| 摘要 |
PURPOSE:To obtain a high-strength silicon nitride sintered compact, suitable as automotive engines, etc., having a density as high as >=99% of the theoretical density and >=1000MPa strength at 1000 deg.C. CONSTITUTION:A silicon nitride sintered compact is characterized as follows. A rare earth metallic oxide and MgAl2O4 in the total amount of 3-8wt.% based on the silicon nitride are contained and the sintered compact is composed of a structure observed as granular crystals and a structure, dispersedly present in the above-mentioned structure and observed as prismatic crystals. The average diameter of the granular crystals and average minor axis of the prismatic crystals are 0.2-0.6mum and the density is >=99% of the theoretical density. The silicon nitride sintered compact is produced by a method characterized as follows. Uniform mixed powder prepared by adding the rare earth metallic oxide powder and MgAl2O4 powder as a sintering assistant in the total amount of 3-8wt.% based on the silicon nitride powder is formed and the resultant formed body is then heated to a temperature within the range of 1530-1650 deg.C and presintered. The pressure is then raised to >=1500atm at the temperature within the above-mentioned temperature range to carry out normal sintering. |
