Vieillissement des systèmes barrière thermique : transformation de phases, oxydation et effet du soufre sur l'adhérence

Abstract : A thermal barrier coating system, used for turbine engine blade, is a multilayer system with a superalloy substrate. This substrate is covered by an alumino-former bond coat, which protects the substrate from oxidation by creating an alumina scale, initiated during the process. Finally a ceramic coating, the thermal barrier coating (TBC), covers the bond coat in order to decrease the work temperature. The ceramic, made of yttrium stabilized zirconia, is permeable to oxygen, leading to the development of the alumina scale all along the system life time. The system life time is limited by the spallation of the TBC, which occurs because of interfacial damage, located in particular at the bond coat/oxide interface. The adherence loss is sensitive to the chemical composition and the microstructure of the system. The aim of this work is to correlate the damage mechanisms to the microstructural and chemical evolution of the TBC system after oxidation treatments. For this purpose, the behaviour of TBC systems based on a AM1 or MCNG substrate covered by a NiAlPt bond coat, with and without TBC, has been studied during isothermal and cyclic oxidation. In addition, the influence of the oxide scale grown after short-term oxidation treatment on the long-term adherence has been tested through a pre-oxidation study. Finally, the distribution of impurities, like sulfur and reactive elements like hafnium has been followed after several oxidation treatments. This work shows that the systems based on MCNG substrate are more resistant to spallation than the ones based on AM1 substrate. This behaviour is explained by the lowest oxidation kinetic of the MCNG systems, probably due to the reactive elements presence. It has also been revealed that the formation of transient oxide during the first stages of oxidation is not detrimental for the long-term adherence. A correlation between impurity segregation at the bond coat / oxide interface and spallation has been evidenced.
Keywords : TEM Adehrence Oxidation
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Theses
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Submitted on : Wednesday, May 28, 2014 - 9:32:59 AM
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  • HAL Id : pastel-00997369, version 1

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Marion Chieux. Vieillissement des systèmes barrière thermique : transformation de phases, oxydation et effet du soufre sur l'adhérence. Matériaux. École Nationale Supérieure des Mines de Paris, 2010. Français. ⟨NNT : 2010ENMP1695⟩. ⟨pastel-00997369⟩

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