The effectiveness of candidate rare earth (RE) bearing oxides to mitigate degradation of thermal barrier coatings by molten silicates is determined by the constitution and crystallization kinetics of the reaction products. The relationships between the oxide composition, test temperature, and reaction product constitution were investigated using sintered pellets of hafnates or zirconates containing YbO1.5, GdO1.5, or LaO1.5. The results suggest that the composition of the reprecipitated ZrO2- or HfO2-based phase, typically fluorite, is a useful indicator of the effectiveness of the silicate crystallization reactions. Meanwhile, the composition of the primary crystalline reaction product, typically a RE oxy-apatite, is relatively insensitive to the experimental variables considered herein. The observed trends indicate that the larger RE cations are more potent in rapidly crystallizing the silicate melt and that their relative effectiveness increases with the REO1.5 concentration in the coating material.
|Original language||English (US)|
|Number of pages||11|
|Journal||Journal of the European Ceramic Society|
|State||Published - Feb 1 2015|
Bibliographical noteFunding Information:
Research supported by the Office of Naval Research under grants N00014-06-1-0522 and N00014-08-1-0322 , monitored by Dr. D.A. Shifler. DP received additional support from the Department of Defense through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program. The research made use of the MRL Shared Experimental Facilities, a member of the NSF-funded Materials Research Facilities Network ( www.mrfn.org ) supported by the MRSEC Program of the NSF under Award No. DMR 1121053. The authors are grateful to K. Wong (UCSB), for assistance with powder synthesis, and to Drs. S. Krämer and G. Seward (UCSB), for support of TEM and EPMA/EBSD analysis, respectively.
© 2014 Elsevier Ltd.
Copyright 2014 Elsevier B.V., All rights reserved.
- Calcium-magnesium-aluminosilicate (CMAS)
- Phase equilibrium
- Rare earth oxide
- Thermal barrier coating