Extraction sintering -: A new route to non-oxide composite ceramics

Boron carbonitride (BCxN) powders were blended with metallic silicon added at equimolar ratios with respect to carbon contents and then hot-pressed at 1850degreesC and 20 MPa in argon. Hexagonal boron nitride (BN) - silicon carbide (SiC) composite ceramics were obtained by this method. The BN phase consisted of well-crystallized equiaxial grains, among which SiC grains were homogeneously dispersed. Formation of SiC showed a positive effect on orientation of BN grains, as above 19 vol.% SiC it was practically randomized. Beside density, especially strength was proportional to the SiC content and reached 250 MPa in the material containing 44 vol.% SiC. The sintering process was found to be based on extraction of carbon from BCxN co-layered crystals with molten silicon. Subsequently, SiC was formed and released BN could crystallize. The sintering process can be therefore referred to as the extraction sintering.