A study of boundary lubrication thin films produced from a perfluoropolyalkylether fluid on M-50 surfaces. I. Film species characterization and mapping studies

A surface thin film was observed in a wear scar area resulting from a boundary lubrication experiment performed on a reciprocating cylinder on plate tribometer. The lubricant used was a perfluoroalkylether (PFPAE) fluid. The wear scar area had blue and yellow colors observable under an optical microscope. The blue area was surrounded by an envelope of yellow scar area. The film thickness found in the blue area was approximately 15 times thicker than that observed in the yellow area. The most dramatic change in thickness occurred at the intermediate area between these two colors. The thin film species was characterized as a perfluorocarboxylate surface species chemisorbed on the wear scar area of a M-50 flat specimen. A monodentate configuration was determined to be the geometry for this surface thin film species. Thickness mapping studies along both x- and y-axes were performed on the wear scar. The x-axis thickness variations can be attributed to the normal stress distribution on the cylinder and the y-axis film thickness variation can be explained by the temperature gradient originating from the cylinder velocity variation. A "hat" model is proposed to represent the physical picture of the surface thin film species chemisorbed on the M-50 wear scar area.