JPS6027664A - Method of joining ceramics and different materials - 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] Regarding the law.

High-temperature parts for vehicles, ships, aircraft, gas turbines, turbochargers, diesel engines, Stirling engines, etc. for power generation, and high-temperature presses for nuclear power, coal, metal manufacturing, ceramics, etc. As corrosion-resistant and wear-resistant mechanical elements such as heat exchangers, high-temperature structural materials, and rollers, valves, and bearings for industrial machinery, it has better heat and corrosion resistance than metals.
If it is possible to use ceramics that are excellent in terms of wear resistance, high temperature strength, light weight, dimensional stability, etc., the function or performance can be greatly improved.

Ceramics in particular are rich in resources and are worthy of attention from the viewpoint of raw material resources. Therefore, in order to use ceramics as the various mechanical parts mentioned above, a technique for joining ceramics and dissimilar materials such as metals is required.

Conventionally, there are the following methods for joining ceramics such as silicon nitride, silicon carbide, zirconia, and alumina with other materials having different coefficients of thermal expansion, particularly metals, and each method has the following drawbacks.

(1) Mechanical fitting Ceramic parts (c) 'r fitted into grooves (b) of metal parts (cL) as shown in Figure 1, or metal parts (,z) as shown in Figure 2. In mechanical fitting such as mating, the ceramic part (C) has a male thread (g) on the female thread (d) engraved on the ceramic part (C).
Since it is susceptible to local stress concentration, it is necessary to make the fit loose and to insert a cushioning material into the gap, making it impossible to obtain a strong joint with high dimensional accuracy.

(11) Shrink fit or cold fit As shown in Figure 3, the metal parts (α
) is heated to fit the ceramic part (c), and the metal part (a) is cooled and shrinks to join or the ceramic part that will be the inside of the fit <c)'tt. , ) and are joined by expansion when the ceramic part (1) returns to room temperature. However, if this is used at high temperatures, the bonding strength will be lost because the thermal expansion of the outer metal is greater.

(iii) Adhesive method As shown in Figure 4, the ceramic part (1) and the metal part (α) are bonded using an organic adhesive such as a thermosetting resin, an inorganic adhesive such as cement, or a brazing alloy. There are adhesives such as metal adhesives that join by force. However, when used at high temperatures, the adhesive (force) loses adhesive strength or the difference in coefficient of thermal expansion between different materials causes the joint to fail. Easy to peel off.

(1v) Direct bonding method There is a method in which the bonding surfaces of ceramics and dissimilar materials are brought into direct contact at high temperature to cause a chemical reaction and bonding. but,
In this case, if the temperature of the bonded portion is changed, the bonded portion is likely to be destroyed due to the difference in coefficient of thermal expansion.

The present invention was made with the aim of eliminating the drawbacks of conventional bonding methods, and is intended to utilize ceramics, which have excellent mechanical properties, corrosion resistance, and wear resistance, and are expected to have great potential as various mechanical parts. By joining ceramics or metals with different coefficients of thermal expansion to ceramics or metals with a ceramic intermediate layer whose coefficient of thermal expansion changes sequentially,
The bond between ceramics and dissimilar materials is to have the same level of strength and rigidity as the base material, and to prevent thermal strain that could lead to destruction from occurring in the bonded area even with temperature fluctuations. Used as mechanical parts such as turbine moving blades, stationary blades and bulkhead plates, turbocharger impellers and bearings, diesel engine piston heads and exhaust valves, hydraulic or water pressure equipment valves, heat exchanger heat transfer tubes, etc. can,
It can be used under high loads and varying temperatures, has improved thermal efficiency compared to conventional metal-only machines, has improved fuel consumption, can operate in harsher conditions, and is highly reliable. The present invention relates to a method for joining ceramics and dissimilar materials, which can achieve long life and the like.

That is, the present invention interposes a small (at least one) intermediate layer between ceramics and ceramics or metals having a different coefficient of thermal expansion (hereinafter referred to as different materials), and joins them by heating with a presser. It is characterized by

Here, the ceramics to be bonded include silicon nitride (843N4), silicon carbide (SiC), and zirconia (
The main components are ZrOz), alumina (Atz03), etc.
If necessary, a material containing a sintering accelerator, a solid solution forming agent, a reinforcing agent, etc. can be used.

The number of intermediate layers between the ceramic and the dissimilar material is
A single layer is required, and generally multiple layers are used. This is necessary to suppress thermal strain that may occur in the joint due to the difference in coefficient of thermal expansion to below an allowable limit.

