## 3 Results and Discussion
The average grain size of the original grains is 2.45 \(\upmu\)m. The small, columnar grains in the region of the CVI-SiC matrix were undefined in the EBSD maps, and it can be deduced that the time step limits of EBSD made the identification of any nanocrystallites within the CVI-SiC matrix difficult. Thus, lamellas were sliced using the FIB technique in each of the LPBF and CVI formed regions for TEM analysis. The results are shown in Figure 5c,d. Regions of interest are highlighted by boxes in Figure 5a. The SiC matrix formed by CVI has nanoscale needle-like grains, and the diffraction pattern results in polycrystalline rings without amorphous features. The diffraction patterns obtained from both the original grain and the Chemical Vapor Infiltration (CVI) matrix confirmed the presence of highly crystalline 3C-SiC, with no observable amorphous regions or pockets. The formation of 3C-SiC indicates that the SiC powder undergoes a partial transformation after laser sintering. The binding of SiC particles is considered a result of the formation of a metastable Si/C mixture as a result of the incongruent melting of SiC. The relative density of the LPBF SiC sample indicates that the samples were still in the initial stages of sintering, where material transport is primarily interparticle neck growth. Thus,  
Figure 4: (**a,b**) Three-dimensional morphology of the LPBF SiC specimen and the LPBF-CVI SiC specimen; (**c,d**) Three-dimensional morphology of the LPBF Si/SiC specimen and the LPBF-CVI Si/SiC specimen. a melting and recrystallization mechanism would explain the formation of 3C-SiC within particular regions, differing from the feedstock 6H-SiC powder [25]. After the silicon addition, it was observed from Figure 6a,b that the original LPBF microstructure preserved the spherical shape, similar to six powders, since the resolidified Si can cover the SiC particles and bind the SiC particles together. The EBSD result shows that the average grain size of the original grains slightly increased to 3.23 \(\upmu\)m. The microstructure of the CVI-SiC matrix area is similar to LPBF-CVI-SiC specimens. Figure 6c depicts the HRTEM image of the microstructure, which comprises large SiC particles embedded within a continuous Si matrix. EDS maps of C and Si are shown in Figure 6d. Selected area diffraction patterns obtained from both the SiC particles and the Si matrix confirmed the presence of Si and 6H-SiC, as depicted in Figure 6c. Residual silicon may adversely affect the chemical stability and high-temperature performance of silicon carbide ceramic parts. Figure 5: (**a**) SEM images of LPBF-CVI SiC ceramic. (**b**) Inverse pole figure map (inset: corresponding grain size diameter in IPF maps). (**c,d**) TEM images and diffraction patterns of the large SiC grain and the CVI-SiC matrix. As illustrated in Figure 7(a1), the Vickers hardness values of SiC in the LPBF-CVI SiC specimens exhibit variation across different regions. In the LPBF-formed SiC region, the hardness value is recorded as 1297 HV\({}_{0.5}\), whereas in the CVI-formed SiC region, it increases to 2651 HV\({}_{0.5}\). Corresponding results are observed in LPBF-CVI Si/SiC specimens, as shown in Figure 7(b1), with the hardness value in the LPBF-formed Si/SiC region recorded as 1798 HV\({}_{0.5}\), and 3315 HV\({}_{0.5}\) in the CVI-formed SiC region. To further investigate the variation in hardness from the LPBF-formed SiC region to the CVI-formed SiC matrix region, a series of nanoindentation tests were performed across the transition zone between the two regions. The nano-hardness of the LPBF-formed SiC region in the LPBF-CVI SiC ceramic specimen is lower (24.2 \(\pm\) 1.0 GPa) due to the larger grain size and the presence of pores. The average nano-hardness of the CVI-formed nanoneedle-like SiC region is 39.2 \(\pm\) 8.4 GPa Figure 7(a4). The hardness of the LPBF-CVI Si/SiC ceramic specimen with a spherical dual-phase structure is slightly higher (25.9 \(\pm\) 4.4 GPa), and the average nano-hardness of the CVI-formed SiC region is 55.3 \(\pm\) 9.3 GPa.