Reaction Bonded Silicon Carbide (RBSiC) is a ceramic material based on silicon carbide. This material is used as high temperature structural members and has good abrasion resistance. A wide range of industrial applications has been reported for this material. These applications include IGBT baseplates and power electronics. The material maintains a high stiffness, thermal conductivity, and wear resistance. It has also been found that this kind silicon carbide ceramic has a better temperature-related thermal properties than the usual nitride bonded silicon carbides.
To produce a RBSiC part, a green body of carbon is infiltrated with silicon. In addition to silicon, there are other ingredients that can be used. For example, boron carbide is known to improve the ceramic properties of the resultant RBSiC part. Boron carbide has similar properties to silicon carbide.After a green body is obtained, it is sintered. In order to avoid shrinkage of the green body, it is preferred to sinter it with low pressure. During firing, the shape of the green body is retained. However, the strength of the fired body is not satisfactory, and its shape can be easily destroyed by a small force. Therefore, the porosity of the green body for Reaction Bonded Silicon Carbide is preferably 45% to 68%.
Using a high volume ratio of silicon carbide to silicon in the Reaction Bonded Silicon Carbide can result in an excellent composite member. Moreover, this method allows the proportion of silicon carbide to be controlled. If the weight ratio of silicon carbide to silicon in the raw material is too low, the RBSiC member has a low density. As a result, the cracking of the RBSiC part can be suppressed. However, too much silicon carbide can lead to the development of pores in the material.
During a reaction sintering, the amount of silicon in the raw material increases. Consequently, the quantity of this kind silicon carbide ceramic can increase as well.In a reaction sintering, the proportion of carbon to silicon in the fired body is determined. Usually, the proportion of carbon to silicon is calculated based on the volume ratio of silicon to carbon. Furthermore, the proportion of silicon carbide to carbon in the fired body is calculated based on the amount of silicon carbide in the reaction sintering. Depending on the volume ratio, the proportion of silicon carbide to carbon can be increased or decreased for Reaction Bonded Silicon Carbide.
During a reaction sintering, a large volume of carbon can be infiltrated with silicon. Infiltration of silicon occurs above the melting point of silicon. Since the silicon expands, the volume of the carbon infiltrated with silicon can be canceled. Alternatively, the volume of silicon infiltrated with silicon can be slowed down by using a binder. Nevertheless, this method has not been applied to make this kind silicon carbide ceramic with a large size. Moreover, the structure of the RBSiC member is not complicated. Rather, it has a low density, which is an indication that the filling rate of the reaction sintering is too low.
