Fluage à haute température d'un superalliage monocristallin : expérimentation in situ en rayonnement synchrotron

Abstract : Nickel-based superalloys are used in aeronautics for turbine blades. This study aims at modelling the creep behaviour of single-crystalline AM1 superalloy with a rafted microstructure during isothermal tests under variable applied stresses. (200) diffraction profiles are obtained with a triple crystal diffractometer and high energy synchrotron radiation at high temperature (950-1150°C) with an applied stress varying between 0 and 300 MPa. For each phase, the elastic strain is deduced from the peaks positions and the stress, plastic strain rate from the lattice mismatch, assuming a model lamellar composite material. Post mortem characterizations by electronic microscopy completes the results: morphology of each phase, dislocations densities and nature. The measurement of lattice mismatch leads to an in situ estimation of the dislocations density at the interfaces. For the phase, during successive jumps of the applied stress, the Von Mises stress increases and then relaxes down to a threshold stress. This stress is in agreement with Orowan stress deduced from the post mortem measurements of the channels width. Plastic strain of the phase is produced by climb of dislocations with Burgers vectors perpendicular to the tensile axis under the mere transversal stress and is controlled by the entrance of dislocations into the rafts from the interfaces. The distribution of elastic strains was simulated by assuming two main contributions: dislocations at the interfaces and within the rafts. The simulation reproduces the absolute magnitude of the peaks width, as well as their increase with dislocation densities.
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Laura Dirand. Fluage à haute température d'un superalliage monocristallin : expérimentation in situ en rayonnement synchrotron. Autre. Institut National Polytechnique de Lorraine, 2011. Français. ⟨NNT : 2011INPL079N⟩. ⟨tel-01749489⟩

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