On the Mechanical Response in a Thermal Barrier System Due to Martensitic Phase Transformation in the Bond Coat

[+] Author and Article Information
A. M. Karlsson

Department of Mechanical Engineering, University of Delaware, Newark, DE 19716

J. Eng. Mater. Technol 125(4), 346-352 (Sep 22, 2003) (7 pages) doi:10.1115/1.1605107 History: Received December 15, 2002; Revised June 17, 2003; Online September 22, 2003
Copyright © 2003 by ASME
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An example of the development of morphological instabilities in a thermal barrier system, based on Pt-modified aluminde bond coat, subjected to thermal cycles (courtesy D.R. Mumm). The downward displacement of the TGO layer into the bond coat increases with thermal cycling (indicated as percentages of life) 11.
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(a) Yield strength and (b) thermal strain of the bond coat material 1819
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An example of the finite element model, consisting of the substrate (2 mm), bond coat (50 μm), TGO (initially 0.5 μm), and top coat (100 μm)
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The response of the system during the first cycle in a typical bond coat particle: (a) The incremental strain and (b) temperature as a function of the steps in the thermal history. (c) Mises stress and (d) thermal strain as a function of the temperature.
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The plastic strain accumulation during 12 cycles comparing “thick” to “thin” bond coat. For thick bond coat, the substrate has identical material properties as the bond coat, including martensitic transformation. For thin bond coat, the substrate does not undergo martensitic transformations.
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Contour plot of the plastic strain accumulation in bond coat during 12 cycles: (a) With Substrate (“thin bond coat”, (b) Thick bond coat (substrate has identical properties as to the bond coat), (c) Using the effective coefficient of thermal expansion ᾱ2, see Fig. 3.
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The development of the amplitude change over 12 cycles, comparing various thermal coefficients of expansion for the substrate
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The development over 12 cycles using and ignoring growth strain: (a) plastic strain and (b) amplitude change.
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The development of the amplitude change over 12 cycles using efficient coefficient of thermal expansion
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Development of stresses in the TBC, using various CTE in the substrate; (a) αsbc; (b) αsbc; (c) αsbc. The difference refers to elevated temperature.




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