PRESSURELESS SINTERING OF SILICON-NITRIDE COMPOSITES

A fabrication method for whisker-reinforced silicon-nitride ceramics i nvolving pressureless sintering is reported together with the mechanic al properties of the resulting composite materials. Silicon-nitride co mposites containing up to 20 wt% of silicon carbide whiskers were slip cast to orientate the whiskers two-dimensionally, parallel to the pla ster mould surfaces, and then pressureless sintered at 1750 or 1825-de grees-C. The sintered body containing 20 wt% of whiskers of average di ameter 1.3 mum displayed a relative density of 98%, a mean flexural st rength of 950 MPa and a fracture toughness of 7.0 MPa square-root m. F urthermore, the thermal shock resistance was found to be as high as 14 00-degrees-C. To date, components successfully produced from this comp osite material include aluminum die-casting ladles and crucibles.