Expérimentation numérique pour l'aide à la spécification de la microstructure et des propriétés mécaniques d'un superalliage base Ni pour des applications moteurs

Abstract : An optimization loop allowing the optimization of the thermal treatment toward the fatigue life of the turbine disk in PM Ni-base superalloy N18 is built. This loop is constituted of three finite elements calculations and one post-processing of the fatigue life. The first calculation is a thermal calculation which allows the determination of the evolution of the temperature in each point of the disk. The second one is a calculation of the precipitation, which gives the microstructural parameters, i.e. the volume fraction and the size of the different population of precipitates. The third one is the calculation of the mechanical response of the disc to the service loading. The behavior in each Gauss point is a function of the microstructural parameters deduced from the second calculation. To build this loop, a model of precipitation was implemented in ZeBuLoN code and recalibrated for coarse grained N18. Moreover the influence of the intragranular microstructure on the fatigue behaviour was studied through specific mechanical tests performed at 450°C. This study shown the fatigue life function is a priori no dependant from the intragranular microstructure. But it has a very strong influence on the yield stress, which has a direct impact on the mean stress at the stabilised cycle. And the mean stress is one of the key parameters for the fatigue resistance of the material. A multiscale model was built to account for the role of the fine microstructure on the fatigue behaviour. The optimization loop is built with a phenomenological model and shows that a slower cooling, leading to a lower yield stress at the critical point of the disk allows to enhance the fatigue life. Meanwhile, the resistance to brsting also constitutes a major criterion for the design of the disc and this one requires a good mechanical resistance of the material.
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Submitted on : Thursday, December 24, 2015 - 3:16:07 PM
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  • HAL Id : tel-01248295, version 1

Citation

Guylaine Boittin. Expérimentation numérique pour l'aide à la spécification de la microstructure et des propriétés mécaniques d'un superalliage base Ni pour des applications moteurs. Mécanique des matériaux [physics.class-ph]. École nationale supérieure des mines de Paris, 2011. Français. ⟨NNT : 2011ENMP0113⟩. ⟨tel-01248295⟩

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