JPH0426557A - Production of silicon nitride-based sintered body - Google Patents

Abstract

PURPOSE:To reduce average grain size and to enhance strength by adding yttria and AlN to Si3N4 contg. beta-Si3N4 and sintering them. CONSTITUTION:Si3N4 of <=1.0mum average particle size contg. 5-95wt.% beta-Si3N4 is prepd. and 3-15wt.%, in total, of 1.0-5.0wt.% yttria of <=1.0mum average particle size and 2.0-10wt.% AlN of <=1.0mum average particle size are added to the Si3N4. They are mixed and sintered at 1,650-1,900 deg.C in an inert gaseous atmosphere or in vacuum to obtain an Si3N4-based sintered body of <=2mum average grain size. The alpha'-Si3N4 content of this sintered body is represented by 0.05-0.50 ratio of presence measured by X-ray diffraction.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing a sintered body containing α-silicon nitride using silicon nitride containing β-silicon nitride as a raw material. .

[Conventional technology]

Sintered bodies of silicon nitride (812N4) have high strength, excellent thermal shock resistance, and corrosion resistance, and are therefore being used for, for example, gas turbine components, heat exchange materials, bearings, and the like.

However, since it is difficult to sinter 5jsNi alone, it is usually used with MgO, MgAztO,, A1.03, Y2
Oxides such as O, etc. are added as sintering aids for sintering. Sintering using these sintering aids is thought to be based on liquid phase sintering mediated by the liquid phase generated during sintering.

In many cases, the liquid phase remains in the sintered body as a glass phase after sintering, degrading high-temperature properties such as high-temperature strength and creep resistance.

Furthermore, due to the presence of the liquid phase, grain growth of S L 2 N<crystal grains is likely to occur, causing a decrease in strength.

For this reason, if the amount of added sintering aid is reduced and the amount of liquid phase is reduced, grain growth can be suppressed to some extent, but on the other hand, sinterability is significantly reduced.

On the other hand, solid solutions of various elements in S iz Na (
(commonly called Sialon) is attracting attention.

For example, in the α-8izNa structure, AA' is at the Si position,
0 is substituted at the N position, and another element (Li
, Mg, Ca, Y, etc.) in solid solution as an interstitial type.
X≦2, M is at least one of Li, Mg, Ca, Y, etc.) α-3isN4 (generally called α-sialon) or β-3isNa structure,
1 is in solid solution at the i position, O is in solid solution at the N position, and the general formula Sls-z
β-3tsNs (generally called β-sialon) represented by Afm Ox N5-s (0<z≦4.2) is attracting attention.

Among the above, silicon nitride sintered bodies containing α-3j s Na have excellent high-temperature properties and are attracting attention as materials for high-temperature structures.

As a method for producing a silicon nitride sintered body containing α-3tsN4, a 5iaN4 raw material with a very high content of α-3isN4 (95% or more) is used and this is sintered. . This is α −3izN of αSi*N4
* and utilizes transformation into β-3is Na or β-SizNn.

In the method of 2, which uses a silicon nitride raw material with a high content of α-3is Na as a raw material, the cost increases because the silicon nitride raw material is expensive.

Moreover, the silicon nitride sintered body manufactured from the above raw materials is
The resulting α-3i*Na crystal grains are large, resulting in a decrease in strength and the like.

[Description of the first invention] The first invention (the invention described in the claims) has been made in view of the drawbacks of the above-mentioned prior art, and uses α as a raw material.
- It is an object of the present invention to provide a method for manufacturing a silicon nitride sintered body containing α' silicon nitride with small crystal grains without using a silicon nitride raw material with a high silicon nitride content.

The method for producing a silicon nitride sintered body of the first invention includes adding yttria and aluminum nitride to silicon nitride containing β-silicon nitride and firing them. It is characterized by forming a body.

According to the first invention, yttria and aluminum nitride act on β-silicon nitride, and during firing, β-silicon nitride transforms into α-silicon nitride, forming a sintered body containing α-silicon nitride. Moreover, the crystal grains of the produced α-silicon nitride become smaller.

Therefore, since silicon nitride raw materials containing a large amount of expensive α-silicon nitride are not used as raw materials, the cost is low. A sintered body containing α'-silicon nitride with small crystal grains can be formed.

