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Effets des microstructures induites par le procédé de forgeage sur la durée de vie de pièces en Inconel 718 DA

Abstract : Optimization of turbine discs in superalloy Nickel based durability is a real industrial challenge. The different regions of a wrought Inconel 718 DA superalloy turbine disk may present a wide range of behavior in fatigue life due to the variability of the microstructure. To improve the fatigue dimensioning, it is necessary to understand the relation between the forging parameters, the microstructure and the fatigue behavior. Firstly, the effect of the forging parameters on the microstructure was realized thanks to simulation calculation via Forge2® and experimental forging were realized. Secondly, fatigue tests under strain control conditions were performed at 450°C for all microstructures. Initiation mechanisms and fracture behavior are identified for each microstructure of this superalloy. Grain size and phases distributions were characterized in the specimens and related to fatigue failure initiation modes. The 3D distribution of the Titanium nitrides was also investigated using synchrotron laminography both in terms of size and spatial distribution. Fatigue crack initiation was seen to occur on large grains in stage I for the larger grain material whereas for the material with slightly smaller grains initiation from internal nitrides caused failure via so-called fish-eye cracks. A relation between the microstructure heterogeneities and the durability is established. Indeed, the initiation mechanism, which depends on the grain size distribution compare to the particles size, impacts the durability. The presence of Σ3 boundaries in large grains proves to be harmful.
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  • HAL Id : tel-02892024, version 2

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Mériem Abikchi. Effets des microstructures induites par le procédé de forgeage sur la durée de vie de pièces en Inconel 718 DA. Mécanique des matériaux [physics.class-ph]. Ecole Nationale Supérieure des Mines de Paris, 2014. Français. ⟨NNT : 2014ENMP0069⟩. ⟨tel-02892024v2⟩

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