JPH08157275A - Method for joining silicon carbide sintered compacts to each other - Google Patents

Abstract

PURPOSE: To improve the strength, heat resistance and thermal shock resistance of a joined part by holding specified sheetlike carbon between silicon carbide sintered compacts contg. free silicon in at least one of them and heating them after pressing in a direction perpendicular to faces to be joined. CONSTITUTION: Sheetlike carbon having several ten to several hundred μm thickness and a bulk density of <=1.9 is held between silicon carbide sintered compacts contg. free silicon in at least one of them and they are fixed by pressing under >=1kg/cm<2> pressure in a direction perpendicular to faces of the sintered compacts to be joined. When silicon is fed from the outside at the time of heating, the sintered compacts are heated to a temp. above the melting temp. of free silicon or that of the fed silicon in a non-oxidizing atmosphere. When silicon is not fed from the outside, they are heated to a temp. above the melting temp. of free silicon in a nonoxidizing atmosphere. The sheetlike carbon is allowed to react with molten silicon to form silicon carbide contg. free silicon. At the same time, the carbon is allowed to react with silicon carbide in the faces of the sintered compacts to be joined and sintering is carried out.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining silicon carbide-based sintered bodies together.

[0003]

[0002]

[0004]

2. Description of the Related Art Among fine ceramics, a silicon carbide sintered body is generally excellent in high temperature strength, thermal conductivity, thermal shock resistance, etc., and is expected to be applied as a high temperature structural material.
For example, application development is underway for automobile turbines, heat exchangers, muffles for various heat treatment furnaces, and the like. In order to fully utilize the functions of the silicon carbide based sintered body for these various uses, it becomes necessary to join these sintered bodies together in the manufacturing process.

[0005]

A method for joining silicon carbide-based sintered bodies to each other is, for example, Japanese Patent Publication No. 58-6714 (hereinafter referred to as Conventional Example 1), US Pat. No. 2319323 (hereinafter referred to as Conventional Example 2), and US Pat.
No. 2907972 (hereinafter referred to as Conventional Example 3), Japanese Patent Publication No. 2-33670
(Hereinafter referred to as Conventional Example 4) and Japanese Examined Patent Publication No. 60-47229 (hereinafter referred to as Conventional Example 5).

[0006]

In the conventional example 1, metal powder silicon or silicon alloy powder is mixed with an organic binder, and the paste-like mixture is used to temporarily bond the sintered bodies together, and then heated to 1300 to 1550 ° C. to melt. It is a joining method of wearing.

[0007]

Conventional Example 2 is a putty made of a carbonizable binder such as carbon and casein, which is obtained by temporarily adhering sintered bodies to each other and then heating them to about 1800 ° C. or higher in the presence of silicon powder. By this method, silicon is infiltrated into the joint portion to convert the joint portion into silicon carbide, and at the same time, the joint state is brought into a state of coexistence with excess silicon.

[0008]

In the conventional examples 3 and 4, a thermosetting resin (for example, phenol resin) and an organic binder (for example, polyethylene glycol) capable of carbonizing silicon carbide powder and carbon powder such as graphite, pitch coke, charcoal, etc. ) In paste form and place at the joint and in the presence of silicon 15
It is a method of joining by causing the molten silicon or silicon vapor to react with the carbon component in the bonding layer by heating to 00 ° C. or higher to form a texture state in which silicon carbide and excess silicon coexist.

[0009]

In Conventional Example 5, silicon powder and a thermosetting resin capable of being carbonized (for example, phenol resin or furan resin) are mixed in a paste form, placed at a joint, and heated at about 1400 ° C. This is a method of forming silicon and joining in the presence of excess silicon.

[0010]

[0008]

[0011]

In the conventional example 1, since the joining is not performed by the reaction sintering method, the joining portion is composed of only the silicon layer. Therefore, various properties such as strength, heat resistance, and thermal shock resistance of the bonded portion are deteriorated as compared with those of the materials to be bonded.

[0012]

The conventional example 2 utilizes the reaction sintering method, but it is a method of arranging only the carbon component in the joint portion and infiltrating silicon to generate silicon carbide. In this case, it is arranged in the joint portion. The formed carbon is likely to be densified, silicon does not infiltrate into the carbon as expected, and unreacted carbon portion which is not silicified remains in the bonding layer, which causes deterioration of the characteristics of the bonding portion.

