DE4430779A1 - Diffusion bonding two workpieces - Google Patents

Abstract

Two workpieces are diffusion bonded together by placing a superplastic material between them, heating to a temperature which is sufficient to cause diffusion bonding, applying a pressure perpendicular to the workpiece surfaces and maintaining the pressure and temperature for a time sufficient to bring about the bonding.

Description

The invention relates to a method for diffusion bonding, d. H. to produce a diffusion connection at low according to pressure.

Diffusion bonding is a special connection technology that the principle of solid diffusion and grain boundary migration Applies to keep materials under heating and application of pressure at a temperature below the melting point of the Materials are connected to each other. That used The principle is similar to that of sintering processes, but will when sintering two powders mixed together, while when Diffusion bonding physical materials metallurgically with be connected to each other. Both diffusion bonding and Sintering is carried out completely in the solid state, d. that is, no melting occurs in the joining process.

When the diffusion bonding technique for joining metals when applied, she can overcome difficulties as she does occur in conventional welding and brazing, such as Er heat cracks during welding, knife cut corrosion and Residual stress, and it also creates a solution for difficulties problems related to the connection of fine ceramic materials lien. It is known that since ceramics have high melting points and are brittle, most conventional ones Welding techniques not for joining ceramic materials can be used with each other or with other substances nen. Since diffusion bonding occurs at a temperature below the Melting point of the materials to be joined becomes, here the difficulties mentioned above to be overcome. It also forms diffusion bonding also with other advanced construction materials, which are difficult to weld, such as intermetallic ver bonds, metal-based materials, complex materia Ceramic-based and refractory superalloys an effective way of connecting to each other and with other materials.

The diffusion bonding technique requires expensive equipment and long execution times, which is why the costs are higher than with conventional welding techniques are if only a small one Number of workpieces must be connected. But when a large number of workpieces are connected, diffusion bonding has the advantages of reducing costs, because joining a large number of workpieces is the same can be carried out in good time.

The process of diffusion bonding includes the application of Print perpendicular to the surface of the diffusion bonding workpieces to be joined, generally a pressure from Z. About 70 x 103 hPa (1000 psi) or even 700 × 10³ hPa is used. This means that during the Diffusion process consumes a lot of energy and is expensive Equipment for applying the pressure is required. About that addition, since the applied pressure is perpendicular to the upper area of the work to be connected by diffusion bonding must stand piece-wise, d. i.e., because uniaxial tension is applied must be, if the workpiece is a complex or has irregular shape, it z. B. a wing for a High-temperature turbine is not carried out, diffusion bonding is not carried out because in such cases the pressure is not high enough can be exercised at right angles to the joint surface.

Furthermore, it requires diffusion bonding that the connection surfaces of the workpieces are as smooth as possible in order for a large contact area to ensure mutual Diffusion of elements and the establishment of an atom-atom To facilitate connection and thus the connection effect to reinforce. So that a smooth connection surface is obtained is, in particular, a surface finishing of the Workpieces required before diffusion bonding, leading to Additional procedures or steps required, the uptime extended and thus the costs increased.

The above difficulties become severe gender, if the diffusion bonding technique is used to connect kera mixer components is used. Because of their fragility possibility at elevated temperature break the to be connected Components at high temperature and high pressure, as they are generally used in diffusion bonding the, easy. In addition, ceramic components have there Ceramics cannot be easily machined, generally have a complex form and are therefore used to connect not suitable for diffusion bonding. Furthermore it is more difficult with ceramic components than with metal materials to obtain a smooth connection surface. Accordingly, diffusion bonding has proven to be suitable in the laboratory net for joining ceramic components, however the technology is not yet mature enough for practical use Application in industry.

The invention is based on the object of a method for Specify diffusion bonding that occurs at low pressure can be used to thereby reduce energy consumption and the Reduce costs, and with which it is possible to use workpieces complex shapes to one another by diffusion bonding associate.

