JPH08337478A - Method for joining ceramics by superplastic diffusion - Google Patents

Abstract

PURPOSE: To enable joining ensuring strength close to that of materials to be joined at low temp. and pressure in a short time by vapordepositing an Si3 N4 - SiC composite material on a ceramic chip, superposing this chip on other ceramic chip and joining them under special conditions. CONSTITUTION: Amorphous powder of <=1μm average particle diameter contg. Si, C and N is press-compacted and fired to obtain an Si3 N4 /SiC composite material having 25-75vol.% SiC content. This composite material is vapor- deposited by CVD on the joining surface of at least one of ceramic chips 1 to be joined. The chips 1 are then superposed on each other, 5-30MPa pressure is applied in the directions of arrows and the chips 1 are joined by heating to 1,550-1,650 deg.C in a nonoxidizing atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to diffusion between silicon nitride (Si ₃ N ₄ ) and silicon carbide (SiC) ceramics using a Si ₃ N ₄ / SiC composite material utilizing superplastic diffusion bonding. Regarding the joining method.

[0002]

2. Description of the Related Art Silicon nitride (Si ₃ N ₄ ) based materials and silicon carbide (SiC) based materials exhibit excellent heat resistance and have a low coefficient of thermal expansion and thus excellent thermal shock resistance and wear resistance. It is known. Therefore, application to various high-strength heat-resistant parts has been attempted. Specific examples include gas turbine parts, engine parts, cutting tools, bearings, chemical plant members, semiconductor manufacturing members, electrical insulating materials, and various fillers for filling. Further, as one of application examples in engines of automobiles and the like, there is a rotor of a turbocharger (supercharger).

There are some problems in joining such silicon nitride or a material containing silicon nitride as a main component. For example, when joining such silicon nitride-based materials with each other by using an insert material such as a brazing filler metal or a metal foil, even if the strength at room temperature is relatively good, the strength at room temperature is high. There was a problem that the strength was inferior to that of the base material. Further, in the case of directly joining the silicon nitride material or the composite material thereof, there is a problem that good results cannot be obtained unless mirror-polishing, which requires cost and time, is performed on the joining surface.

In addition, for example, silicon nitride-based materials and silicon carbide (SiC) -based materials are covalently bonded crystals and have a very high creep resistance, so that they are joined by hot pressing, hot isostatic pressing, or the like. Requires a large press machine. Moreover, since the bonding strength of the interface is inferior, the bonding strength is lower than that of the base material. Further, a high joining temperature near the sintering temperature of the base material ceramics is required. Furthermore, when attempting to join different materials of the same series, a temperature near the sintering temperature of the ceramics as the base material is required for joining, so high residual stress occurs due to the difference in the coefficient of thermal expansion between these materials. However, there is also a problem that the bonding strength is reduced.

[0005]

SUMMARY OF THE INVENTION In view of the problems that occur when joining silicon nitride-based and silicon carbide-based materials as described above, an object of the present invention is to provide a bond having a strength close to that of the base metal. Another object of the present invention is to provide a method for joining silicon nitride-based and silicon carbide-based ceramics, which enables joining at a temperature and pressure lower than conventional ones and in a short time.

[0006]

In order to achieve the above object, in the present invention, a Si ₃ N ₄ / SiC composite material starting from an amorphous powder containing Si / C / N is high. Diffusion bonding is performed by utilizing the superplastic phenomenon indicated by temperature.

The present invention relates to a method for joining Si ₃ N ₄ system or SiC system or Si ₃ N ₄ / SiC system ceramics having a crystal grain size of 1 μm or less obtained by using amorphous powder, A Si ₃ N ₄ / SiC composite material having a particle size of 1 μm or less obtained by using an amorphous powder is used for at least one of the ceramics to be bonded or as an intermediate layer,
Provided is a superplastic diffusion bonding method between ceramics, which comprises performing bonding in a non-oxidizing atmosphere at a temperature of 1550 to 1650 ° C. and a pressure of 5 to 30 MPa.

