## 3 Quality Control of Silicon Carbide Printed Part Formation
### Densification Post-Processing Techniques  
After the completion of binder jetting 3D printing, the strength of the SiC green body primarily relies on the binder's bonding effect, rather than direct interparticle connections among the powder particles. Additionally, since the binder only partially fills the voids between the particles, the green body typically exhibits high porosity. Consequently, additional post-processing steps are required to densify the SiC green body, enhancing its density and mechanical properties to meet practical application requirements. To address the powder spreading challenges inherent in fine particulate systems, the predominant approach in BJ 3D printing manufacturing currently favors the utilization of relatively coarser SiC particles. This methodology, however, presents a fundamental conflict with the thermodynamic requirements for achieving effective post-printing densification at conventional sintering temperatures. While significant advancements have been made in optimizing particle packing behavior through controlled powder characteristics and precisely tuned printing parameters [134], the resultant green bodies persistently demonstrate spatial heterogeneity in their microstructural architecture. Furthermore, the intrinsic material properties of SiC, particularly its exceptionally high melting point, necessitate the implementation of extreme thermal processing conditions, typically exceeding 1800 \({}^{\circ}\)C, to accomplish adequate densification of SiC green bodies [135; 136; 137]. Such high-temperature sintering not only places extremely demanding requirements on equipment, but may also lead to deformation and cracking of the highly porous SiC green bodies. In contrast to conventional sintering, processes including liquid silicon infiltration (LSI), chemical vapor infiltration (CVI), and polymer impregnation and pyrolysis (PIP) can uniformly infiltrate porous preforms to achieve homogeneous densification. This characteristic aligns well with the capability of BJ 3D printing to fabricate green bodies with high porosity (approximately 50%) [138], and these techniques have been increasingly applied in the post-processing densification of complex-shaped SiC components manufactured by BJ technology. The specific details of these three post-processing techniques are presented in Table 5. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Process Name** & **Process Principle** & **Advantages** & **Disadvantages** & **Theoretical** & **Ref.** \\ \hline \multirow{8}{*}{LSI} & The porous SiC-C & & & & \\  & preform is immersed in & & & & \\  & molten silicon, and the & & & & \\  & liquid silicon infiltrates & & & & \\  & into the pores through & & & & \\  & capillary action, reacting & & & & \\  & with carbon to form SiC & & & & \\  & that fills the pores, & & & & \\  & thereby achieving & & & & \\  & densification. & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: General overview of the LSI, CVI, and PIP processes. Although the aforementioned post-processing techniques have achieved corresponding results in the densification of SiC green parts manufactured by BJ 3D printing technology, the limitations of existing post-processing methods and the challenges associated with complex geometries and large-scale production continue to drive extensive research efforts among scholars. Current research trends in post-processing densification of SiC components focus on developing optimization approaches to address existing process limitations or synergistically combining multiple post-processing techniques to enhance efficiency and overcome current densification constraints. For the LSI process specifically, the primary challenge lies in minimizing silicon residue within SiC components, as residual silicon significantly degrades high-temperature performance, mechanical properties, and oxidation resistance. Consequently, porous binder jet 3D-printed SiC preforms must contain sufficient carbon content to achieve complete reaction with silicon.