Tribological Study of Various Graphite Powders Sliding Against Steel

With its high resistance, good hardness and electrical conductibility in the basal plans, graphite is used for many years in various tribological fields such as seals, bearings or electrical motor brushes, and also for applications needing excellent lubrication and wear-reducing properties. But thanks to its low density, graphite is at the moment destined for technologies for which the combination of the possibility of reducing the weight of the components, and the ability of enhancing their efficiency is a fundamental asset. This is especially the case in the aeronautical industry where composites containing carbon, and more particularly graphite, are more and more widespread. In this context, the friction and wear of industrially produced graphite powders were evaluated in order to identify promising tribomaterials for braking use. Six different powders (natural and synthetic) having various grains sizes, were tested when sliding against steel, under various applied normal loads. The morphological and structural modifications of the graphites were observed by Scanning Electron Microscopy and AFM, and analysed by Raman spectroscopy. A classification of the various graphite powders could thus be realised; the determining of the friction and wear mechanisms for the different materials, according to their own characteristics, as well as to the applied normal load, was also achieved.