ON THE RUNNING-IN BEHAVIOR OF DIAMOND-LIKE CARBON COATINGS UNDER THE BALL-ON-DISK CONTACT GEOMETRY

The running-in behaviour of a diamond-like carbon (DLC) coating deposi ted on M42 tool steel substrate has been investigated on a ball-on-dis k wear rig in dry air. During sliding, a classical running-in wear cur ve with a transition in wear rate from a high initial rate to a low ra te with sliding was observed. Variations in friction coefficient with sliding distance were not related with this transition in wear rate. A transfer film was rapidly developed on the uncoated ball surface and wear of the ball was negligible. According to Talysurf measurements an d optical observations, the width of the wear track on the disk specim en kept almost invariant with increase in sliding distance after the v ery initial sliding stages. Major change to the wear track cross-secti on profiles with sliding was the deepening of the wear track. A simula tion model for the variation in wear volume and wear track profiles as a function of sliding distance is presented based on the assumption t hat there are two different dominant wear regimes with respectively a high wear rate and a low wear rate at contact pressures above and belo w some critical contact pressure, p,. The model has been assessed usin g the Hertzian elastic contact analysis and the elastic foundation con tact model respectively to analyse contact pressures between the rubbi ng surfaces. It is shown that the running-in feature of wear results m ainly from the presence of this transition in wear rate at different c ontact pressures. Linear increase in wear volume is expected if the Ar chard's specific wear rate is assumed to be the same at any contact pr essure. Reasonably good agreement between the simulated results and ex perimental observations has been obtained. The elastic foundation mode l can be applied to simulating wear processes under any contact condit ions. (C) 1998 Elsevier Science S.A. Ah rights reserved.