JP2864927B2 - Joining method of silicon carbide member - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining silicon carbide members, and more particularly, to a method for joining a plurality of porous silicon carbide members formed from silicon carbide powder with a mortise and a mortise.
The present invention relates to a method for joining by impregnation of molten silicon.

[0002]

2. Description of the Related Art Silicon carbide has been increasingly used as various types of mechanical parts such as engine parts and plant parts as engineering ceramics having excellent high-temperature strength. However, silicon carbide compacts obtained by molding and sintering silicon carbide powder are difficult to process, as is common in ceramics in general, and when manufacturing parts having complicated shapes, a plurality of silicon carbide The members need to be joined.

[0003] With regard to this joining, a method of superposing a plurality of silicon carbide-based molded bodies (unsintered or calcined bodies) and impregnating with molten silicon in a non-oxidizing atmosphere to join them together,
This is proposed in Japanese Patent Application Laid-Open No. Sho 63-17268. However, depending on the properties of the molded body and the joint, the method of impregnation of the molten silicon, the molten silicon does not sufficiently penetrate the joint,
There was a problem that stable strength could not be obtained.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to stably achieve the joining of a plurality of porous silicon carbide members by a simple method with uniform and sufficient joining strength and no contamination of impurities. It is an object of the present invention to provide a bonding method for a silicon carbide-based member.

[0005]

According to the method for joining silicon carbide-based members of the present invention, a plurality of porous silicon carbide-based members are assembled by a mortise and a mortise provided at the joint, thereby forming molten silicon. A method of joining by impregnating from below, wherein each porous silicon carbide member has a porosity of 20 to 60 v.
ol%, the average pore diameter is 10 μm or less, the clearance k (mm) of the joint and the height h (m
m) satisfies the following equation.

[0006]

(Equation 1)

[0007]

The silicon carbide member used in the method of the present invention is a porous material having a porosity of 20 to 60 vol% and an average pore diameter of 10 μm or less. This porous silicon carbide-based member is obtained by mixing α-type or β-type silicon carbide powder with additives such as a sintering aid (eg, carbon), a binder, and a solvent, if necessary, and then casting and molding. Unsintered compacts obtained by forming by an appropriate method such as pressing and drying if necessary are further pre-fired in an inert atmosphere such as argon or helium.
Any of the calcined bodies (calcined) from which volatile components in the molded body are removed may be used.

The conditions of the pre-firing are not particularly limited as long as the calcined body having the above-mentioned porosity and average pore diameter is produced, but is usually at a temperature of 500 to 1500 ° C. for about 1 to 20 hours.
Since the calcined body has higher strength than the molded body, cutting for forming a tenon and a tenon hole becomes easy. In addition, since the oxygen content contained in the molded body is removed during the preforming, melting 3
There is also an advantage that the wettability by the molten silicon during the impregnation of the recon is good, and the joining becomes easier. However, the method of the present invention can be applied industrially to an unsintered molded body, and a bonding strength comparable to that of a calcined body can be obtained.

The silicon carbide-based member may contain a small amount (generally, 10% by weight or less) of free carbon in addition to silicon carbide. The free carbon reacts with the molten silicon to be impregnated later during sintering to form silicon carbide, and improves the strength of the obtained sintered body.

[0010] According to the joining method of the present invention, a mortise and a mortise are formed at the respective joints of the plurality of silicon carbide members to be joined, and the mortise is inserted into the mortise. Assemble the components. FIG. 1 shows an example in which, among the two silicon carbide members, a mortise is formed in member A and a mortise is formed in member B. These tenons and tenon holes can be formed by cutting. By assembling using a mortise and a mortise, a complicated shape such as a wafer boat can be easily formed.

The assembled silicon carbide-based member is then
While heating to a high temperature of 00 ° C or higher (usually 1450 to 1600 ° C), the lower part is immersed in a molten silicon liquid, and sintering is performed by impregnating the molten silicon entirely from the lower part. The whole silicon member is sintered. Due to the impregnation of the molten silicon, the molten silicon penetrates to the end of the porous silicon carbide member, and the sintering proceeds, and at the same time, the molten silicon uniformly penetrates to the joining portion to perform joining. Thereby, a high-strength bonded body can be obtained without requiring a complicated device such as a hot press or a high load. Further, since no brazing filler metal or the like is used, a high-purity bonded body composed of only silicon carbide and a small amount of silicon can be obtained.

