Abstract
Plastic deformation mechanisms in hexagonal close-packed metals are characterized by dislocation slip and twinning. Therefore, direct observation of dislocation motions and nucleation/growth of deformation twins gives important information for the plasticity mechanisms in hexagonal close-packed metals. From a spatial resolution perspective, transmission electron microscopy is an effective technique that enables direct observation of microstructures. However, regarding in situ deformation experiments, the special boundary conditions in a thin foil type specimen may be problematic, e.g., effects of image force. To overcome this problem, we applied electron channeling contrast imaging (ECCI) to in situ observation, which enables the detection of the lattice defect motions and the evolution of elastic strain fields in bulk specimens. In this work, a Co single crystalline compact tension (CT) specimen of which the thickness was approximately 1 mm was deformed in a field emission scanning electron microscope. We observed the microstructure around the notch during deformation using in situ ECCI. The following in situ ECCI-visualized plasticity-related crucial phenomena were observed: (1) dislocation motions in the parent phase during deformation, (2) nucleation/growth of deformation twins via loading to a higher stress, and (3) crack formation along the matrix/twin boundaries.
