Crystallographic orientation sensitive measurement of strain rate sensitivity in Zircaloy-2 via synchrotron X-ray diffraction

A series of stress relaxation experiments were performed on samples of rolled Zircaloy-2 plate. In situ synchrotron x-ray diffraction was used to observe changes in interatomic lattice spacing during both deformation and relaxation. The concepts of strain rate sensitivity and activation volume are extended from the macroscopic to the microscopic scale using the results of the diffraction analysis. The technique outlined in this paper allows for the precise measurement of thermally activated properties at the level of subsets of grains sharing similar crystal orientations relative to the loading direction. Self-consistent modelling results are used to connect the observed strain rate sensitivity of these grain families with the rate sensitivities of the various active slip systems in zirconium alloys. The results show that the dependence of strain rate sensitivity on crystal orientation occurs primarily due to the differing strain rate sensitivities of the individual slip systems, which ultimately determines the macroscopic value.