For example, as shown in FIG. 5, the intermediate layer (C) is formed from the ceramic FA) side to the dissimilar material (B) side as n layers, that is, C1, . . . , Ct, Cj+i, . . .・・・
, C? When L, the thermal expansion coefficient of each intermediate layer (q is ceramic (A).

CI+..., C? L and the dissimilar material (B) are made to increase or decrease in this order, and the difference in thermal expansion coefficient between adjacent layers is kept within a certain limit. It is desirable that the number of intermediate layers be small, but it is necessary to provide as many intermediate layers as necessary to suppress the difference in thermal expansion coefficient between layers within the allowable limit of thermal distortion. , the joints of each layer are heated to a strong temperature of 'r°C, but when cooled from this joining temperature T°C to room temperature, the total thermal strain that occurs between each layer is 02%.
The following conditions are necessary for forming a highly reliable bond against temperature changes. However, this is based on the assumption that the lowest operating temperature of the joint is room temperature, but the above conditions are approximately sufficient even when considering the use at even lower temperatures.

Therefore, if the difference between room temperature and 0°C is ignored, the nine adjacent layers A-Cz -, C6-C1++, -=, Cn-B, respectively.
, the difference in average thermal expansion coefficient from 0°C to junction temperature T'C is expressed as Δα(A-c, ), . . . , Δα(Ci −Ci
-h )',..., Δα(Cn-B), then thermal strain Δα("+) 'T+"' +Δα(Ci-C
j-h) T, -, Δα(c, 1-113), T is 0 respectively
．． The composition of each intermediate layer (q) is selected so that it is 2% (2X10-3) or less. If the thermal strain between each layer exceeds the coefficient 02, cracking may occur at the joint during cooling to room temperature after joining. Or, when temperature changes or loads are applied under usage conditions, cracking or destruction is likely to occur at or near the joint, making it unusable as a mechanical component.

Next, the selection of the material for the intermediate layer (C) will be explained.

It has a coefficient of thermal expansion intermediate between that of the above-mentioned (the material of the intermediate layer (q must have a predetermined thermal expansion characteristic, so such a ceramic is included) and a different material <B), If there is a material that also has a suitable bonding temperature, use it. Since it is generally difficult to obtain such a material as an existing material, in that case, the following method is taken to obtain the intermediate layer material.

Two materials with different coefficients of thermal expansion, namely ceramics (A
The intermediate layer (C) having a thermal expansion coefficient of an arbitrary value between ) and dissimilar materials) is made of the above two materials (~(B) or two or more materials having similar thermal expansion coefficients to each of them). For example, in the case of silicon nitride, a silicon nitride solid solution such as Sialon can be used as a similar material.
In the case of silicon carbide, metallic silicon can likewise be used.

Next, a method for forming the intermediate layer (q) will be explained.

By directly using the ceramic (A) and the dissimilar material (B) to be joined, or by using two or more materials having similar coefficients of thermal expansion to both (A) and (B), By decreasing or increasing the amount from the ceramic (A) side to the dissimilar material (B) side in the intermediate layers C1, ..., Cn, each intermediate layer is adjusted so that the thermal strain between each layer is 0.2% or less. (Select the coefficient of thermal expansion of q.

Here, when the ceramic (A) is silicon nitride or silicon carbide, the temperature required for sintering the dissimilar material (B) is higher than that of a metal, so simply -
When A) and a different material (B) are mixed and their composition ratios are changed, the optimum sintering temperature may differ for each intermediate layer (q), and at a temperature below the melting temperature of the different material (B). Even with pressure heating, sufficient bonding strength may not be obtained.

In such a case, in addition to the ceramic (A), a material such as silicate glass having a melting temperature lower than the melting temperature or decomposition temperature of either the ceramic (A) or the different material (B) may be mixed. By doing so, the sintering temperature of the ceramics (A) is lowered, and each intermediate layer (q sintering,
The bonding temperature can be brought close to each other, and the bonding strength can be increased.

Each intermediate layer (q may be formed by sequentially sintering and joining from the ceramic (A) side or a different material (cut side), or each intermediate layer C1,...,Cnf may be formed sequentially first, and then Ceramics (A) and dissimilar materials (B) are heated at a temperature lower than the melting temperature or decomposition temperature of (misalignment) to cause sintering of each intermediate layer and bonding between each layer (Δ) (C1 (B)). You may let them.

