Effect of Si Addition on Microstructure and Mechanical Properties of SiC Ceramic Fabricated by Direct LPBF with CVI Technology  
[PERSON]  
1 State Key Laboratory of Precision Weld & Joining of Materials and Structures, Harbin Institute of Technology, Harbin 150001, China; [EMAIL_ADDRESS] (Y.W. ); [EMAIL_ADDRESS] (L.L.) [PERSON]  
2 Henan Key Laboratory of High Performance Carbon Fiber Reinforced Composites, Institute of Carbon Matrix Composites, Henan Academy of Sciences, Zhengzhou 450046, China; [EMAIL_ADDRESS] 222  
require expensive tooling and additional machining. In small-scale production or prototyping, these costs are not cost-effective. Additive manufacturing (AM) techniques are well-suited to the production of complex-shaped parts with small batch sizes or prototypes [6]. SiC can be fabricated utilizing various additive manufacturing technologies, including binder jetting (BJ), direct ink writing (DIW), stereolithography (SL), and selective laser sintering (SLS) [7; 8]. However, it should be noted that these methods utilize an organic binder to bond the silicon carbide powder. Before printing, a powder mixing process is necessary, and subsequent debinding and sintering steps are required to remove the binder. This increases the complexity and cost of the process. AM techniques, particularly laser additive manufacturing, offer high material utilization and enable near-net-shape fabrication. It allows the customization of the microstructure, properties, and texturization of the surface, which affects the surface-related properties, such as lubrication [9]. Laser powder bed fusion (LPBF) has been demonstrated to maintain component stability during the forming process, thereby ensuring stable microstructure and properties. Furthermore, significant advantages have been identified in terms of grain refinement and material property enhancement [10; 11]. The direct fabrication of silicon carbide ceramics using laser powder bed fusion technology eliminates the need for the pre-mixing of powders and obviates subsequent debinding and sintering processes. This approach streamlines the fabrication process and prevents the sample shrinkage and cracking typically associated with debinding and sintering. However, the direct LPBF process of Carbide ceramics (including SiC-based ceramics) without any binder remains a formidable challenge [12]. The SiC ceramic components fabricated by direct LPBF exhibit low densities and mechanical properties, necessitating posttreatment processes for improving both the density and strength [13]. To address the aforementioned challenges, improvements can be made in terms of the powder feedstock, the preheating platform, the addition of silicon powder, and the densification post-processing. Spherical powders with better flowability and higher packing density are considered to be preferable in the LPBF process, which ultimately results in a near-fully dense final component [14]. The preheating of the powder bed has been shown to reduce the high-temperature gradient, thereby alleviating the residual stress [15]. The formation process can be enhanced by utilizing silicon as a binder, while the residual silicon can be converted to regenerate silicon carbide by post-processing. At present, the widely used post-treatment densification processes include liquid silicon infiltration (LSI), polymer impregnation and pyrolysis (PIP), chemical vapor infiltration (CVI), etc. [16; 17; 18; 19]. CVI is especially suitable for depositing SiC matrix in the preform with interconnected pores compared with PIP and RMI [20]. Furthermore, the ceramic matrix fabricated by CVI is characterized by a dense microstructure, high purity, and excellent properties [21]. Therefore, the subsequent introduction of the SiC matrix into the SiC green parts can be carried out by CVI. In this paper, the innovative use of spherical silicon carbide powder with a high-temperature (350 \({}^{\circ}\)C) preheating platform enables the direct laser powder bed fusion printing of silicon carbide without adding any binder.