JPS6048475B2 - Silicon nitride hot press sintered body and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-strength ceramic mainly composed of silicon nitride and a method for producing the same.

As the conditions of use at high temperatures for gas turbine parts and high-temperature roll materials for steelmaking become more severe, materials are being changed from metal-based materials to ceramic-based materials, with high strength and high heat resistance. Silicon nitride is attracting attention as a material due to its impact resistance and high wear resistance.

However, silicon nitride has drawbacks such as being a material that is difficult to sinter when used alone and that it is difficult to obtain high strength, and various methods have been proposed to solve these problems.
The main ones are: (1) Adding an oxide of an alkaline earth element such as magnesium oxide.

(2) Add aluminum oxide.

(3) Adding an oxide of a rare earth element such as yttrium oxide (4) Adding a non-oxide such as aluminum nitride.

There are other methods. However, these methods have the following drawbacks and are still problematic from a practical standpoint. (1) The method of adding magnesium oxide is an effective method in terms of promoting the sintering of silicon nitride, but magnesium oxide reacts with the magnesium oxide formed on the surface of silicon nitride grains, and has a low melting point. Since a glass phase is produced, the high temperature strength or creep resistance of silicon nitride as a whole is impaired, and there is a problem in its application to members that are subjected to loads at high temperatures.

・(2) The method of adding aluminum oxide has the unique effect of accelerating sintering as aluminum oxide forms a solid solution in silicon nitride grains, but the high temperature strength and high temperature creep resistance are still not always sufficient. isn't it.

(3) The method of adding yttrium oxide is the method described in (1) above.
It is true that the drawback of (2) is improved, and the grain boundaries of silicon nitride grains are, for example, highly viscous glass or Si.

N,・Y. O. Since it is made of a crystalline composition such as, high-temperature strength and high-temperature creep resistance are rarely impaired, and it is effective in this respect. However, even with this method of adding yttrium oxide, high-temperature strength etc. are still insufficient depending on the application, and furthermore, it does not satisfy the demand for further lowering the firing temperature. (4
) The method of adding aluminum oxide together with alumina, etc., has the effect of improving hardness, oxidation resistance, etc., but only provides insufficient strength.

The present invention provides a method for solving these drawbacks, and the gist thereof is to provide a silicon nitride hot breath sintered body characterized by containing one or two selected from titanium nitride and tantalum nitride. Titanium nitride in silicon nitride powder,
This is a method for producing a hot-breathed silicon nitride sintered body, which comprises adding one or more kinds of substances selected from substances capable of causing the presence of tantalum nitride and hot-blessing.

Generally, various additives are used to impart sintering properties, but many of these additives tend to form a glass phase or soften at high temperatures, and this is due to nitridation. This is thought to be caused by a glass phase or a low melting point crystalline phase produced as a result of the silicon nitride film formed on the surface of the silicon grains reacting with these additives.

It is true that yttrium oxide, cerium oxide, magnesium oxide, aluminum oxide, etc. are additive components that should have a considerable effect, but as long as they are used alone, they cannot be used for the above reasons. As mentioned above, the expected effects were only unsatisfactory. Therefore, the inventors of the present invention have deeply investigated these points, and as a result, they have discovered that high-temperature strength can be truly improved by adding titanium nitride or tantalum nitride to silicon nitride grains and hot-pressing them. It was an invention.

Why do these nitrides specified in the present invention have such excellent effects?
In particular, it has not yet been fully elucidated whether the effect of improving high-temperature strength is exhibited, but the present inventors speculate as follows.

