Nano-tribological and wear behavior of boric acid solid lubricant

One uses atomic force microscopy to explore the surface morphology, frictional characteristics (ie.,friction mapping) and surface adhesive forces of boric acid-treated aluminum surfaces. In earlier studies, boric acid was shown to be an effective solid lubricant providing 0.02 to 0.1 friction coefficients to the sliding surfaces of metallic and ceramic materials. In this study, the authors mainly focused on the friction and wear behavior of cleaved single crystals of boric acid. Tests were performed on uncoated and boric acid-coated surfaces of aluminum substrates, as well as the bulk boric acid material. The nano-scale wear of the boric acid crystals manifested itself in the displacement of atomic planes which, in turn, resulted in the formation of thr wont area grown by a spiral-growth mechanism. In addition, new crystals in the vicinity of the sliding contact areas were formed. These crystals formed by a spiral dislocation mechanism. The nanoscale friction measurements showed that the friction coefficient of a Si3N4 tip against the boric acid single crystal was in the range of 0.07 to 0.13, depending on the sliding direction with respect to the crystallographic orientation. The friction coefficients of the boric acid-coated aluminum substrates varied between 0.11 and 0.19. While these values were consistent with earlier findings and further demonstrated the lubricity of boric acid, they were higher than the previous measurements (i.e., 0.011-0.1) obtained on a pin-on-disk machine using steel or ceramic pins. An explanation is provided for this phenomenon.