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Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

Manufacturing Optimization for Bondcoat/Thermal Barrier Coating Systems

[+] Author and Article Information
Hans-Peter Bossmann

 ALSTOM, Brown Boveri Strasse 7, CH-5401 Baden, Switzerlandhans-peter.bossmann@power.alstom.com

Sharath Bachegowda, Alexander Schnell

 ALSTOM, Brown Boveri Strasse 7, CH-5401 Baden, Switzerland

J. Eng. Gas Turbines Power 132(2), 022101 (Oct 30, 2009) (7 pages) doi:10.1115/1.3155398 History: Received April 16, 2008; Revised August 15, 2008; Published October 30, 2009

A reliable lifetime prediction rule for bondcoat/thermal barrier coating (BC/TBC) coated parts in gas turbine operation is necessary to determine remnant service life. The specimens investigated were coated with MCrAlY plus yttria partially stabilized zirconia applied by vacuum plasma spraying and atmospheric plasma spraying processes, respectively. The performances of these laboratory specimens were statistically assessed, combining long term oxidation testing with thermal cycling, thus superimposing thermomechanical loading on the laboratory specimens to more accurately represent engine conditions. A design of experiment (DOE) approach was used for manufacturing optimization of the BC/TBC system. The life of the coating system is influenced by several manufacturing parameters such as BC thickness, BC roughness, TBC thickness, TBC porosity, and TBC stiffness. Specimens with a suitable variation in these parameters were produced to ensure a balanced test matrix of fractional factorial DOE. Based on results derived from laboratory testing the specifically tailored parts, first and second order effects of manufacturing parameters on lifetime were quantified. The findings revealed that the second order effects (the interaction of manufacturing parameters) were more important on the lifetime of the BC/TBC system than the corresponding first order effect (single parameter). For instance, the variation in BC thickness or BC roughness led to a scatter of lifetimes of 10% and 60%, respectively, whereas their interaction resulted in a scatter of lifetime of 150% for the same range of coating parameters. Further examples of such pairings are also demonstrated. Finally, a lifetime prediction for three quality classes (high, medium, and low qualities) has been demonstrated. The difference in achievable lifetime highlights the importance of manufacturing parameters in determining the life of the BC/TBC system.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Typical BC/TBC microstructure

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Figure 2

Arrangement of sample in quartz boats for daily cycling in the furnace

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Figure 3

Matrix plot of coating parameters

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Figure 4

Probability plot of coating parameter with high, medium, and low cutoff limits

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Figure 5

Scatter plot of time to spallation versus BC roughness

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Figure 6

Scatter plot of time to spallation versus BC thickness

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Figure 7

Scatter plot of time to spallation versus BC porosity

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Figure 8

Scatter plot of time to spallation versus TBC porosity

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Figure 9

Scatter plot of time to spallation versus TBC thickness

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Figure 10

Definition of “pore orientation based on an ellipse angle”

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Figure 11

Scatter plot of time to spallation versus APO

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Figure 12

Scatter plot of time to spallation versus pore size

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Figure 13

Box plot of combination of TBC porosity and BC roughness

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Figure 14

Surface plot for TBC porosity and BC roughness

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Figure 15

Box plot of combination of TBC porosity and TBC thickness

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Figure 16

Box plot of combination of BC roughness and TBC thickness

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Figure 17

Box plot of combination of BC roughness and BC thickness

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Figure 18

Surface plot for BC thickness and BC roughness

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