Lee Te-Jui Thanks for your professional answer! My understanding is that these bright and dark areas are within the same grain,the size of this grain may be very large. So this also means that my forging process does not refine the grain size or crushing of grains. Because there are indeed excessive reheating during the forging process. If my understanding is right, Why do they have different grain orientations or oxidation region or strain layer in one grain?
Thank you for your attention to this problem. This titanium alloy is designed by ourselves ,the content of iron and chromium is relatively high, around 3%,Tβ≈850℃.Annealing temperature after forging at 730 ℃ for 80 minutes. There is a negative effects on grain size is the times of reheat is relatively high during the forging process, So I want to know why the grain size after forging is still so large, and Is there a possibility of segregation in one grain?@Panayotis Vrettos