PSI - Issue 19

Akifumi Niwa et al. / Procedia Structural Integrity 19 (2019) 106–112 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

109

4

The stress amplitude of the high temperature bending fatigue test which applied axial stress was arranged using the value calculated by the elastic analysis. That is, it is a virtual elastic stress that assumes that the specimen does not yield.

Fig. 4. Conditions of FEM analysis. (a) Temperature distribution of specimen based on measured value. (b) Schematic image of constraint conditions.

2.4. Observation

In order to confirm the grain structure of the specimen, electrolytic etching and the crystal orientation analysis by Electron Backscatter Diffraction (EBSD) method were carried out. And the fractured specimens were observed for fractured surface using a scanning electron microscope and internal cross-sectional observation using an optical microscope to study the failure mechanism.

3. Results and Discussion

3.1. Structure observation

Fig. 5 shows the result of observation using an optical microscope and EBSD method after etching, in order to observe the grain structure of the test piece. From the microstructure observation, it was confirmed that the grain size of this test piece is about several tens of μm in the thickness direction and about several tens to 200 μm in the planar direction, and it is flat shape rolled in the thickness direction of the test piece. In addition, it was confirmed that the crystal orientation was in a random state and the material is in a homogeneous state.

Fig. 5. Crystal structure and orientation distribution map.