Third body processes and friction of solid lubricants studied by in situ optical and Raman tribometry

摘要

A tribometer incorporating in situ optical microscopy and Raman spectroscopy has been used to study third body processes and friction during sliding against three low friction coatings: amorphous Pb-Mo-S; diamond-like nanocomposite (DLN); and annealed boron carbide. Reciprocating sliding tests were performed in both dry and humid air with transparent hemispheres (glass or sapphire) loaded against the coatings. Videos and Raman spectra of the sliding contact were recorded during the tests. In all three cases, the friction behavior could be explained in terms of the relative motion between a transfer film on the hemisphere and the wear track. With amorphous Pb-Mo-S, the transfer film was MoS_2; with DLN, it was a graphite-like carbon; and with annealed boron carbide, it was either a mix of H_3BO_3 and carbon (at μ = 0.08) or, when the H_3BO_3 wore away, carbon alone (at μ = 0.2). Friction rises with Pb-Mo-S and DLN in humid air were ascribed to a change in interfacial shear strength; friction spikes and fluctuations with DLN were associated with periodic loss of transfer film thickness. For all three coatings, interfacial sliding was the dominant velocity accommodation mode.