**1. Introduction**

SiC ceramic has attracted extensive attention due to its excellent performance, such as appropriate high-temperature strength, relatively high oxidation, corrosion and thermal-shock resistance [1–4], etc. SiC ceramic can be used in coating materials, especially in fiber-reinforced ceramic matrix composites (FRCMCs) to improve the bond strength between the fiber and matrix. After introducing SiC interphases, weak fiber/matrix interfaces can be obtained in FRCMCs and several toughening mechanisms like crack deflection, fiber debonding, bridging and subsequent pullout can occur, all of which contribute to damage tolerance [5–7]. Our previous works proved that SiC interphases were suitable for the strength improvement of high-temperature structural and functional materials due to its oxidation tolerance and relatively temperature-stable dielectric characteristics [8,9].

SiC coatings have been successfully deposited by CVD on silicon carbide fibers, carbon fibers, oxide fibers and more [10–12]. Most research has focused on the coatings' e ffects on microstructure and mechanical properties of those fibers, the strength improvement of the fiber-reinforced ceramic matrix composites, or the degradation mechanism of the coatings [13,14]. However, research on the deposition mechanism and thickness control of CVD SiC coatings on oxide fibers is rare.

In the present study, SiC coatings were synthesized on NextelTM440 fibers by CVD using the gas system of CH3SiCl3–H2–Ar. The coating thickness was adjusted by varying the deposition time, and the deposition mechanism was investigated by the aid of microstructure and composition analysis.
