Wear by friction between diamonds studied by electron microscopical techniques

This paper deals with an experimental study of possible structural changes which occur upon frictional sliding of a diamond stylus on a diamond flat. Reflection electron energy loss spectroscopy in the scanning transmission electron microscope has been applied to determine the structure of a cleaved {111} diamond surface, of a friction track on this surface and of the debris produced during frictional sliding. The structure of the debris appeared to be graphitic and different from the structure of the surface in the track, which was still diamond. As the surface studied was the cleaved {111} face, which is the hardest surface of diamond, it is assumed that the debris mainly consists of material originally belonging to the stylus. So far, no definite conclusion can be drawn about when the transformation of diamond into less dense forms of carbon takes place. The debris acts as a lubricating material which is demonstrated by monitoring the friction coefficient upon removing debris from the stylus. The outcome of this type of research is expected to throw light on the friction and polishing behaviour of different diamond surfaces. With the improving control of the orientational growth of CVD diamond, results will also be relevant to the friction and processing of these polycrystalline diamond surfaces.