That is, these nitrides are dissolved in silicon nitride, albeit in a small amount, or form a solid solution with Sl at grain boundaries. N. It is thought that sinterability is improved by having a eutectic composition of the nitride. It is also believed that the coexistence of these nitrides with Si3N and SiO2, which is thought to normally cover the grain surfaces, also contributes to sintering. This means that the amount of oxygen in the sintered body is 0.
This is also inferred from the fact that it is difficult to obtain a relatively high-density sintered body when the content is less than 3%. These nitrides thus play a role as a binder, and at the same time, these nitrides with high melting points exist at the grain boundaries of silicon nitride grains and have a remarkable effect on mechanical properties at high temperatures such as high-temperature strength. considered to be a thing. In the present invention, one or two selected from substances that can make titanium nitride and tantalum nitride exist, which are added to silicon nitride grains.
0.1 to 40 when converted to titanium nitride or tantalum nitride
The reason why it is recommended to limit it to 1 to 30% by weight is that if it is less than 0.1% by weight, it is insufficient in quantity to effectively bond the silicon nitride grains, and it may cause insufficient sintering locally. and as a result, the strength decreases, and
When the volume is 4% or more, the strength decreases due to the increase in the amount of nitride interposed between silicon nitride grains, and the properties of the nitride itself, such as high expansibility, affect the properties of the silicon nitride sintered body. This is because it will have a big impact.

In addition, the reason why it is preferable to limit the amount of oxygen present in the sintered body to 0.3 to 5% by weight is that if it is less than 0.3% by weight, even by adding nitrides such as TIN, it is not always possible to increase the density sufficiently. If the content exceeds 5% by weight, a relatively large amount of glass phase will be formed at the grain boundaries, making it difficult to obtain the desired strength at high temperatures.

The titanium nitride and tantalum nitride that can be preferably used in the present invention are industrially available with a purity of about 90% or higher and are sufficient, and the finer the particle size, the better, but submicron grade is not necessarily necessary. Depending on the particle size of the silicon nitride particles used, one having an average particle size of about 0.5 to 44 pm may be appropriately selected.

The reason for this is that in the usual method of cold pressing and firing without adding another sintering accelerator, the bonding effect of titanium nitride and tantalum nitride to silicon nitride grains is not always possible. This is thought to be due to the fact that the hot press means, which is not sufficient and heats at the same time, provides an effective bonding effect.

The hot-breathing conditions are those normally used for hot-breathing of non-oxides such as silicon nitride, i.e., the temperature is 16
00~1900℃, pressure 100~500k9/c,
The atmosphere may be a non-oxidizing atmosphere such as reducing or neutral atmosphere. Note that if the substance that can cause the presence of titanium nitride or tantalum nitride is a substance that does not contain nitrogen, such as metal Ti or metal Ta, a nitrogen atmosphere is required.

The thus obtained silicon nitride sintered body according to the present invention contains a substance capable of containing titanium nitride or tantalum nitride in an amount of 0.1 to 40% by weight in terms of titanium nitride or tantalum nitride, depending on the manufacturing conditions. , at least 70k9/T at room temperature when the oxygen content is between 0.3 and 5% by weight! Uf
It has an excellent bending strength of 40k9/1 or more at 1400°C.

The present invention will be explained in more detail with reference to Examples below.

Examples Table 1 shows the results of measurements made by preparing samples using commercially available raw materials.

A sample of 60φ×127WL was obtained by pulverizing and mixing raw materials in the proportions shown in Table 1 in a pot mill for 5 days. Hot breath conditions are 350kg/d x 1750℃
It was hot for x1 hour. The bending strength was measured by a three-point bending method. As can be seen from Table 1, Examples 1 to 5
In particular, Takabuchi' (shows excellent properties of strength).

Claims (1)

[Scope of Claims] 1. A silicon nitride hot-pressed sintered body characterized by containing one or two selected from titanium nitride and tantalum nitride. 2 Claim 1 containing 0.1 to 40% by weight of one or two selected from titanium nitride and tantalum nitride
sintered body. 3. The sintered body according to claim 1 or 2, having an oxygen content of less than 5% by weight. 4. The sintered body according to claim 1, 2 or 3, having an oxygen content of more than 0.3% by weight. 5. A method for producing a silicon nitride hot-pressed sintered body, which comprises adding one or more selected from substances capable of causing the presence of titanium nitride and tantalum nitride to silicon nitride powder and hot-pressing the mixture. 6. The manufacturing method according to claim 5, in which 0.1 to 40% by weight, calculated as titanium nitride or tantalum nitride, of one or more selected from substances that can cause titanium nitride and tantalum nitride to exist is added. .