THE FORMATION OF ALUMINUM-OXIDE SCALES ON HIGH-TEMPERATURE ALLOYS

This paper is a brief review of the extensive literature relating to the formation of protective alpha-Al2O3 scales on alloys at high temperature. Emphasis is placed on the proposed mechanisms of scale growth based on observations of scale morphologies and microstructures, inert-marker experiments and the distribution of oxygen isotope tracers within thermally-grown oxides. Attention is also given to the determination of ionic-transport mechanisms by electrochemical methods and to the effects of reactive elements such as yttrium in modifying ionic-diffusion processes.