The deformation of polycrystalline metals is carried by the movement of dislocations through the material and their ability to pass obstacles, such as grain boundaries which represent very effective barriers to dislocation motion. As a fundamental study, deformation at selected grain boundaries in high purity nickel under cyclic loading conditions was studied by in situ and ex situ microcompression.
After surface preparation and annealing, electron backscatter diffraction measurements and cross sections were used to characterize the grain boundaries and to select the testing regions. Then, the microcompression samples were created by focussed ion beam milling directly at the grain boundaries and for comparison also in the adjacent single-crystalline regions. Different pillar shapes and sizes were created to investigate the influence of the grain boundaries relative to the bicrystalline volume. For the in situ experiments inside the scanning electron microscope, the pillars were marked with platinum patterns to facility tracking of the local strain development using digital image correlation. The microcompression samples were tested under monotonic and cyclic loading with up to 100 load cycles. In this presentation, the focus lies on the influence of the alignments of slip planes and the grain boundary with the loading direction on the local strain distribution. In combination with the strain distribution, the analysis of the slip traces at the surface will give further insight into the role of grain boundaries in the cyclic deformation process.