Adhesion of SM1140+ coatings to silicon carbide substrate in Sigma monofilament

Abstract

The adhesion of carbon coatings to Sigma silicon carbide monofilament is primarily dependent on the electrical power used to heat the monofilament. The adherence of the coating can be detected by performing bend tests on the fibre. It is suggested that in order to bond the carbon to the surface, a chemical reaction involving the formation of SiCl₄ takes place on the surface of the silicon carbide. This etches the surface and provides a good key for the carbon. If there is too little power the chemical reaction is suppressed. Too much power results in over etching and fibre damage. An additional factor of importance is the coefficient of thermal expansion of the coating. As power increases the carbon coefficient of thermal expansion reduces. The increased compressive stresses in the coating can lead to debonding.

MST/3000