Ceramics to be bonded in the present invention
Is Si₃N_FourSystem, SiC system, Si₃N_Four/ SiC composite
System ceramics. The average particle size of ceramics is
It is preferably about 1 μm or less, and the lower limit is particularly limited.
It is thought that it is not decided. If the average particle size is 1 μm or more
If so, the deformation resistance becomes high and superplastic deformation is hard to occur.
It becomes. In the case of ceramics that meet these conditions,
The average particle size of the starting material should be about 0.8 μm or less.
However, its manufacturing method is not particularly limited. Also the starting material
The range of the average particle size is preferably 0.2 to 0.6 μm.
It In general, the larger the particle size of the starting material, the more
The particle size of the mix becomes large, which is not preferable, and the start
If the particle size of the material is too small, the surface energy will increase
Then, aggregation of particles is likely to occur, which is not preferable.
These ceramics are essentially Si ₃N_FourOr S
In addition to iC or both, before firing
It contains additives such as known sintering aids to be added.
You may. Usually a ceramic with some impurity phase
Cus forms an amorphous phase at the grain boundaries,
The deformation resistance is small, which is preferable. Range of particle size after firing
Is usually about 1 to 5 μm.

The Si ₃ N ₄ / SiC composite material of the present invention, which is bonded to these ceramics, is made of Si,
A ceramic having an average particle size of about 1 μm or less, which is produced by using an amorphous powder containing C and N as a starting material. With the amorphous powder obtained by the CVD method, even if the particle size is small, a fine powder uniformly distributed can be obtained. The preferred range of particle size for this starting material is about 0.02-0.6 μm.
Is.

The reason why a two-phase mixed composite material is used instead of a single-phase substance is that grain growth during firing is suppressed and the aspect ratio of the grains is close to 1. The weight fraction of SiC in this ceramic may be generally in the range of 0 to 100% by weight, but about 25% by weight to 75% by weight in order to obtain excellent bondability in terms of bonding strength and bonding time. Volume% is desirable. Ceramics with SiC in the range of 25 to 75% by weight are excellent as a joining material because superplastic deformation occurs at low stress. If the SiC content is 25% by weight or less, it is difficult for the particles to become fine due to the particle dispersion effect of SiC, and the deformation resistance increases. In addition, the amount of SiC is 7
If it exceeds 5% by weight, the deformation resistance increases remarkably. Although it is possible to directly bond Si ₃ N ₄ and SiC, the bonding strength becomes about half due to residual stress caused by the difference in thermal expansion coefficient.

As a method for producing this Si ₃ N ₄ / SiC composite material, a known CVD method is suitable. A ceramic composite material is usually obtained by mixing powders having different compositions, press-molding them, and then firing them. At this time, if the particle size of the powder becomes small, the surface energy increases, and the powders of the same kind tend to agglomerate, and the fluidity decreases. As a result, a defect is generated inside the obtained sintered body, which easily becomes a source of destruction. Therefore, it is desirable to obtain a powder raw material in which the second phase particles are uniformly dispersed in the first layer particles without mixing different powders prepared separately. In the composite powder obtained by the CVD method, fine particles are uniformly dispersed, and a sintered body having no defects can be obtained. It is also advantageous that the composition can be freely changed by changing the gas flow rate.

The aspect ratio of the ceramic particles to be joined is preferably about 1 to 2, and most preferably close to 1. The closer the value is to 1, the more easily the grain boundary slip occurs, and the smaller the deformation resistance becomes, which is advantageous for superplastic bonding. The temperature at the time of joining is preferably 1550 to 1650 ° C, which is the superplasticity developing temperature range. At a temperature lower than 1550 ° C., the plastic deformation resistance of the material is high, and it is difficult to adhere to the bonding interface. At temperatures above 1650 ° C,
The strength deterioration due to the thermal decomposition of Si ₃ N ₄ becomes remarkable.

