## 3 Quality Control of Silicon Carbide Printed Part Formation
### Densification Post-Processing Techniques
(From left to right: microstructures after zero PRBI treatments followed by CLSI, one PRBI treatment followed by CLSI, two PRBI treatments followed by CLSI, and three PRBI treatments followed by CLSI). was introduced by mixing additional carbon sources into the initial powder before printing. Their experimental results demonstrated that this additional carbonization method could significantly reduce the residual silicon content to as low as 15% or even lower, offering a new approach to addressing the issue of residual silicon in the LSI process. It is worth noting that, in the study by [PERSON] et al. [147], mechanical properties were not reported. Building upon this research, [PERSON] et al. [17] further conducted a comprehensive study on the effects of PRBI cycle count and printing layer thickness on formation accuracy, silicon content, and mechanical properties. Their findings indicated that, with a layer thickness of 0.15 mm--where green body compression performance and dimensional accuracy were optimal--samples subjected to LSI treatment with two PRBI cycles exhibited the highest flexural strength (257 \(\pm\) 14.26 MPa) and the lowest residual silicon content, estimated at 10.2 vol% based on SEM images and 12.23 vol% based on XRD analysis. Secondly, for the PIP process, the prevalent issues of cracks and excessive open porosity in the processed SiC materials remain significant challenges. Studies on the effects of PIP cycles on the density and pore structure development of binder jetting-printed SiC have shown that the residual porosity in PIP samples originates from several factors. These include localized cracking during pyrolysis due to volume shrinkage of polymer precursors in highly infiltrated regions, as well as the formation of large internal cracks caused by gas accumulation and increased pressure during pyrolysis [156]. [PERSON] et al. [24] mitigated regions with low particle packing density and large open pores by controlling the printing layer thickness (set at 50 \(\upmu\)m), thereby reducing the occurrence of cracking due to polymer precursor volume shrinkage during pyrolysis. After seven PIP cycles, they obtained SiC ceramics with a strength of 228.7 \(\pm\) 14.2 MPa. Their study highlighted that additional low-temperature curing and impregnation before pyrolysis could significantly improve yield and density after the first PIP cycle. With only three PIP cycles, they achieved a room-temperature flexural strength of 66.8 \(\pm\) 2.5 MPa and a Young's modulus of 69.5 \(\pm\) 2.8 GPa, enhancing the efficiency of the PIP process. The above optimizations focus on the process parameters of PIP. On the other hand, researchers have been developing superior polymer-derived SiC precursors to mitigate gas accumulation during pyrolysis, thereby reducing internal cracking in PIP samples. Compared to the commonly used SiC-based precursor--polycarbosilane (PCS)--innovations in novel SiC-based PIP process precursors are summarized in Table 6. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Precursor Polymer** & **Description of the Precursor** & **The Prepared** & **Number of** & **Densification Effect** & **Ref.** \\ \cline{1-1} \cline{4-6}  & & & & & The material density & \\ Hyperbranched polymer (mPMS) & Modified by adding 12 wt\% & & & & is 2.5 \(\pm\) 0.05 g/cm\({}^{3}\), & \\  & crosslinking agent to polymethylsiloxane (PMS) & & & & reaching 90 \(\pm\) 2\% of the & [157] \\  & & & & the & theoretical density. & \\ \hline Liquid & Prepared by using & & & & \\ polycarbosilane with & 2,4,6,8-tetravinyl-2,4,6,8- & SiC fiber-reinforced & & & \\ active Si–H and & tetramethylcyclotetrasiloxane (V4) as the curing agent and & SiC matrix & & 10 & The material density & \\  & 3 CHaCH2 groups (LPVCS) & liquid polycrystalline as the & SiC matrix & & & porosity of 6.7\%. \\  & & & & & \\ Polycarbosilane (PCS) modified with & polycarbosilane (PCS) & & & & & \\ divinylbenzene & precursor with 20\% of & SiC matrix & & & \\  & & & & & porosity of 14\%. \\ \hline \end{tabular}
\end{table}