Rare earth oxide coatings for life extension of chromia forming alloys

• Published in: Elevated Temperature Coatings: Science and Technology IV; New Orleans, LA; USA; 11-15 Feb. 2001 pp. 197 - 208
• Main Authors: Fernandes, S M C, Ramanathan, L V
• Format: Conference Proceeding
• Language: English
• Published: 11-02-2001
• ISBN: 0873394895; 9780873394895

The influence of adding small quantities of rare earth elements to high temperature alloys on improvements in oxidation rate and oxide scale adhesion is well known. Traditionally, the rare earths (RE) have been added to the alloys in elemental form or as an oxide. The RE can be also applied as coatings to alloy surfaces. Several methods can be used to apply RE coatings to alloy substrates and the sol-gel process is considered to be more efficient and is known to generate the smallest oxide particles. This paper presents the influence of surface coatings of Ce, La, Nd, Pr, Dy, and Y oxide gels on the oxidation behavior of Fe-20Cr alloys at 1000 deg C. The morphology of the rare earth (RE) oxide coatings varied with the nature of RE. The oxidation rate of RE oxide coated Fe-20Cr was significantly less than that of the uncoated alloy. The extent of influence; that the RE oxide coatings exercised on oxidation rate decreased in the following order: La, Nd, Ce, Pr, Dy, Y. The scale formed in the presence of RE oxide was very thin, fine grained and adherent chromia. A direct correlation between rare earth ion radius and the extent of influence on chromia growth rate at 1000 deg C was observed.