## 3 Experiment and Result Analysis
### Analysis of Density and Molten Pool Morphology  
The variation in the density of the Inconel 718 samples formed by SLM with laser power is shown in Table 4. When the laser power increased from 260 W to 360 W, the density remained above 99%. It showed a trend of first increasing and then gradually decreasing. When the laser power was at a minimum of 260 W, the relative density was 99.31%. It can be seen that there are many smaller pores in Figure 4. When the laser power increased from 285 W to 360 W, the relative density gradually decreased. When the laser power was set at 260 W, the low laser energy density resulted in a low working temperature within the molten pool. Therefore, powder melting was insufficient. This led to an incomplete filling of the molten pool that decreased the overlap rate. As a result, many pores were present on the surface of the sample. As the laser power gradually increased to 285 W, the laser energy density slightly increased, and the Marangoni effect within the molten pool promoted the rheological properties of the molten pool, thereby increasing the density. When the laser power increased from 285 W to 360 W, the laser energy density further increased. The increase in working temperature in the molten pool promotes the evaporation of gases and the vaporization of low-melting-point alloys. Therefore, the relative density gradually decreases. The morphology of the molten pool perpendicular to the forming direction of the Inconel 718 sample formed by SLM is shown in Figure 5. The width and depth of different molten pools in Figure 4a,b are uneven, which was mainly due to the rapid heating and cooling in the SLM forming process. In this process, the molten material is cooled and solidified layer by layer. Therefore, during the cooling process of each laser-irradiated  
Figure 3: XRD patterns of the XY plane of Inconel 718 samples formed by SLM under different laser powers: (**a**) scan within a large angle range 20 = 30–100\({}^{\circ}\); (**b**) small-angle scanning, 20 = 40–46\({}^{\circ}\). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Laser Power/W** & **20 Location/deg** & **Intensity/cps** & **FWHM/deg** & **D\({}_{\text{C}}\)/nm** \\ \hline
260 & 43.49 & 5948 & 0.16 & 52.99 \\
285 & 43.46 & 6745 & 0.16 & 53.45 \\
310 & 43.48 & 4652 & 0.17 & 50.29 \\
335 & 43.44 & 2670 & 0.17 & 50.30 \\
360 & 43.43 & 3901 & 0.16 & 53.44 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The 20 values of the main peak, diffraction peak intensity, and half-peak width in the XRD spectra and the average thickness of the grain perpendicular to the crystal plane. molten material, each layer is affected by the adjacent cladding layer and the previous solidification layer. When the laser power was 310 W, the depth of the molten pool was approximately 85.71 \(\pm\) 10 \(\upmu\)m. When the laser power was 335 W, the depth of the molten pool was approximately 103.45 \(\pm\) 10 \(\upmu\)m. When the laser power was 360 W, the depth of the molten pool was approximately 123.08 \(\pm\) 10 \(\upmu\)m (Figure 5). As the laser power increased, the depth of the molten pool gradually increased. The shape of the molten pool is determined by the thermal field and fluid flow conditions inside the pool, and the crystal growth mode is significantly impacted by the temperature gradient [26]. When the laser power was 310 W, due to the lower absorption of laser energy and the reduction in heat accumulation, the Marangoni flow in the molten pool was reduced. In contrast, when the laser power was 360 W, the laser energy density increased. The higher intensity laser energy irradiated the material surface, leading to a stronger flow and the formation of a deeper molten pool [27]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Samples** & **Laser Power/W** & **Relative Density/\%** \\ \hline
1 & 260 & 99.31 \(\pm\) 0.08 \\
2 & 285 & 99.82 \(\pm\) 0.08 \\
3 & 310 & 99.75 \(\pm\) 0.08 \\
4 & 335 & 99.54 \(\pm\) 0.08 \\
5 & 360 & 99.79 \(\pm\) 0.08 \\ \hline \hline \end{tabular}
\end{table}