DE4430779C2 - Process for making a diffusion bond at low pressure - Google Patents

Description

The invention relates to a method for producing a Diffusion connection, i.e. for diffusion bonding, at low according to pressure.

Diffusion bonding is a special connection technique that the principle of solid diffusion and grain boundary migration applies to materials under heating and application of pressure at a temperature below the melting point of the Materials are connected. The used The principle is similar to that of sintering processes, however when sintering two powders are mixed together, while during Diffusion bonding of physical materials with metallurgical be connected. Both diffusion bonding as well Sintering is carried out completely in the solid state,  d. that is, no melting occurs in the joining process.

If the diffusion bonding technique for joining metals applied, it can overcome difficulties like it occur in conventional welding and soldering like He heat cracks during welding, knife cut corrosion and Residual stresses, and it also creates a solution at Schwie skills regarding the connection of fine ceramic materials lien. It is known that because ceramics have high melting points exhibit and are brittle, most conventional Welding techniques not for joining ceramic materials can be used with each other or with other substances nen. Because diffusion bonding at a temperature below the Melting point of the materials to be joined the difficulties mentioned above can arise here be overcome. It also forms diffusion bonds also with other advanced construction materials, which are difficult to weld, such as intermetallic ver bonds, metal-based materials, complex materia ceramic-based and high-melting superalloys an effective method of connecting with 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 for conventional welding techniques are, if only a small Number of workpieces must be connected. But when a large number of workpieces are connected, diffusion bonding has the advantages of reducing costs, because connecting a large number of workpieces is the same can be carried out in good time.

Diffusion bonding involves the creation of Pressure perpendicular to the surface by diffusion bonding workpieces to be joined, generally a pressure  from Z. B. about 70 × 10³ hPa or even 700 × 10³ hPa is used. This means that during the Diffusion process consumes a lot of energy and is expensive Equipment to apply the pressure is required. About that In addition, since the pressure applied is perpendicular to the upper area of the work to be connected by diffusion connection must be in place, d. i.e. since uniaxial tension is exerted must be when the workpiece is a complex or irregular shape, z. B. a wing for one High temperature turbine is, diffusion bonding is not carried out because in such cases the pressure is not high enough can be exercised perpendicular to the connecting surface.

Furthermore, diffusion bonding requires that the connection surfaces of the workpieces are as smooth as possible in order for a large contact area to ensure the mutual Diffusion of elements and the establishment of an atom-atom ver to facilitate binding 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 increased costs.

The above difficulties become severe gender if the diffusion bonding technique for connecting kera mixer components is used. Because of their shattering at elevated temperature, the parts to be connected break Components at high temperature and pressure, as generally used in diffusion bonding that, easy. In addition, ceramic components indicate that Ceramics cannot be easily machined, generally complex in shape and are therefore related not suitable due to diffusion bonding. Furthermore it is more difficult with ceramic components than with metal  materials to get a smooth connection surface. Accordingly, diffusion bonding has proven to be suitable in the laboratory shown for connecting ceramic components, however the technology is not yet mature enough for practical purposes Application in industry.  

In a known method (FR 2 672 833 A1) for producing a diffusion sionsverbindung between an oxidation protection layer and one against Oxi The substrate to be protected from a titanium alloy becomes a non-oxi dier, sheet material, e.g. B. from a FeCrAl alloy, on a Surface of the substrate to be protected applied. Then the arrangement thus formed in a vacuum with an external pressure of 70 × 10³ hPa to 350 × 10³ hPa and to a temperature between 900 ° C 1100 ° C heated. In order to obtain a diffusion connection, the Pressure-heat treatment is carried out for a period of 60 min to 300 min.

The invention has for its object a method for manufacturing a diffusion connection to indicate that at low pressure can be led to thereby reduce energy consumption and the Reduce costs, and with which it is possible to work with complex shapes through a diffusion connection connect.

The inventive method is based on the teaching of Claim 1 given. Enough in its application Pressures of approximately 7 x 10³ hPa and approximately 21 × 10³ hPa in contrast to the about ten times as much high pressures in the prior art from diffusion to achieve stable connections. It is also possible Workpieces with rough connection surfaces to each other connect.

Other objects and advantages of the invention emerge from the following detailed description with reference to the drawings.

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 diagrams showing the connection interface between a TiAl6V4-plate and a superplastic TiAl6V4-plate, as obtained in processes according to an example 1 and an example 2; and

FIG. 6a, 6b and 6c are images show the surface of the bonding interface between two TiAl6V4 plates and a superplastic TiAl6V4-plate as in methods in accordance with the comparison beispiellen 1, were obtained 2 and 2;

Fig. 7a and 7b are diagrams showing the joint interface between a steel plate and a X2CrNiMoN246-plate as one example, 4 or 5 to an example were obtained in accordance with procedures; and

Fig. 8a, 8b and 8c are pictures which surface the bonding interface between two steel plates show as Comparative Examples 4 to 6 obtained in accordance with procedure.

