Investigation of the strain induced rafting of the gamma prime precipitates in single crystal nickel based superalloys.

Abstract : Single crystal nickel based superalloys find their application in aerospace engineering since they exhibit a very good mechanical behaviour at high temperature (1100°C). These peculiar properties are strongly correlated with a morphology change from cuboids to rafts of the hardening γ' precipitate phase. This microstructure evolution, also called rafting was first revealed during a creep test. In this work, we show the results of small angle neutron scattering, high resolution diffraction of synchrotron X-radiation and electron microscopy investigations. This allows the establishment of a correlation between the development of plastic flow and microstructure evolution of these superalloys. The use of small angle neutron scattering during an in-situ high temperature annealing of a deformed sample allows the characterisation of the kinetics of strain induced rafting of the γ' particles. Moreover, the in-situ analysis of the evolution of internal stresses during rafting has enabled the identification of the micromechanisms involved. Electron microscopy observations of the resulting microstructure and dislocation structure confirm these results. In addition, a model based on the inclusion theory of anisotropic elasticity combined with a mean field approach is developed. A correlation between the experimental results and creep behaviour is thus obtained. Results show that the anisotropic relaxation of the lattice parameter mismatch induced by matrix plastic deformation is the driving force for the diffusion phenomena involved in the directional coarsening of the γ' particles.
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Submitted on : Thursday, December 13, 2007 - 2:30:14 PM
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Nicolas Ratel-Ramond. Investigation of the strain induced rafting of the gamma prime precipitates in single crystal nickel based superalloys.. Mechanics [physics.med-ph]. Université Joseph-Fourier - Grenoble I, 2007. English. ⟨tel-00196745⟩

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