This study systematically investigated for the first time the effects of varying the temperature, pressure, C/Si molar ratio, and H 2 /Si molar ratio on β-SiC coatings produced via chemical vapor deposition (CVD) using the SiCl 4 –CH 4 –H 2 –N 2 system. Thermodynamic theoretical calculations were performed using the HSC Chemistry software. The temperature and C/Si molar ratio considerably affected the morphology, phase, and composition of β-SiC coatings. High-quality β-SiC coatings along the (111) crystal plane exhibiting a uniform surface, high density, low roughness, and good crystallinity were successfully synthesized at 1523.15 K and 200 Pa with a C/Si molar ratio of 1.0 and H 2 /Si molar ratio of 6.5. Additionally, when N 2 was used as the dilution gas instead of Ar, the resulting β-SiC coatings demonstrated reduced roughness, fewer free carbon, increased hardness (37.05 GPa vs. 39.19 GPa), enhanced modulus of elasticity (237.26 GPa vs. 264.24 GPa), and superior coating adhesion (16.48 MPa vs. 18.29 MPa).
The mechanism of β-SiC preparation via chemical vapor deposition (CVD) of the SiCl4–CH4–H2–N2 system remains unclear. Consequently, the change of molar Gibbs free energy of the CVD β-SiC chemical reaction in the SiCl4–CH4–H2–N2 system has been studied by the Helsinki Software Corporation (HSC) Chemistry code for the first time. The role of nitrogen in the reaction was confirmed. Seven potential reaction pathways of CVD β-SiC were presented, and the thermodynamic equilibrium components of each reaction were calculated systematically. The most viable reaction pathway and corresponding optimal temperature range for CVD β-SiC were determined. In addition, a kinetic study of CVD β-SiC was conducted. The microscopic morphology and crystal structure of β-SiC coatings prepared on the graphite surface at different temperatures were charactered by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman, etc. Ultimately, through SEM, XRD, and Raman observation, uniform and dense β-SiC coatings with fine grains and high crystallinity were successfully obtained. Furthermore, large β-SiC-coated graphite trays with diameters of 230 and 465 mm were prepared by CVD using the SiCl4–CH4–H2–N2 system, and the average thickness of β-SiC was about 100.6 μm. This study provides a theoretical basis and technical recommendations for the fabrication of SiC-coated graphite trays used in metal–organic chemical vapor deposition (MOCVD) equipment.
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