In this case, it is not always possible to form a bond with a sufficiently high strength by heating without applying pressure.
It is necessary to heat while applying a pressure of at least K9 f/ca or higher. As a pressurizing method, a pressure difference between atmospheric pressure and a vacuum can be used simply, but it is preferable to use a hot press or a hot isostatic press. In order to form a highly reliable bond, the higher the pressure, the better; however, for industrial practicality, the maximum pressure that can be used with the hot press or hot isostatic press is approximately 5000 kg//C+4. it is conceivable that.

Methods for forming the bonding intermediate layer before heating and pressurizing include forming a powder layer by applying or spraying a slurry in which powder is dispersed in an aqueous or organic solvent, and plasma spraying. Alternatively, there is a method of forming a semi-sintered powder layer by flame spraying, a method of forming a dense film by a PVD method such as sputtering, and the like.

Next, an example in which two types of ceramics having different coefficients of thermal expansion are joined by the joining method of the present invention and an example in which they are simply joined will be compared and explained.

As two types of ceramics, a silicon nitride sintered body containing 5% by weight of cerium oxide and 3% by weight of aluminum oxide, and a sintered silicon carbide body containing 1.5% by weight of boron carbide and 5% by weight of carbon were used, respectively. Next, after polishing the contact surfaces of the disc-shaped products, they are brought into direct contact and heated in a vacuum hot press.
Bonding was attempted at 800°C and a pressure of 2ooKgl/lri. However, this method was not successful in joining the two types of ceramics because no intermediate gold film was deposited between the joint surfaces.

The reason for this is that the thermal expansion coefficient of the silicon nitride sintered body is 3.5Xb, and the thermal expansion coefficient of the silicon nitride body is 5.0X10-6℃-1.
When joining is attempted at 1800° C. and then cooled to room temperature, the thermal strain at the interface is approximately 0.6%.

On the other hand, 40% by weight of silicon nitride and 40% by weight of silicon carbide
Weight: 10% by weight of cerium oxide, 1% by weight of aluminum oxide
A mixed powder consisting of 0% by weight is applied as a slurry onto the polished surface of the silicon carbide sintered body, and the silicon nitride sintered body is stacked so as to sandwich the coated layer, and hot pressing is performed under the same conditions as above. This made it possible to form a strong bond.

When the intermediate layer made of silicon nitride, silicon carbide, etc. is made into a sintered body, the thermal expansion coefficient is 4.4X1.
0-6°C-1, and based on the value of the expansion coefficient, the difference in thermal expansion coefficient between adjacent layers of the joined body is 0.9X10-6 between the silicon nitride sintered body and the intermediate layer. C.-1, and the thickness between the intermediate layer and silicon carbide is 6X10-6 C.-1.

When the sintered body was cooled from 1800° C. to room temperature, the thermal strain was 0.16% for the former and 0.16% for the latter, and the thermal strain between each layer was well below 0.2% in both cases.

In this way, one or more intermediate layers (q) are provided between the ceramic (A) and the dissimilar material (I3), and the thermal strain between each layer is suppressed to 0.2% or less from the bonding temperature to room temperature. Furthermore, since the intermediate bonding layer is formed in advance as an intermediate layer and heated under pressure to densify and form the bond, it has swing strength and rigidity comparable to those of the base material.

As described above, according to the method of joining ceramics and dissimilar materials of the present invention, (I) Since the ceramics and dissimilar materials are joined with at least one intermediate layer interposed between them,
It is possible to join dissimilar materials, especially metals, with different coefficients of thermal expansion. The operating temperature can be changed from low temperatures to high temperatures below the bonding temperature. (III) Therefore, parts made by bonding ceramics and dissimilar materials can be manufactured, so they can be used even under severe operating conditions such as high temperatures, corrosion, and wear. Improving the performance of machines by using ceramics for only parts and metal for other parts.
It exhibits various excellent effects such as high reliability and long life.

EXAMPLES Below, examples of the present invention will be listed and more specifically explained, but the present invention is not limited to these examples in any way.

Example 1 A cylindrical product of silicon nitride sintered body containing 10% by weight of aluminum oxide and 5% by weight of aluminum nitride is used as a ceramic, and a nickel-based alloy containing 165% by weight of chromium, 15% by weight of molybdenum, 5% by weight of iron, etc. Using cylindrical products of the same diameter of Hastelloy C as different materials, the end faces of each were polished, and a powder mixture of each component of the six types of intermediate layers shown in Table 1 below was dispersed as a slurry in ethanol. An intermediate layer was formed by sequentially spraying /I61 to /166 on the end face of the sintered body, and Hastelloy C cylinders were layered so as to sandwich the intermediate layer, and heated at 1250°C in a vacuum.
A strong bond could be formed by hot pressing at 100 Kgf/cd.