[Description of other inventions of the first invention] Other inventions that make the first invention more specific will be described.

In the present invention, itria and aluminum nitride are added to silicon nitride containing β-silicon nitride (first step), and the raw material composition is fired (second step).

In this $1 step, a raw material composition is prepared by adding ytria and aluminum nitride to silicon nitride (M silicon raw material) containing β-silicon nitride.

As silicon nitride (SizNn) raw materials, β-3t, Na
It contains. Note that the silicon nitride raw material contains β
-3t s In addition to N4, α-8isNa etc. may be included. The content of β-5i2r'J4 is desirably 5% by weight or more based on the entire silicon nitride raw material. If it is 5% by weight or more, 5i=N other than β-3i2N4 is β
-8isNa or β-3isNa, resulting in grain growth or α-5 contained in the silicon nitride raw material
i2 Na to β-3isN4 or β-3isNa
It is possible to form fine crystal grains by suppressing grain growth accompanying the transformation to . Moreover, if there is a large amount of α-3i*Na in the raw material, this α-3ixN4 will dissolve in the liquid phase produced during firing, and β-5i=N.

Or it re-precipitates as β'-S 1 s Na,
Grain growth of crystal grains progresses, resulting in a sintered body with coarse crystal grains and low strength. Therefore, it is desirable that the content of α-3isN4 is 95% or less based on the entire silicon nitride raw material.

Ittria and aluminum nitride added to the silicon nitride raw material containing β-3jsNa have the effect of transforming β-3i*Na in the silicon nitride raw material into α-3i*Na during firing. Moreover, the crystal grains of α-3izN4 are made smaller (and furthermore, the grains of 5i other than α-31zN4 are
The crystal grains of zN4 are also made smaller.

Ittria (Y,○,) and aluminum nitride (Af
The amount of N) added is silicon nitride raw material, Y, 0. and Y, O, or 1, for the entire raw material composition including AIN.
Desirably, the IN is 0 to 5.0% by weight, and the IN is 2.0 to IO. Further, the total amount of Y, 0, and AIN added is preferably 3 to 15% by weight based on the entire raw material composition.

If the amount added is less than this range, sinterability will decrease significantly,
Furthermore, if the amount added is greater than this range, grain growth will become significant and the strength will decrease.

The raw material composition is preferably used in powder form.

In this case, the average particle diameter of the silicon nitride raw material powder containing β-8i2Na is in the range of 1.0 μm or less, Y.

0, the average particle size of the powder is preferably in the range of 1.0 μm or less, and the average particle size of the AiN powder is also preferably in the range of 1.0 μm or less.

The raw material composition includes YN, α-3i in addition to the silicon nitride raw material containing β-5izNn, Y, 01, and AfN.
A sintering aid such as Na may be included.

The raw material compositions are preferably used in combination. Examples of the mixing method include a wet mixing method using an organic solvent.

In the second step, the raw material composition is fired to obtain α-Si
A silicon nitride sintered body containing tNa is formed.

As the firing method, a normal pressure sintering method, a gas pressure sintering method, a hot isostatic pressure sintering (HIP) method, etc. can be used. The firing atmosphere is preferably an inert gas atmosphere such as N, gas, or argon gas, or a non-oxidizing atmosphere such as vacuum. The firing temperature is preferably 1650 to 1900°C. If the firing temperature is lower than 1650°C, densification will not proceed sufficiently, and if it exceeds 1900°C, grain growth will become significant and sufficient strength will not be obtained.

In addition, by controlling the amount of β-3iiI'L, the amount of sintering aid added, and the firing conditions, the content ratio of α-3ixN4 in the sintered body,
Grain size and composition can be controlled.

The silicon nitride sintered body to be manufactured has an α-3isN4 content or an abundance ratio of 0°05 to 0.50 according to X-ray diffraction.
, and the balance is other substances such as β-3iiNa or β-8isNa, and it is desirable that the total amount is 1.

Also, regarding the grain size of α'-3isN4,
It is desirable that the average particle size is in the range of 2 μm or less.

