Hamid Zaidi

Wear mechanism in graphite–copper electrical sliding contact

The electrical conduction tensor of highly anisotropic graphite is not compatible with the mechanical and tribological tensors that leads to low friction and low mechanical wear rate in sliding electrical contact. This incompatibility increases the electrical resistance and increases thus the thermal effect and the electrical contact wear. The aim of this paper is to present the tribological behaviour of couple and to discuss the effect of the antagonistic mechanical/electrical properties of polycrystalline graphite in thin rubbed layers during sliding electrical tests.

Metals transfer and oxidation of copper—steel surfaces in electrical sliding contact

Abstract Metal transfer and oxidation in a copper—steel couple sliding electric contact are studied. In previous papers we have demonstrated the influence of an electric field and a high thermal gradient. These two phenomena influence the adhesive transfer and the oxide growth at the interface that leads to the decrease of contact adhesion and to abrasive wear. The diffusion processes of oxygen in the transferred oxide layer will be summarized and a model proposed.

Combined influence of an inert gas environment and a mechanical action on a graphite surface

Abstract The adsorption and reactivity properties of graphite wear fragments produced in a tribocontact depend on the gaseous environment surrounding the contact which conditions the type of wear (fatigue or abrasive wear) and the surface reactivity. The determination of the specific area of the wear fragments, using a nitrogen adsorption method (Brunauer, Emett and Teller method), permits to reach a description of the surface structure. We carried out on a pin on disc tribometer located in a vacuum chamber wear experiments on two samples of polycrystalline graphites, under different inert gaseous environments. We observed that the size of wear fragments (as well as the friction coefficient) mainly depends on the orientation of the crystallites. This mechanical phenomenon principally depends on the nature of the environment and on the normal load. Depending on these conditions, the powder can have different colorations, and its specific area shows variations from 140 m 2 g −1 to 285 m 2 g −1 . Wear particles produced under inert environment present many active sites (edge sites) but their reactivity depends on their size and specific area. The most reactive can exhibit pyrophoric properties, when exposed to the ambient air.

Influence of Mechanical Parameters on the Friction and Wear of Sliding Brass-Steel Couple

This paper presents an experimental study of the tribological behavior of a sliding contact pin-disc. This study concerns a brass-steel dry dynamic contact where friction and wear are studied in terms of mechanical parameters, without passage of electric current. To release this study, a tribometer, pin brass rubbing against a rotating steel disc is used in an atmospheric ambiance. The testing parameters are: the normal load (5–30 N) and sliding velocity (0.1–0.5 m/s). The duration of each test is 30 min. Experimental results show that these parameters have a significant effect on the tribological behavior of the studied couple. The discussion of results is based on observations, using a profilometer, worn surfaces and interfacial phenomena resulting from the sliding contact process.