13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- 25 μm 25 μm 25 μm Table 4. Estimated grain sizes and fraction of <111> grains. Specimen Grain size with large misorientation (μm) Grain size involving subgrains (μm) Fraction of <111> grains (%) A 10 1.8 61 B 12 3.9 80 C 50 5.5 85 (a) z axis (b) x axis (c) y axis Fig. 11. IPF images and IP figures of longitudinal cross-section at center of B specimen. grains, as is typically demonstrated by Fig. 12. This result is consistent with the results of EBSD analyses mentioned above. However, A specimen has the broadest peaks, while C specimen has the most narrow peaks, as shown in Fig. 13. Since the grain sizes of the present specimens are too large to contribute to the broadening of XRD peaks, the internal stress is attributed to the broadening in A and B specimens [6]. The internal stress due to precipitates is considered to be nearly the same in all specimens, because the same aging condition is applied. Therefore the broadening of XRD peaks is considered to be brought by the difference in the dislocation density; A specimen has the largest dislocation density, the density in B specimen is the second largest and the density in C specimen is comparable to that of the annealed one which shows distinct peaks of Kα1 and Kα2 X-rays. Fig. 12. X ray peaks in B specimen. Fig. 13. Peaks of (111) reflection. Inte nsity (cou nts) 111 200 220 400 2 θ (deg) 0 0.5 1.0 1.5 37.8 38.0 38.2 38.4 38.6 38.8 39.0 A specimen B specimen C specimen Intensity (x 106 counts) 2 θ (deg)
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