SINTERED SILICON NITRIDE HAVING CONTROLLED FINE STRUCTURE OF INNER AND OUTER LAYER AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To provide a sintered silicon nitride having a high strength as well as fracture toughness and provide its production process. SOLUTION: The objective sintered silicon nitride composed of an inner layer having a fine particle structure and an outer layer having a mixed structure containing coarse particles and fine particles and having a controlled fine structure of the inner and the outer layers is produced by adding 2-16 wt.% of Yb2 O3 sintering assistant powder to Si3 N4 powder, slurrying the mixed powder with a ball mill, drying and classifying the slurry, forming the obtained powder under hydrostatic pressure and sintering the formed product at a temp. of 1800-1950 deg.C.