Characterization of polycrystalline materials by X-ray diffraction contrast tomography

National audienceSynchrotron based X-ray imaging and diffraction techniques offer interesting possibilities for characterizing the grain microstructure in a variety of polycrystalline mono-and multiphase materials. Direct visualization of the three-dimensional grain boundary network or of two-phase (duplex) grain structures by means of absorption and/or phase contrast techniques is possible, but restricted to specific material systems (Ludwig 2009b). However, conventional attenuation or phase contrast imaging techniques do not give access to the crystallographic orientation of the grains and additional diffraction measurements are required. On the other hand, three-dimensional X-ray diffraction methods like Differential Aperture X-ray Microscopy (DAXM, (Larson, 2002) or 3D X-ray Diffraction Microscopy (3DXRD) (Poulsen, 2004) can analyse the 3D grain structure and/or elastic strain tensors of individual grains in polycrystalline materials, but are blind to the microstructural features (inclusions, cracks and porosity) visible in attenuation and/or phase contrast imaging techniques . A recent extension of the 3DXRD methodology, termed X-ray diffraction contrast tomography (DCT) (Ludwig 2009a), combines the principles of 3DXRD and X-ray absorption tomography. With a single scan, DCT can provide simultaneous access to the grain shape, crystallographic orientation, full elastic strain tensor and the local attenuation coefficient distribution in three dimensions. The technique applies to a range of plastically undeformed, polycrystalline mono-phase materials, fulfilling some conditions on grain size and texture. The straightforward combination with in-situ microtomographic observations opens interesting new possibilities for the characterization of microstructure related damage and deformation mechanisms in these materials