Preparation process of SIC coating

At present, the preparation methods of SiC coating mainly include gel-sol method, embedding method, brush coating method, plasma spraying method, chemical vapor reaction method (CVR) and chemical vapor deposition method (CVD).

Embedding method
This method is a kind of high-temperature solid-phase sintering, which mainly uses Si powder and C powder as embedding powder, places the graphite matrix in the embedding powder, and sinters at high temperature in inert gas, and finally obtains SiC coating on the surface of graphite matrix. This method is simple in process, and the coating and the matrix are well bonded, but the coating uniformity along the thickness direction is poor, and it is easy to produce more holes, resulting in poor oxidation resistance.

Brush coating method
The brush coating method mainly brushes the liquid raw material on the surface of the graphite matrix, and then solidifies the raw material at a certain temperature to prepare the coating. This method is simple in process and low in cost, but the coating prepared by the brush coating method has a weak bond with the matrix, poor coating uniformity, thin coating and low oxidation resistance, and requires other methods to assist.

Plasma spraying method
Plasma spraying method mainly uses a plasma gun to spray molten or semi-molten raw materials on the surface of the graphite substrate, and then solidifies and bonds to form a coating. This method is simple to operate and can prepare a relatively dense silicon carbide coating, but the silicon carbide coating prepared by this method is often too weak to have strong oxidation resistance, so it is generally used to prepare SiC composite coatings to improve the quality of the coating.

Gel-sol method
The gel-sol method mainly prepares a uniform and transparent sol solution to cover the surface of the substrate, dries it into a gel, and then sinters it to obtain a coating. This method is simple to operate and has low cost, but the prepared coating has disadvantages such as low thermal shock resistance and easy cracking, and cannot be widely used.

Chemical vapor reaction method (CVR)
CVR mainly generates SiO vapor by using Si and SiO2 powder at high temperature, and a series of chemical reactions occur on the surface of the C material substrate to generate SiC coating. The SiC coating prepared by this method is tightly bonded to the substrate, but the reaction temperature is high and the cost is also high.