Abstract
Interfacial segregants in thermally grown α-Al2O 3 scales formed during high temperature exposure of thermal barrier coating systems reflect the oxygen-active dopants present in the bond coating and substrate, such as Y and Hf. These dopants diffuse outward and segregate to the substrate-alumina interface and the alumina grain boundaries. Related studies suggest that these segregants affect the growth and mechanical properties of the alumina-scale; however, the characterization of segregation in alumina formed on coated superalloy systems has been limited. Segregation examples evaluated using analytical transmission electron microscopy are given from traditional Pt-modified aluminide coatings and newer Pt diffusion coatings. Model systems are used to illustrate that grain boundary segregants on the columnar alumina boundaries are not because of the reverse diffusion of cations from the Y2O3-stabilized ZrO2 top coating, and that interstitial elements in the substrate likely affect the outward flux of cation dopants. The dynamic nature of this segregation and oxygen-potential gradient-driven diffusion is discussed in light of observations of substrate dopant and interstitial contents affecting coating performance.
| Original language | English |
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| Pages (from-to) | 1676-1686 |
| Number of pages | 11 |
| Journal | Journal of Materials Science |
| Volume | 44 |
| Issue number | 7 |
| DOIs | |
| State | Published - Apr 2009 |
Funding
Acknowledgements The authors would like to thank C. Leyens, DLR, Köln, Germany for coating the FeCrAl substrate; K. Cooley, L. D. Chitwood, G. Garner, K. S. Reeves, J. L. Moser, H. Longmire, and D. Coffey at ORNL for assistance with the experimental work; I. G. Wright and M. P. Brady at ORNL; P. Y. Hou at LBL for manuscript comments. This research was sponsored by the U.S. Department of Energy, Office of Coal and Power R&D, Office of Fossil Energy (R. Dennis—program manager) under contract DE-AC05-00OR22725 with UT-Battelle, LLC.