Microstructural Evolution of Alumina Layers on an Al–Cu–Fe Quasicrystal during High-Temperature Oxidation.

The oxidation of a quasicrystal with the nominal compositionAl63Cu25Fe12 was studied around 800°Cin environmental and synthetic air by means of thermogravimetric analysis,electron microscopy, and analytical electron spectroscopy. In an earlyoxidation stage, γ-Al2O3 formed with an orientational relationship tothe quasicrystal. At the oxide–metal interface, γ-Al2O3transformed into large hexagonal shaped α-Al2O3grains. The change in surface morphology indicated that at theoxide–gas interface γ-Al2O3 continued togrow as Θ-Al2O3. Locally the metastable aluminalayer was transformed thoroughly into α-Al2O3,which then continued to grow with a nodular morphology. On top of the oxidenodules, several at.% of Cu2+ were detected. [ABSTRACT FROM AUTHOR]