[0013]

In Conventional Examples 3 and 4, by adding silicon carbide particles to the bonding paste agent as compared with Conventional Example 2, the fluidity of molten silicon is improved and the reaction between carbon and silicon is promoted so that unreacted. Although carbon is prevented from remaining, if the particle size of silicon carbide, carbon, etc., the mixing ratio of various raw materials, the degree of mixing, etc. are not adjusted properly, silicon flow will be affected and it will be difficult to convert to silicon carbide. , And even if it could be compared,
This is a very time-consuming method and costly.

[0014]

The conventional example 5 is not a method of infiltrating silicon from the outside as in the conventional examples 2, 3 and 4, but a method of mixing with a bonding paste agent, and it is not necessary to consider the fluidity of silicon. After all, it is difficult to adjust the particle size of the silicon powder, the compounding ratio with the resin, the degree of mixing, etc., which is troublesome and costly, and if the bonding conditions are not well controlled as compared with the conventional examples 3 and 4, the bonding paste agent Even if the carbon components therein are silicified, it is difficult to obtain a state in which they are sintered together. Further, since molten silicon causes volume expansion when solidifying, there is a phenomenon that a semicircular silicon body called silicon bleeding appears on the surface. In this method in which silicon is mixed in the bonding paste agent, particularly heat treatment is performed. When joining muffles through which objects pass, silicon bleeding is likely to occur on the inner diameter side of the joined parts, and problems such as damage to heat-treated objects occur. In addition, a silicon layer is easily formed on the interface, which causes deterioration of the characteristics of the bonded portion.

[0015]

In the conventional examples 2, 3, 4 and 5, when a carbonizable organic substance such as a thermosetting resin is used as the bonding agent,
Work such as hardening treatment and carbonization treatment is required in the joining process, which is troublesome.

[0016]

In all of the conventional examples, when the bonding agent is used in the form of a paste, protrusion occurs when the bonding agent is sandwiched between the materials to be bonded, and if the wiping work is not performed, the protruding portion is also made of silicon carbide after bonding. Therefore, it becomes very difficult to remove. In addition, the amount of the bonding agent affects the bonding conditions, so it is necessary to supply a fixed amount, but if it is a paste agent, the amount of interposition between the materials to be bonded is difficult to adjust,
As a result, it causes variations in the performance of the bonded body, which causes a problem in terms of reliability.

[0017]

[0014]

[0018]

According to a first aspect of the present invention, there is provided a method of joining silicon carbide-based sintered bodies, at least one of which contains free silicon, wherein the bulk density (weight is defined as the volume of the solid portion). Sheet carbon of 1.9 or less (divided by the volume of open pores and volume of closed pores) is sandwiched between silicon carbide sintered bodies and perpendicular to the bonding surface of the silicon carbide sintered bodies. After pressing and fixing in different directions, when supplying silicon from the outside, heat it to the melting temperature of free silicon or silicon supplied from the outside or more, and if not supplying silicon from the outside, melt temperature of free silicon or more It is characterized in that the sheet-shaped carbon is reacted with the molten silicon to be converted into free silicon-containing silicon carbide by being heated to the above, and is also reacted and sintered with the silicon carbide on the joint surface of the silicon carbide sintered body.

[0019]

According to a second aspect of the present invention, there is provided a method of joining silicon carbide-based sintered bodies containing no free silicon, wherein sheet carbon having a bulk density of 1.9 or less is sandwiched between the silicon carbide-based sintered bodies. After pressing and fixing in a direction perpendicular to the bonding surface of the silicon-based sintered body, silicon is supplied from the outside and heated above the melting temperature of silicon to cause the sheet carbon to react with the molten silicon. It is characterized in that it is converted to silicon carbide containing free silicon and is reacted and sintered with silicon carbide on the joint surface of the silicon carbide based sintered body.

[0020]

Further, in the third aspect, the pressure is equal to or higher than the pressure at which the sheet-like carbon follows the joint surface of the silicon carbide sintered body,
Moreover, the bulk density of the sheet-like carbon that changes with pressure is 1.
It is characterized in that the pressure is 9 or less.

