## 3 Experiment and Result Analysis
### Texture and Grain Boundary Analysis  
The texture maps of Inconel 718 samples formed by SLM under different laser powers parallel to the forming direction are shown in Figure 8a-c. It can be seen that the three groups of samples dis not have an obvious preferred orientation, and the crystal morphology parallel to the forming direction was mainly composed of a small amount of equiaxed crystals and elongated columnar crystals. In a rapid solidification process, equiaxed grains with fine grains are conducive to the establishment of a strengthening mechanism according to the Hall-Petch mechanism. At the same time, heat is directed from the current processing layer to the deposited layer and substrate. Therefore, some crystals mainly grow along the forming direction and eventually pass through the melt pool to form columnar crystals. In addition, the columnar crystal structure has anisotropy and high texture strength in the growth direction, which is also a key factor in improving the mechanical properties. As shown in Figure 9, the pole maps of the YZ plane of the samples under the three different laser powers were obtained using EBSD. The size of the texture index is known to represent the anisotropy intensity of a sample, which is calculated using the orientation distribution function. As shown in Figure 9a-c, when the laser power was 310 W, 335 W, and 360 W, the texture intensity was not high, and the texture index values did not differ significantly. From the pole diagram in Figure 9b, it can be seen that when the laser power was 335 W, the texture of 001 was strong, with the highest texture index of 4.251. When the laser power was 310 W and 360 W, the texture index was 3.834 and 3.809, respectively. The misorientation angle between the Inconel 718 grains formed by SLM under different laser powers is shown in Figure 10. An interface misalignment angle between grains between 2\({}^{\circ}\) and 10\({}^{\circ}\) is considered a low-angle grain boundary (LAGB) and is represented by blue lines in the figure. Conversely, a misalignment angle greater than 10\({}^{\circ}\) is considered a high-angle grain boundary (HAGB) and is represented by red lines in the figure. The specific grain boundary fraction and average grain size (d) are shown in Table 5. It can be seen that the average grain size did not change much when the laser power was 310 W, 335 W, 360 W, and the minimum average grain size was 47.49 \(\upmu\)m when the laser power was 310 W (Figure 10a). At a laser power of 360 W, the highest low-angle grain boundary fraction was 20.1% (Figure 10c). At the same time, it can be observed that the fraction of high-angle grain boundaries was greater than that of low-angle grain boundaries. When forming a new layer, the previously solidified layer was heated or partially remelted. This process is similar to the annealing treatment and can lead to recrystallization, resulting in the formation of high-angle grain boundaries (HAGBs). However, due to the short  
Figure 8: Orientation imaging of cross sections parallel to the forming direction of Inconel 718 samples formed by SLM under different laser powers: (**a**) P = 310 W, (**b**) P = 335 W, (**c**) P = 360 W.  
reheating or remelting time of the previous layer, the recrystallization was not completed, resulting in residual low-angle grain boundaries (LAGBs) [31]. As the laser power increased from 310 W to 335 W, the energy density input also increased, and the average grain size increased from 47.49 \(\upmu\)m to 50.57 \(\upmu\)m (Figure 10b). The increase in the HAGB content was mainly due to the increase in energy density. This led to a relatively longer reheating or remelting time, thereby prolonging the recrystallization time. However, as the laser power further increased to 360 W, the increase in defects such as pores resulted in a decrease in the high-angle grain boundary fraction.