In addition, β-311Na or β′S j
If s Na is included, β-3is Na or β
It is desirable that the average particle size in the −3isNa direction is 5 μm or less and the short axis direction is 1 μm or less.

Note that when producing the silicon nitride sintered body as a molded article, it is preferable to mold the raw material composition.

As this molding method, mold pressing, rubber pressing, extrusion, slip casting, injection molding, etc. can be used.

〔Example〕

The present invention will be explained in detail below.

(Example 1) 5isNa raw material powder containing β-3izNa and having an average particle size of approximately 0.5 μm or less (the content is the value shown in Table 1 for β-3isN4, and the total amount of metal impurities is 0°1 wt% or less) , the remainder is α-31zNa, making a total of 100wt%), and the average particle size is about 0.5μ to this 5izN* raw material powder.
Y of high purity (99.9%) below m, 0. powder, and high-purity (99.9%) AIN powder with an average particle size of about 0.5 μm or less, respectively, by weight 94%, 2.3%, and 3%.
．． They were mixed at a blending ratio of 7%. This mixture was molded using a mold press, and then fired using a hot press method.

Note that hot pressing was performed at 1800°C for 12 hours. In this way, silicon nitride sintered bodies (sample magnets 1 to 9) containing α'-3ixNt having constituent phases and crystal grains as shown in Table 1 were manufactured. Note that the above sintered body also contains β'=SL2N4, and its constituent phases and crystal grains are also shown in Table 1.

In addition, α'-3i, N, was prepared in the same manner as above, except that the blending ratios of the S 12 N4 raw material, Yt 01 and IN were 91%, 3.4%, and 5°6% by weight. A silicon nitride sintered body (sample NCLIO-17) containing the following was manufactured. Table 1 shows the constituent phases and crystal grains of the produced sintered body.

In addition, for comparison, the above β-8izN was used as a raw material composition.
5ijN4 raw material powder containing 4 has an average particle size of 0.5 μm.
α'-S i 2 N4 (Y・, *
(S i, Af) It (0, N) +-) powder to 2
5wt% added (the blended amount is 5isN4 raw material 75%)
A silicon nitride sintered body (sample & Cl-C3
) was manufactured. Table 1 shows the constituent phases and crystal grains in the sintered body.

In addition, α -8j3N4, β' - in the obtained sintered body
The abundance ratio of 3i2N4 and the average grain size of the crystal grains were determined by X-ray diffraction, and the four-point bending strength was measured according to JISR1601. The results are shown in Table 1. In addition, α
The abundance ratio of -3isN4 can be determined by comparing the sum of the top two peaks with high intensity of α type and the sum of the top two peaks with high intensity of β type in the X-ray diffraction chart of the sintered body. It was done by The abundance ratio of α-3t*Na in the table is a value when the sum of the abundance ratios of α'-3isN4 and β'-3iiNa is set to 1.

As is clear from Table 1, it can be seen that the sintered bodies manufactured according to this example have smaller average crystal grain diameters and higher strength than those of the comparative examples.

(Example 2) Using the same starting materials as in Example 1, the mixture was molded in the same manner as in Example 1, and α
' A silicon nitride sintered body containing 5izN4 was manufactured. The content of β-3tzNi in the above starting material is as shown in Table 2.
The test was carried out at 50°C for 14 hours. Also, samples Nll8-24 in Table 2 are under the same conditions as samples it-9 in Table 1, and sample fish 25-31 in Table 2 are under the same conditions as samples NCL in Table 1.
The conditions are similar to IO-17. Also, sample N in Table 2
chC4-C7 were produced in the same manner as above under the same conditions as samples NciC1-C3 in Table 1.

α'-3i3Na and β'-8isNa of the obtained sintered body
The abundance ratio, average grain size of crystal grains, and four-point bending strength were measured in the same manner as in Example 1. The results are shown in Table 2.

As is clear from Table 2, it can be seen that the sintered bodies manufactured according to this example have smaller average crystal grain diameters and higher strength than those of the comparative examples.

Claims (1)

[Claims] A silicon nitride sintered body, characterized in that a sintered body containing α'-silicon nitride is formed by adding yttria and aluminum nitride to silicon nitride containing β-silicon nitride and firing these. Production method.