JPH046680B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to joining silicon nitride reaction sintered bodies,
It includes a silicon nitride reaction sintered body for bonding, a method for manufacturing the same, and a bonding method using the same.

Among silicon nitride Si ₃ N ₄ products, those called reaction sintered bodies are usually made by applying nitrogen gas to a molded body of Si powder or a molded body of (Si + Si ₃ N ₄ ) powder mixture while nitriding it. Manufactured by sintering. This kind of product has thermal shock resistance, hardness,
It has excellent electrical insulation and chemical stability at high temperatures, and has almost no shrinkage during reaction sintering.
Because it has the advantage of achieving high dimensional accuracy,
Widely used in applications such as fireproof materials, wear-resistant materials, corrosion-resistant materials, and insulation materials.

However, when manufacturing various parts from silicon nitride reaction sintered bodies, it is often necessary to bond and integrate them with other materials, such as metals. Even if it is possible or desirable for the entire member to be a silicon nitride reaction sintered body, if the shape is complex, it is difficult to mold it in one piece, and two or more nitride Parts of silicon reaction sintered body must be joined.

The present inventor has made a silicon nitride reaction sintered body mutually,
In view of the current situation where there is a desire for technology to join with other materials such as metals, we have conducted repeated research and established a silicon nitride reaction sintered body for bonding, its manufacturing method, and bonding method.

The silicon nitride reaction sintered body for bonding of the present invention has a dense interior and a surface layer that is porous to the extent that the bonding material can penetrate therethrough. Having a dense and high internal density is important for obtaining sufficient mechanical strength. According to the method already invented and disclosed by the present inventor, the relative density is 90%, and the numerical value is 2.86.
A silicon nitride reaction sintered body with a high density exceeding g/cm ³ is obtained. It is necessary for the surface layer to be porous so that the bonding material can penetrate and bond firmly to the sintered body. The degree of porosity should be 35% or more in terms of porosity, but if the porosity is too high, the strength will be low, so a suitable range is 35 to 70%. The thickness of the porous surface layer needs to be at least 0.1 mm, but 1 mm or less is sufficient.

Here, the "bonding material" is liquid at the time of application, but it solidifies later and firmly bonds with the surface layer of the silicon nitride reaction sintered body, making this reaction sintered body another reaction sintered body. , or something that can be combined with other materials. When joining two or more parts,
Although it can be said to be an adhesive in a broad sense, as shown in the example below, the bonding material itself can serve as a structural material, so the term bonding material includes adhesives.
It has a broader meaning.

As is easily understood, "porous surface layer"
It does not need to exist over the entire surface of the silicon nitride reaction sintered body for bonding, it just needs to exist at least in the part where the bonding is performed, and in the non-bonded areas,
It is also possible to have a structure in which the porous surface layer is removed.

The method of the present invention for producing a silicon nitride reaction sintered body for bonding involves molding silicon powder with an average particle size of 15μ or less, and heating the molded body to a temperature of 1100°C or higher and lower than the melting point of silicon. The pre-sintered body is pre-sintered to obtain a pre-sintered body in which the porosity of the surface layer is higher than that of the inner part, and this pre-sintered body is nitrided by applying nitrogen at a temperature of 1100 to 1500°C to make the interior dense. The process consists of producing a silicon nitride reaction sintered body whose surface layer is porous.

It is necessary to use a raw material Si powder with an average particle size of 15 μm or less in order to produce a reaction sintered body whose interior is dense and whose surface layer is porous. In addition, for the production of normal silicon nitride reaction sintered bodies,
It is said that the higher the purity of Si, the better, but in the present invention, one containing O of 0.5% or more, preferably 1% or a little more, reduces the density difference between the inside and the surface layer. It is useful for producing The reason is not clear enough, but as mentioned above
During preliminary sintering of Si, Si is volatilized as SiO, making the surface layer porous, and the presence of O is thought to promote this.

In implementing the above manufacturing method, one or both of a substance that enhances the sinterability of Si and a substance that promotes nitridation is used according to a technique invented by the present inventor together with collaborators or alone. It is preferable to add. The former is represented by boron, and the latter is
The effects of Fe and many other metals are known.

Specifically, this recommended practice:
In the raw Si powder, 0.15 to 5.0% by weight of boron or its compound as B, and (or) Fe, Co,
Ni, Cr, Mo, Mn, W, Ti, Zr, Ta, Nb, V,
One or more elements selected from Mg, Ca, Cu, Zn, and Sn, or their compounds as the above elements (in the case of two or more, the total amount) is 0.05 to 2.0
It consists of adding % by weight, shaping, pre-sintering and subsequent nitriding.

The limits and reasons for the content of the above-mentioned substances that have the effect of promoting sintering or nitriding are as disclosed above. That is, in order to expect the effect of B, it is necessary to contain at least 0.15% by weight. However, B is boron nitride BN in the nitriding process.
is generated, and when it becomes large, it inhibits reaction sintering. Therefore, it must be kept within 5.0% by weight.

