1. Size of compound phase
Figure 1 shows the microstructure of the defective sample and the normal sample. Through comparison, it can be seen that the compound phase of the defective sample is coarser than that of the normal sample. The maximum size of the compound phase of the defective sample is 314.74 μ m. The average size is 33.6 ± 0.5 μ ｍ； The maximum size of the compound phase of the normal sample is 78.24 μ m. The average size is 24.3 ± 0.5 μｍ。
2. Size distribution of compound phase
The statistical results of the size range of all compound phases are shown in Figure 2. It can be seen that the compound phase size of normal samples is mainly distributed in 15 ~ 20 μM, showing a typical normal distribution; However, the size of the compound phase of the defect sample shows a bimodal distribution, concentrated in 10 ~ 15 μ M and 55 ~ 60 μ In the range of M, there are even abnormally coarse compound phases distributed in 310 ~ 315.
2. Area fraction of compound phase
The software extraction diagram of the area fraction of the compound phase is shown in Figure 3. It can be seen that the compound in the defective sample is coarse and concentrated, while the compound in the normal sample is fine and dispersed. The area fraction of the compound phase of the defective sample is 2.32%, when the critical size of the compound reaches 50 μ M, the area fraction is 1.56%; The area fraction of the compound phase in the normal sample is 2.01%, when the critical size of the compound reaches 50 μ M, the area fraction is only 0.15%.
4. Morphology of compound phase
In order to compare the morphology of the compound phase between the defect and the normal sample, the ratio of the long axis to the short axis of the ellipse, which is equivalent to the morphology of the compound, is used to describe. The larger the ratio of major axis to minor axis is, the more slender the compound phase is, on the contrary, the more rounded the compound phase is. Figure 4 shows the distribution frequency histogram of major axis / minor axis ratio of defect and normal samples, with interval interval of 0.5. Through comparison, it can be seen that the long axis / short axis ratio of defects and normal samples are concentrated in the range of 1 ~ 1.5, so the morphology of the compound phase is mostly granular. However, the long axis / short axis ratio of defective samples is in the range of 3 ~ 6, accounting for 3.4%, so there are many abnormally thick and slender rod-shaped compound phases.