JPS59182275A - Manufacture of high strength silicon nitride sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a method for producing a high-strength silicon nitride sintered body, and more particularly, silicon nitride is combined with beryllium oxide (Bed) and aluminum oxide (Ax20s) as binders.
The present invention relates to a method for producing a silicon nitride sintered body, which is characterized in that the two components or the three components of beryl oxide, aluminum oxide, and magnesium oxide are mixed and sintered in a predetermined ratio.

Sintered bodies containing Si3N4 as the main component have heat resistance, high strength, and a low coefficient of thermal expansion, so they have been attracting attention in recent years, as they are used in, for example, automobile engine parts, gas turbine parts, and cutting tools. Bathing.

By the way, conventionally, in order to increase the strength and density of this silicon nitride sintered body, a sintering aid of Eli 5N4 and L "
CY2O2-A (8205, MJ70, A/h05Mg
Attempts have been made to add an o-based compound to Si 3 N4 and sinter it. However, even the sintered bodies obtained by adding these sintering aids have not always had sufficient strength.

As a result of extensive research into increasing the strength of silicon nitride sintered bodies compared to the conventional products, the present inventors discovered that two components of Si3N4, BeO and AA20s or B
By sintering a composition of eO, AIJ20s, M, and i90 in a predetermined ratio at a certain temperature,
We have found a way to achieve this objective, and based on this knowledge, we have completed the present invention.

That is, the invention consists of 5i3N45Q~99.9 parts by weight, Be0 and Al2O5, and A4203/B
A method for producing a high-strength silicon nitride sintered body, which comprises sintering a composition to be sintered having an eO value in the range of 3.4 to 4.9 on a weight basis at a temperature of 1300 to 1850°C. , and Sj, 450 to 99.9 parts by weight of 3N and BeO and A
IJ203 and M! 70, and A4 size by weight
2o3 eOO value is 3.4-4.9, M, 90. /E3
A composition to be sintered having an eCX1) value of 0.40 or less and a Mgo/Al2O3 value of 0.08 or less was
The present invention provides a method for producing a high-strength silicon nitride sintered body characterized by sintering at a temperature of 850°C.

In the method of the present invention, Si3N+ is α-type, β-type,
Any amorphous type may be used, or a mixture thereof may be used, and the amount thereof should be 50 to 99.9 parts by weight in the composition to be sintered.

In the uninvented method, B is used as a sintering aid for Si3N4.
Binary components of eO and Al2O3, or Be0- Al2O
Three components, 5 and M, 90, are used, and the amount of these sintering aids ranges from 0.1 to 50 parts by weight in the composition to be sintered.

If this amount is less than 0.1 parts by weight, sintering will be difficult, and if it exceeds 500 parts by weight, the original characteristics of the silicon nitride sintered body will be lost.

BeO and Al2O are used as sintering aids in the method of the present invention.
When the two components No. 3 are used, the ratio of their use is such that the value of Al2O3/BeO is in the range of 3.4 to 4.9, more preferably 3.88 to 4.28, on a weight basis.

In addition, as sintering aids Bed, Al2O5 and M, 90
When using the three components, their usage ratio is as follows:
MgO/BeO value on weight basis is 40 or less, preferably 018 or less, MI O/A12030) value is 0.08
below, preferably 0.05 or below, and All 2
03/Be O values are in the same range as above.

In addition, A6 is present as an impurity in the raw material S i 5 N 4.
If the sintering aid contains 20s or Fe2O3, or if it contains impurities that produce Fe2O3 upon sintering, an amount of A6205 corresponding to the impurity can be removed from the sintering aid.

Furthermore, the method of the present invention uses Bed as a sintering aid from the beginning.
Instead of using oxides such as Al2O3, Mgo, etc., it also includes scales using salts of beryllium, aluminum, and magnesium, which convert to these oxides during the sintering process. Also, BeO, Al2O3, M, and 90 should be added as independent oxide raw materials instead.

It is also possible to use a mixed oxide solid solution that has been reacted in advance and has an aluminate type crystal structure.

Next, an embodiment of the present invention will be described. First, a composition to be sintered is prepared by mixing BeO powder and Al1203 powder or BeO powder, Al2O3 powder, and MgO powder in a predetermined ratio to Si 3N4 powder as a raw material. . Next, a binder is added to this composition as needed and pressed to obtain a predetermined molded product.
1300-1850°C, preferably 1400-1800
Sinter under pressure in the temperature range of °C. At this time, if the proportion of the sintering aid is within a range that satisfies the following formula on a weight basis, pressurization is not necessarily required.

Pressure sintering is usually carried out in a graphite mold using a uniaxial hot press or a hot isostatic press. In general, the higher the pressure, the better the results will be obtained, but for graphite type it is usually 100
~400Kg/crl, 1000 in hot isostatic press
-2000 Kg/cdl range.

