JPS6022675B2 - Method for manufacturing silicon nitride sintered body - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing silicon nitride sintered bodies.

Furthermore, the present invention relates to a method of manufacturing a silicon nitride striped body having high density and high oxidation resistance. Silicon nitride sintered body has high temperature strength,
Due to its high thermal shock resistance due to low expansion, in recent years it has been increasingly applied to industrial parts used at high temperatures, such as gas turbines, diesel engine parts, radiant tubes, gears, and dies. .

Silicon nitride itself is a covalent crystal, and is a material that is difficult to scale by itself, so improving the strength of the Akatsuki compact is the first goal, and various additives are used to promote cohesion. Efforts have been made to improve high-temperature strength. As a result, additive components such as M, AI203, and Y203 have been provided as additives that are effective in promoting burning streaks and improving high-temperature strength.

Although it is recognized that these additives can be added alone or in combination to achieve the desired effect to a considerable extent, they are not currently required as silicon nitride competitive substances. - One property, ie, oxidation resistance, is not necessarily sufficiently effective.

Therefore, the present inventors have developed a silicon nitride compact that does not impair high-temperature strength and has sufficiently high oxidation resistance without using the hot pressing method.
The present invention was developed as a result of repeated research with the aim of obtaining it by conventional molding and firing methods.
The gist of the present invention is a method for manufacturing a silicon nitride sintered body, which comprises molding a mixed powder of up to 10% by weight and the balance being silicon nitride, and then firing it in a non-oxidizing atmosphere.

It is well known that there are two ways to obtain a silicon nitride sintered body: the hot pressing method and the two-step method of forming and firing (usually referred to as the Akatsuki Aya method here), just as in the case of other ceramics. .

In general, it is easier to obtain high density and high strength using the hot press method, but in order to obtain products with complex shapes,
Special hot pressing methods, such as hot isostatic pressing methods, must be employed. However, this method is still insufficient in terms of equipment, operability, and mass production, and is still only carried out on a laboratory scale. When trying to apply silicon nitride geometries for the purposes mentioned above, they often have complex shapes, and there is no way to provide them with satisfactory high-temperature strength and oxidation resistance without relying on hot pressing. Not proposed yet.

The present invention provides a method to solve all of these problems. Although there are many reports on the method of adding aluminum oxide to silicon nitride, the addition of aluminum oxide alone is insufficient to promote sintering, and therefore high-temperature strength and oxidation resistance are insufficient.

However, it has been found that when aluminum oxide and zirconium oxide are used together, sufficient accelerating properties, high temperature strength, and oxidation resistance can be obtained. That is, 3 to 15% by weight of aluminum oxide and 0.5 to 1% by weight of zirconium oxide, preferably 5 to 15% by weight of aluminum oxide and 3 to 8% by weight of zirconium oxide, are added to silicon nitride, mixed, and shaped. It has been found that when fired in a non-oxidizing atmosphere, a product with excellent properties as described above can be obtained.

If aluminum oxide is less than 3% by weight, sufficient density cannot be achieved and high strength cannot be obtained;
If the weight percentage is exceeded, the density will be high and the strength will be low.

If the amount of zirconium oxide is less than 0.5% by weight, sufficient densification will not be achieved, and if it is more than 1% by weight,
The oxidation resistance and strength of the composite will be insufficient.

Example A mixed raw material prepared by mixing silicon nitride fine powder, aluminum oxide fine powder, zirconium oxide fine powder, and binder in the proportions shown in Table 1 was pressurized to 200 x 9/base in a mold and then pressed to 2000 k9 with a hydraulic press. It was molded into a cube of 5 x 5 x 2 cubes using a pressure of /cm.

Next, this was fired at 1750o0 for 5 hours in a nitrogen atmosphere to obtain a silicon nitride compact. For these samples,
The results of measuring the density, bending strength, and oxidation resistance after firing are also listed in Table 1. Table 1 *1 The ratio between the density after firing and the theoretical density is shown in 100%.

Claims (1)

[Claims] 1. Production of a silicon nitride sintered body, characterized in that a mixed powder consisting of 3 to 15% by weight of aluminum oxide, 0.5 to 10% by weight of zirconium oxide, and the balance silicon nitride is molded and then fired in a non-oxidizing atmosphere. Method.