INTERFACIAL CHEMISTRY OF HIGH-TEMPERATURE SCALING

This paper summarizes some recent work concerning the chemistry of interfaces, particularly impurity segregation to interfaces and displacement reactions which can occur at the metal/oxide interface. Different methods of specimen preparation to examine interfaces include a sputter ion plating technique which simulates oxide spalling and ultrahigh vacuum in situ bending and scratching techniques. Data are obtained most commonly from techniques such as Auger electron spectroscopy and secondary ion mass spectrometry. Surveys, profiles and elemental maps provide 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 shows that impurity segregation and interfacial displacement reactions are important in defining and understanding the chemistry of interfaces, and in turn are likely to influence mechanical properties such as oxide adhesion and spalling.