EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

High angular resolution electron backscatter diffraction technique (HR-EBSD), coupled with a SEM in-situ nanoindenter, allows characterizing microstructural changes, strains, stresses and lattice defects evolution during deformation with a sub-100nm resolution, and while the mate-rial is under load, making it ideal to study small-scale mechanics. However, HR-EBSD is a near surface technique, where only the first few tens of nm is probed underneath the surface, which may not be characteristic of the entire volume of the materials. 3D HR-EBSD technique, using FIB tomography, has been developed to address this issue and to characterize the crystal de-fect and residual stresses distributions in the deformed materials with a sub-100nm3 voxel resolution. We applied this combination of techniques to study deformation twinning mechanisms in magnesium. Micro-tensile and micro-pillar compression tests on single crystal magnesium show a strong dependence of crystal orientation in twin initiation and propagation mechanisms. When loaded perfectly along the c-axis, magnesium shows surprisingly very limited twin formation at the micron-scale, while a loading a few degrees off the c-axis shows abun-dant twin formation and propagation at the same scale [1]. We show that this is due the role of basal slip, which acts as a trigger for {10-12} twin initiation and propagation. 3D HR-EBSD is used to characterize the defects and the residual stresses present in twin-twin interactions in the deformed material. Strain-rate effect on twinning mechanism has been also investigated on mi-cropillar compression along the [1-100] axis and will be addressed.

[1] N. Della Ventura, S. Kalscska, D. Casari, T.E.J. Edwards, A. Sharma, J. Michler, R. Logé, X. Maeder. Materials & Design 197, 2021, 109206.