## 3 Quality Control of Silicon Carbide Printed Part Formation
### The Impact and Control of Key Printing Parameters on Green Part Formation Quality
#### 3.1.2 Uniform and Dense Powder Bed
Additionally, some researchers argue that using nanoparticles as flow agents to enhance the flowability of SiC powders offers greater advantages compared to the cost and technical challenges involved in the preparation of spherical SiC particles. [PERSON] et al. [84] examined improvement of the mechanical and tribological properties of SiC produced by AM using ultrasonic nanocrystal surface modification (UNSM) at 23 \({}^{\circ}\)C (room temperature, RT) and 900 \({}^{\circ}\)C (high temperature, HT). The results indicate that, after UMSM treatment, the surface roughness of the printed SiC samples showed a decreasing trend at both temperatures. This type of surface coating can enhance the flowability, uniformity, and handling properties of the powder, making it easier to process and use [90]. On the other hand, research has been proposed on mixing multimodal powders during the pretreatment process to improve powder bed density. For monomodal powders, wider particle size distribution leads to higher packing density of the powder bed. [PERSON] et al. [91] experimentally compared the powder bed density of two types of 316 L stainless steel powders with similar average particle sizes but different widths of particle size distribution. The comparison results showed that powders with a wider particle size distribution achieved higher powder bed densities. In a wider distribution, smaller powder particles at the lower end of the particle size range can fill the voids of larger particles at the upper end, resulting in improved powder bed density and uniformity. Thus, to address the issue of poor spreadability of fine SiC powders during the binder jetting printing process, preparing multimodal SiC powders by mixing powders of different sizes is an important method to improve the flowability of the powder bed, which enhances the strength and surface quality of the green bodies. The preparation of bimodal powders is illustrated in Figure 10.  
However, to achieve the aforementioned improvements in performance, it is essential to consider factors related to the powders when preparing bimodal powders [92; 93; 94]. It is worth noting that the use of multimodal powders may also negatively affect powder bed density. Research by [PERSON] et al. [92] indicates that mixing 10 \(\upmu\)m and 2 \(\upmu\)m alumina powders reduces powder bed density. This may be attributed to segregation phenomena among the particles, leading to separation or agglomeration of the powder particles during the mixing process. Therefore, while using multimodal powders or powders with a broad distribution can enhance powder bed density, it is also important to consider the impact of particle segregation on powder bed quality. Introducing external stimuli during the powder spreading process (such as mechanical vibration [95], sound waves [96], and magnetic stirring [97]) can improve the flowability and packing density of SiC powders to varying  
Figure 10: Preparation of bimodal powder by mixing particles of two distinct size ranges [44]. degrees. However, additional processing steps and units, along with high operational costs, are inevitable. In contrast, preparation and processing of SiC during the pretreatment process represent a more economical and efficient method for improving print quality, attracting significant attention from numerous researchers regarding its research value and prospects. * Fine powder spreading process  
In addition to the aforementioned modification and pretreatment processes for SiC fine powder, the powder spreading process can also contribute to the fabrication of uniform and dense powder beds. In binder jetting 3D printing, the spreaders evenly distribute SiC powder from the powder reservoir to the printing chamber, enabling subsequent printing operations. The rational design and selection of the spreaders are crucial for obtaining uniform and compact powder layers. Powder spreaders can be classified into two main types: wipers and rollers. Regarding wipers, different wiper profiles demonstrate distinct powder spreading performance.