Lateral Force Microscopy with micrometer-sized particles: Effect of wear on adhesion and friction

In this work, Lateral Force Microscopy (LFM) has been used to measure the frictional characteristics of the contact of 20μm glass beads and UO3 particles attached to silicon tapping mode cantilevers. The substrates used were glass, mica and UO2 single crystals cleaved to form flat surfaces. Flatness of the substrate is necessary to remove the influence of the topography of the substrate on the friction signal. Reverse imaging was used to ensure that the particles attached to the cantilevers were free from contamination and to detect any alteration to the particles surfaces such as wear. Atomic Force Microscopy (AFM) tapping mode images of the substrates acquired before and after the friction experiment were used to identify any wear of the substrates, or the presence of wear debris from the particles. The adhesion between particle and substrate was also measured during the experiment. Two kinds of wear mechanisms were identified: adhesive wear and abrasive wear. In the case of adhesive wear the particle was flattened, the adhesion increased during the experimental run and wear debris from the particle was left on the substrate after the experiment. In the case of abrasive wear, the particle excavated a groove in the substrate. The dependence of the friction and adhesion forces with the load force specific to the type of wear is discussed.