CHARACTERIZATION OF SURFACE-LAYERS ON M-50 STEEL EXPOSED TO PERFLUOROPOLYALKYLETHERS AT ELEVATED-TEMPERATURES

Complex surface layers have been identified on M-50 steel samples expo sed to a linear perfluoropolyalkyether (PFPAE) in the presence of air at 260 degrees C, An understanding of the mechanisms that drive the fo rmation of these layers is believed to be crucial for efforts to devel op PFPAEs as effective lubricants for advanced high temperature turbin e engines, Work presented here shows that the extreme surface region c ontains physisorbed PFPAE and Fe fluoride under which an Fe3O4 layer i s observed followed by an FeF2, layer which is adjacent to the substra te, similar layered structures have been observed for Fe-containing ma terials exposed to HF but have not been reported for PFPAE systems. X- ray photoelectron spectroscopy (XPS) and conversion electron Mossbauer spectroscopy (CEMS) were used to unambiguously characterize these lay ers, (C) 1998 Elsevier Science B.V. All rights reserved.