Interfacial adhesion of CVD-SiC coatings on graphite substrates: Role of temperature in microstructure and mechanical properties

Silicon carbide (SiC) coatings are critical for protecting graphite substrates in high-performance applications, such as semiconductor manufacturing and aerospace, where extreme thermal and chemical environments demand robust adhesion and durability. This study investigates the temperature-driven microstructural evolution of SiC coatings deposited on graphite by chemical vapor deposition (CVD) at 1260 °C, 1280 °C, and 1320 °C, elucidating the mechanism of their impact on interfacial adhesion. Advanced analytical techniques, including field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), white-light confocal microscopy, nanoindentation, and scratch testing, were employed to characterize the coatings. The results show that when the deposition temperature increases from 1260 °C to 1320 °C, the SiC coating grain aggregate transforms from an irregular structure to a truncated polyhedron structure, and the (111) surface texture coefficient increases significantly. Additionally, the SiC grain aggregates are relatively loose at low temperatures, whereas they form a continuous and dense fused structure at high temperatures. XPS analysis shows that with increasing temperature, the Si-C bond density increases and the stacking faults decrease, thereby enhancing the bonding strength between the coating and the substrate. It is worth noting that the critical bonding force increases from 20.8 N at 1260 °C to 28.5 N at 1320 °C, which is consistent with the increase in nanohardness. These findings highlight that within the studied 1260–1320 °C range, increasing the deposition temperature significantly improves the microstructure and adhesion of SiC coatings.