Synthesis and characterization of non-oxide ceramic coatings on graphite substrates by solid–vapor reaction process

Silicon carbide (SiC) and silicon carbide/silicon nitride (SiC/Si3N4) were successfully synthesized on graphite substrates by the use of solid–vapor reaction (SVR) process. Layers of SiC and SiC/Si3N4 were synthesized on graphite substrate through the reaction between SiO and substrate the (SiO(vapor) + 2C(from graphite)) and N2 and substrate the (3SiO(vapor) + 2N2 (vapor) + 3C(from graphite)), respectively. With the increase of dwell time and synthesis temperature the thickness of SiC layers increases up to 1500 °C temperature. Also, with the increase of synthesis temperature hardness value of SiC coatings is increased, which is 10–15 times higher than the substrate. The critical load of SiC coatings for wear resistance is about 22 N, which was observed by scratch tests. The synthesized SiC coatings appear to consist of a β-SiC phase mixed with a minor amount of an α-SiC phase, and its thickness is mainly affected by porosity of the substrate. The thickness of SiC/Si3N4 coatings is much thinner than that of SiC coatings, but gives higher value of surface hardness.