Nanofriction of diamond coatings obtained by flame process

Abstract

With its noteworthy physical and chemical properties, diamond is expected to find many applications in various industrial fields, particularly with the expansion of the new nanotechnologies. In order to optimise their use in these specific conditions, it is essential to better understand the very complex tribological behaviour of diamond coatings. This latest is studied from a macroscopic point of view, but essential facts which occur at a nanoscopic scale are still not well known. The mechanisms involved not only in the nucleation and growth of the diamond crystals, but also in the nanofriction of the coatings, must be understood. One way to reach this purpose is to analyse the crystals morphology and behaviour at a very small scale : atomic force microscopy (AFM) seems to be a suitable technique for this work.The crystals morphology is initially studied in tapping mode; the first observations indicated that secondary growth happened on the facets. Experiments in contact mode are then carried out : the observed behaviours are different on a facet, on a crystal, or on a part of the coating. The load applied to the tip seems to have an influence too as the friction force increases when the contact load becomes higher; moreover, these variations are clearly linked to the topography of the scanned surfaces. The purpose of this nano-experimental work is to get information to better understand the friction properties of the diamond coatings at a nanoscopic scale, and to establish, if possible, a potential correlation between the behaviour noticed at the macroscopic scale, and the one obtained with AFM measurements.