## 3 Results and Discussion
Figure 6: (**a**) SEM images of LPBF-CVI Si/SiC ceramic. (**b**) Inverse pole figure map (inset: corresponding grain size diameter in IPF maps). (**c**) The distribution state of SiC particles within the Si matrix (inset: Diffraction patterns of Si and SiC from (**c**), regions of interest are highlighted by boxes). (**d**) The elemental surface distribution results within (**c**) region. The stress-strain curve obtained from the compressive strength test is depicted in Figure 8(a1). The results indicate that the compressive strength of the LPBF SiC specimen is 5.89 \(\pm\) 1.21 MPa, while its compressive strength is greatly increased after the CVI densification post-treatment, reaching 38.59 \(\pm\) 12.99 MPa. Figure 8(a2) illustrates that the interior is not completely densified after CVI treatment and still retains a columnar structure. There are also porosity defects inside the columnar structure. After compression, a fracture occurs at the columnar structure. The fracture morphology of the LPBF-CVI SiC specimen is illustrated in Figure 8(a3), showcasing a typical brittle fracture. The LPBF grain particles exhibited planar and smooth cleavage planes, indicative of trans-granular fracture features; tiny pores around grain particles were observed, hindering the compressive strength of the sample. In Figure 8(b1), it is illustrated that the LPBF-fabricated Si/SiC specimens exhibit an ultimate compressive strength of 19 \(\pm\) 8 MPa. When compared to the LPBF Si/SiC samples, the LPBF-CVI Si/SiC specimens display a significantly higher ultimate compressive strength, achieving a value of 90 \(\pm\) 8 MPa. As can be seen in Figure 8(b2), after Si addition, the specimen is similarly incompletely densified internally, and the fracture penetrates through the original spheroidal microstructure and is deep inside the microstructure, significantly enhancing its mechanical properties. With the addition of Si powders, resolidified Si could fill in the pores and bind the SiC grain particles together, as shown in Figure 8(b3), with SiC formed by CVI wrapping around the original spheroidal microstructure, resulting in a highly dense structure; the multiple river-like patterns indicate trans-granular fracture. Combined with the relative density improvement, the addition of Si significantly increased the load-bearing area, thereby improving the compressive strength. Figure 9a,b schematically explain the fracture mechanisms of the two distinct ceramic specimens. Figure 7: LPBF-CVI SiC specimens of **(a1)** Vickers Microhardness map; **(a2)** Variation in nano-hardness from LPBF-forming SiC region to CVI-forming SiC region; **(a3,a4)** nano-hardness of the LPBF-forming SiC region and CVI-forming SiC region; LPBF-CVI Si/SiC specimens of **(b1)** Vickers Microhardness map; **(b2)** Variation in nano-hardness from LPBF-forming SiC region to CVI-forming SiC region; **(b3,b4)** nano-hardness of the LPBF-forming Si/SiC region and CVI-forming SiC region. In summary, the relative densities and compressive strengths of the SiC ceramics and Si/SiC composite ceramics fabricated by LPBF and LPBF-CVI are summarized in Table 3.  
Figure 8: LPBF-CVI SiC specimens of **(a1)** Compressive stress-strain curves; **(a2)** Fracture surface in low magnification; **(a3)** Fracture surface in high magnification; LPBF-CVI Si/SiC specimens of **(b1)** Compressive stress-strain curves; **(b2)** Fracture surface in low magnification; **(b3)** Fracture surface in high magnification. Figure 9: Schematic illustration of the fracture of **(a)** LPBF-CVI SiC specimens; **(b)** LPBF-CVI Si/SiC specimens.