JPS59223274A - Method of getting high strength silicon nitride reaction 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 present invention provides a method for obtaining a high-strength silicon nitride reaction sintered body!
I! do.

Among products of silicon nitride Sf 3N4, those called reaction sintered bodies are usually molded bodies of Si powder or (3i
+Si 3N4) It is manufactured by applying nitrogen gas to a molded body of a powder mixture to nitriding it and sintering it.

This type of product has excellent thermal shock resistance, hardness, electrical insulation properties at high temperatures, and chemical stability, and also has the advantage of almost no shrinkage during reaction sintering and a high degree of dimension. Therefore, it is widely used in applications such as fireproof materials, wear-resistant materials, corrosion-resistant materials, and insulation materials.

The drawback of conventional silicon nitride reaction sintered bodies is that they are mechanically weak, and even if the bending strength is as high as 20Kg/l1lI112, it is only 30K(] f7mm2, which is unsatisfactory as a heat-resistant structural material R4. This is because even products obtained by completely nitriding silicon are only relatively low-density sintered bodies with a porosity of 20 to 30%. In order to obtain a body, it is necessary to manufacture something with high density.

If a reaction sintered body with higher density can be produced, it will be possible to improve not only its strength from room temperature to temperature but also other opening properties. C is extremely useful as a material.

The measures taken so far to increase the density of reaction sintered bodies are to increase the density of 3i or (Si + Si 3N4) compacts. Specifically, the first step is to increase the powder compaction pressure, but even if a high pressure is applied to the practical limit, the density of the product after nitriding is at most 2.39 (1/
cm3 (75% of the theoretical density). Attempts were made to adjust the particle size of the powder and blend powders with various particle sizes, but the density of the reaction sintered body was still 2.54 CI/c.
m3 was considered to be the limit.

In order to obtain a reaction sintered body with even higher density, we introduced pre-sintering of the 3i bottom molding, that is, sintering in an inert atmosphere prior to nitriding, to create a high density sintered body with the 3i bottom molding. This has been proposed in Japanese Patent Application Laid-open No. 121613/1983).

However, in the method disclosed above, in order to effectively restore the high density of the S: compact due to preliminary sintering, the average grain size is 0.2
The essential condition is to use extremely fine Si powder of less than μ. Setting aside the problem that such fine powder is not easy to manufacture, the density of the reaction sintered body calculated by 1η is still 2,390/cm3 (92% of the theoretical density).
%) was the limit.

The inventor of the present invention has conducted research together with his collaborators with the intention of further increasing the density of 3i bottom molding using pre-sintering, and has achieved a maximum density of 3.05g7crn3 (96% of the theoretical density).
%), we succeeded in obtaining a reaction sintered body with an extremely high C density, which we would like to disclose in Japanese Patent Application Laid-Open No. 57-188465.
No. 57-188466). The method is 3i
Add a certain amount of boron to the powder to improve sinterability, or
or specific elements, i.e. Fe, co, Nt,
Cr, MO, Mn SW, Ti, Zl', T'a, Nb
,V.

Mg, Ca, Cu, 7n and 3n to gill/v
The gist is to promote nitriding by adding a certain amount of an element or a compound thereof for 1 or 2 seconds or more.゛In subsequent research, J: ``It was found that nitriding accelerators such as e have the effect of improving sinterability and are useful in a wide range of addition amounts. , Mochiro/V
(It is also possible to use lf, which is preferable.

Furthermore, the present inventors have added consideration from the viewpoint of what is the direct means to increase the strength of the silicon nitride reaction sintered body.
In reaction sintered compacts, the density of the surface layer is often lower than that of the inner layer.
It was found that the strength was unsatisfactory.

The reason why the surface layer of the pre-sintered body has a low density is not completely clear, but the reason why the surface layer of the pre-sintered body has a low density is that the raw material 3i is on the surface of the powder.
This is thought to be because the phenomenon of reaction with SiO and volatilization in the form of SiO is more likely to occur in the surface layer.

