Page 11 - Shimadzu Journal vol.6 Issue1

Material Science

Observation and Analysis of Inclusions with an Table 4 Size of Inclusions
Electron Probe Micro Analyzer
To examine the fractured surface condition as well as the size and kind of
inclusions in metal materials after a fatigue test, we used the electron probe
micro analyzer, EPMA-8050G. Fig. 3, Fig. 4 and Fig. 5 show respective
observation images (secondary electron images) of the fractured surfaces
and inclusions on specimens #1, #2 and #3. On all specimens, the fracture
was developed from an internal inclusion, indicating that inclusions are the
origin of fatigue fractures. The size (major diameter) of the inclusion
obtained from the images is listed in Table 4. Table 3 and Table 4 together
indicate that the larger the inclusion size is, the smaller the number of
cycles to failure, suggesting that fatigue strength is affected by the size of
the inclusion. Following the above observation, we performed a mapping
analysis to determine the constituent elements of inclusions on the
specimens. The mapping analysis results of the inclusion of specimen #1 are
shown in Fig. 6. Image (a) in Fig. 6 shows the secondary electron image
which is suitable for grasping the profile of the inclusion. Image (b) helps to
understand the relative composition of constituent elements. In this
backscattered electron image, the smaller the mean atomic number the
darker it appears and the larger the brighter. Images (c) to (f) show the
distribution images of O, Al, S, and Mn and indicate that these elements
are contained in inclusions at high concentrations. From these results, the
n
inclusions proved to be alumina (Al2O3) and manganese sulfide (M S).
Inclusions in specimens #2 and #3 were also found to be mainly alumina
and manganese sulfide.

Fig. 6 Mapping Analysis Results of Specimen #1
(a) Secondary Electron Image,
(b) Backscattered Electron (Composition) Image,
(c) O-distribution Image, (d) Al-distribution Image,
Fig. 3 Observation Image of an Inclusion in Specimen #1 (Secondary Electron Image) (e) S-distribution Image, (f) Mn-distribution Image

Conclusion
In this experiment, we performed the detection of inclusions in metal
materials using an ultrasonic fatigue testing system. Actual fatigue
testing is the best way for detecting inclusions which may cause an
internal fracture and an ultrasonic fatigue testing system is an
effective means to drastically shorten the testing time. In addition, we
analyzed the inclusions using an electron probe micro analyzer to
determine the size and constituent elements of each inclusion. From
this, we confirmed that the size of inclusions may be affecting the
Fig. 4 Observation Image of an Inclusion in Specimen #2 (Secondary Electron Image) variation in the number of cycles to failure and that observation of the
fractured surface is indispensable in ultrasonic fatigue testing.

References

*1 Yoshiyuki Furuya, Saburo Matsuoka, Takayuki Abe:
Tetsu-to-Hagane, Vol. 88 (2002) No. 10 (in Japanese)
*2 Application News No. i258
*3 Yoshiaki Akiba, Keisuke Tanaka, Akira Nakatsu: Transactions of the
JSME (Part A) Vol. 70 No. 695 (2004-8) (in Japanese)

Fig. 5 Observation Image of an Inclusion in Specimen #3 (Secondary Electron Image)

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