Role of H₂ and Ar as the diluent gas in continuous hot-wire CVD synthesis of SiC fiber

W-core SiC fiber was synthesized with CH₃SiCl₃ as the precursor by continuous hot-wire CVD approach. Using H₂ and Ar as the diluent gas, the temperature profile and the production of atomic hydrogen (H) in high-speed deposition process were studied by computational flow dynamics (CFD) simulation, and the growth kinetics and microstructure of the deposit were systematically investigated. H₂ significantly increases the H production, which reduces the formation of amorphous phase and structural defects (e.g. stacking faults and twins) during SiC growth. Ar could establish a steep thermal gradient in reactor, which enhances the deposit's surface quality. The mean tensile strength of SiC fiber reaches its peak value (3.15 GPa) with H₂ at 1200 sccm, and a high Weibull modulus (14.7) is achieved with Ar at 1600 sccm. These findings indicate H₂ is crucial to promote the mechanical performance of SiC fiber, while Ar is beneficial to improving its uniformity.