It is known to the person skilled in the art that when producing a Diffusion connection, i.e. during diffusion bonding applied pressure on the surfaces of the plant to be connected leads to microscopic, plastic deformation. This means that the rough contact surfaces of the to be connected Workpieces locally plastically ver by the applied pressure are formed, which creates the contact surfaces of the workpieces enlarge. The pressure applied also affects the grain boundary diffusion and the volume diffusion as they are at the Connection interfaces of the workpieces occur. These two Solid diffusion effects are the main mechanism which is an atom-atom bond between the partially in close contact areas as well as the process of baking holes between the partially do not touch the surfaces. The pressure applied can also Grain boundary migration at the connecting surfaces of the plant affect pieces, d. that is, 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 connecting surfaces become detached.

However, the inventors have found that the applied  Pressure the grain boundary diffusion and the volume diffusion influenced inside the workpieces, but only that Grain boundary diffusion and volume diffusion in the rich increase parallel to the pressure applied. The Korngren diffusion and volume diffusion in the right direction on the other hand, they decrease at an angle to the pressure applied. The Solid diffusion, for hole healing during diffusion bonding takes place, but takes place parallel to the connection surfaces, 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 fusion are taken into account. Whatever else, have the inventors also found that the created Pressure has no noticeable effect on the grain boundary walls tion.

As for workpieces to ver by diffusion bonding are binding, their connecting surfaces in general first machined to make the connection as smooth as possible to achieve areas. However, the mechanically bear still processed microscopically a certain roughness. Although during the Diffu sionsbondens applied pressure less than the yield strength the work piece is d. that is, although no macroscopic pla to observe the static deformation of a workpiece as a whole , the pressure applied is sufficient for plastic deformation generation on the microscopically rough surfaces. By the microscopic deformation shows the connecting surfaces the workpieces have larger areas of mutual contact, which are the main areas where diffusion bonding is he follows. Accordingly, those by the microscopic plasti deformation caused at the connecting surfaces mutual contact area, the larger the larger the applied pressure, and the easier it is to diffuse sion bonds are carried out.  

The inventors have therefore come to the conclusion that the to Connection surfaces at right angles apply the grain boundary diffusion, volume diffusion and grain boundaries migration during the diffusion bonding process only little influences, but he actually becomes microscopic, plasti shear deformation of the connecting surfaces. Accordingly any measure that leads to microscopic, plastic deformation leads on the connecting surfaces, the required Strength of the to be applied during the diffusion bonding process Influence pressure in a critical manner.

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

In addition, to achieve a diffusion connection required temperature is higher than half the absolute Melting temperature of the material be what essentially with the main requirement of creating a "microscope plastic deformation ". In view of the The inventors have found above that if microscopic, plastic deformation at the connector areas as required for diffusion bonding superplastic deformation is brought about in the right pressure to be applied at an angular direction can be greatly reduced can and therefore the one required for diffusion bonding Pressure can be reduced to a very low level.  

In practice, however, most are diffusion materials to be bonded no superplastic Materials, d. that is, their grain size is larger than 10 µm and they don't have two-phase microstructure, which is because of them as long as they haven't undergone any special treatment become, are not suitable to micro on connecting surfaces plastic deformation according to the principle of superplastic To achieve deformation at low pressure, thereby the Increase contact area and a diffusion connection to get.

In order to overcome this difficulty, the invention a thin sheet of superplastic Material that is suitable for diffusion bonding between the Workpieces to be joined by diffusion bonding tet, and therefore these, even if they are not from su perplastic material exist, are processed so that it using the principle of superplastic deformation for microplastic deformation at very low pressure is coming.

In the method according to the invention, this is in the direction at right angles to the plate made of superplastic material legendary pressure in the range of approximately 7 × 10³ hPa to about 21 x 10³ hPa, and the plate superplastic material and the workpieces are made 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 in use of the method according to the invention preferably a thickness between approximately 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 is held in close contact with the two workpieces 1 , 2 by a piston 10 actuated by a hydraulic unit 9 . The alloy of the thin 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 down to a pressure of approximately 10 ^-5 hPa (10 ^-5 Torr) using a diffusion pump 5 and a mechanical pump 6 . 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 about 7 × 10³ hPa to about 21 × 10³ hPa. The hydraulic control 11 , the temperature controller 7 and the mechanical pump 6 are all controlled by a central control unit 12 which is programmed to maintain the applied pressure and temperature for about 10 minutes to 2 hours.

