Proceedings of the 3rd International Symposium on High Temperature Corrosion and Protection of Materials
Actes du 3ème Colloque International sur la Corrosion et la Protection des Matériaux à Haute Température

J. Phys. IV France 03 (1993) C9-217-C9-230
DOI: 10.1051/jp4:1993920

The reactive element effect (REE) in oxidation of alloys

Yasutoshi Saito^{1, 2}, Bülent Önay^{3, 2} and Toshio Maruyama<sup>4

1</sup>  National Institution for Academic Degrees, 4259 Nagatsuta-cho, Midori-ku, Yokohama 227, Japan
²  Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152, Japan.
³  High Temperature Materials Section, 2nd Materials Department, Hitachi Research Laboratory, Hitachi Ltd., 3-1-1 Saiwai-cho, Hitachi-shi, Ibaraki-ken 317, Japan
⁴  Department of Metallurgical Engineering, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152, Japan

Abstract
The reactive element effect (REE) in high temperature oxidation is discussed, for chromia-forming alloys, in terms of a mechanistic model based on postulations that (a) reactive element/oxide additions promote nucleation of Cr₂O₃ and (b) reactive element-oxides react with Cr₂O₃ to form perovskite-type compounds, such as YCrO₃, along scale boundaries which promote inward oxygen diffusion. The standard Gibbs energy of formation and concentrations of ionic defects for YCrO₃ are calculated. For silicon-containing chromia-forming alloys, the degradation of the scale adherence is shown to be the result of the α-β phase transformation in cristobalite. Morphologies of alumina scales formed over yttrium-containing Fe-20Cr-4Al alloys indicated that yttrium increased the stability of metastable alumina phases at 1173 K and decreased the amount of wrinkling in the α-alumina scale at 1273 K.

© EDP Sciences 1993