## 3 Results and Discussion  
The X-ray diffraction patterns presented in Figure 3a illustrate that the diffraction peaks of silicon were detected after the direct LPBF process, indicating that a small amount of SiC decomposed to liquid Si and solid C. After the CVI process, the diffraction peaks of silicon disappeared, and the positions of the peaks were consistent with the diffraction peaks of the SiC powder, indicating that the high-temperature process of CVI converted free silicon and carbon to silicon carbide again, and ultimately the high-purity and highly crystalline silicon carbide ceramics were obtained. After the addition of 10 wt% silicon powder, the diffraction peaks of the silicon phase were detected from the direct LPBF \begin{table}
\begin{tabular}{l l l l l} \hline
**Laser Power** & **Scanning Speed** & **Layer Thickness** & **Scanning Spacing** & **Preheating Temperature** \\ \hline
300 & 500 & 60 & 70 & 350 \\ \hline \end{tabular}
\end{table} 
Table 1: The LPBF processing parameters. \begin{table}
\begin{tabular}{l l l l l} \hline
**Pressure (kPa)** & **Temperature (\({}^{\circ}\)C)** & **CH\({}_{3}\)Cl\({}_{3}\)Si (mL/min)** & **H\({}_{2}\) (mL/min)** & **Ar (mL/min)** & **Duration (Hours)** \\ \hline
5–15 & 900–1200 & 50–200 & 500–1500 & 400–800 & 2–8 \\ \hline \end{tabular}
\end{table} 
Table 2: The CVI process parameters. specimen, which is consistent with the diffraction peaks of the Si powder. After the CVI processing, it was found that the surface of the LPBF-CVI specimen is \(\beta\)-sic, which is a typical crystalline structure of CVI-SiC [21]. The diffraction peaks of silicon in the interior were reduced and the diffraction intensity was weakened. The silicon diffraction peaks at (311), (422), and (440) disappeared, while the intensities of the (111), (220), (311), and (400) peaks were significantly reduced. This result may be due to an augmentation in the silicon carbide content and a decrease in the relative content of silicon after CVI, so the diffraction intensity is reduced. It also indicates that not all the silicon was reacted to yield silicon carbide during the CVI process. There is a small amount of silicon residue in the ceramics. Compared with previously published results, the SiC ceramics fabricated in this work exhibit a very low residual silicon content, and the CVI processing further reduces the relative silicon fraction. In contrast, densification methods such as PIP and LSI tend to increase the amount of residual silicon [23,24]. Figure 4a-d shows the three-dimensional morphology of LPBF SiC, LPBF-CVI SiC, LPBF Si/SiC, and LPBF-CVI Si/SiC samples. It is essential to highlight that the grey region is the SiC ceramic, while the dark region is porous. Columnar structures along the BD direction are present inside the LPBF SiC sample, and between the columnar structures are large-volume connecting pores. The distance between the columnar structures is consistent with the scanning spacing. After CVI treatment, the surface of the specimen forms a shell layer with a thickness of a few hundred micrometers, and the relative density of the specimen was increased from 65.7% to 76.4%. Figure 4c demonstrates that adding silicon improves the specimens' relative densities from 65.7% to 70.5%. Moreover, the addition of silicon resulted in the refinement of the columnar structure morphology of the specimen, with a concomitant decrease in the prevalence of small-sized synapse-like morphologies. After the CVI processing, the relative density of the Si/SiC ceramic specimens was increased from 70.5% to 78.3%, as plotted in Figure 4d. Figure 3: (a) XRD patterns of SiC powder, LPBF SiC parts, LPBF-CVI SiC parts; (b) XRD patterns of Si powder, LPBF Si/SiC parts, and LPBF-CVI Si/SiC parts. As demonstrated in Figure 5a,b, the SEM and EBSD results after CVI densification reveal that the microstructure consists of original large equiaxed grains surrounded by the typical small, columnar grains formed by CVI densification.