Defect-Diffusion-Stress Relationships in Modeling the Oxidation and Degradation Processes of Alumina Formers: A Brief Survey
In the modeling of the oxidation and degradation processes of the superior metallic materials in terms of the high temperature oxidation resistance, being the so-called alumina formers, the matter transport only via grain boundaries of α-Al2O3 is usually taken into account. This paper indicates that such an approach needs to be re-visited. It is pointed out that the following factors should be taken into account (i) diffusion via point defects in the unstable alumina polymorphs (γ, δ, θ) which grow during the early oxidation stages; (ii) dislocation-related processes; (iii) formation of the oxide in three-dimensional defects, being the cracks in the oxide layer; (iv) outward oxide growth resulting from the formation of the new oxide within the existing layer. The mentioned above effects as well as the other ones, related to the interfacial and stress-induced processes are illustrated and discussed. It is pointed out that alumina formers constitute a wide group of materials and several categories should be distinguished among them with respect to their composition and production route on one hand, and the oxidation and degradation mechanisms, on the other hand. It is shown that the comprehensive approach enables better and self-consistent modeling of the oxidation and degradation mechanisms of alumina formers.
M. Danielewski, R. Filipek, R. Kozubski, W. Kucza, P. Zieba, Z. Zurek
J. Jedlinski "Defect-Diffusion-Stress Relationships in Modeling the Oxidation and Degradation Processes of Alumina Formers: A Brief Survey", Defect and Diffusion Forum, Vols. 237-240, pp. 911-921, 2005