High resolution imaging of macroscopic wear scars in the initial stage

Abstract

The topography of wear scars on the surface of a steel disc coated with a diamond-like carbon (DLC) layer has been investigated with an Atomic Force Microscope (AFM).AFM topography images have been combined together taking advantage of the stitching technique for the study of wear scars in their initial stage. Moreover, the topography of the sample has been acquired before and after the sliding tests. In this way even very small changes of the sample surface (<10nm) can be detected.Three main phenomena taking place at the very initial stage of wear could be identified: the abrasion of small asperities bulging out of the sample surface, the carving of swallow grooves with depth under 20nm, and the partial or total closure of cavities present on the surface. This last phenomenon shows that, before the carving of a wear scar, the plastic deformation of particular regions of the sample, i.e. the volume around the cavities, takes place already after few cycles (in this case between 400 and 800) in the initial phase of the sliding test.