By sintering in this manner, a novel silicon nitride sintered body containing a MgA6z04-BeA4204 solid solution having a beryllium aluminate type crystal structure and an oxynitride solid solution phase with Si3N4 can be obtained. The composition of this sintered body is almost exclusively a crystalline phase consisting of 513N4 that has shifted to the β type and the above-mentioned oxynitride solid solution phase, and contains almost no glass phase.

The new high-strength silicon nitride sintered body obtained by the uninvented method is superior to the conventional silicon nitride sintered body in terms of strength at temperatures below 1300°C, and therefore this sintered body is resistant to stress such as impact and fatigue. Suitable for structural materials where concentration is a problem.

The reason why the silicon nitride sintered body of the present invention has excellent strength is that the double oxide solid solution having a beryllium aluminate type crystal structure easily reacts with Si5N4 to form oxynitrides during the sintering process. This is thought to be because a solid solution is formed and a sintered body having a uniform composition and uniform structure is obtained without forming a foreign crystal phase or glass phase between particles.

In addition, the thermal expansion coefficient of this oxynitrided solid solution is about 3×10/”C in both the a-axis direction and the c-axis direction, which is extremely close to the thermal expansion coefficient of β-type Si3N4, so the grain boundary phase It is thought that a sintered body with a low coefficient of thermal expansion, high resistance to thermal shock, and high strength even at high temperatures can be obtained.

Furthermore, impurities such as Fe2O3, which caused a decrease in strength in conventional sintered bodies, are incorporated into the oxynitride solid solution in the sintered body of the present invention, resulting in a sintered body with a uniform structure. This is also considered to be one of the factors contributing to the improvement in strength.

Next, the invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded.

Example 1 α type 9 with purity factor 99 and average particle diameter (50 factor diameter) 0.7 μm
0%, β-type 10φ silicon nitride powder, 19.3 parts by weight of beryllium oxide of 99.9 purity, 99.9 parts by weight of silicon nitride powder. Add 10 parts by weight of a sintering aid consisting of 0.7 parts by weight of magnesium oxide and 80 parts by weight of aluminum oxide of 99.9% purity using an alumina pot and an alumina ball. The resulting mixture was pulverized and mixed for a period of time to a diameter of 40 mm and a thickness of about 5 mm.
It was molded into a disk shape and pressure sintered in nitrogen gas at a temperature of 1750°C and a pressure of 300 K9/c for 30 minutes. The obtained sintered body was processed into a square bar of 3×3×30 mm, and then subjected to a bending test to measure the bending strength. In addition, the constituent substances were identified by transverse refraction intensity values and X-ray diffraction. The results are shown in Table 1.

Example 2 Purity: 99.9, average particle size: 0.35 μm, 1α type, 85:
Beryllium phosphorous oxide obtained by mixing 92 parts by weight of silicon nitride powder consisting of β-type 15 nitride with the same molar ratio of beryllium oxide and aluminum oxide used in Example 1, and firing the mixture at 1300°C for 3 hours. 8 parts by weight of aluminum bot and alumina balls were added, ethanol was added, and wet pulverization was performed. After molding in the same way, it was molded in alco gas at a temperature of 1700℃ and a pressure of 200K.
g, /C4 for 30 minutes. This sintered body was cut into the same dimensions as in Example 1, and the bending strength was measured.

The results are shown in Table 1 along with the identified constituent substances.

The ratio to the density calculated from the theoretical density value is shown as a percentage. As can be seen from Table 1, the silicon nitride sintered body obtained by the VC1 method of the present invention has an anti-degradation bow fluorescence of 93 to 93 when left at room temperature.
It shows an extremely large value of 98Kg/-. This is because MiO5A1203 reacts with 5i31h during the sintering process to form an oxynitride phase with the same crystal structure as β-8iN4 at the grain boundaries. This is thought to be due to the strong bonding between particles Jt.

Claims (1)

[Claims] I5ixN450-99.9% by weight and BeO and A
A composition to be sintered consisting of ltos and having an Al2O3/Be0Q ratio in the range of 3.4 to 4.9 on a weight basis was
A method for producing a high-strength silicon nitride sintered body, characterized by sintering at a temperature of 300 to 1850°C. 2 5i5Na50~99.9 weight factor and BeO and Al
Consisting of 2O3 and M, 170, and Al2O on a weight basis
5/ BeO value is 3.4 to 4.9, MgO, /BeO
The composition to be sintered has a value of 0.40 or less and a value of MjjO/Al1203 of 0.08 or less.
A method for producing a high-strength silicon nitride sintered body, characterized by sintering at a temperature of 0°C.