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Theses

Modélisation des effets de l'évolution microstructurale sur le comportement mécanique du superalliage monocristallin AM1

Abstract : The framework of this thesis is the modelling and the lifetime prediction of high pressure aeronautical turbine blades. These parts are realized in nickel base single crystal superalloys. This work is focused on the microstructural evolution arising at high temperatures under mechanical loading known as the directionnal coarsening. In a first time, this work consists in studying the mechanical behaviour of the initial non-aged material. Tests have been performed at 950°C in order to enrich the available data base. They have allowed us to identify a hyperbolic sinus viscosity model over a wide range of stain rates. The initial behaviour has also been studied at the mesoscopic scale. A constitutive model has been identified for both phases in order to reproduce the macroscopic behaviour of the material. This study, performed in the classical viscoplasticity framework, shows the limits of this approach. In particular, it does not allow to model the length scale effects observed in plasticity. In the same time, we have studied the directionnal coarsening phenomenon in both experimental and numeric ways. Mechanical test after ageing have been realized. Various ageing conditions have been tested, in creep at different temperatures and stresses and along different cristallographic orientations but also under cyclic loading. Tests have shown an effect of the directionnal coarsening on the hardening. More precisely, the directionnal corasening induces a softening of the material behaviour. Directionnal coarsening has also been simulated with the phase field method. We have proposed a coupling between the phase field model and a viscoplastic crystal plasticity model in order to take into account the plasticity in the evolving matrix channels. Simulations have shown an increase in the kinetics of the rafting evolution induced by plasticity and a more realistic morphology of the precipitates as observed axperimentally, in particular under cyclic ageing. In order to understand the influence of the directionnal coarsening on the mechanical behaviour, length scale effects were analyzed in the framework of generalized continuum approaches like the Cosserat and the microcurl models. In order to compare the results obtained with both approaches, a two--phase laminate loaded in shear has been studied analytically. Both models deliver a linear kinematic hardening dependant on the size of the microstructure. Finally, the previous developement and the tests performed during this work allow to propose and identify an extended macroscopic model which takes into account the effects of the directionnal coarsening on the machanical behaviour of the AM1 superalloy.
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https://pastel.archives-ouvertes.fr/pastel-00580004
Contributor : Bibliothèque Mines Paristech <>
Submitted on : Friday, March 25, 2011 - 4:14:49 PM
Last modification on : Thursday, September 24, 2020 - 6:30:07 PM
Long-term archiving on: : Thursday, November 8, 2012 - 12:40:09 PM

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  • HAL Id : pastel-00580004, version 1

Citation

Anaïs Gaubert. Modélisation des effets de l'évolution microstructurale sur le comportement mécanique du superalliage monocristallin AM1. Matériaux. École Nationale Supérieure des Mines de Paris, 2009. Français. ⟨pastel-00580004⟩

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