2.2.3 Microstructure observation methods
After fatigue tests, the microstructure of the material was
characterized by a scanning electron microscope (SEM, JEOL 7800F). The
detection mode was SEI (secondary electronic imaging) mode, and the
acceleration voltage is set to 15 kV, respectively. The SEM observation
area was concentrated on the fracture surface and specimen surface.
Especially, we carried out higher magnifications for the regions near
the crack initiation sites, which is focused on the crack initiation
behavior of the material. On the other hand, the EBSD (electron
backscatter diffraction) technique was applied to determine the grain
orientation of the material. The area detected is the cross-section of
the material, and the diffraction direction is perpendicular to the
cross-section.