Open Access Version (externer Anbieter)

Abstract:
The high temperature performance of iron aluminides depends on the formation of a protective α-Al2O3 scale which adheres to the metal substrate and prevents destructive oxidation or corrosion. The present thesis is concerned with two important aspects of the oxidation resistance of iron aluminides: the formation of less protective Al2O3 polymorphs and the development of internal stresses within the oxide scale, which are intrinsic to the oxidation process. In order to monitor the evolution of phase composition and internal stresses in oxide scales a series of in-situ experiments using synchrotron X-ray diffraction were performed on different iron aluminide samples, submitted to both low and high temperature oxidation regimes. The in-situ diffraction studies were supplemented by a number of additional ex-situ experiments, with special attention to X-ray photoelectron spectroscopy and transmission electron microscopy, which allowed for the characterization of oxide scale microstructures, chemical and phase composition. By applying synchrotron radiation to in-situ investigations of the oxidation process, the evolution of internal stresses and the formation of crystallographic texture could be visualized in multi-layered oxide scales with thicknesses as low as 80-100nm. Since studies of such thin oxide films have rarely been performed, the present investigations were able to clarify important aspects of the mechanisms of strain formation during oxidation, which remain yet to be fully understood for a number of metal-oxide systems, especially for multi-phased oxide scales.