The method according to the invention is based on the teaching of the attached claim 1 given. Sufficient when using it Pressures of about 7x10³ hPa (100 psi) and about 21 x 10³ hPa (300 psi) as opposed to about ten times that high pressures in the prior art in order to by diffusion to achieve stable connections. It is also possible Workpieces with rough connection surfaces to one another associate.

Other objects and advantages of the invention are apparent from US Pat following detailed description with reference to FIG the drawings emerge.

Figs. 1 to 4 schematically show respectively a Ausführungsbei play an apparatus for performing the inventive method for diffusion bonding;

FIGS. 5a and 5b are images that zei gen the bonding interface between a C-Ti64-plate and a SP-Ti64-plate, as obtained in processes according to an example 1 and an example 2; and

FIG. 6a, 6b and 6c are images that the surface Verbindungsgrenzflä between two C-Ti64 plates and show a SP-Ti64-plate, as obtained in processes according to Comparative Examples 1, 2 and 2, respectively;

Fig. 7a and 7b are images that gene the connection interface between an SS 316 and a plate-plate Dux65 zei, as one example, 4 or 5 to an example were obtained in accordance with procedures; and

Fig. 8a, 6b and 8c are pictures that che the Verbindungsgrenzflä, point between two SS-316 plates as ren at procedural according to Comparative Examples 4 to 6 obtained.

It is known to those skilled in the art that the diffusion bonding applied pressure on the surfaces to be connected to the work pieces leads to microscopic, plastic deformation. This means that the rough contact surfaces of the Workpieces locally plastically due to the applied pressure be formed, whereby the contact surfaces of the workpieces enlarge. The pressure applied also affects the grain boundary diffusion and the volume diffusion as they are to the Connection interfaces of the workpieces occur. These two Solid diffusion effects are the main mechanism represents an atom-atom bond between the partially in close contact surfaces as well as the process of Aushei development of holes between which sometimes do not touch the surfaces. The applied pressure can also be the Grain boundary migration at the joint surfaces of the plant affect pieces, d. i.e., he can take a hike to the Create connecting surfaces (formation of a new grain limit at which atom-atom bond was established, whereby the original connection surfaces loosen.

However, the inventors found that the applied Pressure is the grain boundary diffusion and the volume diffusion affects inside the workpieces, but only the Grain boundary diffusion and the volume diffusion in the rich increase parallel to the applied pressure. The Korngren zendiffusion and the volume diffusion in the right direction at an angle to the applied pressure, on the other hand, decrease. the Solid diffusion, which is responsible for hole healing during diffusion bonding, but takes place in parallel to the connection areas, d. H. perpendicular to the direction of the applied Pressure. Therefore, the pressure has an adverse effect when only the effects of grain boundary diffusion and volume diff merger should be taken into account. As for other things, have the inventors also found that the applied Pressure has no noticeable effect on the grain boundary walls tion has.

As for workpieces to be ver bind, their connecting surfaces are in general first mechanically processed to achieve the smoothest possible connection to achieve application areas. However, the mechanically bear Still working connection surfaces seen microscopically a certain roughness. Although the during the diffu sion bond pressure is less than the yield point the work piece is, d. i.e., although no macroscopic pla to observe the structural deformation of a workpiece as a whole is, the pressure applied is sufficient to produce plastic deformation generation on the microscopically rough surfaces. By the microscopic deformation is exhibited by the connecting surfaces the workpieces have larger areas of mutual contact, which are the main areas in which diffusion bonding he follows. Accordingly, the microscopic plasti cal deformation caused at the connecting surfaces mutual contact area the larger, the larger the applied pressure, and the easier the diffusion can be sion bonding are carried out.

The inventors have therefore come to the conclusion that the Connecting surfaces at right angles pressure the grain boundary diffusion, the volume diffusion and the grain boundaries migration during the diffusion bonding process is only slight influences, but it actually becomes more microscopic, plasti leads to shear deformation of the connecting surfaces. Accordingly, will any measure that leads to microscopic, plastic defor tion on the connecting surfaces leads to the required Thickness of the amount to be applied during the diffusion bonding process Influence pressure in a critical way.

