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5117 |
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Wednesday, May 11, 2016, Yellow River Hall 1:40 PM Aviation Industry II |
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The evolution of crack driving force and fracture resistance during thermal cycling of thermal barrier coatings |
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Matthias Oechsner* / Technische Universität Darmstadt, Germany Martin Fromherz/ Technische Universität Darmstadt, Germany Peter Wittig/ Technische Universität Darmstadt, Germany Alfred Scholz/ Technische Universität Darmstadt, Germany |
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Key words: Thermal Barrier Coatings, fracture toughness, sintering, stiffness Abstract Two fundamental properties have a high impact on the performance and reliability of ceramic TBCs: the planar stiffness and the fracture resistance regarding delamination cracks. Those properties are known to change during service life, i.e. when the coating is exposed over long times to high temperatures. Knowledge of those properties and their kinetics are a prerequisite to understand coating reliability and to assess coating life. Various bending methods and dynamic measurements were conducted to evaluate the influence of thermal loading on coating stiffness. The ceramic coatings were thermally treated prior to determining their stiffness isothermally, cyclically or under a thermal gradient. During thermal exposure, the coating has been either free standing or attached to a substrate material, i.e. constraint regarding its ability to shrink. The paper will discuss the evolution of coating in-plane stiffness dependent on thermal loading conditions as well as state of constraint. With respect to the in-plane fracture resistance, fracture mechanical testing has been performed to determine the evolution of the critical strain energy release rate as a function of cyclic or isothermal exposure to service relevant temperatures. The evolution of the fracture resistance at the TBC bond coat interface, i.e. the adhesive fracture resistance, as well as the evolution of the fracture resistance within the ceramic TBC, i.e. the cohesive fracture resistance, will be discussed. |