Structural Control of Multiphase Silicon Carbide Ceramics with Composite Particles

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Composite particles were used for producing SiC-BN nanocomposites, to which TiB_2 particles and SiC whiskers were further added. The following results were obtained with respect to the structure and properties of the multiphase silicon carbide ceramics.1. Fine SiC-BN composite particles (<0.1mum) were prepared by a high-temperature vapor phase reaction in Si(CH_3)_4-BCl_3-NH_3-H_2 system. Nanocomposites were produced by hot-pressing of the composite powder, in which fine BN particles (<0.5mum) were dispersed in SiC matrix. They exhibited an excellent thermal-shock resistance but the fracture toughness was low.2. TiB_2 particles (2mum) or SiC whiskers (diameter 1.2mum, length 40mum) were added to SiC-BN composite powder and the mixtures were hot-pressed. The multiphase composites exhibited an improved fracture toughness. The thermal shock resistance was somewhat lowered but higher than that of monolithic SiC.3. The composite powder was also prepared by the deposition of BN from BCl_3-NH_3-H_2 gas phase on SiC particles (0.3mum) in a fluidized bed. The improvement of thermal shock resistance was observed in the sintered body of the composite powder. SiC-TiB_2-BN composite powder was prepared by this method to improve the fracture toughness.As described above, the ceramic materials with excellent thermal-shock resistance and fracture toughness can be produced by the control of the structure of multiphase composite with composite powders.