Early Stage of Plastic Deformation in Metals Studied by In Situ X-Ray Synchrotron Topotomography and Crystal Plasticity FEM Simulations

N. Gueninchault¹, H. Proudhon¹, S. Forest¹, W. Ludwig²

¹ MINES ParisTech, PSL Research University, MAT - Centre des matériaux, CNRS UMR 7633, Evry, France

² ESRF, The european synchrotron, Grenoble, France

With  the development of recent X-ray sources and detectors, scan times decreased drastically, enabling time resolved studies. But performing mechanical testing while imaging in 3D deformed materials could be difficult, and specifically designed rigs are needed, to fit the severe space constraints of a synchrotron beamline. 4 stress rigs were designed enabling tomographic imaging with the most recent techniques (fast X-ray CT, diffraction contrast tomography, topotomography, laminography, dark-field microscopy). More focus is paid here on NANOX, a tensile stress rig designed to fit into the ID11 diffractometer, and which allow a FRELON microscope to be less than 3mm far from the sample.

In situ X-ray synchrotron topotomography on a 3-grains cluster within the bulk of a binary AlLi alloy has been performed for the first time on the ID11 beamline of the ESRF. Thanks to the specifically designed NANOX device, the very first plastic events in the individual grains have been captured, and the effect of plastic instabilities to the lattice orientation were observed. Single or multiple slip bands formation is observed depending on the grain orientation and load level. 3D rocking curves analysis shows a strong lattice curvature corresponding to the previously identified active slip systems.

The 3D microstructure (grain shape and orientation) of the entire sample was characterized by diffraction contrast tomography. This reconstruction was used to generate a realistic mesh of the specimen and to perform crystal plasticity finite element (FE) simulations within the finite strain framework. The mechanical behaviour at the grain level observed experimentally was compared with  FE simulation results by using special post-processing routines simulating diffraction patterns of the deformed crystals.