Nissan Motor Company Limited

National Institute for Research in Inorganic Materials

Motohide Ando

Naoto Hirosaki

Mamoru Mitomo

A high strength and toughness .beta.-silicon nitride sintered body suitable for the material of a variety of structural parts. The sintered body contains .beta.-silicon nitride (Si.sub.3 N.sub.4) in an amount not less than 95% by weight of total silicon nitride; oxygen in a total amount not more than 3% by weight of the sintered body; and columnar grains each of which has a diameter not less than 5 .mu.m and an aspect ratio not less than 5, the columnar grains being in an amount not less than 0.5% by volume of total of raw materials in the sintered body; the sintered body having a bulk density not less than 96% of a theoretical density. Such a sintered body is produced by a method comprising the following steps in the sequence set forth: preparing powder of a starting material including .beta.-silicon nitride in an amount not less than 80% by weight of the starting material; adding oxide of at least one element selected from the group IIIa of the periodic table of elements in an amount ranging from 0.2% to 6% by weight (as a sintering assistant) to the starting material powder to form a mixture powder; compacting the mixture powder to form a compact; firing the compact under a nitrogen gas pressure ranging from 1 to 500 atm. at a temperature ranging from 1700.degree. to 2100 .degree. C. to form the sintered body; and continuing the firing step until a bulk density of the sintered body reaches a value not less than 96% of a theoretical density of the sintered body.

.beta.-silicon nitride sintered body

A high strength and toughness .beta.-silicon nitride sintered body suitable for the material of a variety of structural parts. The sintered body contains .beta.-silicon nitride (Si.sub.3 N.sub.4) in an amount not less than 95% by weight of total silicon nitride; oxygen in a total amount not more than 3% by weight of the sintered body; and columnar grains each of which has a diameter not less than 5 .mu.m and an aspect ratio not less than 5, the columnar grains being in an amount not less than 0.5% by volume of total of raw materials in the sintered body; the sintered body having a bulk density not less than 96% of a theoretical density. Such a sintered body is produced by a method comprising the following steps in the sequence set forth: preparing powder of a starting material including .beta.-silicon nitride in an amount not less than 80% by weight of the starting material; adding oxide of at least one element selected from the group IIIa of the periodic table of elements in an amount ranging from 0.2% to 6% by weight (as a sintering assistant) to the starting material powder to form a mixture powder; compacting the mixture powder to form a compact; firing the compact under a nitrogen gas pressure ranging from 1 to 500 atm. at a temperature ranging from 1700.degree. to 2100.degree. C. to form the sintered body; and continuing the firing step until a bulk density of the sintered body reaches a value not less than 96% of a theoretical density of the sintered body.

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Yokosuka, Japan

Motohide Ando