The atmosphere for heating the bonding is preferably a non-oxidizing atmosphere in order to prevent the oxidation of silicon nitride and silicon carbide. Nitrogen (N ₂ ) is used as the non-oxidizing atmosphere.
It is particularly preferable to fill the furnace with gas or argon (Ar) gas. The joining pressure is preferably 5 to 30 MPa. If it is 5 MPa or less, the adhesion of the bonding interface is insufficient, and if it is 30 MPa or more, problems such as creep deformation of the compression jig may occur. Further, a pressure of 30 MPa or more is usually required to sufficiently achieve the bonding according to the present invention.
Not necessary. This is because the bonding strength generally increases with the bonding pressure, but when it exceeds a certain value, it shows a constant value. (If a higher pressure is required, it is necessary to raise the bonding temperature.) Since bonding can be performed in such a pressure range, hot pressing, hot isostatic pressing (HIP)
However, a hand press or the like can be used.

It is sufficient to finish the ceramics surface to be bonded before the bonding is heated with a polishing material such as a diamond wheel of about # 200 or # 400. For example, time-consuming and costly finishing such as mirror finishing is unnecessary. Further, the above-mentioned CVD method can be used to deposit the Si ₃ N ₄ / SiC composite material as an amorphous film on the surface of the ceramic to be bonded. Ceramics are bonded with this amorphous film sandwiched,
By pressure sintering, ceramics of the same kind or different kinds can be joined to manufacture a component having a complicated shape. Further, by depositing a film having an intermediate composition by the CVD method, it becomes possible to firmly bond two ceramic pieces having considerably different compositions. Also,
According to the method of the present invention, not only two ceramic pieces can be joined but also three or more ceramic pieces can be overlapped and joined at one time. Furthermore, by laminating ceramic thin plates whose composition is changed stepwise or continuously,
It is possible to manufacture a functionally gradient material by simultaneously joining and integrating them.

[0015]

【Example】

(Example 1) As a material of the test piece, Si was 58 wt%, C was 7 wt%, and N was 33.
9% by weight, O less than 1% by weight, Fe, Al, Ca total less than 50 ppm, average particle size of about 0.3
6 wt% Y ₂ O ₃ and 2 wt% Al ₂ O ₃ were added as sintering aids to the Si ₃ N ₄ / SiC amorphous powder of μm, and hot pressing pressure was applied in N ₂ gas. 34 MPa, 1
It was sintered under the condition of 650 ° C. for 1 hour.
The obtained sintered body was cut with a diamond cutter to obtain # 4.
A diamond wheel No. 00 was used for surface grinding to prepare a joint surface. The surface roughness of the joint surface was Rmax <3 μm. The final dimensions of the test piece were 15 x 25 x 20 mm. The crystal grain size of the test piece was about 0.6 μm.

Two of the joining test pieces thus prepared were put together on the joining surfaces described above, and set on a SiC jig in a furnace attached to the universal material tester. After evacuating,
N ₂ was flowed to make the inside of the furnace an N ₂ atmosphere, and the temperature was raised to a joining temperature of 1600 ° C. The N ₂ atmosphere is used to prevent oxidation of the test piece. After the temperature inside the furnace was stabilized, the test piece was deformed by 10% with a joining pressure of 20 MPa,
After holding for 30 minutes, the furnace was cooled. The pressure was applied at this time in the manner shown in FIG. Two test pieces 1 were stacked, a SiC plate 2 was placed on the upper and lower sides thereof, and pressure was further applied by a SiC rod 3 in the direction of the arrow. The obtained sintered body was cut with a diamond cutter, surface-ground with a diamond wheel, and the bonding strength was evaluated by a bending test based on JIS1601. Crosshead speed is 0.5
It was mm / min. As a result, the bonding strength is 615.
MPa, and a strength of about 90% of the base material strength of 670 MPa was obtained.

(Embodiment 2) Even if the composition of two test pieces to be joined is different, Si is 58 in order to clarify that strong joining can be obtained by the diffusion joining method according to the present invention.
Wt%, C 7 wt%, N 33.9 wt% (Fig. 2
4) in (A), and two kinds of amorphous powders of 60% by weight of Si, 0% by weight of C, and 40% by weight of N (5 in FIG. 2A) are prepared and implemented. Two test pieces were prepared in the same manner as in Example 1. The joining test pieces were joined together under the same conditions as in Example 1 by bringing the surfaces ground by a # 400 diamond wheel into pieces. The obtained bonding strength shows 580 MPa, which is about 8 of the base metal strength of 670 MPa.
A strength of 7% was obtained. FIG. 2B shows a case where composite material pieces 6 having different compositions are further stacked and three test pieces are joined.

