Three-dimensional sub-grain mapping of elastic strain state and orientations in the bulk of polycrystals

Péter Reischig (1) , Wolfgang Ludwig (1, 2)

1 ESRF - European Synchrotron Radiation Facility
2 MATEIS - Matériaux, ingénierie et science [Villeurbanne]

Detailed information on the sub-grain deformation state in polycrystals at the micrometre scale and below is essential to fully understand a vast variety of interplay between microstructure and mechanical properties. We demonstrate the possibility of efficiently mapping the complete local strain tensor, including hydrostatic strain, at the sub-grain level in three dimensions inside a polycrystal, along with the local crystal orientations and crystal structure, in a non-destructive way. The resulting three dimensional maps have a strain resolution in the order of 10-4 , spatial resolution in the order of micrometres, and can cover several hundred micrometres in size and include hundreds or thousands of grains. Datasets are obtained via Diffraction Contract Tomography (DCT), where the effects of the grain shapes and the deformation fields are convoluted in the recorded diffraction spots. The grain shapes and the local sub-grain crystal orientation and strain information is inferred in a novel data processing approach using a forward model and an iterative non-linear solver. The method uses a parallel, monochromatic synchrotron X-ray beam and the scan consists of a single rotation of the specimen, enabling short scanning times and a robust setup. The challenges in achieving high spatial, orientation and strain resolution, and of the mathematical problem of resolving the local deformation are described, and preliminary validation test results are presented.

Mots clés: X-ray diffraction; lattice strain tensor; tomography; polycrystal

Domaines: Traitement du signal et de l'image [eess.SP]; Mécanique des matériaux [physics.class-ph]

Péter Reischig, Wolfgang Ludwig. Three-dimensional sub-grain mapping of elastic strain state and orientations in the bulk of polycrystals. 40th Risoe International Symposium on Metal Microstructures in 2D, 3D and 4D, Sep 2019, Risoe, Denmark. ⟨hal-02404435⟩