Conventional NICALON fiber has a refractoriness of only about 1200°C because of its high oxygen content. Recently a new fiber HI-NICALON with improved refractoriness has been developed. The slurry process developed by the authors was adopted for the fabrication of HI-NICALON fiber-reinforced Si3N4 composites. Carbon-coated HI-NICALON fiber-reinforced composites showed high strength and toughness. At room temperature, samples hot-pressed at 1550°C showed a flexural strength of 890±10MPa and KIC of 29±8MPa√m, respectively. Samples hot-pressed at 1600°C showed high values at 1200°C; 640±70MPa of flexural strength and 18.3±0.8MPa√m of KIC. On the other hand, non-coated HI-NICALON fiber-reinforced composites showed a higher flexural strength at 1400°C than the coated ones, however, they showed a brittle fracture and KIC values were only 3 to 4MPa√m.
