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| Home > Publications database > Innovative Plasma Sprayed Thermal Barrier Coatings for Enhanced Flexibility in Gas Turbine Operation |
| Book/Dissertation / PhD Thesis | FZJ-2025-02817 |
2025
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-827-8
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Please use a persistent id in citations: doi:10.34734/FZJ-2025-02817
Abstract: Thermal barrier coatings (TBCs) in power plant turbines are primarily designed for high thermal insulation properties. As a result, they enable a high combustion temperature in the turbine, making the power generation process very efficient. In the future, however, the operational flexibility of modern power plant turbines will become increasingly important to maintain grid stability. Frequent fluctuations in the amount of electricity fed into the grid due to the high volatility of renewable energy sources, as well as changing loads, require constant adjustment of power generation. In the future, this will be made possible by gas turbines that must be started up and shut down quickly and flexibly. The challenges for the coating system arise from the different properties of the materials applied. The different expansion of layers and substrates during temperature changes introduces stresses into the coating system when the turbine is started up or shut down. In addition, the high operating temperatures lead to detrimental phase transformations and sintering of the ceramic top layer, reducing the strain tolerance and thus the flexible application of the coatings. The objective of this study was therefore to develop an optimized TBC system capable of withstanding rapid mechanical load and temperature changes. The development focused on the optimization of the bond coat as well as the top layer of the TBC system. For the bond coat optimization, aspects such as surface roughness, thermal expansion coefficients and the effect of pre-oxidation of the bond coat on the performance of the coatings during thermal cycling were investigated. In contrast, the effect of different microstructures produced by different plasma spraying processes on the thermal cycling performance of the ceramic topcoats was investigated. In addition, innovative analysis methods were used for the various plasma-sprayed thermal barrier coatings to investigate coating properties and failure mechanisms in detail. These methods include digital image correlation, which enables to analyze strain changes on the sample surface during thermal cycling. In this way, the forced elongation of the ceramic top layer by the substrate material could be shown, as well as local changes in elongation over the cycles, which finally might result in coating failure. A further method is the laser shock adhesion test. This allows to determine the interfacial bonding of coatings and to introduce specific defects into coating systems. The growth of these defects can be observed during thermal cycling, providing important insights for investigating the failure mechanisms in thermal barrier coating systems. Overall, the optimizations more than doubled the service life of the thermal barrier coatings compared to a reference coating system as used in today’s turbines. In addition, insights were gained into the failure mechanisms that occur with differently structured topcoatings. At the end of the work, further opportunities for improvement were identified that can be investigated in the future.
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