## 3 Results and Discussion
During the operation of EAST, the monoblocks bear an uneven thermal load, and the maximum heat is often concentrated at the leading edge [30]. Recrystallized grains were observed in the upper right corner of Figure 3d, whereas no recrystallized grains were observed in Figure 4d; this happened on the same monoblock, indicating that #W511-14 suffered more heat flux at the corner near #W511-13 (upper right corner in Figure 3d), where there exists a temperature gradient along the T/thickness direction. Although the above monoblocks showed recrystallization and cracking, the dimensions of the leading edge which received the most critical heat flux had no obvious change. The microstructure had changed partly, but the structural integrity was still intact. Contrary to the previous studies by [PERSON] [36], no macrocracks were found in the center of the monoblock, which may be due to the difference in the heat flux and heat flux angle. The grain orientation maps are shown in Figure 5. Recrystallization grains are seen in #W511-7 and #W511-11, and the recrystallization area is concentrated on the leading edge of the monoblocks, which corresponds to the temperature concentration area in Figure 3 and the metallography pictures in Figure 4. Besides the recrystallization area, the original deformed structure that has not been affected by heat flux can also be seen in the grain orientation maps. The color in the maps indicates different orientations of grains. The difference in the original microstructure can be seen from the different orientations of three blocks in the area of the deformed state. Considering the position of string No. W511 in EAST, we believe that the strings on both sides of the outer target will suffer high temperatures and be recrystallized. One side receives a high heat flux due to the large misalignment, and the other side suffers from heat radiation from the adjacent string. Figure 3: **(a)** Monoblock view direction (the viewing direction is shown by the arrow, and the viewing area is shown by the circle); **(b)** H-W plane of the metallographic picture of #W511-7 (the red circle part is shown in **(e)**); **(c)** H-W plane of the metallographic picture of #W511-11 (the red circle part is shown in **(f)**); **(d)** H-W plane of the metallographic picture of #W511-14 (the red circle part is shown in **(e)**, the numbers on the lower side of the picture represent the number of adjacent monoblocks); **(e)** the higher magnification of the metallographic picture in the red circle in **(b)**; **(f)** the higher magnification of the metallographic picture in the red circle in **(c)**; **(g)** the higher magnification of the metallographic picture in the red circle in **(d)**. The grain boundary maps shown in Figure 6 can accurately characterize the recrystallization range and recrystallization grains. The recrystallization range of monoblocks #W511-7 and #W511-11 is 1000-1100 \(\upmu\)m along the H direction, but #W511-7 has a larger recrystallization range along the W direction, indicating that #W511-7 sustained a larger high-temperature distribution area. The recrystallization area is consistent with the contour distribution of the temperature analyzed in reference [30], in which the isothermal region extends for longer in the W direction, whereas there is little extension in the H direction. The top-surface grain size near the heat load is larger in the area close to the deformed state but is still recrystallized; in Figure 6a,b, there are some white grains, which contain some low-angle boundaries (green lines in the figure), and therefore, these grains are not identified as recrystallized grains. The difference in image size is meant to unify the scale bar. The damage and recrystallization statistics of three typical tungsten monoblocks are shown in Figure 7. Even though #W511-7 has the largest recrystallization area, its crack density (crack numbers per unit length along the T direction) is the lowest, whereas the crack density of #W511-11 and #W511-14 increased significantly.