Nanoscale Evolution of Sliding Metal Surfaces During Running-in

We studied the formation of tribologically induced nanocrystalline layers in lubricated contacts during running-in using a pin-on-disk tribometer coupled to a radionuclide high-resolution wear measurement system. The experiments were stopped after different running times and the sliding surfaces were analysed by atomic force microscopy, auger electron spectroscopy and focused ion beam analysis. Initially, at very high wear rates, zinc phosphate anti-wear films are formed in the contact regions of the surfaces, which slow down the wear process. During rubbing the formed films will submerge below the surface of the materials as result of large plastic deformations. This process affects the friction coefficient and the wear rate and is considered to be a key mechanism for the running-in.