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Investigation of Thermal High Cycle and Low Cycle Fatigue Mechanisms of Thick Thermal Barrier CoatingsThick thermal barrier coating systems in a diesel engine experience severe thermal low cycle fatigue (LCF) and high cycle fatigue (HCF) during engine operation. In this paper, the mechanisms of fatigue crack initiation and propagation in a ZrO2-8wt% Y2O3 thermal barrier coating, under simulated engine thermal LCF and HCF conditions, are investigated using a high power CO2 laser. Experiments showed that the combined LCF-HCF tests induced more severe coating surface cracking, microspallation and accelerated crack growth, as compared to the pure LCF test. Lateral crack branching and the ceramic/bond coat interface delaminations were also facilitated by HCF thermal loads, even in the absence of severe interfacial oxidation. Fatigue damage at crack wake surfaces, due to such phenomena as asperity/debris contact induced cracking and splat pull-out bending during cycling, was observed especially for the combined LCF-HCF tests. It is found that the failure associated with LCF is closely related to coating sintering and creep at high temperatures, which induce tensile stresses in the coating after cooling. The failure associated with HCF process, however, is mainly associated with a surface wedging mechanism. The interaction between the LCF, HCF and ceramic coating creep, and the relative importance of LCF and HCF in crack propagation are also discussed based on the experimental evidence.
Document ID
19990062743
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Zhu, Dongming
(NASA Lewis Research Center Cleveland, OH United States)
Miller, Robert A.
(NASA Lewis Research Center Cleveland, OH United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 1998
Publication Information
Publication: Materials Science and Engineering
Publisher: Elsevier Science Publishers
Volume: A245
ISSN: 0921-5093
Subject Category
Nonmetallic Materials
Distribution Limits
Public
Copyright
Other

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