A MODEL FOR THE BOUNDARY FILM FORMATION AND TRIBOLOGICAL BEHAVIOR OF A PHOSPHAZENE LUBRICANT ON STEEL

The dynamics of formation and loss of the boundary films formed during the lubricated sliding of steel surfaces were investigated over a ran ge of temperature and applied load. Tests were performed on a cylinder -on-disk machine using a phosphazene lubricant (X-1P), a polyphenyl et her, and mineral oil with and without addition of zinc dialkyldithioph osphate (ZDP). Among these lubricants, X-1P was found to have the best high-temperature, high-load performance. The thickness and refractive index of the boundary films were monitored in situ with an ellipsomet er, and the composition of the films was analyzed by X-ray photoelectr on spectroscopy (XPS). The performance of the lubricants was found to be closely associated with boundary film-forming ability. In order to achieve high load-carrying capacity, a boundary film must be formed. T he films formed in X-1P grow more slowly than those in ZDP-containing mineral oil, but they remain thick even at high load and high temperat ure (250 degrees C). These films are durable and effective in reducing friction and preventing scuffing. The film formed with X-1P consists of a mixture of compounds containing Fe, O, C, F, P, and N. Among the compounds formed, some form of iron fluoride appears to be most import ant in determining the performance of the film.