Crack Paths 2012

in the FGA.Whereas a long crack propagation occurs in the fisheye, the F G Ashows a

type of short crack growth, which needs to be analysed in more detail.

Figure 6. Cross section through inclusion, F G Aand fisheye

Another characteristic of the F G Ais a fine granular part in the microstructure just below

the crack path, as seen at higher magnification in Fig. 6A. Investigations by T E M

(Fig. 7) showed that the grain size within those fine granular parts is far below 100 nm.

In comparison, the average grain size in the original material is about 1-2 μm. In

conclusion the F G Ais not merely a fine granular looking area at the fracture surface,

but the F G Aconsists of a fine granular microstructure at and below the crack path.

Figure 7. Selected area diffraction pattern by T E M

As mentioned above, different mechanisms for forming the F G Ahave been postulated

in the literature. Our investigations seem to support the postulated mechanism of

Sakai et. al. [2]. They explain the formation of this area by three steps: at first a

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