Slip localization and grain boundary sliding analysis at sub-voxel resolution using phase contrast tomography

Microplasticity of a polycrystalline Ni-based superalloy was investigated using phase contrast tomography (PCT) and laser scanning confocal microscopy (LSCM). Incremental tensile testing was performed on three miniaturized specimens to investigate strain localization at low plastic deformation at room temperature and 650 ^∘C. Microplasticity events, such as slip activity, deformation twinning, and grain boundary sliding, are free to emerge at the specimen surface and generate sub-micrometer topographic features. High resolution digital image correlation was conducted using LSCM to have a description of the in-plane and out-of-plane kinematics of the specimen surface. Despite slip amplitudes substantially smaller than the voxel size, PCT was capable to evidence the out-of-plane component of slip traces at the onset of plasticity. The technique was also used at 650 ^∘C, a temperature at which grain boundary sliding occurs, but surface reactivity is severe enough not to allow for topographic measurements using LSCM. Therefore, PCT was found particularly adapted to evidence “surface” microplasticity events hidden by an extra surface oxidation layer.