Oriented Silicon Carbide Whisker Reinforced Mullite Composites: LaminateProcessing, Structure and Properties. Topical Report, September 1, 1986-November 30, 1989

摘要

Dense SiC whisker-reinforced mullite composites with up to 50 vol% whiskers canbe obtained by tape casting and hot pressing. The tape casting process results in high degrees of SiC whisker orientation as determined visually and by x-ray diffraction. The ability to achieve dense composites with as much as 50 vol% whiskers is attributed to the higher percolation threshold of aligned whiskers. The factors affecting the degree of whisker orientation during tape casting are described using a fluid dynamics model derived from Jeffery's equations and shows that the orientation of anisometric particles is enhanced primarily by the casting rate and particle aspect ratio. The elastic modulus, coefficient of thermal expansion, flexural strength and fracture toughness of the oriented composites of tape-cast, laminated and hot-pressed mullite reinforced with 10 to 50 vol% SiC whiskers have been investigated with respect to the effects of whisker volume fraction and whisker orientation. The Young's modulus of the composites was reasonably well predicted with the Halpin-Tsai equations. The coefficient of thermal expansion was in good agreement with the Schapery predictions. The flexural strength and fracture toughness of the composites were improved. The properties were strongly dependent on whisker orientation.