Interaction of M-50 Steel with a Perfluoroalkylether Fluid and a 1% Additive Fluid Formulation

X-ray photoelectron spectroscopy (XPS) has been used to characterize the passivation film formed on the surface of M-50 tool steel coupons during oxidation-corrosion (O-C) testing in a perfluoroalkylether fluid containing a perfluoroalkylether aryl phosphine additive. Prior to analysis of the metal coupons, samples of the additive and fluid which had not undergone O-C testing were characterized with XPS. The measured At% compositions of the fluid and additive were found to agree well with the compositions ascertained from the formulae. On metal coupons which had undergone O-C testing in additive-fluid formulations, there were corroded regions as well as regions protected from corrosion. Surface phosphorous levels on the protected regions were found to be roughly five hundred times greater than in the additive alone and five hundred times that expected from the formulation. This suggests that in the protective action afforded during the O-C test, the additive has changed chemistry and the new adduct is bound to the surface of the steel.