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
The reactive element effect (REE) in oxidation of alloysYasutoshi Saito1, 2, Bülent Önay3, 2 and Toshio Maruyama4
1 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
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