9. Stress Distribution in APS-TBCs Under Thermal Cycling Loading Conditions
- Dongming Zhu and
- Kevin Plucknett
Published Online: 26 MAR 2008
Copyright © 2005 The American Ceramics Society
Advances in Ceramic Coatings and Ceramic-Metal Systems: Ceramic Engineering and Science Proceedings, Volume 26, Number 3
How to Cite
Bednarz, P., Herzog, R., Trunova, E., Steinbrech, R. W., Echsler, H., Quadakkers, W. J., Schubert, F. and Singheiser, L. (2008) Stress Distribution in APS-TBCs Under Thermal Cycling Loading Conditions, in Advances in Ceramic Coatings and Ceramic-Metal Systems: Ceramic Engineering and Science Proceedings, Volume 26, Number 3 (eds D. Zhu and K. Plucknett), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470291238.ch9
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 2005
Print ISBN: 9781574982336
Online ISBN: 9780470291238
Oxidation induced spallation of plasma-sprayed thermal barrier coatings (APS-TBCs) is regarded as one major failure mode of ceramic coated gas turbine components. A failure crack path, which is located partly in the thermally grown oxide (TGO) and partly in the TBC characterizes this type of failure (gray failure). Recent investigations have shown that the related damage evolution starts within the first 10% of lifetime by the formation of micro cracks in the TGO and by opening of pre-existing micro cracks in the TBC. Crack growth and linking of these cracks along the metal/ceramic interface lead to final spallation. However, parameters, which govern the kinetics and thus the lifetime are not sufficiently known.
The present contribution is to determine the stresses near the TGO as a function of time under cyclic oxidation using the finite element method. The loading cycle consists of thermal cycling between 20°C and 1050°C and a dwell-time of 2 h at 1050°C to activate oxidation. TGO growth is considered in out-of-plane (thickness increase) and in-plane (lateral growth) direction. In order to include realistic material parameters, the deformation properties (elastic and creep) of a NiCoCrAlY bond coat and a plasma-sprayed TBC (ZrO2 with 7-8 wt. % Y2O3) have been experimentally determined and implemented for the simulations. The stress response of both coatings to the loading cycle is characterized by stress redistribution with increasing cycle number. The interface undulation causes initially a characteristic distribution of local tensile and compressive stress regions at micrometer scale. As a consequence of stress redistribution near the TGO, which is strongly affected by creep relaxation, the initial local compressive stresses (out-of-plane) decrease and tensile stress zones broaden. The process of stress redistribution may contribute significantly to crack growth and linking along the interface.