Date of Completion

8-23-2013

Embargo Period

8-23-2014

Keywords

Thermal Barrier Coatings, Rumpling, Surface Geometry

Major Advisor

Eric H Jordan

Associate Advisor

Mark Aindow

Associate Advisor

Hanchen Huang

Associate Advisor

Michael Renfro

Associate Advisor

Wei Sun

Field of Study

Mechanical Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Thermal barrier coatings (TBCs) are used in gas turbines to reduce the metal temperature for a given operating condition. The temperature drop in the TBC can be exploited by running the engine at a higher firing temperature leading to greater fuel efficiency and/or increased durability. Eventually TBCs spall off. One of the contributing factors to the failure in any TBC system is the surface geometry change of the interface commonly known as Bond-coat rumpling. Though rumpling is a three dimensional behavior, previous efforts of studying rumpling were mainly two-dimensional and/or lacked the 3D quantification of surface geometry change. In this study, rumpling of bond-coats have been investigated using 3 advanced 3D imaging techniques, namely 3D SEM stereo-photogrammetry, X-ray computed tomography and optical coherence tomography. The standard procedures of each of these techniques have to be modified and optimized to be applicable for the study of TBCs and in particular rumpling. The modifications are discussed in detailed and the fidelity and repeatability of the optimized methods are verified and improved where necessary. The existence of rumpling in MCrAlY systems has been definitively proven and three dimensional characterizations were performed to gain insights on the typical behavior of surface change. In addition, rumpling under the TBC was first examined non-destructively and the effect of the top-coat is examined. Finally, bond-coat rumpling was shown to be a potential metric for assessing damage in TBC systems and predicting the remaining life nondestructively when using OCT.

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