Effect of loading mode on lattice strain measurements via neutron diffraction

The study of lattice strain evolution during uniaxial deformation via in situ neutron diffraction is a well established technique for characterizing the deformation behavior of metals. However, the relatively low flux of neutron facilities results in count times on the order of several minutes, requiring experimenters to choose between either applying a very slow strain rate, or loading the sample incrementally rather than continuously. Here we investigate the effects on lattice strain data obtained by using stress, strain, and position controlled incremental loading, as well as continuous loading, on samples of Zircaloy-2 under uniaxial compression. It was found that both qualitative and quantitative differences arise in the lattice strain behavior of certain grain families, particularly {101¯0} and {112¯0}, while other grain families show no discernible effect. The differences in lattice strain evolution brought on by the variation in loading modes are believed to be the result of thermally activated dislocation motion.