The content of Fe and other substances is 0.05 to Si powder.
If the amount is less than % by weight, no effect will be obtained. If it is less than this lower limit, the density of the pre-sintered body may become high, and the time required to nitridize Si to a high degree becomes impractically long. On the other hand, a content exceeding 2.0% causes significant grain growth and prevents high density during preliminary sintering, and must be avoided. The preferred range varies depending on the element used, but is usually 0.1 to 0.6% by weight.

In the case of boron, the existing form may be metallic boron, an amorphous substance, or a metallic boride, and Fe and others may be in an elemental state or in a compound such as an oxide. , and compounds of the same type are of course preferred. When both are used together, it is preferable to select a compound of boron and these elements because both can be present at once.

The sintering accelerator and the nitriding accelerator are also desirably fine particles with a particle size equal to or smaller than that of the Si powder.

Powder compaction and preliminary sintering may be performed according to conventionally known techniques. That is, it goes without saying that the raw material powder or powder mixture can be formed by any means such as conventional die forming, isostatic pressing, slip casting, injection molding, and the like.

The density of the compact to be pre-sintered is 0.82 g/cm ³ (the theoretical density) to facilitate handling and processing and to ensure sinterability during pre-sintering.
35%) or more. If the density is lower than this, even if the density can be increased by pre-sintering, it will be difficult to obtain a reaction sintered body having a uniform and dense structure inside.

In addition to free sintering, the preliminary sintering can be carried out by conventional methods such as uniaxial pressure sintering (so-called hot press) and hot isostatic pressure sintering.

Pre-sintering is performed at a temperature of 1100°C or higher. At temperatures lower than this, high density cannot be expected even if fine powder is used. The upper limit temperature is, of course, the melting point of Si. Of course, an inert gas such as argon can be used as the atmosphere, but vacuum, H ₂ gas, or an inert gas containing H ₂ is more likely to cause a density difference with the inner surface layer of the pre-sintered body. This trend is observed and is desirable.

Although it is desirable that the density of the obtained pre-sintered body be high, in order to sufficiently nitrid the inside, it is not beneficial to increase the density too much, and it is appropriate to limit the density to 2.05 g/cm ³ or less. The density of the surface layer is 0.80 in order to obtain a reaction sintered body with suitable porosity.
A range of 1.4 g/cm ³ is desirable. In order to produce a pre-sintered body with such density values in the internal and surface layers, the raw Si powder and its additives, as well as the sintering conditions such as temperature and atmosphere, are selected.

The nitriding of the Si pre-sintered body can be carried out in the same manner as in the production of conventional silicon nitride reaction sintered bodies. That is, it is generally heated to a temperature of 1100 to 1500°C under a nitrogen gas atmosphere at atmospheric pressure. The temperature can also be increased stepwise from the low temperature side of 1100 to 1350°C. To adjust the reaction rate, reduce the nitrogen pressure (up to 100
Pressurized (up to 1/2 atm) to pressurized (maximum 2000 atm)
You can choose within the range. In addition to pure nitrogen gas, hydrogen-mixed nitrogen gas and ammonia can also be used. The time required for nitriding varies greatly depending on the density of the preliminary sintered body, average grain size, nitriding temperature, and atmospheric conditions, as well as on the allowable amount of residual Si, but ranges from several hours to about 200 hours.

The above-mentioned porous formation of the surface layer of the Si pre-sintered body is
This is carried over even after the nitriding treatment, and the silicon nitride reaction sintered body is obtained with a porous surface layer. The thickness varies depending on manufacturing conditions, but is at least 0.05 mm, and may reach 3 mm in some cases. Since the thickness necessary for the above-mentioned bonding is included in this range, manufacturing conditions should be selected so as to obtain a preferable value.

The method of the present invention for joining the silicon nitride reaction sintered body for bonding manufactured as described above has a method of joining the silicon nitride reaction sintered body for bonding which has a dense interior and a porous surface layer. From joining a silicon nitride reaction sintered body for joining with a similar sintered body or other materials by applying a joining material and allowing a part of it to penetrate into the pores of the surface layer and solidify it. Become.

Typical examples of bonding materials are adhesives, and if you do not expect heat resistance from the silicon nitride reaction sintered body and you want it to exhibit wear resistance, organic adhesives such as epoxy resins may be used. is available. When bonding the reactive sintered body and other materials, the silicon nitride reactive sintered body for bonding can be bonded with any adhesive in the porous surface layer, so it is suitable for other materials. Just choose a suitable adhesive.

As mentioned above, the bonding material is not limited to adhesives, but is melted by heating or is at least in a softened state, penetrates into the pores of the surface layer of the silicon nitride reaction sintered body for bonding, and then solidifies. However, metals, or inorganic or organic compounds can be used as long as they can be combined with this. As a joining method, a variety of techniques such as casting, brazing, and thermal spraying can be used, so depending on the desired characteristics of the parts to be manufactured using silicon nitride reaction sintered bodies,
Select as appropriate.

