Structural Control of Multiphase Silicon Carbide Ceramics with Composite Particles

采用复合颗粒制备SiC-BN纳米复合材料，并在复合颗粒中加入TiB_2颗粒和SiC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SiC-BN复合微粒（<0.1 μ m）。通过热压复合粉末制备纳米复合材料，其中细BN颗粒（<0.5 μ m）分散在SiC基体中。它们表现出优异的抗热震性，但断裂韧性较低.在SiC-BN复合粉体中加入TiB_2颗粒（2 μ m）或SiC晶须（直径1.2 μ m，长度40 μ m），热压成型。多相复合材料表现出改善的断裂韧性。抗热震性有所降低，但高于单片SiC。在流化床中，用BCl_3-NH_3-H_2气相沉积法将BN沉积在0.3 μ m的SiC颗粒上，制备了复合粉体。在复合粉末的烧结体中观察到抗热震性的改善。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多相复合结构，可以制备出具有优良抗热震性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.