(Example 3) Si for bonding by the CVD method
A C / Si ₃ N ₄ film was formed and two test pieces were joined. The composition of the first test piece was Si ₃ N ₄ and the second test piece was SiC. Hexamethyldisilazane was reacted in an atmosphere of N ₂ + NH ₃ at 1000 ° C., and heat-treated in N ₂ at 1350 ° C. for 6 hours. An amorphous vapor deposition film having a thickness was formed. Here, the surface grinding of the joint surface as in Examples 1 and 2 is not particularly necessary. The composition of the deposited film was Si 62% by weight, N 31% by weight, C 6.7% by weight, and the amorphous grain size was about 0.4 μm. After that, align the second test piece with this evaporated film,
Diffusion bonding was performed under the same conditions as in Example 1. The obtained bonding strength shows 520 MPa, which is about 7 times the base metal strength.
A strength of 8% was obtained.

(Embodiment 4) According to the joining technique according to the present invention, ceramic thin plates having an average grain size of 1 μm or less, the composition of which is changed stepwise or continuously, are laminated and simultaneously joined and integrated. By doing so, a functionally graded material can be manufactured. A plurality of thin plates of SiC / Si ₃ N ₄ composite material having different compositions after grinding with a # 400 diamond wheel were laminated in the order of composition between the SiC piece and the Si ₃ N ₄ piece, and the joining temperature was 1600 ° C. in N ₂ . Bonding pressure 18M
Bonding was performed under the conditions of Pa and a deformation amount of 15%. The composition is shown in FIG. The interface between the materials was completely adhered by superplastic deformation.

[0020]

As described in detail above, according to the present invention, a bonding strength close to that of the base material can be obtained at a relatively low temperature and pressure for a short time. The bonding strength is high not only at room temperature but also at high temperature. It is also possible to perform molding at the same time as joining. Furthermore, it is not necessary to mirror-finish the joint surface before joining, and sufficient joining strength can be obtained even if joining is performed with a relatively simple surface finish. Therefore, the method of the present invention can also be used for joining a turbo rotor and its shaft portion that are subjected to severe conditions both in terms of temperature and stress.

[Brief description of drawings]

FIG. 1 is a view for explaining the procedure of a ceramics joining method according to the present invention.

FIG. 2 shows the method of the present invention for Si₃N_FourSystem or SiC system
Si for ceramics₃N _Four/ SiC composite material
When joining to ceramics of (A) and (B)
And show it.

FIG. 3 shows an example in which the method of the present invention is applied to the production of a Si ₃ N ₄ —SiC functionally gradient material.

[Explanation of symbols]

 1 Test piece 2 SiC plate 3 SiC rod

Claims (3)

[Claims] 1. Si ₃ N ₄ system or SiC system or Si
A ₃ N ₄ / bonding method between SiC-based ceramics, the ceramics pieces with an average particle diameter of the Si ₃ N ₄ / SiC composite material obtained using the following amorphous powder 1 [mu] m, bonded A superplastic diffusion bonding method between ceramics, which is used for at least one of the ceramic pieces and is bonded in a temperature of 1550 to 1650 ° C., a pressure of 5 to 30 MPa, and a non-oxidizing atmosphere. 2. Si ₃ N ₄ system or SiC system or Si
_A method for joining ₃ N ₄ / SiC-based ceramics, which is obtained by using amorphous powder and has a particle size of 1 μm or less.
After depositing the i ₃ N ₄ / SiC-based composite material on at least one bonding surface of the ceramic pieces to be bonded by the CVD method and stacking it on the other ceramic piece, 1550 to 16
A superplastic diffusion bonding method between ceramics, which comprises performing bonding in a non-oxidizing atmosphere at a temperature of 50 ° C. and a pressure of 5 to 30 MPa. 3. The superplastic diffusion bonding method between ceramics according to claim 1, wherein the ceramic pieces to be bonded have different compositions.