This phenomenon includes the purity of the raw S1 powder, the source, the grinding method,
Many factors can be considered, such as particle size and particle size distribution, molding method and pre-sintering conditions, such as temperature, time, and atmosphere.
To some extent, aG is not available.

Therefore, as a countermeasure to this problem, the method of protecting the strength silicon nitride reaction sintered body of the present invention is to use boron or its compound as B and 0.15 to 5.0 fflfTi%, and/or Fe, Go, NiN15Cr1. Mn, W.
Ti, Zr, 1-a, NtzV, Mg, Ca, Cu
, Zn and 3n or 2P! A silicon powder containing 0.05 to 2.0% by weight of the above elements or their compounds as the above elements (in the case of two or more, the total amount) is molded, and the molded body is heated to i, ioo in an inert gas atmosphere. ℃ or higher but lower than the melting point of Sl. The method for producing a high-strength silicon nitride reaction sintered body is characterized in that the surface layer portion of the pre-II sintered viscous body is removed and then subjected to nitriding treatment.

As is well known, S f 3 N 4 is a very hard material, so it is difficult to remove the surface layer from the reactive sintered product and requires C1 diamond machining.

However, the surface of the pre-sintered body of S1 powder is extremely easy to shave off, and can be cut with a lathe, or simply with emery paper.

The blending and molding of the 3i powder, as well as the conditions for pre-sintering, were carried out in accordance with the techniques previously disclosed by the present inventors. , preferably both are blended. The reason for the limit on the amount of boron contained is as previously disclosed. In order to expect the effect of boron, it is necessary to contain at least 0.15% by weight. However, boron is nitrided in the nitriding process. Boron BN is generated, and when it becomes large, it inhibits reaction sintering. Therefore, 5.0 f
It must be stopped within fim%.

The content of Fe and other substances is 0.05 for S1 powder.
If the amount is less than % by weight, no effect will be obtained.

Below this lower limit, the density of the preliminary sintered body may become high, and the time required to nitride Si to B degree becomes too long to be practical. On the other hand, if the content exceeds 2.0%, it will cause coarse grain growth and prevent high density during preliminary sintering, so LJ must be avoided. The preferred range varies depending on the element used, but is usually 0.1 to 0.6.
Weight pay%.

In the case of boron, the existing form may be metal boron, amorphous material, metal boride, etc.
Other C, which is in an elemental state, may also be a compound such as an oxide, and compounds of these are, of course, preferable.

When both are used together, it is preferable to select a compound of boron and these elements because both can be present together.

The raw material 3i powder should preferably have an average particle size of 15 μm or less, and preferably a fine powder of 1 μm or less in order to facilitate densification in preliminary sintering.

It is desirable that the sintering accelerator a3 and the nitriding accelerator be fine particles having a particle size equal to or smaller than that of the 3i powder.

Of course, the raw material powder or powder mixture can be formed by any means such as conventional die forming, isostatic pressing, slip molding, and injection molding.

The density of the compact to be pre-sintered should be at least 0.82 g/cm3 (35% of the theoretical density) in order to facilitate its handling and processing and to ensure sinterability during pre-sintering. Should. If the density is too low, it is difficult to obtain a sintered body with a uniform structure even if the density can be increased by preliminary sintering.

As the pre-sintering method, in addition to free sintering, normal methods such as -axial force 1 T sintering (so-called pot press) and hot isostatic pressure sintering can be used.

Preliminary sintering is performed at a temperature of 1.100° C. or higher. At temperatures lower than this, high density cannot be expected even if fine powder is used. "Of course, the temperature of the second limit is /
It is the melting point of vsf. The atmosphere is preferably an inert gas such as argon, but may also be a vacuum.

The degree of densification at the preliminary sintering stage is determined by the amount of shrinkage caused by sintering. This is not the same depending on the density of the sintered compact, but in order to provide the high-density reaction sintered product that the present invention aims to achieve, the volumetric shrinkage rate must be at least 10%, and 20%. It is preferable that there be more than one.

