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| Dissertation / PhD Thesis/Book | PreJuSER-58846 |
;
2002
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/304
Report No.: Juel-3954
Abstract: Thermal barrier coatings are increasingly utilized to protect gas turbine components from high temperature exposure. Thus the use of TBCs allows an improvement of the system efficiency, since the coated components can support higher inlet temperatures. For stationary gas turbine applications, the combination of an oxidation resistant MCrAlY bond coat and a 7-8 WL % Y$_{2}$O$_{3}$-ZrO$_{2}$ plasma sprayed top coat is currently the favored TBC-system. To predict the life duration of the TBC-system, the determination of the high temperature behavior of the protective coatings in composite geometry is indispensable. Also the residual stresses, which result from spraying process and thermal expansion misfit between the bonded layers, are of crucial importance. In the present study, experiments were selected to evaluate the thermoelastic properties of a plasma sprayed TBC in composite geometry. The curvature behavior of three-layer specimen strips was observed between room temperature and 1000°C, when submitted exclusively to temperature. Also isothermal 4-point bending tests were performed at room temperature, 600°C and 950°C. During curvature and bending experiments, shape and structure changes were monitored in-situ using a high resolution telescope in combination with a digital data acquisition system. In parallel, a linear-elastic model was developed to calculate analytically the stress distribution in multi-layered systems. The high temperature experiments on the TBC-specimen strips demonstrate that the bonded materials behave elastically up to 600°C. Depending on the specimens geometry, i.e. on the stress distribution, non-elastic effects can occur above 600°C (crack formation in the ceramic coating or stress relaxation and phase changes in the bond coat). When all layers show an elastic behavior, the stress distribution can be calculated at room and at high temperatures. Using the proposed linear-elastic model, the temperature dependent elastic modulus of the ceramic TBC in composite geometry can also be derived. The obtained values are about 20 % behind the modulus offree standing layers.
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