Silicon carbide coatings

Technique to coat substrates with SiC that can be operated as low as 1300°C, which opens up the coating technique to many nonrefractory materials and some commercially important metals such as steel and titanium


Grains of silicon carbide (SiC) can be bonded together by sintering to form very hard ceramics widely used in applications requiring high endurance, such as car brakes, car clutches, and ceramic plates in bulletproof vests. SiC is a hard, strong, chemically resistant material that is thermally and electrically conductive and as such is used in semiconductor electronics that operate at high temperatures or high voltages.

Due to its covalent bonding, SiC is very difficult to densify without the use of additives that compromise its material properties. However, in many cases a monolithic material is not needed. SiC can be deposited as a coating by techniques such as chemical vapor deposition (CVD), plasma-enhanced CVD, and direct chemical reaction between carbon and molten silicon. SiC coatings are used to protect a weaker or less resistant material by isolating it from the environment. This protection can be mechanical protection against abrasion or chemical protection in corrosive or reactive environments. Examples of mechanical protection are wear-resistant coatings on bearings and wear plates. Examples of chemical protection are coated filters for molten metals and coatings for the chemical industry. An example of combined mechanical and chemical protection is SiC coatings used in gas turbine engines.

Using CVD with SiC requires specialized equipment that can sustain temperatures of 2000°C at a pressure of 0.5 Torr+/−0.001 for up to 10 days. The growth process is slow and expensive. The gases used, methylsilane and trimethylsilane, are extremely flammable and considered hazardous.

Navy researchers have overcome these problems with a method of forming β-SiC material or coating by mixing SiOwith carbon and heating the mixture in vacuum. At that point, the carbon is oxidized to CO gas and reduces the SiOto SiO gas. The reaction occurs at a temperature range of 1300 to 1600°C. This process results in a SiC material or a SiC coating on a substrate.

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