Most materials, after being subjected to such a special treatment, show that they have miniature grains (smaller than 10 µm) and two-phase microstructures, show superplastic deformation, i.e. a very large deformation when they are subjected to special conditions such as a strain rate below 10 ^{- 4} sec ^-1 and a temperature that is greater than half the absolute melting temperature. The stress required for this superplastic deformation is very small.

In addition, the must to achieve a diffusion connection required temperature higher than the absolute Melting temperature of the material will be what is essentially with the main requirement of creating a "microscope plastic deformation ". In view of the The inventors have found above that then, if microscopic, plastic deformation at the conn application surfaces, as required for diffusion bonding, through superplastic deformation that is brought about in right angular direction the pressure to be applied can be greatly reduced can and accordingly that required in diffusion bonding Pressure can be reduced to very low levels.

In practice, however, most are by diffusion processing binding materials to be joined are not superplastic Materials, d. that is, their grain size is larger than 10 µm and they do not have a two-phase microstructure, wes because of them, as long as they have not undergone any special treatment are not suitable to micro plastic deformation according to the principle of superplastic To achieve deformation at low pressure to thereby reduce the Increase contact area and create a diffusion connection to get.

In order to overcome this difficulty, the invention according to the method, a thin plate of superplastic Material suitable for diffusion bonding between the embedded workpieces to be connected by diffusion bonding tet, and therefore, even if they are not from su perplastic material exist, are processed in such a way that it using the principle of superplastic deformation to microplastic deformation at very low pressure comes.

In the case of the method according to the invention, this lies in the direction at right angles to the plate made of superplastic material legendary pressure in the range of approximately 7 × 10³ hPa (100 psi) to about 21 x 10³ hPa (300 psi), and the plate off superplastic material and the work pieces are sold for 10 Minutes to 2 hours heated to a temperature that at least half of the absolute melting temperature of the corresponds to superplastic material.

The plate made of superplastic material has when used of the method according to the invention preferably a thickness between about 0.5 mm and 3 mm.

Fig. 1 shows an embodiment of an apparatus for carrying out the diffusion bonding process of the invention. A thin plate 3 made of a superplastic alloy is embedded between two workpieces 1 and 2, and it is held in close contact with the two workpieces 1, 2 by a piston 10 actuated by a hydraulic unit 9. The thin alloy plate 3 is suitable for diffusion bonding with the workpieces 1 and 2. The layer structure is placed in a vacuum chamber 4 in which the air is pumped out using a diffusion pump 5 and a mechanical pump 6 down to a pressure of approximately 10 ^-5 hPa (10 ^-5 Torr). Several heaters 8 are arranged next to the two workpieces 1 and 2, and they are controlled by a temperature controller 7. The hydraulic unit 9 is controlled by a hydraulic controller 11 so that it adjusts the pressure applied to the workpiece 1 in the range of approximately 7 × 10 3 hPa to approximately 42 × 10 3 hPa. The hydraulic control 11, temperature controller 7 and mechanical pump 6 are all controlled by a central control unit 12 which is programmed to maintain the applied pressure and temperature for approximately 10 minutes to 2 hours. Reference is now made to FIG. 2, which shows another exemplary embodiment from an apparatus for carrying out the diffusion bonding method according to the invention. In this exemplary embodiment, the diffusion bonding process is carried out in a protective or reducing atmosphere. The work pieces 1 , 2 and the plate 3 made of a superplastic alloy Le are enclosed in a space 13 made of heat-resistant steel, which is filled via a gas cylinder 14 with the protective or reducing gas. The flow rate of the protective gas or the reducing gas is adjusted by a flow regulator 15. In order to ensure airtightness of the space 13 made of heat-resistant steel, a copper cooling ring 16 is provided around the piston 10 .

