Date of Completion

8-25-2014

Embargo Period

8-25-2015

Keywords

Thermal barrier coating, X-ray microscopy, Non-destructive imaging

Major Advisor

Eric jordan

Associate Advisor

Brice Cassenti

Associate Advisor

Michael Renfro

Field of Study

Mechanical Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Zirconia-based thermal barrier coatings are widely used as a protection of the underlying metal from the hot gas stream in turbine engines TBCs are made of four layers including: a ceramic top coat, thermally grown oxide (TGO), a metallic bond coat, and super alloy substrate and each layer has different thermo mechanical properties. To investigate the behavior of TBC systems using traditional imaging techniques such as, SEM micrographs taken from serial sectioning, white light interferometry, optical coherence tomography, mid infrared reflectance imaging, and thermal wave imaging will not give the opportunity of performing non-destructive evaluation and 3D imaging simultaneously. Three-dimensional non-destructive information allows a unique opportunity to follow the progression of crack damage. A number of fundamental questions can be addressed with such data which include: a) Is there a correlation between the bond coat interface geometric features and the location of the cracks? b) What are the shapes of bond coat cracks as needed for modeling? c) Do large cracks grow faster than the smaller cracks? d) What is the nature and role of crack linking in damage progression? e) What is the relationship between the geometry change at the hidden bond coat to ceramic interface and the ceramic free surface and can the free surface geometry change that is more easily measured be used to assess the extent of bond coat interface geometry change? Bond coat geometry change can in some cases be used to predict failure offering a potential non-destructive inspection method. This

work will demonstrate the feasibility of 3D non-destructive imaging for obtaining the desired information by X-ray tomography. Then tomography will be used to address the fundamental questions listed above. The present work first establishes a method for monitoring the progression of cracking in TBCs using x-ray tomography and then uses this information to answer the important questions a-c above. Also a partially successful attempt to develop confocal microscopy for the same purpose will be briefly described.

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