Reference is now made to FIG. 2, which shows another exemplary embodiment of a device 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 are enclosed in a space 13 made of heat-resistant steel, which is filled with the protective or reducing gas via a gas bottle 14 . The flow rate of the protective gas or the reducing gas is set 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 several 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 approximately 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 is first beigt directly with screws 19 and can be arranged in an oven with a protective gas atmosphere for heating. When the temperature is increased, the layer structure expands, and the force generated during the expansion is sufficient to achieve the pressure required for this diffusion bonding process.

The following specific examples are intended to illustrate the invention illustrate more fully without sacrificing their protection should limit the range, since the expert has numerous modes certifications and changes are recognizable.

example 1

In this example, two workpieces made of C-TiAl6V4 plates (non-superplastic alloy TiAl6V4) were connected to one another using the method according to the invention. The surfaces of the two C-TiAl6V4 plates to be joined together were first ground with SiC paper of fineness 600 and then polished with 0.3 µm aluminum oxide powder. The two plates were then placed in the device shown in FIG . Between the two C-TiAl6V4 plates, a 1 mm thick plate of SP-TiAl6V4 (superplastic alloy (TiAl6V4) was embedded and the layer structure was heated to a temperature of 930 ° C. After the temperature had reached 930 ° C. a pressure of 7 x 10³ hPa (100 psi) was applied to the upper C-TiAl6V4 plate and maintained for 30 minutes via the piston 10. The two C-TiAl6V4 plates were thus connected to each other by the SP-TiAl6V4 plate. An image of the connection interface is shown in Figure 5. As can be seen from this, there are no voids at the connection interface.

Example 2

The same procedures and materials as in example 1 were used, with the exception that the surfaces of the two C-TiAl6V4 plates to be joined together were only ground with SiC paper of fineness 600. The polishing course fell away. An image of the resulting connection interface is shown in Fig. 5b. As can be seen from this, even if the polishing process with aluminum oxide powder is omitted, the connection interface is acceptable.

Example 3

The same procedures and materials as in Example 1 were used to make four samples, making changes consisted of the surface of the two to be joined C-TiAl6V4 plates for each sample only with fine SiC paper 80 were ground and a pressure of 42 × 10³ hPa (600 psi), 21 × 10³ hPa or 7 × 10³ hPa was applied to the top C-TiAl6V4 plate of each sample. The two C-TiAl6V4 plates were joined together and the Connection interface was found to be acceptable.

Comparative Example 1

In this comparative example, two workpiece plates made of C-TiAl6V4 (non-superplastic alloy TiAl6V4) were bonded together using a conventional method. The surfaces of the two C-TiAl6V4 plates to be joined were first ground with SiC paper of fineness 600 and then polished with aluminum powder of 0.3 µm. Then 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 7 × 10 3 hPa was applied to the upper C-TiAl6V4 plate via the piston 10 and maintained for 30 minutes. So the two C-TiAl6V4 plates were connected to each other. An image for the connection interface is shown in Fig. 6a. As seen in Figure 6a, there are voids at the connection interface, indicating that the connection is unacceptable.

Comparative Example 2

The same processes and materials were used as in comparative example 1, with the exception that the upper surfaces of the two C-TiAl6V4 plates to be joined together were only ground with SiC paper of fineness 600. An image of the resulting connection interface is shown in Fig. 6b. As can be seen from this, the connection 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 × 10³ hPa, that of 70 × 10³ hPa was applied. An image of the resulting connection interface is shown in Fig. 6c. As can be seen from this, the connection interface is acceptable, but there is a disadvantage that the pressure applied is ten times the pressure used in Example 1.

Comparative Example 4

The same procedures and materials as for Ver same example 1 used to prepare four samples, with the exception that the surfaces of the two connect the C-TiAl6V4 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, 21 x 103 hPa or 7 × 10³ hPa (100 psi) to the top C-Ti64 plate of each Sample was created. The two C-TiAl6V4 plates were joined together connected, but the connection interfaces were not acceptable.

There were tensile properties of the by diffusion bonding interconnected C-TiAl6V4 plates in the above examples len and comparative examples, and they are in the Table 1 summarized below.  

Table 1

Example 4

In this example, two workpiece plates made of SS 316 stainless steel (non-superplastic alloy) were joined together using the method according to the invention. The surfaces of the two plates to be bonded to one another were first sanded with 80-grade SiC paper and then polished with 0.3 μm aluminum oxide powder. The two plates were then placed in the device shown in FIG . Between the two workpiece plates to be connected, a thin plate made of the stainless, superplastic duplex steel Superdux 65 (superplastic alloy X2 CrNiMoN 246) of 1 mm thickness was embedded. Four samples with this layer structure were produced. Each of the layer structures was heated to 1020 ° C. After this temperature was reached, a pressure of 70 × 10³ kPa, 42 × 10³ hPa, 21 × 10³ hPa and 7 × 10³ hPa was applied and maintained for 30 minutes via the piston 10 to the upper plate. For each sample, the two SS 316 stainless steel plates were joined together by the thin Superdux 65 plate. An image of the joint interface on the sample to which a pressure of 21 x 103 hPa was applied is shown in Figure 7a. As shown in Figure 7a, there were no voids at the connection interface.

