La voie sol-gel pour la mise en oeuvre de barrières thermiques aéronautiques : optimisation du procédé et étude de leur comportement mécanique

Abstract : The main objectives of this PhD are first to improve and optimise the elaboration protocol of thermal barrier coatings (TBC) manufactured by the sol-gel route and then to characterise their adhesion and investigate the possibility to enhance their lifetime. A preliminary study is focused on the selection and validation of a new dispersing agent to optimise the composite sol formulation before shaping TBC. Indeed, the new dispersant induced a microstructure allowing to significantly increase the cyclic oxidation lifetime of the system but also to simplify the elaboration process as the reinforcement step was suppressed. The parametric study of TBC surface microstructure proved that the initial micro-cracks network remained stable during ageing including the formation of a crack sub-network. To understand the damage mechanisms of sol-gel TBC and to compare them to those corresponding to industrial EB-PVD TBC, the method of interfacial indentation was developed to investigate the subtrate/top-coat interface. The apparent toughness values were determined to compare both BTSG and BTEB-PVD adhesions. From these results, phenomenological models for damage mechanisms were proposed. For BTEB-PVD, crack initiation and propagation are located at the top-coat/bond-coat interface, either on one side or the other side of the thermally grown oxide (TGO) depending of the conditions. For BTSG, the damage is a consequence of the release of the elastic strain energy stored in the system, increasing with the ageing temperature.
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Fabien Blas. La voie sol-gel pour la mise en oeuvre de barrières thermiques aéronautiques : optimisation du procédé et étude de leur comportement mécanique. Matériaux. Université Paul Sabatier - Toulouse III, 2016. Français. ⟨NNT : 2016TOU30124⟩. ⟨tel-01492842⟩

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