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Analyse des processus d’endommagement aux joints de grains dans les superalliages base Nickel

Abstract : Nickel-based superalloys used in turbine disks are subjected to severe stresses ranging from creep to fatigue at temperatures up to 700°C. Under these conditions, the literature shows that grain boundaries are the weakest structural element. Depending on these conditions, the grain boundaries can slide, transmit or accumulate deformation and are favorable locations for oxidation. Thus, intergranular damage is closely related to these deformation processes.The purpose of this work is to contribute to the understanding of the deformation and damage mechanisms that occur at grain boundaries. To study quantitatively the early stages of plasticity and damage, a new non-contact measurement approach taking into account displacement discontinuities is presented: Heaviside-DIC. It was validated before being used in the study of high temperature inter and intragranular sliding. Afirst qualitative study has shown greater intergranular damage in creep at 700°C / 700 MPa compared to tension at different temperatures. The implementation of H-DIC at 2 scales coupled with EBSD, allowed to identify a detrimental microstructural configuration in turbine disks polycrystalline superalloys: coherent twin boundaries. Comparison with a turbine blade columnar superalloy with no twins confirms these observations.In this light, and based on literature, a scenario explaining the transition between deformation and intergranular damage is proposed.
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https://tel.archives-ouvertes.fr/tel-03079088
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Submitted on : Thursday, December 17, 2020 - 9:41:21 AM
Last modification on : Wednesday, October 27, 2021 - 7:05:36 AM
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François Bourdin. Analyse des processus d’endommagement aux joints de grains dans les superalliages base Nickel. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2020. Français. ⟨NNT : 2020ESMA0013⟩. ⟨tel-03079088⟩

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