On the state of deformation in a polycrystalline material in three-dimension: Elastic strains, lattice rotations, and deformation mechanisms

The deformation of polycrystalline zirconium is analysed at the individual grain level using three-dimensional Synchrotron X-ray Diffraction (3D-XRD) in combination with a Crystal Plasticity Finite Element (CPFE) model. The effects of elastic strains and lattice rotations on the shape and position of diffracted peaks are studied in detail. For this purpose, the three dimensional measured microstructure of a commercially pure zirconium (CPZr) sample was imported into a crystal plasticity finite element (CPFE) model to simulate the deformation of measured grains. The calculated lattice rotations and strains of the selected most active grains were subsequently used to forward simulate diffracted peaks. The simulated peaks are then compared to the 3D-XRD measured ones. It is shown that although the sample was deformed to 1.2% strain, soft grains exhibit significant peak smearing. Peak broadening is mostly affected by the deformation induced lattice rotation and less affected by the elastic strains. Further, the comparison of CPFE modelling and 3D-XRD results confirms that prism and basal slip are the most active systems and pyramidal is present but only slightly active. A method is developed to determine the activity of possible slip systems. As an example, by comparing the simulated and measured peak positions as well as the rotations of the most affected diffraction peaks, it is shown that pyramidal slip system is not active significantly at room temperature.