The bonding may be performed in an atmosphere of an inert gas such as argon, but the bonding is preferably performed under reduced pressure since the impregnation of the molten silicon is improved. The impregnation time varies depending on conditions such as the size, composition, pore size and density, and calcining temperature of the molded body, but is suitably about 30 minutes to 20 hours. The rate of temperature rise may be appropriately adjusted according to the dimensions and thickness of the member.

In the present invention, the porosity and the average pore diameter of the silicon carbide-based member to be joined are optimized so that the molten silicon is surely and uniformly penetrated into the entire silicon carbide-based member by a capillary phenomenon, and the sintered body is sintered. I do. In addition, by optimizing the clearance and the impregnation height (the height of the joint from the liquid surface of the molten silicon) of the joint after assembling the silicon carbide-based member, the joint is filled with molten silicon without gaps. And sufficient bonding strength can be stably obtained.

The porosity of each silicon carbide member to be joined is 20 to
It should be within the range of 60 vol%. If the porosity is less than 20 vol%,
Since there are not enough continuous open pores, it is difficult to uniformly impregnate the entire member with molten silicon. On the other hand, the porosity is 60
Since the silicon carbide-based member exceeding vol% has insufficient strength itself and a large pore diameter, it becomes difficult to infiltrate the molten silicon by capillary action.

The average pore diameter of each silicon carbide-based member is 10 μm or less. If the average pore diameter exceeds 10 μm, the dispersion of the pore diameter increases, the impregnation of silicon becomes non-uniform, and the driving force for permeation due to the capillary phenomenon decreases.
Long products cannot be joined.

If the porosity and the average pore diameter of the silicon carbide-based member are not appropriate, the penetration and sintering of the molten silicon into the entire member cannot be performed sufficiently as described above. As a result, the filling of the molten silicon in the joint is insufficient or uneven, and the joining is not performed. However, even if the joining is possible, there is a defect, and the joining strength is greatly reduced.

The porosity and average pore diameter of the silicon carbide-based member are determined by the average particle diameter of the silicon carbide powder used for molding, the molding method, molding conditions (eg, molding pressure in the case of pressure molding), and calcination conditions ( It can be adjusted by changing conditions such as temperature, atmosphere, and time.

The driving force when the porous silicon is impregnated with the molten silicon is explained by the capillary phenomenon. The maximum rising height hmax of the liquid due to the capillary _action is expressed by the following equation.

[0019]

(Equation 2)

[0020] [rho: Liquid density, alpha: contact angle sigma: surface tension, r: the temperature at the capillary radius impregnation is constant, because the surface tension and specific gravity of the liquid is constant, the maximum rise height h _max Depends on the capillary radius and the contact angle.

When two porous silicon carbide members having a porosity of 20 to 60 vol% and an average pore diameter of 10 μm or less are combined and then impregnated with molten silicon, the maximum impregnation height h ′ of the molten silicon is h ′. It has become clear from the results of many experiments that _max is inversely proportional to the size of the clearance at the joint between the two members, and the relationship between the two is expressed by the following equation.

[0022]

(Equation 3)

H ' _max : Maximum impregnation height of molten silicon (mm) k: Clearance between two members at the joint (mm) Therefore, the above-mentioned equation (1)

[0024]

(Equation 1)

If the condition indicated by (h: height from the liquid level of the molten silicon at the junction) is satisfied, the junction is filled with the molten silicon without any gap. In other words, if the product of the height h (impregnation height) of the joint from the silicon liquid surface and the clearance k of the joint is 100 mm ² or less, the clearance is completely filled with the molten silicon. Conversely, if this product exceeds 100 mm ² , the molten silicon will not completely fill the clearance, leaving voids and reducing the strength of the joint, and in extreme cases, no joining will be performed.

For example, when the impregnation height is 100 mm, 1 mm
Clearances up to 0.2 mm for impregnation heights up to 500 mm. Even if the porous silicon carbide-based member is an unsintered molded body that is more difficult to process, it is easy to cut the mortise and mortise with this level of clearance. The method of the present invention has an impregnation height of about
It is preferably applied to members up to about 1000 mm.

