PSI - Issue 13

Atsuhisa Kitade et al. / Procedia Structural Integrity 13 (2018) 1845–1854 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig.6 General of the polishing process

Finally, the surface was processed by FIB (focused ion beam) and sufficiently flat surface is polished so as to obtain EBSD image. The above process is schematically shown in Fig.6 Black lines shows the focused portion. After doing these, information of the crystal orientation around the trigger point of brittle fracture was obtained by performing EBSD observation from the top of the photograph.

Fig.7 EBSD Inverse Pole figure map

2.3. EBSD analysis result

Fig.7 is inverse pole figure map near the fracture trigger point acquired by EBSD. This represents the crystal orientation by color, and it can be judged that the same color part can be regarded as the same crystal grain. The portion of the black arrow is the brittle fracture trigger point. The boundary of the effective crystal grains in which the fracture trigger point locates shows black lines. Compared with other part of the base material, this grain size seems extremely large. So, it was suggested that the MA, which works as the trigger of brittle fracture origin, was selected from MAs located in large crystal grains. This evidence can tell us that large crystal grains leads to promote brittle fracture, as is the model proposed by [Smith, 1966], because the pile-up effect of dislocation may be greatly involved. In order to verify the pile-up effect of dislocation, observation was performed by enlarging the vicinity of the trigger point portion, and the Inverse Pole figure map, the Image Quality map (IQ map), the Grain Reference Orientation Deviation map (GROD map) and the Kernel Average Misorientation map (KAM map) were depicted respectively. Where, the definitions of GROD and KAM are shown in Fig. 8 and equations (1) and (2). [Install Software OIM v7.3b].

(1)

i reference   = −

GROD