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Etude des effets des préparations de surface avant projection thermique : application barrière thermique

Abstract : Coating adhesion is requiered to rpomote specific surface properties by thermal spraying. Conventional prior-surface treatments have been developed to create anchoring zones but the adhesion strenght and their applications are limited. Laser surface texturing increases and adapts the adhesion surface. Therefore, two interface failure modes have been related to texture morphologies for tensile and shear stresses. The energy released rate at the interface increases up to coating toughness when the crack path is sharp. Mixed-mode failures have been observed with adhesive and cohesive cracks around and above pattern respectively. So, the adhesion stengyh is function of the contact aera precisely linked to pattern distribution and morphology. Thermal barrier coating system without bond coat life-span has been evaluated for thermomechanical stresses (YSZ coating on single crystal based Nickel). The bond coat has been remplaced by an adapted substrate surface topography. According ti the laser parameters (energy per pulse, pulse numbers) pattern morphology can be created. Therefore, textured surface filling by melted particles has been studies to minimize interface defaults and created mixed-mode failures for during plasma spray coatings. The drilling mechanisms have been evaluated by numerical modeling and experimental analysis. The pattern dimensions and heat affected zones has been identified. The laser treatment changes the microstructure locally.Oxydation tests have been performed to study the surface pre-tratments effects on oxide nature and mass gain rate. The damaging mechanisms ave been studied under isotherm and cyclic high temperature tests and also under creeping and thermo-mechanical fatigue tests. Grit-blasting change the natural oxides, limits life-span and bucking failure mode have been obeserved. Natural oxides have been analyzed for the textured substraes also but anchoring mechanism enables large life-span under high temperature tests. Mechanical applied stresses (constant and cyclic) validate the beneficial effects of patterned surfaces. The interface is stronger than the coating toughness and the patterns do not create early cracks under thermo-mechanical solicitations.
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Robin Kromer. Etude des effets des préparations de surface avant projection thermique : application barrière thermique. Matériaux. Université de Technologie de Belfort-Montbeliard, 2016. Français. ⟨NNT : 2016BELF0297⟩. ⟨tel-01872628⟩

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