Friction and nanowear of hard coatings in reciprocating sliding at milli-Newton loads

In this work, wear and friction at loads in the milli-Newton range was investigated under reciprocating sliding where wear and dissipated energy are in the range of nanometers and microjoules, respectively. Reciprocating sliding tests were performed with a modular micro-tribometer that was operated at normal forces of milli-Newton. This tribometer bridges the gap between macroscale test equipments and the atomic force microscopes. Nanowear tests were carried out for different test durations on hard coatings like DLC and TiN, with silicon nitride balls as the counterbody. After the reciprocating sliding tests at very low loads, the wear tracks were investigated with an atomic force microscope to observe topographical changes in the wear tracks, and to analyze the nanowear. The importance of AFM for characterizing the nanowear appears clearly from this work. The obtained results are compared with existing theories on friction and wear to observe their validity in low load range. The importance of contact pressure and third body interactions in the wear track is also discussed based on AFM observations.