JPH0513104B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing silicon nitride ceramics that have excellent mechanical strength from room temperature to high temperature. [Prior Art] Silicon nitride ceramics have excellent mechanical strength, oxidation resistance, and wear resistance, and are therefore expected to be used as new structural members. However, silicon nitride ceramics have the disadvantage that their mechanical strength significantly decreases at high temperatures, so they cannot be applied to high-temperature parts and the like. Therefore, various attempts have been made to improve the high temperature strength of silicon nitride ceramics. for example,
A method that leaves no grain boundary glass phase by using Al ₂ O ₃ as a sintering aid and dissolving it in Si ₃ N ₄ in the final sintered body, or crystallizing the grain boundary glass phase by heat treatment. Several methods have been proposed. However, such conventional methods for improving high-temperature strength have the disadvantage that room-temperature strength decreases as the grain boundary glass phase decreases, and silicon nitride, which can stably maintain excellent strength from room temperature to high temperature, It has been difficult to provide high-quality ceramics. [Problems to be Solved by the Invention] In view of the conventional circumstances, an object of the present invention is to provide a method for manufacturing silicon nitride ceramics that can stably maintain excellent strength from room temperature to high temperature. . [Means for Solving the Problems] The method for producing silicon nitride ceramics of the present invention includes silicon nitride powder of 80% by weight or more and 0.1 to 10% by weight of silicon nitride powder.
% by weight of group a element oxide powder and the total amount
Mix alumina powder and aluminum nitride powder with a molar ratio of 0.1 to 10% by weight and a mutual molar ratio of 0.5 to 2.0, and place this mixed powder in a non-oxidizing atmosphere.
The sintered body is sintered at 1600-1850℃, densified by hot isostatic pressing at 1600-2000℃ in a non-oxidizing atmosphere, and then heated at 1200-1600℃ without pressure in a non-oxidizing atmosphere. It is characterized by heat treatment. [Function] In the method for producing silicon nitride ceramics of the present invention, in addition to the oxide of a group A element, alumina powder and aluminum nitride powder are used in a molar ratio of
By simultaneously adding it to the silicon nitride powder in the range of 0.5 to 2.0, it is possible to obtain silicon nitride ceramics that stably maintain excellent strength not only at room temperature but also at high temperatures. The reason for this is thought to be that the range of the above molar ratio is a region where an increase in the strength of grain boundaries due to an increase in aluminum nitride relative to alumina and a decrease in strength due to deterioration of sinterability are appropriately balanced. The reason why the amount of silicon nitride powder is 80% by weight or more is that if it is less than 80% by weight, the properties of silicon nitride ceramics cannot be maintained due to a decrease in oxidation resistance and heat resistance. _Y2O3 , _{CeO2, etc.} can be used as oxides of group a elements, but if the amount added is less than 0.1% by weight, it will not be effective as a sintering aid, and if it exceeds 10% by weight, the oxidation resistance will be reduced. There is a significant decrease in hardness and high-temperature strength. When the total amount of alumina powder and aluminum nitride powder is less than 0.1% by weight, there is no effect of improving high-temperature strength, and when the total amount exceeds 10% by weight, high-temperature strength is significantly reduced. Further, it is desirable to use the alumina powder and the aluminum nitride powder in equal molar numbers, but silicon nitride ceramics with good properties can be obtained if the molar ratio is within the range of 0.5 to 2.0. Furthermore, using a polytype containing silicon oxide as aluminum nitride also stabilizes the composition and yields favorable results. In the method of the present invention, a mixed powder obtained by mixing each of the above powders is vacuum-treated to prevent oxidation of silicon nitride.
Sintering is carried out in a non-oxidizing atmosphere such as nitrogen gas or argon gas at 1600 to 1850° C. for 30 minutes or more, preferably 120 minutes or more. The obtained sintered body is densified by hot isostatic pressing at 1600 to 2000°C in a non-oxidizing atmosphere. Hot isostatic press is
Preferably, the heating is carried out for 30 minutes or more using a nitrogen-containing gas at a pressure of 100 atmospheres or more. It is difficult to densify this composition without hot isostatic pressing, and hot isostatic pressing is an essential requirement of the present invention. Finally, the dense sintered body was heated to 1200°C without pressure in a non-oxidizing atmosphere.
By performing heat treatment at ~1600°C, preferably for 60 minutes or more, the grain boundary phase whose crystallization is delayed is crystallized. The silicon nitride ceramic thus produced has a porosity of 2% or less and a flexural strength of 100 Kg/mm ² or more at room temperature and 85 Kg/mm ^{2 or} more at high temperature (1200°C). Shows excellent properties. [Example] Example 1 Y ₂ O _{3 ,} CeO _{2 or} Gd ₂ O ₃ powder (purity
99.9%, average particle size 0.5μm), α-type Al ₂ O ₃ powder (average particle size 0.5μm) and AlN powder (purity 99%, average particle size
1.0 μm) was added in the formulation shown in Table 1, and mixed in a ball mill for 3 days. The mixed powder was sintered at 1800° C. for 2 hours in nitrogen gas at 4 atmospheres. The obtained sintered body was further subjected to hot isostatic pressing at 1800°C for 1 hour in nitrogen gas at 1000 atm, and then heated at 1400°C in nitrogen gas without pressure.
Heat treated at ℃ for 10 hours. Density (%) of the obtained Si ₃ N ₄ ceramics,
Bending strength at room temperature and high temperature (1200℃) (Kg/mm ² )
was measured and the results are shown in Table 1.

[Table] (Note) *marks are comparative examples.
Example 2 Powders having the same composition as No. 1 in Table 1 of Example 1 were sintered, hot isostatically pressed (HIP) and heat treated under the conditions shown in Table 2. The properties of each sintered body after heat treatment (no pressure) were measured in the same manner as in Example 1 and are shown in Table 2.

【table】

[Table] (Note) *marks are comparative examples.
[Effects of the Invention] According to the present invention, it is possible to provide silicon nitride ceramics that can stably maintain excellent strength from room temperature to high temperature.

Claims (1)

[Claims] 1 80% by weight or more of silicon nitride powder and 0.1 to 10
% by weight of group a element oxide powder and the total amount
Mix alumina powder and aluminum nitride powder with a molar ratio of 0.1 to 10% by weight and a mutual molar ratio of 0.5 to 2.0, and place this mixed powder in a non-oxidizing atmosphere.
The sintered body is sintered at 1600-1850℃, densified by hot isostatic pressing at 1600-2000℃ in a non-oxidizing atmosphere, and then heated at 1200-1600℃ without pressure in a non-oxidizing atmosphere. 1. A method for producing silicon nitride ceramics, characterized by heat-treating the silicon nitride ceramics.