Deformation induced microstructure of stress relieved Zircaloy-4 cladding

Abstract

This work evaluates the microstructural evolution of cold-worked, stress-relieved Zircaloy-4 cladding from pristine to uniaxial and biaxial deformed states. Differential aperture Laue diffraction and electron backscatter diffraction techniques are used to characterize intragranular strains, strain gradients, and grain fragmentation as metrics of deformation microstructure. The effects of mechanical anisotropy on deformation microstructure are investigated by comparing characterization results of samples subjected to different applied loads, including biaxial internal pressure and uniaxial tension along the rolled direction at 400 °C. Quantitative comparisons are made between the pristine microstructure and deformation-induced microstructure under both loading modes. Viscoplastic self-consistent simulations are performed to further investigate the microstructural evolution. Results indicate that biaxial loading from internal pressurization increases the deformation microstructure more than uniaxial loading along the rolled direction due to the relationship between loading and texture symmetry. Additionally, characterization results and simulations show distinct deformation-induced micro-textures: axial loading promotes a prismatic $\left(10.0\right)$ fiber texture in the rolled direction, which strengthens the micro-texture inherited from pilgering, whereas pressure loading results in a $\left(2\overline{1}.0\right)$ texture fiber, weakening the original micro-texture inherited from pilgering.