High-temperature evolution of diamond-SiC composites

Diamond-SiC composites are attractive for improving the catastrophic fracture behaviour of SiC. However, fundamental knowledge is missing about the structure of this system and the mechanism of diamond graphitization. We used spark plasma sintering to study the diamond-Si-SiC system between 1600 and 2000 degrees C in the function of nanocrystalline (ND) and microcrystalline (MD) diamond addition as well as the quantity of Sibonding phase. Increasing sintering temperature induces intense graphitization and formation of nano-onions, few-layered graphene and well-ordered graphite in the prepared composites at elevated temperature. High resolution transmission electron microscopy study demonstrates the occurrence of the previously erroneously identified 5H-SiC polytype in the samples prepared at 2000 degrees C. Regardless of Si and diamond contents, SiC formation is not confirmed even at high temperature.