According to FIG. 3, the pressure applied to the layer structure can also be achieved using a plurality of weights 17 which are placed on the workpiece 1 instead of using a hydraulic unit. This is because the pressure used in the method according to the invention is only about 7 × 10³ hPa to 21 × 10³ hPa.

According to Fig. 4 in the case of, aristocratic can a diffusion connection to a workpiece having a complex or irregular shape moderate, z. B. a high-temperature turbine blade 18, the layer structure first BEFE directly with screws 19 and placed in an oven with a protective gas atmosphere for heating. When the temperature is increased, the layer structure expands, and the force generated by the expansion is sufficient to achieve the pressure required in this diffusion bonding process.

example 1

In this example, two workpieces made of C-Ti64 plat (non-superplastic alloy Ti-6Al-4V) were verbun using the method according to the invention. The surfaces of the two C-Ti64 plates to be joined together were first ground with 600 gauge SiC paper and then polished with 0.3 µm aluminum oxide powder. The two plates were then placed in the device shown in FIG. A 1 mm thick plate made of SP-Ti64 (superpla tical alloy Ti-6Al-4V) was embedded between the two C-Ti64 plates and the layer structure was heated to a temperature of 930 ° C. After the temperature reached 930 ° C, a pressure of 7x10³ hPa (100 psi) was applied to the upper C-Ti64 plate via the flask 10 and maintained for 30 minutes. The two C-Ti64 plates were thus connected to one another by the SP-Ti64 plate. An image of the bond interface is shown in Figure 5a. As can be seen from this, no voids occur at the connection interface.

Example 2

The same processes and materials were used as in the case of game 1, with the exception that the surfaces of the two C-Ti64 plates to be joined were only sanded with 600-gauge SiC paper. The polishing step was omitted. An image of the resulting bond interface is shown in Figure 5b. As can be seen from this, even if the polishing process with alumina powder is omitted, the bonding interface is acceptable.

Example 3

The same procedures and materials as in Example 1 were used used to make four samples, with changes consisted of the surface of the two to be joined C-Ti64 plates for each sample only with fine SiC paper unit 80 were ground and a pressure of 42 × 10³ hPa (600 psi), 21 x 10³ hPa (300 psi) or 7 x 10³ hPa (100 psi) was applied to the top C-Ti64 plate of each sample. the two C-Ti64 plates were joined together and the Bond interface was found to be acceptable.

Comparative example 1

In this comparative example, two workpiece plates made of C-Ti64 (non-superplastic alloy Ti6Al4V) were bonded together using a conventional method. The surfaces of the two C-Ti64 plates to be joined were first ground with 600-gauge SiC paper and then polished with 0.3 µm aluminum powder. Thereafter, the two plates were placed in the device shown in FIG. 1 and heated to a temperature of 930 ° C. After the temperature reached 930 ° C, a pressure of 7x10³ hPa (100 psi) was applied to the upper C-Ti64 plate via the flask 10 and maintained for 30 minutes. This is how the two C-Ti64 plates were connected to one another. An image for the bond interface is shown in Figure 6a. As can be seen from Figure 6a, there are voids at the bond interface, indicating that the bond is not acceptable.

Comparative example 2

The same procedures and materials were used as in Comparative Example 1, with the exception that the upper surfaces of the two C-Ti64 plates to be joined were only sanded with 600-gauge SiC paper. An image of the resulting bond interface is shown in Figure 6b. As can be seen from this, the joint interface contains voids and is therefore not acceptable.

Comparative example 3

The same procedures and materials as in Comparative Example 1 were used with the exception that instead of a pressure of 7 × 10 3 hPa, a pressure of 70 × 10 3 hPa (1000 psi) was applied. An image of the resulting bond interface is shown in Figure 6c. As can be seen from this, although the bonding interface is acceptable, there is a disadvantage that the pressure applied is ten times that used in Example 1. The interface shown in FIG.