[0027] Among the plurality of silicon carbide members to be joined,
The member that is not immersed in the molten silicon (the member B in the example shown in FIG. 1) is infiltrated with silicon through the joint. If it takes a long time to impregnate the silicon through the bonding portion with respect to this member, after the bonding portion is completely filled with the molten silicon, the member immersed in silicon may be changed and the reaction sintering may be continued. .

[0028]

【Example】

(Example 1) 80% by weight of α-type silicon carbide powder having an average particle size of 30 μm
Then, 10% by weight of a phenolic resin as a binder and 10% by weight of methanol as a solvent are added, kneaded, dried, and granulated.
CIP was applied under pressure of 1.5 TON / cm ² , and the obtained compact was pre-baked at 1500 ° C for 2 hours in an argon atmosphere to obtain a cylindrical shape of 15 mm diameter x 200 mm length and 50 x
Two calcined bodies having a plate shape of 50 × 10 mm were obtained.

As shown in FIG. 1, a ten mm diameter mortise is provided on the end face of the columnar calcined body, and a mortise hole having a size into which the mortise fits is provided at the center of the main plane of the plate-like calcined body. It was formed by cutting. A tenon was inserted into the tenon hole to assemble two calcined bodies, and impregnated with molten silicon at 1500 ° C. for 1 hour under reduced pressure. As a result, a bonded body in which the clearance was filled with silicon was obtained. Table 1 shows the porosity and average pore diameter of the joining member (calcined body), joining conditions (height of the joint from the silicon liquid level = impregnation height, joint clearance), and properties and bending strength of the joint. Shown in

(Comparative Example 1) The pressure molding was performed at a CIP pressure of 300 kg / cm ^2.
The molding, pre-firing, and joining were performed in the same manner as in Example 1 except that the joining was performed in Example 1. However, the joining portion was not filled with molten silicon, and the joining was not possible.

(Comparative Example 2) The joining condition was set to a clearance of 0.8 mm.
The molding, pre-firing, and joining were performed in the same manner as in Example 1 except that the silicon filling at the joint was uneven and defects were recognized.

Example 2 Using an α-type silicon carbide powder having an average particle size of 2 μm, molding, preliminary firing, and joining were performed in the same manner as in Example 1.

(Comparative Example 3) Molding, pre-baking and joining were performed in the same manner as in Example 2 except that the impregnation height was changed to 1000 mm by changing the length of the columnar calcined body. The portion was not filled with silicon, and joining was not possible.

(Example 3) In Example 1, molding and joining were performed in the same manner as in Example 1 except that the molded body was directly joined without performing pre-baking at 1500 ° C, and a joined body was obtained. Obtained.

The porosity and average pore diameter, bonding conditions, and bonding results of the bonding members (Example 3 is a molded body, and the other is a calcined body) in the above Examples 2-3 and Comparative Examples 1-3 are shown in Tables. 1 is also shown.

[0036]

[Table 1]

As can be seen from the results in Table 1, when the porosity and the average pore diameter of the silicon carbide-based member to be joined are not appropriate, the filling of the joint clearance with molten silicon becomes incomplete or uneven (Comparative Example 1). ). On the other hand, even if the porosity and the average pore diameter are appropriate, the product of clearance × impregnation height is 1000
If the formula (1) is no longer satisfied when the distance exceeds mm, the silicon filling of the joint clearance becomes uneven and the bonding strength decreases (Comparative Example 2). (Comparative Example 3).

[0038]

As described above, according to the method of the present invention, the porous silicon carbide members can be stably bonded with sufficient bonding strength without mixing impurities into the bonded portions. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic view of a bonding method according to the present invention.

Claims (1)

(57) [Claims] 1. A method of assembling a plurality of porous silicon carbide members with a mortise and a mortise provided at a joint thereof and joining the members by impregnating molten silicon from below. The porosity is 20-60 vol%,
The average pore diameter is 10 μm or less, and the clearance k at the joint is k
(mm) and height h (mm) of the joint from the molten silicon liquid level
Is related to A method for joining silicon carbide-based members, characterized in that: