Evaluation of Anti-Wear Performance of PFPE-Soluble Additives under Sliding Contact in High Vacuum

The anti-wear performances of perfluoropolyether (PFPE)-soluble additives were evaluated under vacuum using a vacuum four-ball tribometer with 440C stainless steel balls as test specimens. PFPE derivatives having the hydroxyl, carboxyl and phosphate groups at the end of the Type D-PFPE molecules were studied. The addition of either PFPE-soluble carboxylic acid or PFPE-soluble phosphates to the PFPE base oil remarkably reduced steady wear rates in a vacuum environment, whereas the addition of PFPE-soluble alcohol did not. Contrary to the performance in vacuum, an appreciable increase in wear rate was observed in the air atmosphere with all the types of additives used. The effect of moisture is studied in explaining the high wear rates obtained with the additives in the air environment. The mechanism of boundary lubrication with PFPE-soluble additives is discussed. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Lahaina, Hawaii, October 16–20, 1994