Comparative example 4

The same procedures and materials were used as in the Ver same example 1 used to produce four samples, except that the surfaces of the two connect the C-Ti64 plates of each sample only with fine SiC paper unit 80 was ground and a pressure of 70 × 10³ hPa (1000 psi), 42 x 103 hPa (600 psi), 21 x 103 hPa (300 psi) and 7 x 103 hPa (100 psi), respectively, to the top C-Ti64 plate of each Sample was created. The two C-Ti64 plates were included connected to the other, but the bond interfaces were not acceptable.

There were tensile properties of the diffusion bonding with interconnected C-Ti64 plates in the above examples len and comparative examples measured, and they are in the Table 1 below.

Table 1

Example 4

In this example, two workpiece plates made of the stainless steel SS 316 (non-superplastic alloy) were connected to one another using the method according to the invention. The surfaces of the two plates to be connected to one another were first ground with SiC paper of fineness 80 and then polished with aluminum oxide powder of 0.3 μm. The two plates were then placed in the device shown in FIG. A thin plate made of the stainless, superplastic duplex steel Superdux 65 (superplastic alloy) with a thickness of 1 mm was embedded between the two workpiece plates to be connected. Four samples with this layer structure were produced. Each of the layer structures was heated to 1020 ° C. After this temperature was reached, the top plate was pressurized by piston 10 to 70 x 103 hPa (1000 psi), 42 x 103 hPa (600 psi), 21 x 103 hPa (300 psi) and 7 x 103 hPa, respectively (100 psi) and held for 30 minutes. For each sample, the two plates made of SS 316 stainless steel were connected to one another by the thin plate made of Superdux 65. An image of the bond interface for the sample subjected to a pressure of 21 x 103 hPa (300 psi) is shown in Figure 7a. As shown in Figure 7a, there were no voids at the bond interface.

Example 5

The same procedures and materials were used as in Example 4, with the exception that the surfaces of the two SS 316 stainless steel plates to be joined were ground only with 80 gauge SiC paper. The surfaces to be connected were not polished. An image of the resulting bond interface for a sample subjected to a pressure of 21 x 103 hPa (300 psi) is shown in Figure 7b. As shown in Fig. 7b, even without polishing with alumina powder, the joint interface is acceptable.

Comparative example 5

In this comparative example, two workpieces made of SS 316 stainless steel (non-superplastic alloy) were joined together using a conventional method. Four samples were made. For each sample, the surfaces of the two plates to be joined were first sanded with 80 gauge SiC paper and then polished with 0.3 µm aluminum oxide powder. Thereafter, the two plates were placed in the device shown in FIG. 1 and heated to 1020 ° C. After this temperature was reached, the top plate was pressurized by piston 10 to 70 x 103 hPa (1000 psi), 42 x 103 hPa (600 psi), 21 x 103 hPa (300 psi) and 7 x 103, respectively hPa (100 psi) applied and held for 30 minutes. The two plates were thereby connected to one another. Bil of the boundary surfaces of the samples to which a pressure of 21 × 10³ kPa (300 psi) or 70 x 10³ hPa was applied (1000 psi), 8a and FIG. 8b are shown in in Fig.. As shown in Figure 8a, there were voids at the bond interface, indicating that the bond is unacceptable. As shown in FIG. 8b, no cavities can be observed there, but the connection interface can still be seen.

Comparative example 6

The same procedures and materials were used as in Comparative Example 5, with the exception that the upper surfaces of the two plates to be joined in each sample were only sanded with 80 gauge SiC paper. An image of the resulting bond interface is shown in Figure 8c for the sample pressurized to 70 x 103 hPa (1000 psi). It can be seen that the bonding interface has voids and is therefore not acceptable.

The tensile properties of the bonded by diffusion bonding Plates made from the stainless steel SS-316 were used for the above Examples and comparative examples mentioned above were measured and they are listed in Table 2 below.

Table 2

Some process conditions for carrying out the fiction according to the method for connecting two workpieces Diffusion bonds are summarized in Table 3 below collected.