The thickness of the porous, low-density surface layer of the pre-sintered body is influenced by many factors as described above, but at its thinnest it is 0.
．． 05nu++, number 3 if thick. It reaches Qmm.

Therefore, within this range, if a thickness suitable for each case is removed, J: 0.

As shown in the example shown later, the boundary between the low-density surface layer and the high-density interior can be seen relatively clearly, so it is easy to determine the thickness of the surface layer to be removed.

The nitriding of the 3i pre-sintered body can be carried out in the same manner as is done in the production of conventional silicon nitride reaction sintered bodies. 4. Generally, heating is performed to a temperature of 1.100 to 1.500°C under a nitrogen gas atmosphere at atmospheric pressure.The temperature is gradually increased from the low temperature side of 1,100 to 1.350°C It is also possible to increase the temperature. In order to adjust the reaction rate, the nitrogen pressure can be selected from a range of reduced pressure (up to about 1/100 atm) to increased pressure (up to 2,000 atm). In addition to pure nitrogen gas, hydrogen-mixed nitrogen gas and ammonia can also be used.

The time required for nitriding varies depending on the density of the preliminary sintered body, the average grain size, the nitriding temperature, and the atmosphere system f'1, and on the allowable amount of residual Si, but it varies from vi time to 200
It takes about an hour.

When the preliminary sintered body from which the low-density surface layer portion has been removed is nitrided according to the present invention, the resulting reaction sintered body has high density throughout and has no weak spots on the surface, resulting in improved strength.

Example: 81 powder with average grain size t￥0.15μ, amorphous power B0.4%
and ZrO21.2%, wet-mixed in a polyethylene ball mill with n-hexane medium to volatilize the l)-benzene, and then rubber press molded (pressure 2 ton 7cm2) L/ A tablet with a diameter of 10 mm and a height of 10III11 was made.

This molded body was preliminarily sintered by heating at 1360° C. for 2 hours in a Δr air flow. The figure shows a cross section near the surface layer of the obtained pre-sintered body. Approximately 0.8 Il from the surface
It is recognized that a porous low-density stone layer exists with a thickness of 1 m.

Therefore, the surface layer of the preliminary sintered body was scraped off to a thickness of 0.8 mm with emery paper, and
℃ x 4B hours → 1385℃ x 96 hours → 1420℃ x 2
It was nitrided by heating for 4 hours.

The density of the reaction sintered body was 2.83 (1/cm3), the bending strength was 42, and the reaction sintered body was nitrided without removing the surface layer of the preliminary sintered body for comparison. The sintered body had a density of 2.440 cm3 and a bending strength of 28.3 ka/cm2.

[Brief explanation of the drawing]

The drawing shows a cross section near the surface layer A1 of a pre-sintered body of Si powder prepared in Example 5 of the present invention, at a magnification of 5.
This is a 0x micrograph. Patent applicant Daido Steel Co., Ltd. Agent Patent attorney Souo Suga

Claims (2)

[Claims] (1) 0°15~ with boron or the compound of A as 8
5.0% by weight and/or Fe. Go, Ni, Or, Mo, Mn5W, Ti, Zr,
One or more of the following elements, Nb 1 V, MO, ca , cu , 7n, and 3n, or their compounds are used as the above elements (in the case of two or more, by cutting) 0.0
Silicon powder containing 5% to 2.0% seedlings is molded to form a molded body.
in an inert gas atmosphere at a temperature of 1.100℃ or higher but 3i
High-strength silicon nitride reaction sintering consists of pre-sintering by heating to a temperature lower than the melting point of A method for producing a compact comprising: removing the surface layer of the C1 preliminary sintered compact and then subjecting it to nitriding treatment. (2) The method according to claim 1, wherein the surface layer portion is removed over a depth of 0.05 to 3.0 m1n.