an abrasive effect, or (b) the debris slows down the wear compared to the case where the contact zone is free of any debris, resulting in a protective effect.

Nanotribology on individual phases of duplex steel: combining roughness, material effects, and friction

In this study, lateral force microscopy (LFM) technique was used to investigate local friction and wear behaviour on individual phases of dual phase steel. Important factors influencing friction interpretation at nanoscale are investigated. A nanoprobe made of silicon nitride (20 nm tip radius) was used for this investigation. The difference in phases is clearly apparent when the surface is smooth but with a slight increase in surface roughness, the frictional difference between the phases got masked. A clear direct dependence of friction force on normal force was observed at nanoscale as predicted by Derjaguins friction model. This model appeared to be valid irrespective of the surface roughness modifications on different phases of the material. The tip wear phenomenon was detected through adhesion force measurements before and after the test. Even at nanoscales, the wear resistance was found to be directly dependent on the hardness of the phases.