[0021]

In the present invention, the sheet carbon is
The bulk density is 1.9 or less, preferably 0.8 to 1.5, and when it is more than 1.5, the fluidity of silicon is deteriorated. Therefore, if the bonding time is not lengthened, unreacted carbon remains. If the bulk density exceeds 1.9, the unreacted carbon part may remain and cannot be used in most cases. Conversely, if less than 0.8,
Although bonding is possible, the proportion of free silicon inside the bonding layer increases and the bonding characteristics deteriorate. Also, the thickness of the sheet-like carbon is suitably several tens to several hundreds of μm, and may be selected according to the gap generated when the joining surfaces of the materials to be joined are butted against each other.
However, if the thickness is too thick, it takes time for silicon to penetrate into the interior, so that the bonding time must be lengthened. The sheet-like carbon is required to have elasticity and flexibility that imitate all the joining surfaces when the sheet-like carbon is sandwiched between the materials to be joined. Naturally, it is important that the pores of the carbon sheet are uniformly dispersed, and preferably the carbon is layered (mica-like) or fibrous or felt-like (cavernous). Is desirable. This influences the structure of the silicon carbide in the joint after joining and improves the joining characteristics. For example, a sheet obtained by press-molding expanded graphite powder by roll rolling has a mica shape. These sheet-like carbons are commercially available and can be purchased at low cost.

[0022]

During joining, the pressure applied in the direction perpendicular to the joining surface is not less than the pressure at which the sheet-like carbon follows the joining surface of the material to be joined, for example, in the case of commercially available sheet-like carbon, 1 kg / cm ² or more. Good. When it is less than that, a contact state between the sheet-like carbon and the material to be joined is deteriorated and a gap is generated, and even if joining is possible, a silicon layer is formed in the gap portion and the joining characteristic is deteriorated. Even if the applied pressure is too strong, the sheet-like carbon becomes dense and the bulk density of the sheet-like carbon after pressurization becomes larger than 1.9, which causes the flow of the silicon to be impeded at the time of joining and does not react with the joint. Because it may leave carbon
The pressure should be less than that. For example, commercially available sheet carbon may be used in an amount of 15 kg / cm ² or less.

[0023]

When at least one of the silicon carbide-based sintered bodies, which is the material to be joined, is silicon carbide containing free silicon, the free silicon in the material is joined without giving silicon to impregnate the sheet-like carbon from the outside. It can also be joined by moving it to the section. When silicon is provided, the state of the silicon may be molten silicon or silicon vapor. When joining the muffle for heat treatment, it is desirable to give silicon from the outer diameter side of the pipe.

[0024]

The atmosphere during bonding is preferably a non-oxidizing atmosphere such as nitrogen gas or argon gas. The bonding temperature may be the silicon melting temperature or higher, and is preferably 1400 ° C. or higher. The heating source is
It may be indirect heating such as heater or lamp heating, or may be direct heating such as electric heating or induction heating of the material. For joining long and large products, it is desirable to locally heat only the vicinity of the joint.

[0025]

[0021]

[0026]

By using the above-mentioned sheet-like carbon and applying a predetermined pressure at the time of joining, when heating and joining, the sheet-like carbon penetrates silicon, so that a dense silicon carbide is produced. The joint will be composed of strong free silicon-containing silicon carbide. In addition, since sheet carbon has good contact with the material to be joined, at the interface between the material to be joined and the joint, the sintering reaction between the silicon carbide of the material to be joined and the silicon carbide generated at the joint occurs, resulting in a strong bond. A smooth interface can be obtained. Therefore, the bonded portion has a structure similar to that of the material, and the characteristics of the bonded body are not so inferior to those of the material.

[0027]

[0022]

[0028]

【Example】

Example 1 φ20 / φ13 × 100 mm Pipe-shaped reaction-bonded silicon carbide containing free silicon (silicon content: 20% by weight or less)
The cross sections of the pipes were butted against each other, and a 200 mm joined body was produced. The sheet-like carbon was commercially available, and its bulk density and thickness were changed as shown in Table 1 to carry out the joining.
The pressure applied during joining was 3 kg / cm ² . The atmosphere was an argon gas atmosphere, and the heating means was induction heating for directly heating the silicon carbide material. The bonding temperature and the holding time thereof are as shown in Table 1. The evaluation of the zygote is
The strength of the thus-obtained bonded body was evaluated by bending it at three points with the lower span of 100 mm horizontally in the axial direction. Table 1 shows the results.

[0029]

[Table 1]

[0030]

From Table 1, it was found that good bonding strength (150 MPa or more) was obtained when the bulk density was 1.9 or less.

[0031]

In this embodiment, silicon contained in the silicon carbide sintered body is used. However, if the content of silicon is particularly small, silicon may be supplied from the outside during heating for bonding.

[0032]

<Example 2> The bulk density of the sheet-like carbon was 1.
0, the thickness is 200 μm, and the heating condition is the bonding temperature.
Bonding was carried out in the same manner as in Example 1 except that the pressure applied during bonding was changed at 1600 ° C. for 20 minutes and the strength was evaluated by three-point bending. The results are shown in Table 2.

