Neue Oxidationsschutzschichtenkonzepte für zukünftige Kraftwerke mit hohem Wirkungsgrad und integrierter CO2-Abtrennung
Zusammenfassung der Projektergebnisse
In gas-turbine components MCrAlY-type (M=Fe, Ni, Co) alloys and coatings are commonly used due to their exceptional high-temperature oxidation resistance. The high-temperature oxidation resistance of these materials relies upon the formation of slow growing and adherent alumina (Al2O3) surface scales. For the scale formation Al is depleted from the coating (alloy), whereas the rate of Al consumption is accelerated in the case of scale spallation during temperature cycling. Upon critical Al-depletion the coatings fail to re-form the alumina scale. In this case the material corrode at a much faster rate since the growth rates of Cr and Ni oxides are significantly higher than that of Al2O3 resulting in a rapid component failure. In the critical application of MCrAlY materials as bondcoats for ceramic thermal barrier coatings (TBCs) on internally cooled gas-turbine components the alumina scale spallation should be prevented since it can initiate failure of the TBC topcoat. In the power plants with CO2-capture the operating conditions of gas turbines are going to change with respect to the conventional gas turbines resulting in: 1) significantly higher water vapour content and possibly higher SO2 content in the turbine environment, 2) higher temperature cyclic frequency to cope with increasing percentage of energy generation by renewable sources and 3) higher operating temperature to compensate the turbine efficiency losses for the CO2-capture processes. The above changes in the operating conditions are expected to result in increase of the degradation rates of the protective coating systems, including TBCs. In Phase I of the present project extensive cyclic oxidation testing under conditions simulating environments of gas turbines in power plants with CO2-capture have been performed on the state of the art coatings. It has been found that the effect of new operating conditions on the oxidation behaviour and lifetime strongly depends on the system studied. For example it was found that the higher water vapor content in the environment results in shortening the lifetime of the EB-PVD (electron beam physical vapor deposited) TBC systems with MCrAlY-bondcoats, whereas no such detrimental effect was observed for EB-PVD TBC systems with NiPtAl bondcoats as well as for APS (air plasma sprayed) TBC systems with MCrAlY bondcoats. On the other hand the higher temperature cycling frequency was found to shorten the lifetime of APS-TBC systems but not EB-PVD TBC systems with conventional MCrAlY-bondcoats. The observed differences could be attributed to different mechanisms of oxide scale formation and TBC failure in the various studied systems. In addition, the role of several strengthening additions in particular that of Ti and Ta in MCrAl, Ni-base alloys in oxidation and corrosion resistance in SO2-containing environments has been elucidated. Based on the testing and analytical results of Phase I, cost-effective TBC systems with improved bondcoat microstructure have been developed in Phase II of the project to extend the lifetime of the current TBC systems under the modified turbine operating conditions in power plants with CO2-capture. The results of accelerated cyclic oxidation tests indicated substantially better performance of the new system than with the state of the art bondcoats produced by conventional high velocity oxyfuel (HVOF) spraying.
Projektbezogene Publikationen (Auswahl)
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Effect of Zr Additions on the Oxidation Kinetics of FeCrAlY Alloys in Low and High pO2 Gases, Metallurgical and Materials Transactions A (2011) Vol. 42, No. 5 (2011) 1173-1183
D. J. Young, D. Naumenko, E. Wessel, L. Singheiser and W.J. Quadakkers
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Blistering of MCrAlY-coatings in H2/H2O-atmospheres, Corrosion Science 51(3), (2009) 446-450
M. Subanovic, D. Naumenko, M. Kamruddin, G. Meier, L. Singheiser, W.J. Quadakkers
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Effect of exposure conditions on the oxidation of MCrAlY-bondcoats and lifetime of thermal barrier coatings, Surface and Coatings Technology 204 (2009) 820-823
M. Subanovic, P. Song, E. Wessel, R. Vassen, D. Naumenko, L. Singheiser, W.J. Quadakkers
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Failure mechanisms of thermal barrier coatings on MCrAlY-type bondcoats associated with the formation of the thermally grown oxide, Journal of Materials Science 44(7), (2009) 1687–1703
D. Naumenko, V. Shemet, L. Singheiser, W.J. Quadakkers
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Y-rich oxide distribution in plasma sprayed MCrAlY-coatings studied by SEM with a cathodoluminescence detector and Raman spectroscopy, Surface and Coatings Technology, 204 (2009) 531–538
A. Gil, D. Naumenko, R. Vassen, J. Toscano, M. Subanovic, L. Singheiser, W.J. Quadakkers
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Oxidation kinetics of Y-doped FeCrAl-alloys in low and high pO2 gases, Materials and Corrosion, 61 (2010) 838-844
D. J. Young, D. Naumenko, L. Niewolak, E. Wessel, L. Singheiser and W.J. Quadakkers
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Influence of material and testing parameters on the lifetime of TBC systems with MCrAlY and NiPtAl bondcoats, PhD Thesis, RWTH-Aachen (2011)
P. Song
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Effect of oxygen content in NiCoCrAlY bondcoat on the lifetimes of EB-PVD and APS thermal barrier coatings, Surface and Coatings Technology 221, (2013) 207-213
P. Song, D. Naumenko, R. Vassen, L. Singheiser, W.J. Quadakkers
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Influence of manufacturing parameters on the lifetime of APS-TBC systems, 2nd International Conference on Materials for Energy, EnMat II, May 12-16 (2013) Karlsruhe Convention Center, Germany
W. Nowak, D. Naumenko, D. Mack, F. Mor, L. Singheiser and W.J. Quadakkers
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Influence of vacuum heat treatment parameters on the surface composition of MCrAlY coatings, Surface and Coatings Technology 215 (2013) 24-29
I. Keller, D. Naumenko, W.J. Quadakkers, R. Vaßen, L. Singheiser
