Rare Earth Oxide Coatings to Decrease High Temperature Degradation of Chromia Forming Alloys

The addition of small quantities of reactive elements such as rare earths (RE) to chromia or alumina forming alloys improves the high temperature oxidation resistance. Traditionally, these elements are alloying additions or are added as oxides to form a dispersion. The alloys can also be coated with RE oxides. Several methods can be used to coat alloy substrates with RE oxides and the sol-gel process is considered to be quite efficient, as it generates the very small oxide particles. This paper presents the influence of surface coatings of Ce, La, Pr, and Y oxide gels on the oxida-tion behavior of an Fe-20Cr alloy at 1000 °C. The morphology of the rare earth (RE) oxide coat-ings varied with the nature of RE. The oxidation rate of RE oxide coated Fe-20Cr was signifi-cantly less than that of the uncoated alloy. The extent of influence the RE oxide coating exercised on the oxidation rate decreased in the following order: La, Ce, Pr, Y. The scale formed in the presence of RE oxide was very thin, fine grained and adherent chromia. A direct correlation be-tween rare earth ion radius and the extent of influence on chromia growth rate at 1000 °C was observed