Table 1 (The content of each component is weight%) The coefficient of thermal expansion of the silicon nitride sintered body is 3.5X10-6℃-1
The coefficient of thermal expansion of Hastelloy C is 13×10 −6° C. −1, so if they are bonded as is, the thermal strain generated between the bonding surfaces will be extremely large, making it impossible to bond. .

However, as mentioned above (6 intermediate layers e 1. Si3 N
41A/L203, by sequentially decreasing the amount of MyO and increasing the amount of Ni accordingly, the coefficient of thermal expansion of each intermediate layer was increased sequentially, and silicic acid was added to the intermediate layer containing a large amount of 5isNa f at a high sintering temperature. By adding a proportionate amount of glass, the sintering temperature was lowered to below the melting point of Hastelloy C, making the thermal strain between each layer about 0.15% on average.
Since the bonding temperature was kept below 2%, no cracks or the like occurred in the bonded portion even when the bonding temperature was cooled to room temperature. That is, the decomposition temperature of silicon nitride is 1900°C, the melting point of Hastelloy C is 1570°C, and 5j3N4K Atz03tM
yOk The sintering temperature of the mixed powder system is 1500°C or higher, but by mixing according to the amount of low melting point silicate glass powder 'ksi3N+, it can be sintered at 1250°C. The middle layer of the layer at a single temperature of 125
This made it possible to sinter and bond at 0°C.

Comparative Example 1-1 Using the same ceramics (silicon nitride sintered cylindrical product) and different materials (steroy C cylindrical product) as in Example 1, three types of compositions shown in Table 2 below were prepared. An intermediate layer was formed in the same manner as in Example 1, and a silicon nitride cylinder and a steroid C cylinder sandwiching the intermediate layer were hot pressed in the same manner as in Example 1.

Table 2 When hot-pressed and then cooled to room temperature, cracks were observed in the bonded intermediate layer and a sufficient bond could not be formed. The reason for this is that the number of intermediate layers was too small and the average thermal strain between each layer was about 0.6%, which exceeded 0.2%.

Comparative Example 1-2 Using the same ceramics (cylindrical product of silicon nitride sintered body) and different materials (cylindrical product of Hastelloy C) as in Example 1, six types of intermediate layers with the compositions shown in Table 5 below were prepared. Example 1
A silicon nitride cylinder and a Hastelloy C cylinder sandwiching the intermediate layer were formed by the same method as above and heated at 1250°C and 100K.
Hot press under gf/cni conditions.

Table 3 (Content of each component is weight%) Although hot pressing was performed, the intermediate layer, especially the layer closer to the silicon nitride sintered body, was insufficiently sintered, making it difficult to form a sufficient bond. could not.

The reason for this is that the sintering temperature of the intermediate layer closer to the silicon sintered body is higher than 1250° C. since it does not contain silicate glass with a low melting point.

Example 2 Using the same ceramics (silicon nitride sintered cylindrical product) and different materials (Hastelloy C cylindrical product) as in Example 1, six types of intermediate layers with the compositions shown in Table 1 were created. Example 1
A silicon nitride sintered body cylinder and a Hastelloy C cylinder are sandwiched between the intermediate layer and vacuum sealed in a Pyrex glass tube while being in contact with each other, and then introduced into a furnace. Bonding was attempted under a condition where the temperature was raised to 11,250° C. and a pressure difference f 1 Kg f /ca between the air in the furnace and the vacuum was applied. After cooling, the glass container was broken and the bonded body was taken out and tested, and it was confirmed that a sufficient bond had been formed between the silicon nitride and the steroid C.

The intermediate layer formed in the same manner as in Example 2 was sandwiched between a silicon nitride sintered body cylinder and a Hastelloy C cylinder, and these were held in a state where they were merely in contact with each other, and the intermediate layer was heated without being sealed in a glass tube.
When heated to 1250° C. in an argon atmosphere at atmospheric pressure, a dense bond at the bonded portion could not be obtained after cooling. Pressure of 1 atmosphere or more is required to form a strong bond.

