Abstract
The role of pre-oxidation surface treatments on the oxide microstructure and the failure mechanism of multi-layer thermal barrier systems based on Pt-modified NiAl bond coats and electron beam deposited thermal barrier coatings (TBCs) have been studied. The primary pre-oxidation experimental variable was the partial pressure of oxygen in the pre-oxidizing atmosphere at constant temperature and bond coat composition. The durability of TBCs deposited on surfaces following different pre-oxidation treatments were measured and compared using furnace cycling tests. The oxide layers corresponding to different levels of TBC performance were characterized microstructurally, chemically, and compositionally using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. TBC performance was enhanced by the formation of a surface oxide having a coarse-grained columnar structure during the pre-oxidation process. Increased TBC durability was consistent with a slower oxide growth rate during exposure of the TBC to high-temperature, cyclic conditions, as was observed for this particular pre-oxidation condition. An oxide microstructure having fewer through-thickness transport pathways (grain boundaries) should also result in slower lateral oxide growth rates, consistent with a slowed rate of ratcheting as was observed in the pre-oxidized samples that had the best TBC performance. The desired surface oxide grain structure was achieved by pre-oxidizing the bond coat prior to TBC deposition at an intermediate partial pressure of oxygen.
Original language | English |
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Pages (from-to) | 322-333 |
Number of pages | 12 |
Journal | Materials Science and Engineering: A |
Volume | 417 |
Issue number | 1-2 |
DOIs | |
State | Published - Feb 15 2006 |
Funding
Research at ORNL was sponsored by the U.S. Department of Energy, Assistant Secretary for Energy Efficiency and Renewable Energy, Distributed Energy Program, under contract DE-AC05-00OR22725 with UT–Battelle, LLC.
Funders | Funder number |
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Assistant Secretary for Energy Efficiency and Renewable Energy, Distributed Energy Program | DE-AC05-00OR22725 |
U.S. Department of Energy | |
Battelle |
Keywords
- Durability
- Lateral oxide growth
- Microstructure
- Oxide grain structure
- Pre-oxidation displacement instability
- Ratcheting
- Thermal barrier coatings
- Thermally grown oxide