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TECHNICAL PAPERS: Gas Turbines: Manufacturing, Materials, and Metallurgy

Hot Corrosion of Lanthanum Zirconate and Partially Stabilized Zirconia Thermal Barrier Coatings

[+] Author and Article Information
Basil R. Marple1

 National Research Council Canada, Industrial Materials Institute, 75 de Mortagne Boulevard, Boucherville, QC J4B 6Y4, Canadabasil.marple@nrc.ca

Joël Voyer2

 National Research Council Canada, Industrial Materials Institute, 75 de Mortagne Boulevard, Boucherville, QC J4B 6Y4, Canada

Michel Thibodeau

 National Research Council Canada, Industrial Materials Institute, 75 de Mortagne Boulevard, Boucherville, QC J4B 6Y4, Canada

Douglas R. Nagy

 Liburdi Engineering Limited, 400 Highway 6 North, Dundas, ON L9H 7K4, Canada

Robert Vassen

Institute for Materials and Processes in Energy Systems, Forschungszentrum Jülich Gmbh, D-52425 Jülich, Germany

1

To whom correspondence should be addressed.

2

Currently at ARC Leichtmetallkompetenzzentrum GmbH, Ranshofen, Austria.

J. Eng. Gas Turbines Power 128(1), 144-152 (Jul 30, 2004) (9 pages) doi:10.1115/1.1924534 History: Received February 08, 2004; Revised July 30, 2004

The hot corrosion resistance of lanthanum zirconate and 8wt.% yttria-stabilized zirconia coatings produced by thermal spraying for use as thermal barriers on industrial gas turbines or in aerospace applications was evaluated. The two ceramic oxide coatings were exposed for various periods of time at temperatures up to 1000°C to vanadium- and sulfur-containing compounds, species often produced during the combustion of typical fuels used in these applications. Changes in the coatings were studied using a scanning electron microscope to observe the microstructure and x-ray diffraction techniques to analyze the phase composition. The results showed different behaviors for the two materials: the zirconia-based coating being rapidly degraded by the vanadium compounds and resistant to attack by the sulfur materials while the lanthanum zirconate was less damaged by exposure to vanadia but severely attacked in the presence of sulfur-containing species.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Overall appearance of the 8YSZ (a–c) and La2Zr2O7 (d–f) TBCs at various stages: in the as-deposited state (a) and (d), after a 3-h dwell at 1000°C (b) and (e), and following a 3-h corrosion test at 1000°C in contact with V2O5 (c) and (f)

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Figure 2

Structure of 8YSZ (a–c) and La2Zr2O7 (d–f) coatings in the as-sprayed state (a and d), after 3h at 1000°C (b and e), and following contact with V2O5 at 1000°C for 3h (c and f)

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Figure 3

X-ray diffraction spectra for the La2Zr2O7 coating in the as-sprayed state and following a 3-h treatment at 1000°C in contact with V2O5

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Figure 4

Photographs of the coated test specimens following 360h of exposure to sulfur-containing salts at 900°C: (a) ZrO2–8wt.%Y2O3 and (b) La2Zr2O7

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Figure 5

Micrographs of the coated test specimens following 360h of exposure to sulfur-containing salts at 900°C: (a) and (c) ZrO2–8wt.%Y2O3 and (b) and (d) La2Zr2O7

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Figure 6

Photograph of a La2Zr2O7 coating following only 4.5h of exposure to sulfur-containing compounds at 900°C

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Figure 7

X-ray diffraction spectra for the La2Zr2O7 coating following 360h of exposure to sulfur-containing salts at 900°C [sample shown in Fig. 5].

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Figure 8

Appearance of the coatings following exposure to a combination of sulfur- and vanadium-containing compounds at 900°C: (a) YSZ after 60h and (b) La2Zr2O7 after 20h.

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Figure 9

Micrographs of the cross section of coatings exposed to a combination of sulfur- and vanadium-containing compounds at 900°C: (a) and (c) YSZ after 60h and (b) and (d) La2Zr2O7 after 20h

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Figure 10

EDS dot maps showing the distribution of (a) zirconium and (b) vanadium in a region of the YSZ coating from the micrograph shown in Fig. 9 and maps for lanthanum (c) and vanadium (d) for a region of the La2Zr2O7 coating shown in Fig. 9. It is important to note that, due to the similarity of the energies for the VKα and LaLβ1 peaks, the V map for the La2Zr2O7 coating has a component due to La.

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Figure 11

X-ray spectra for coatings in the as-sprayed state and following exposure to a combination of sulfur- and vanadium-containing compounds at 900°C: (a) YSZ and (b) La2Zr2O7

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