Structural Control of Multiphase Silicon Carbide Ceramics with Composite Particles

利用复合颗粒制备了SiC-BN纳米复合材料，并在其中添加了TiB2颗粒和碳化硅晶须。对复相碳化硅陶瓷的结构和性能进行了研究。在Si(CH_3)_4-BCl_3-NH_3-H_2体系中，采用高温气相反应法制备了细小的碳化硅-氮化硼复合颗粒(~lt；0.1um)。将细小的BN颗粒(&lt；0.5um)分散在碳化硅基体中，采用热压法制备了纳米复合材料。它们具有良好的抗热震性，但断裂韧性较低。将TiB_2颗粒(2微米)或碳化硅晶须(直径1.2微米，长度40微米)加入到碳化硅-氮化硼复合粉末中，并对混合物进行热压。多相复合材料表现出较高的断裂韧性。其抗热震性略有下降，但高于单片SiC.3。在流态化条件下，BCl3-NH3-H2气相沉积BN在0.3um的碳化硅颗粒上制备了复合粉末。复合粉末的烧结体具有良好的抗热震性能。为了提高陶瓷材料的断裂韧性，采用该方法制备了SiC-TiB_2-BN复合粉末，通过控制复合粉末的复相结构，可以制备出具有良好的抗热震性能和断裂韧性的陶瓷材料。

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.