Développement de matériaux réfractaires pour applications turbines aéronautiques : étude des effets microstructuraux sur le comportement en oxydation des alliages composites Nbss-Nb5Si3 et optimisation des solutions de protection associées

Abstract : Progress in the field of gas-turbine engines for aircrafts is controlled by the availability of new structural materials able to withstand higher temperatures than nickel based superalloys. The present PhD work was conducted in this context, within the framework of the European FP7-HYSOP project, in which Nbss-Nb5Si3 alloys are studied. From a mechanical point of view, the physicochemical properties (room temperature fracture toughness and creep rate) are compatible with the targeted temperature (1300°C). However, starting from the intermediate temperatures (800°C), the oxidation resistance of those alloys is the major obstacle to their use. In this work, two ways are investigated to improve this behavior: The first one aims at studying the effect of a refinement of microstructure synthesizing the Nbss-Nb5Si3 alloy both by fusion method and powder metallurgy route. It was shown that refining the microstructure led to decrease the oxidation kinetics at 1100°C and suppressed the catastrophic breakaway oxidation (pesting) typical of the Nb-Si alloys with coarse microstructure at 815°C. Furthermore, diffusion models were proposed to describe oxidation kinetics both at 815°C and 1100°C. The second part of this study is devoted to the development of silica forming protective coatings. Diffusion silicide coatings were manufactured by the halide activated pack-cementation method. The various conditions of oxidation/corrosion tests (isothermal or cyclic, in air, air containing water vapor, CMAS silicate melt) allowed assessing and ranking the performance of coated systems
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Léo Portebois. Développement de matériaux réfractaires pour applications turbines aéronautiques : étude des effets microstructuraux sur le comportement en oxydation des alliages composites Nbss-Nb5Si3 et optimisation des solutions de protection associées. Autre. Université de Lorraine, 2014. Français. ⟨NNT : 2014LORR0153⟩. ⟨tel-01751060⟩

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