A study of boundary lubrication thin filmsproduced from a perfluoropolyalkylether fluid on M-50 surfaces.II. Humidity effect and topography studies

Abstract

Tribology experiments under controlled humidity were conductedusing a Cameron-Plint tribometer with an M-50 cylinder slidingon an M-50 flat specimen in the presence of a linearperfluoropolyalkylether fluid. The tests were conducted at 100,70, 59, 10, 7 and 5% relative humidities. The surface thin filmsformed on the M-50 flat specimen were studied by grazing-angle-microscope/FTIR technique. A thicker surface filmof R_fCOOH was observed for the tests conducted atrelative humidities equal to or larger than 15%. A monodentatemodel discussed in the preceding paper was adopted to be thesurface film configuration. For the lower humidity tests, anultra-thin surface film of R_fCOOH-type was observed.An asymmetrical bridging model was proposed to account for thisobservation. In addition, theν_asym,OCO band shifted to lower wavenumbers as the relative humidity of the controlled environmentwas decreased. These band shifts at different humidities warrantthe use of the multilayer model over the metal soap model toaccount for the experimentalobservation. Topographical and frictional image studies on thecylinder wear scars tested at 100, 98, 70, 59, 15 and 5% relativehumidities have been carried out using atomic force andfrictional force microscopies. Residual surface features werefound to be present on those specimens tested at 100, 98, 70, 59and 15% relative humidities. These findings are complementarywith the results obtained from the M-50 flat specimens studiedby GAM/FTIR technique.