3D-Modelling of thermo-mechanically and thermo-chemically coupled microstructural changes in high-temperature nickel-base superalloys

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The proposal presents a tightly integrated combination and enhancement of experimental and numerical methods aiming at an improved understanding of creep in polycrystalline nickel-based superalloys. Focus of the initial study was on the acquisition of crystal orientation in superalloys and, therefore, an appropriate physics-based crystal plasticity grain model was developed. A numerical framework is outlined on two scales that attempts to capture the effect of: 1) a rafting γ/γ´-microstructure on creep properties at the grain scale and 2) grain boundary (GB) type and slip orientations on grain boundary failure. A full 3D crystal plasticity rafting model is described which will be calibrated by creep curves and micrographs (scanning and transmission electron microscopy) from single crystals with similar y/y´-microstructure as observed in polycrystalline IN738LC. The rafting model, based on the extended finite element method (XFEM) in conjunction with level sets, will yield physics-based data to creep anisotropy on the grain scale. By means of deformation-tracking electron backscatter diffraction (EBSD) measurements and high temperature digital image correlation (DIC), GB type will be correlated to GB failure and strength. The correlation serves as input to the extension of the grain scale model to intergranular failure. X-ray microscopy, including bulk grain orientation and 3D grain geometry, will generate data for the validation of the grain model.