[0033]

[Table 2]

[0034]

From Table 2, it was found that a good bonding strength (150 MPa or more) was obtained at 1 to 15 kg / cm ² , and the strength was lowered by the pressurization outside the range.

[0035]

<Embodiment 3> The material used is a reaction-sintered silicon carbide containing no free silicon, and the dimensions and the dimensions of the bonded body are the same as in Embodiment 1. Sheet carbon has bulk density
A film having a thickness of 1.0 and a thickness of 200 μm was used. In the case of joining silicon carbide materials that do not contain silicon, it is necessary to supply silicon from the outside at the time of heating for joining. In this example, silicon grains (about 1 g) were placed on the outer diameter side of the joint before heating, and the silicon carbide material was directly heated to 1400 ° C. or higher by both electric heating and induction heating to melt the molten silicon. Then, a means for permeating the joint was adopted. The heating conditions were a joining temperature of 1600 ° C and a holding time of 20 min. In addition, joining and evaluation were performed in the same manner as in Example 1. As a result, the joint strength was about 170 MPa, which was a good joint. By the way, similar results were obtained even when the silicon to be supplied was arranged on the inner diameter side.

[0036]

<Example 4> The kind and size of the silicon carbide material were the same as those in Example 1, and the sheet carbon was the same as that in Example 2, and the heating was performed in an atmosphere furnace. . The pressure applied during joining was 5 to 10 kg / cm ² . The atmosphere was a nitrogen gas or argon gas atmosphere. The heating conditions were a joining temperature of 1600 ° C and a holding time of 20 min. As a result of the strength evaluation, a strength of about 200 MPa was obtained regardless of the atmosphere.

[0037]

[0029]

[0038]

As described above, according to the invention described in claim 1, the sheet-like carbon is a high technology for preparing the bonding agent as compared with the powder agent and the powder pasting agent used in the prior art. It does not require any cost, and does not require work such as adjusting the coating amount at the time of joining or removing the agent when the agent is sandwiched between the materials to be joined. Further, by using this sheet-shaped carbon, the joining can be performed particularly effectively when the material joining surface is somewhat rough or has a large area.

[0039]

Further, in particular, according to the invention described in claim 2, even for a silicon carbide-based sintered body containing no free silicon,
Similar to the joining of free silicon-containing silicon carbide, a good joined body having a large joining strength can be obtained.

[0040]

More particularly, according to the invention described in claim 3, by appropriately adjusting the pressure applied at the time of bonding, the bonding layer portion can be made of silicon carbide having a dense free silicon-impregnated silicon carbide,
Moreover, since the sheet-like carbon closely follows the material joining surface,
Even at the bonding interface, dense free silicon-impregnated silicon carbide can be formed, and a strong bonded portion can be obtained.

Claims (3)

[Claims] 1. A method for joining silicon carbide-based sintered bodies, at least one of which contains free silicon, wherein sheet-like carbon having a bulk density of 1.9 or less is sandwiched between the silicon carbide-based sintered bodies. When silicon is supplied from the outside after pressing and fixing in a direction perpendicular to the bonding surface of the sintered material, the silicon is heated from above the melting temperature of the free silicon or the silicon supplied from the outside to remove the silicon from the outside. When not supplied, the sheet-shaped carbon is reacted with the molten silicon to form free silicon-containing silicon carbide by heating the free silicon to a temperature higher than the melting temperature of the free silicon, and carbonization of the bonding surface of the silicon carbide sintered body is performed. A method for joining silicon carbide-based sintered bodies to each other by reacting and sintering with silicon. 2. A method of joining silicon carbide-based sintered bodies containing no free silicon, wherein sheet-like carbon having a bulk density of 1.9 or less is sandwiched between the silicon carbide-based sintered bodies, and the silicon carbide-based sintered body is sintered. After pressing and fixing in a direction perpendicular to the joint surface of the united body, silicon is supplied from the outside and heated above the melting temperature of the silicon to cause the sheet carbon to react with the melted silicon and release. A method for joining silicon carbide-based sintered bodies to each other, wherein silicon carbide containing silicon carbide is formed and the silicon carbide-based sintered bodies are reacted and sintered with silicon carbide on the bonding surface. 3. The pressure is equal to or higher than the pressure at which the sheet-like carbon follows the joint surface of the silicon carbide sintered body, and the bulk density of the sheet-like carbon which changes due to the pressure is 1.9 or less. The method for joining silicon carbide-based sintered bodies according to claim 1 or 2, wherein the pressure is not more than the pressure.