Example Si powder with an average particle size of 0.11μ and an oxygen content of 4.3% was placed in a mold and pressed at a pressure of 500Kg/ ^cm2 to form a width of 15mm.
It was preformed into a plate shape of mm×length 35mm×thickness 5mm, which was then subjected to main molding by applying a pressure of 2000 kg/cm ² using a rubber press.

The molded body was heated to 1270℃ in a vacuum of 1×10 ^-3 Torr.
Pre-sintered by heating for 1 hour, the internal density is 1.82g/cm ³ (equivalent density 78.1%), and the surface layer is approximately 1.5g/cm 3 (equivalent density 78.1%).
A pre-sintered body of 1.09 g/cm ³ (46.8%) was obtained between mm.

This pre-sintered body was heated at 1370°C x 48°C in a _N2 stream.
Nitriding (reaction sintering) was carried out by heating for time → 1385°C x 96 hours → 1420°C x 24 hours. The density of the obtained reaction sintered body was 2.73 g/cm ³ (85.7%) in the interior and 1.63 g/cm ³ (51.4%) in the approximately 1.5 mm surface layer.

For comparison, using Si powder with an average particle size of 17μ,
Molding and nitriding were carried out in accordance with the prior art (the nitriding conditions were the same as above) to obtain a reaction sintered body having a uniform density of 2.52 g/cm ³ (79.2%) almost throughout.

Next, the two reaction sintered bodies of the present invention and the comparative example obtained as described above were bonded as described below, and their performance was examined.

(1) Apply epoxy resin adhesive to both sides and make a diameter of 10mm.
Two nylon round rods were glued together so that their axes were aligned in a straight line. When the adhesive strength was measured by pulling a round bar, the stress at the time of peeling at the joint was 3.5 kg/mm for the present invention ^and 1.7 kg for the comparative example.

(2) Leave the widest one out of the six surfaces of the reaction sintered body and cover the remaining five surfaces.
Cast with SUS304 stainless steel.

A three-point bending test was conducted in which a stress was applied to the reaction sintered body so that it was pushed out from behind, and the following results were obtained.

The present invention was one piece until it broke.

Comparative example...Peeling occurred at a displacement of 0.09 mm.

(3) A Ni-Cr alloy was thermally sprayed onto one surface of the reaction sintered body to bond it.

By machining, the thickness of the sprayed part was finished to 3mm. The evaluation by the three-point bending test is as follows.

In the present invention... Cracks occurred in the silicon nitride reaction sintered body, but no peeling occurred.

Comparative example: The sintered body cracked and peeled off from the metal layer.

Claims (1)

[Claims] 1. A silicon nitride reaction sintered body for bonding, which has a dense interior and a surface layer that is porous enough to allow penetration of a bonding material. 2. The silicon nitride reaction sintered body for bonding according to claim 1, wherein the porosity of the surface layer portion is 35% or more. 3 Silicon powder with an average particle size of 15μ or less is molded, and the molded body is pre-sintered by heating to a temperature of 1100°C or higher but lower than the melting point of silicon, so that the porosity of the surface layer is lower than that of the inside. To obtain a high-quality pre-sintered body and to nitride this pre-sintered body with nitrogen at a temperature of 1100 to 1500°C to produce a silicon nitride reaction sintered body with a dense interior and a porous surface layer. A method for manufacturing a silicon nitride reaction sintered body for bonding. 4. The manufacturing method according to claim 3, in which silicon powder containing 0:0.5% or more is used as the raw material silicon powder. 5 0.15 to 5.0% by weight of boron or its compound as B to the raw silicon powder, and (or)
Fe, Co, Ni, Cr, Mo, Mn, W, Ti, Zr, Ta,
The above elements include one or more elements selected from Nb, V, Mg, Ca, Cu, Zn, and Sn, or their compounds (in the case of two or more, the total amount)
The manufacturing method according to claim 3, wherein 0.05 to 2.0% by weight is added and molded. 6 By applying a bonding material to the surface of a silicon nitride reaction sintered body for bonding, which has a dense interior and a porous surface layer, a part of the bonding material penetrates into the pores of the surface layer and solidifies. A method for joining a silicon nitride reaction sintered body, which comprises joining a silicon nitride reaction sintered body for bonding to a similar sintered body or another material. 7. The bonding method according to claim 6, wherein the bonding material is an adhesive, and the silicon nitride reaction sintered bodies for bonding are bonded to each other or to another material. 8 Silicon nitride reaction sintered bodies for bonding, where the bonding material is a metal or inorganic or organic compound that is melted or at least softened by heating, and the bonding method is casting, brazing, or thermal spraying, and a metal or inorganic compound. or a member made of an organic compound.