To improve component design, the fatigue behaviour of gas turbine materials has to be fundamentally understood. Since Ni-alloys exhibit an extreme elastic anisotropy, the local grain orientation strongly affects the stress and strain distribution in the material under mechanical loadings [1]. Our contribution addresses the characterization of anisotropic elastic-plastic deformation and its consequences for crack initiation of nickel base super alloy IN617 under tensile fatigue loadings.

Small specimens were loaded in-situ until failure in a scanning electron microscope (SEM) to correlate the deformation behaviour with the local grain structure determined by electron backscatter diffraction (EBSD) measurements taken at different deformations. For further understanding of elastic and plastic deformation, the EBSD-data was transmitted into a finite element simulation to calculate stresses and strains, with the aim review the theories based on Schmidt factor and anisotropic Young’s modulus, and to eventually upscale the microscopic simulations to the component scale. A mathematical optical flow method, which is capable to calculate the transformation of each EBSD measuring point as well as of every FEM node during deformation, was applied to the EBSD data to compare the deformations measured by EBSD and finite element simulation [2].

In order to predict the crack initiation sites considering the texture of the microstructure, we compared the Young’s modulus and Schmidt factor as well as their product (E ⋅ m) of each grain close to the experimentally determined crack initiation site. Previous theories predict a failure at regions of grains with high E ⋅ m or single grains with low E ⋅ m surrounded by grains with higher E ⋅ m as crack initiation sites [3]. Our results shown in figure 1 revealed that the material fails at grains with high Schmidt factors and high Young’s moduli, which, at least partially, confirms the findings published in [3].

[1] B. Engel, L. Mäde, P. Lion, N. Moch, H. Gottschalk, T. Beck, MDPI Metals, 2019, 9(8), 813, https://doi.org/10.3390/met9080813

[2] M. Gräf, S. Neumeyer, R. Hielscher, G. Steidl, M. Liesegang, T. Beck, SIAM Journal on Imaging Sciences, 2021, arXiv:2106.05645v2. [3] B. Engel, M. Huth, C. Hyde, MDPI Crystals, 2022, 12(1); 100, https://doi.org/10.3390/cryst12010100