INTERFACIAL CHEMISTRY OF HIGH-TEMPERATURE SCALING

This paper summarizes some recent work concerning the chemistry of int erfaces, particularly impurity segregation to interfaces and displacem ent reactions which can occur at the metal/oxide interface. Different methods of specimen preparation to examine interfaces include a sputte r ion plating technique which simulates oxide spalling and ultrahigh v acuum in situ bending and scratching techniques. Data are obtained mos t commonly from techniques such as Auger electron spectroscopy and sec ondary ion mass spectrometry. Surveys, profiles and elemental maps pro vide information regarding the chemical composition of the interface. Emphasis is placed on studies of Cr2O3 on Fe-Cr alloys and Fe-Cr-Ni-Nb -stabilized steel and Al2O3 on Fe-Cr-Al and beta-NiAl. The observation of sulphur segregation at the metal/oxide interface is considered in some detail, as well as the role of reactive elements. The research sh ows that impurity segregation and interfacial displacement reactions a re important in defining and understanding the chemistry of interfaces , and in turn are likely to influence mechanical properties such as ox ide adhesion and spalling.