## 2 Materials and Methods  
Si/SiC mixed powders were obtained by mixing SiC powders (15-53 \(\upmu\)m, purity 99.9%, Shandong Yinuo Rongshen Composite Materials Co., Ltd., Liawu, China) with Si particles (15-53 \(\upmu\)m, Qinghe County Chuangjia Welding Materials Co., Ltd., Xingtai, China) in an inert argon atmosphere. This mixing process was facilitated by a three-dimensional shaker mixer (TURBULA T2 GE, Muttenz, Switzerland) at a speed of 72 RPM, and its mass ratio of Si and SiC was 1/9. The SiC powder exhibited a near-spherical morphology (Figure 1a). From Figure 1c,d, it can be seen that there are pores inside the powder, which may adversely affect the relative density of the formed specimens. The size distribution of the powder is shown in Figure 1b. The Si powder exhibited a near-spherical morphology, as shown in Figure 2a, and the corresponding EDS map is shown in Figure 2b.  
SiC and Si/SiC cuboid samples with a dimension of 5 mm \(\times\) 5 mm and a thickness of about 12.5 mm were fabricated using the LPBF equipment HBD 150 (Shanghai Hanbang, United 3D Tech Co., Ltd., Shanghai, China) based on optimized LPBF parameters. The LPBF processing parameters were obtained through initial optimization design experiments. The process parameters were set as shown in Table 1.  
Figure 1: SiC powders of (**a**) SEM micrographs; (**b**) Powder particle size distribution; (**c**) Pores distribution; (**d**) Micro-CT result.  
Figure 2: Si powders of (**a**) SEM micrographs for Si powders; (**b**) corresponding EDS maps.  
The SiC ceramic specimens and the Si/SiC ceramic specimens fabricated via direct LPBF will hereafter be referred to as 'LPBF SiC' and 'LPBF Si/SiC', respectively. The LPBF specimens underwent chemical vapor infiltration treatment to obtain the final SiC ceramic samples. The process parameters were set as shown in Table 2. The LPBF SiC ceramic specimens and the LPBF Si/SiC ceramic specimens subjected to the CVI densification will hereafter be denoted as 'LPBF-CVI SiC' and 'LPBF-CVI Si/SiC', respectively.  
The phase identification of the samples was carried out through X-ray diffraction (XRD, Empyrean, Malvern, UK) using Cu K\(\alpha\) radiation. The measurement range of XRD was set from 20\({}^{\circ}\) to 110\({}^{\circ}\), the step size was set to 0.0131303\({}^{\circ}\), and the total number of steps was 6854. X-ray computed tomography (Micro-CT, ZEISS Xradia 515 Versa, Oberkochen and Jena, Germany) was conducted to identify the pore distribution in the specimens. The resulting 3D images with a voxel size of 1.5 \(\upmu\)m were analyzed using Dragonfly V2024.1 software. A scanning electron microscope (SEM, Gemini SEM 360, Oberkochen, Germany) was used for microstructure and fracture surface characterization. The SEM device was equipped with an electron backscatter diffraction device (EBSD, OXFORD Symmetry S3, Abingdon, UK). The microstructure was observed using a transmission electron microscope (TEM, Talos F200S, Hillsboro, OR, USA) equipped with an energy-dispersive X-ray (EDS, OXFORD X-MaxN 807 IE250, Abingdon, UK) detector. The TEM specimens were precisely extracted from designated areas using a focused ion beam (FEI Strata 400s Dual Beam FIB, Hillsboro, OR, USA). Room-temperature compression tests were performed following the GB/T 8489-2006 standard [22] using a universal testing machine (LD26.504, Lishi Instruments Co., Ltd., Shanghai, China). For each set of parameters, five specimens were tested for compressive strength. A Vickers hardness tester (QHV-1000 SPTA, Laizhou weiyi Experimental Machine Manufacturing Co., Ltd., Yantai, China) was used to test the microhardness of the LPBF specimens. The test force was 500 gf, the holding time was 15 s, and the measured Vickers hardness values were uniformly represented by the symbol HV\({}_{0.5}\). Nanoindentation testing was performed using a Nanoindenter (CV500, NANOVEA Inc., Irvine, CA, USA) with a maximum load of 50 mN, a 100 mN/min loading rate, and a 5 s dwell time at the peak load; the distance between each indentation was set to 5 \(\upmu\)m.