Formation and sintering mechanisms of reaction bonded silicon carbide-boron carbide composites

Reaction sintering of boron carbide represents an attractive densification process. In this work, sintering mechanisms of silicon carbide and boron carbide composites were studied. Mixed boron carbide/graphite mixtures were sintered in a vacuumed graphite furnace between 1380 and 1450 degrees C. The samples were in contact with bulk silicon metal which melts at 1410 degrees C. Reaction sequence of the composition was investigated by X-ray diffraction, SEM and TEM. It was found that a reaction between molten silicon and B4C Occurred and the reaction produced silicon carbide and silicon-containing boron carbide. Dense composites can be achieved by pressureless sintering at 1450 degrees C and the final microstructure consists of silicon carbide, boron carbide, silicon-containing boron carbide and residual silicon at grain boundaries.