Formation of composite SiC-C coatings on graphite via annealing Si-melt in CO

A method for the synthesis of silicon carbide-graphite composite coatings is proposed and described. The method is based on the two simultaneous chemical reactions involving graphite. One of these reactions consists of the chemical interaction of a silicon molten mass with carbon monoxide on the surface of the graphite at a temperature slightly exceeding the melting point of silicon. It transforms Si into gaseous silicon monoxide (SiO) and SiC. Simultaneously, a second reaction involves the SiO in the transformation of the graphite itself into SiC. A coating with a thickness exceeding 1 mm is formed during the synthesis. The resulting coating has high mechanical strength and hardness. Samples of the composite coating were investigated via scanning electron microscopy, energy-dispersive spectroscopy, Raman spectroscopy, XRD, and nanoindentation. The coating has a complicated structure. It consists of a dense overlayer of SiC and has a branched structure consisting of dendrite-like SiC crystals extending into the depth of the graphite. The dendrites are interspersed with large (up to 20 mu m) single-crystalline SiC grains consisting of predominantly cubic polytypes. The coating leads to significant hardening of the material: the composite has a hardness of 28 GPa, which is similar to 254 times higher than the hardness of the original graphite surface.