Role of surface chemistry on the nature of passive oxide film growth on Fe-Cr (low and high) steels at high temperatures

High temperature materials degradation or protection of Fe-Cr alloys are often related to the nature of their oxide scale formation. Breakdown of passive oxide films lead to localized corrosion. Various alloying elements are often incorporated in these alloys to prevent high temperature oxidation. The addition of selected alloying elements is cumbersome and not always cost effective. In this article, we investigate the role of rare earth oxide coatings on high temperature corrosion prevention of both low and high Cr steel. An in situ high temperature oxidation setup has been built to study the oxidation kinetics of both coated and uncoated low and high Cr steels under ambient pressure and dry air. Reduction in scale growth kinetics is observed in the presence of coating. While scanning electron microscopy and x-ray diffraction are employed to study the structure and morphology bf the oxide films, x-ray photoelectron spectroscopy and Auger electron spectroscopy are used to study the surface chemistry of the oxide layer. This article relates some of these data to explain the nature of scale growth kinetics (linear or logarithmic or parabolic) observed in both low and high Cr steels. (C) 1999 American Vacuum Society. [S0734-2101(99)11304-6].