The morphology of silicon carbide in C/C–SiC composites

In the present investigations C/C–SiC has been studied by means of SEM, X-ray diffraction (XRD) and TEM to reveal the morphology of the silicon carbide areas. It was found that there exist two different areas of SiC, a fine grained β-SiC layer with a high amount of stacking faults at the C–SiC interface, and a zone of coarser β-SiC at the SiC–Si interface. From these observations, reaction mechanisms governing the siliconization of porous C/C preforms are proposed. After an initial reaction of carbon with silicon vapour, liquid silicon has to diffuse through the already formed SiC. A violent reaction far away from equilibrium conditions and a high number of nucleation sites leads to the observed formation of a fine grained SiC with a high density of stacking faults. Thermodynamically this is an instable configuration so that the coarser grained zone emerges by solution and precipitation.