Deposition behavior and mechanism of thermal sprayed SiC

It is widely known that silicon carbide (SiC) is challenging to thermal spray. However, the nature of deposition and the underlying mechanisms are still not clearly understood. In the current work, the process of atmospheric plasma-sprayed SiC was investigated in detail. SiC exhibits sublimation severely under the plasma spraying (PS). More than 65 mol.% SiC particles lost by sublimation during PS estimated by calculation. Due to the nonuniformity of temperature in plasma flame, a small amount of SiC particles was retained. Moreover, a small amount of Si and SiO₂ was experimentally observed after deposition process from the single-splat characterization. According to the first-principles calculations, the detachment energy of C atom from the lattice (0.591 eV) is lower than that of Si atom (1.257 eV). The adsorption energies of an O atom on the Si- and C-terminated surfaces are −9.549 and −7.631 eV, respectively. Therefore, C is more likely to form gaseous products after decomposition, and Si is more likely to be retained to form Si and SiO₂. Mullite was found on the grain boundaries of molten Si, which was attributed to the rapid diffusion of the Al₂O₃ substrate along the grain boundaries of Si, promoting the spreading of molten splats. It is difficult to stack particles through self-diffusion among SiC particles to form coatings. The discovery on thermal deposition mechanism of SiC in PS is helpful to promote the practical application of SiC coatings on preparation optimization and interfacial bonding improvement.