Deformation mode-determined misorientation and microstructural characteristics in rolled pure Zr sheet

Abstract

In this work, commercially pure Zr sheets were subjected to β air cooling and then rolled to different reductions (10% and 50%) at room temperature. Microstructures of both the β-air-cooled and the rolled specimens were well characterized by electron channelling contrast imaging and electron backscatter diffraction techniques, with special attentions paid to their misorientation characteristics. Results show that the β-air-cooled specimen owns a Widmanstatten structure featured by lamellar grains with typical phase transformation misorientations. The 10% rolling allows prismatic slip and tensile twinning ({11-21} and {10-12} ) to be activated profusely, which produce new low-angle (~3°–5°) and high-angle (~35° and ~85°) misorientation peaks, respectively. After increasing the rolling reduction to 50%, twinning is suppressed and dislocation slip becomes the dominant deformation mode, with the lamellar grains highly elongated and aligned towards the rolling direction. Meanwhile, only one strong low-angle misorientation peak related to the prismatic slip is presented in the 50%-rolled specimen, with all other peaks disappeared. Analyses on local misorientations reveal that hardly any residual strains exist in the β-air-cooled specimen, which should be related to their sufficient relaxation during slow cooling. Residual strains introduced by 10% rolling are heterogeneously distributed near grain/twin boundaries while heavier deformation (50% rolling) produces much larger residual strains pervasively existing throughout the specimen microstructure.