Research Papers: Gas Turbines: Structures and Dynamics

Determination of Thermal Barrier Coatings Average Surface Temperature After Engine Operation for Lifetime Validation

[+] Author and Article Information
Grégoire Witz

e-mail: gregoire.witz@power.alstom.com

Hans-Peter Bossmann

e-mail: hans-peter.bossmann@power.alstom.com
Brown boveri strasse 7,
5401 Baden, Switzerland

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 26, 2012; final manuscript received July 2, 2012; published online October 22, 2012. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 134(12), 122507 (Oct 22, 2012) (7 pages) doi:10.1115/1.4007343 History: Received June 26, 2012; Revised July 02, 2012

Assessment of ex-service parts is important for the power generation industry. It gives us the opportunity to correlate part conditions to specific operating conditions like fuel used, local atmospheric conditions, operating regime, and temperature load. For assessment of thermal barrier coatings, one of the most valuable pieces of information is the local thermal condition. A method has been developed in Alstom, allowing determination of a thermal barrier coating average surface temperature after engine operation. It is based on the analysis of the phase composition of the thermal barrier coating by the acquisition of an X-ray diffraction spectrum of the coating surface, and its analysis using Rietveld refinement. The method has been validated by comparing its outcome to thermal models and base metal temperature mapping data. It is used for assessment of combustor and turbine coatings with various purposes: Determination of remnant coating life, building of lifing models, or determination of the coating degradation mechanisms under some specific operating conditions. Examples will be presented showing applications of this method.

Copyright © 2012 by ASME
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Fig. 1

Phase diagram of the yttria zirconia system reproduced for the data of Scott [7]

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Fig. 2

XRD spectrum of an as-deposited TBC (a), and a TBC after aging at high temperature (b)

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Fig. 3

Experimental data and solid state reaction models. The empirical model used for temperature mapping is shown as the black solid line.

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Fig. 4

Picture of a typical GT13E2 Blade 1, where TBC samples were taken for temperature mapping at the locations 1 and 2 indicated by the red dots

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Fig. 5

Estimated average base alloy temperature as a function of the average TBC surface temperature

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Fig. 6

Picture of a GT13E2 Zone 1 combustor tile (bottom left inset) with the modeled temperature profile calculated along the dotted line, together with the results of the temperature mapping at selected locations. The temperature tick marks are spaced by 25 °C.

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Fig. 7

Measured versus predicted TBC surface temperature at six positions of a GT26 LPT Blade 1. The temperature tick marks are spaced by 25 °C.

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Fig. 8

Decrease of the strain to crack formation in the TBC compared to a virgin TBC as a function of 1/T for various GT24/GT26 SEV combustor liners segments. The temperature is given in relative units (divided by the average of all samples temperature).

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Fig. 9

Phase composition determined by XRD of TBC samples showing an increase in c-YSZ content at the TBC outer surface

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Fig. 10

Electron probe microanalysis of the TBC sample of Fig. 9 showing Ca and Mg diffusion into the TBC from its outer surface

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Fig. 11

XRD spectrum from the inner surface of a delaminated TBC sample taken in an engine where accelerated TBC degradation was observed

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Fig. 12

Electron probe microanalysis of the TBC sample measured by XRD in Fig. 10 close to its inner surface




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