Example 6 As shown in Fig. 6, a diesel engine exhaust valve (1
The tip part (2) of ) is manufactured from zirconia ceramics consisting of a sintered body of partially stabilized zirconia containing 3% by weight of yttrium oxide and a metastable crystal phase of tetragonal crystal. A
A metal part (3) made of a nickel-based alloy containing 195% by weight of nichrome, 2.5% by weight of titanium, 1.5% of aluminum, etc.) was joined as follows.
4) shows the bonding intermediate layer, and (5) shows the metal shaft.

The back side of the zirconia ceramic tip part (2) was ground flat and three intermediate layers having the compositions shown in Table 4 below were sequentially formed by plasma spraying.

(The content of each component is % by weight) In addition, an alloy N consisting of Nj-Cγ-At-Y was formed as a fourth intermediate layer on the end face of the metal part (3) to be joined by plasma spraying. I let it happen.

After that, zirconia ceramic valve tip part (2)
and metal parts (3) in vacuum at 1200°C and 100K.
Multi-junctions could be formed by hot pressing at yf/ca.

The difference in thermal expansion coefficient between zirconia ceramics and stainless steel is approximately 3X10-6℃-1, but by forming an intermediate layer with sequentially varying thermal expansion coefficients, the total thermal strain when cooled to room temperature after bonding is reduced. Between each layer, each layer is 0.1%,
Since it was possible to suppress the amount to 0.2% or less, it became possible to form a strong bond.

In this way, the zirconia ceramic tip part (
After forming a bond between the metal part (3) and the metal part (3), the metal part (3) and the metal shaft (5) made of the same material are further bonded by diffusion bonding in a vacuum hot press, and the diesel engine An exhaust valve (1) was manufactured.

Example 4 As shown in FIG. 7, a turbine disk (ceramics made of a silicon nitride sintered body containing 5% by weight of aluminum oxide, 3% by weight of aluminum nitride, and 10% by weight of zirconium oxide) with an outer diameter of about 70 mm It was manufactured in the shape of a disc, and was joined to a shaft (7) made of nickel-chromium-molybdenum steel as described below.

First, a turbine disk (6) made of silicon nitride sintered body
After polishing the central shaft portion of the sample, six intermediate layers having the same composition as shown in Table 1 were successively formed on the polished surface. From Su1,
5% by weight organic binder in isopropyl alcohol and 0
．． Mixed powders of each of the above compositions were mixed in a solution containing 2% by weight of a deflocculant to create a slurry, and the mixture was sequentially sprayed with a spray gun to form an intermediate layer (
8) was formed.

The disk (6) on which the intermediate layer was formed was gradually heated to 400° C. in a nitrogen atmosphere to remove the solvent and the like, and then joined to the metal shaft (force) by hot pressing.

For joining, a graphite pedestal (9) having a recess that matches the profile of one side of the ceramic turbine disk (6) as shown in Fig. 7 is manufactured, and the pedestal (9) and the turbine are connected together.・In the gap between the disks (6), a boron nitride powder layer with a thickness of approximately 2 m is provided as a buffer layer αq, and on top of that, the metal shaft (7) is sufficiently aligned with the central axis of the turbine disk (6). It was fixed to the plunger of a hot press while being matched. The atmosphere of the hot press is high purity argon.
After raising the temperature to 1200° C., a pressure of 70 kg//lrA was applied to perform bonding. After cooling to room temperature, the disk shaft assembly was taken out and inspected. No defects were found in the broken joint, and a rotation test using a spin tester revealed that the number of rotations was i oooooo γ, pom.

It has been confirmed that it can withstand up to 100% without being destroyed.

[Brief explanation of drawings]

Figures 1 to 4 are diagrams showing conventional methods of joining ceramics and metal. Figure 1 is mechanical fitting, Figure 2 is mechanical threading, and Figure 5 is shrink fit/cold fitting. Joining by tightening, 4th
5 is an enlarged schematic diagram of the joining method of the present invention, FIG. 6 is a diagram showing an exhaust valve of a diesel engine by the joining method of the present invention, and FIG. 7 is a diagram showing the joining method of the present invention. It is a figure which shows the turbine disk by the joining method. (A) is ceramics, (B) is different material, (C) is intermediate layer, (2) is tip part, (3) is metal part, (4) is bonded intermediate layer, (6) is turbine disk, ( The force is the axis, (
8) indicates the middle layer. Patent applicant Ishikawajima Harima Heavy Industries Co., Ltd.

Claims (1)

[Claims] 1) A method of bonding ceramics and dissimilar materials characterized by interposing a small (at least one) intermediate layer between the ceramic and the ceramic or metal having a different coefficient of thermal expansion, and joining by heating with a presser. Joining method.