The interphase in continuous SiC fiber-reinforced ceramic matrix composites is critical to their mechanical reliability, and graphene is a promising interphase material. However, the effect of substrate surface condition on graphene growth on SiC fibers remains unclear. Here, graphene grown by chemical vapor deposition on pristine SiC fibers and pre-oxidized SiO₂/SiC fibers is systematically compared. Experiments show that pristine SiC promotes early multi-point nucleation and an outward-propagating SK-like mode, whereas the pre-oxidized surface favors conformal layer-by-layer growth, leading to a smoother FM-like morphology. First-principles calculations reveal that SiC more strongly catalyzes carbon-source cracking and generates active carbon species, while SiO₂ is more favorable for carbon diffusion and conformal growth. In addition, graphene edges, steps, and curved regions tend to act as secondary nucleation sites, inducing disordered multilayer growth at later stages. These results provide guidance for tailoring graphene interphases on SiC fibers by surface pretreatment.

In order to understand the process of direct graphene growth on the silicon carbide surface, this study employed density functional theory to analyze its growth mechanism and verifies it experimentally, and draws the following conclusions: (1) Acetylene and ethylene exhibit strong adsorption on both SiC(0001) and ( $000\overline{1}$) surfaces, with adsorption energies ranging from −5 to −2 eV. These energies enable effective adsorption and subsequent dissociation of acetylene and ethylene on the SiC surface, catalyzing the formation of active carbon species. Based on the cleavage energy barriers and the population of different carbon-active species of acetylene and ethylene, it is tentatively confirmed that CHCH is the most probable main active species in the two subsequent steps (nucleation and edge growth). (2) At low chemical potentials, CHCH exhibits a stronger nucleation tendency on the ( $000\overline{1}$) surface. In contrast, at higher chemical potentials, nucleation is more favorable on the (0001) surface. (3) The experimental results show that acetylene provides a more efficient carbon source and significantly accelerates the graphene growth; graphene has fewer defects in the conformal growth on the Si surface and more defects on the C surface.