Table 3

Claims (20)

1. A method for producing a diffusion connection between a first workpiece and a second workpiece, characterized in that it comprises the following steps to enable working at low pressure:

• (a) embedding a plate ( 3 ) of superplastic material between the first work piece ( 1 ) and the second work piece ( 2 ), the superplastic material being suitable for producing a diffusion bond to the first work piece and to the second work piece;
• (b) heating the plate of superplastic material and the two workpieces to a temperature sufficient to create a diffusion bond between the first and second workpiece;
• (c) applying pressure perpendicular to the surface of the plate of superplastic material and
• (d) maintaining the pressure and temperature for a time sufficient to diffuse the plate of superplastic material to the first workpiece and the second workpiece.

2. The method according to claim 1, characterized in that the pressure between 7 x 10³ hPa (100 psi) and 21 x 10³ hPa (300 psi). 3. The method according to claim 1 or claim 2, characterized characterized in that the superplastic material in the crotch (b) is heated to an absolute temperature which is higher than half the melting temperature of the material of the first and second workpiece. 4. The method according to any one of the preceding claims, there characterized in that the time is 10 minutes to 120 minutes ten is. 5. The method according to any one of the preceding claims, there characterized in that the two workpieces from one Titanium alloy are made up of between 800 ° C and temperature 930 ° C and the time is 30 minutes to 60 minutes. 6. The method according to any one of the preceding claims, there characterized in that the plate is made of superplastic Material has a thickness between 0.5 mm and 3 mm. 7. The method according to claim 5, characterized in that the two workpieces are made of SP-Ti64. 8. The method according to claim 5, characterized in that the two workpieces are made of SP-Ti662. 9. The method according to any one of claims 1 to 4, characterized characterized in that the two workpieces are made of one iron alloy and the time 60 minutes to 120 minutes amounts to. 10. The method according to claim 8, characterized in that the superplastic material is Superdux 65 and the tempe temperature is between 900 ° C and 975 ° C. 11. The method according to claim 8, characterized in that the superplastic material is UHCS and the temperature is between 600 ° C and 650 ° C. 12. The method according to any one of claims 1 to 4, characterized characterized in that the two workpieces are made of one alloy They are nickel-based, the plate is made of superplastic Shem material consists of SP-Inconel 718, the temperature between 850 ° C and 975 ° C and the time between 90 Wed utes and 120 minutes lies. 13. The method according to any one of claims 1 to 4, characterized characterized in that the two workpieces are made of one alloy tion based on cobalt, the plate made of superplastic Shem material consists of Co10Al, the temperature between 1000 ° C and 2000 ° C and the time between 90 minutes and 120 minutes. 14. The method according to any one of claims 1 to 4, characterized characterized in that the two workpieces are made of one alloy tion based on zirconium, the plate made of superpla elastic material consists of Zr2.5Nb, the temperature between between 800 ° C and 1000 ° C and the time between 90 minutes ten and 120 minutes. 15. The method according to any one of claims 1 to 4, characterized characterized in that the two workpieces are made of one alloy tion based on copper, the plate from superplasti Shem material consists of IN836, the temperature between 500 ° C and 600 ° C and the time between 60 minutes and 120 minutes. 16. The method according to any one of claims 1 to 4, characterized characterized in that the two workpieces are made of one alloy tion based on oxide ceramics, the superplastic Material is made of SP-Ti64, the temperature between 900 ° C and 930 ° C and the time between 90 minutes and 120 Minutes. 17. The method according to any one of claims 1 to 4, characterized marked that the two workpieces from one not oxide ceramic material, the superplastic Material consists of Zr-2.5Nb, the temperature between 900 ° C and 1000 ° C and the time between 90 minutes and 120 Minutes. 18. The method according to any one of claims 1 to 4, characterized characterized in that the two workpieces are made of an aluminum nium alloy, the temperature between 450 ° C and 530 ° C and the time is 10 to 30 minutes. 19. The method according to claim 18, characterized in that the superplastic material consists of 7475AlZnMg. 20. The method according to claim 18, characterized in that the superplastic material consists of 8090AlLi.