Example 5

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

Comparative Example 5

In this comparative example, two workpieces made of SS 316 stainless steel (non-superplastic alloy) were joined using a conventional method. Four samples were made. In each sample, the surfaces of the two plates to be joined together were first ground with SiC paper of fineness 80 and then polished with 0.3 µm aluminum oxide powder. The two plates were then placed in the device shown in FIG. 1 and heated to 1020 ° C. After this temperature was reached, was applied across the piston 10 to the upper plate, a pressure of 70 × 10³ kPa, 42 × 10³ hPa (600 psi), 21 × 10³ hPa and 7 × 10³ hPa (100 psi) and Maintain for 30 minutes. The two plates were thereby connected. Bil of the boundary surfaces of the samples to which a pressure of 21 × 10 × 10 hPa and 70 hPa was applied, 8a and FIG. 8b are shown in in Fig.. As shown in Figure 8a, voids were at the connection interface, indicating that the connection 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 as in comparative example 5 were used, with the exception that the upper surfaces of the two plates to be connected to each sample were only ground with SiC paper of fineness 80. An image of the resulting bond interface is shown in Figure 8c for the sample to which a pressure of 70 x 103 hPa was applied. It can be seen that the connection interface has voids and is therefore not acceptable.

The tensile properties of the plates connected by diffusion bonding from the SS-316 stainless steel was used for the above examples and ver Comparative examples were measured and are listed in Table 2 below.

Table 2

Some process conditions for performing the Invention According to the method for connecting two workpieces Diffusion bonding is summarized in Table 3 below composed.

Table 3

Claims (17)

Method for establishing a diffusion connection between a first workpiece ( 1 ) and a second workpiece ( 2 ) with the following steps:

• (a) Embedding a plate ( 3 ) made of superplastic material with a grain size of less than 10 microns and a two-phase microstructure between the first and the second workpiece ( 1 , 2 ), the superperplastic material for establishing a diffusion connection to the two Workpieces ( 1 , 2 ),
• (b) heating the plate ( 3 ) made of superplastic material and that of the workpieces ( 1 , 2 ) to a temperature which is between 0.6 to 0.8 of the absolute melting temperature of the material of the two workpieces ( 1 , 2 ) and its Melting temperature is
• (c) applying a pressure between 7 × 10³ hPa (100 psi) and 21 × 10³ hPa (300 psi) perpendicular to the surface of the plate ( 3 ) made of superplastic material and
• (d) Maintaining the pressure and the temperature for a time which is between 10 min and 120 min and is sufficient to achieve a diffusion connection of the plate ( 3 ) made of superplastic material to both workpieces.

2. The method according to claim 1, characterized in that the temperature between 800 ° C and 930 ° C and the time between 30 min and 60 min are selected for the two workpieces ( 1, 2 ) titanium alloys. 3. The method according to claim 1 or 2, characterized in that a thickness between 0.5 mm and 3 mm is selected for the plate ( 3 ) made of superplastic material. 4. The method according to claim 2, characterized in that superplastic TiAl6V4 is used for the plate ( 3 ) made of superplastic material. 5. The method according to claim 2, characterized in that superplastic TiAl6V6Sn2 is used for the plate ( 3 ) made of superplastic material. 6. The method according to claim 1, characterized in that for the two workpieces ( 1, 2 ) iron alloys and the time between 60 min and 120 min are selected. 7. The method according to claim 6, characterized in that for the plate ( 3 ) made of superplastic material, superplastic, rust-free duplex steel (X2CrNiMoN246) is used. 8. The method according to claim 6, characterized in that a temperature between 600 ° C and 650 ° C is selected for the plate ( 3 ) made of superplastic material, superplastic, ultra-high carbon steel. 9. The method according to claim 1, characterized in that for the two workpieces ( 1, 2 ) alloys based on nickel, the plate ( 3 ) made of superplastic material of a superplastic Inconel 718 alloy used, the temperature between 850 ° C and 975 ° C and the time between 90 min and 120 min is selected. 10. The method according to claim 1, characterized in that for the two workpieces ( 1, 2 ) alloys based on cobalt, the plate ( 3 ) made of superplastic material made of a superplastic CoAl10 alloy, the temperature between 1000 ° C and 2000 ° C. and the time is selected between 90 minutes and 120 minutes. 11. The method according to claim 1, characterized in that for the two workpieces ( 1, 2 ) zirconium-based alloys, the plate ( 3 ) made of superplastic material made of a superplastic ZrNb2.5 alloy, the temperature between 800 ° C and 1000 ° C and the time between 90 min and 120 min is selected. 12. The method according to claim 1, characterized in that for the two workpieces ( 1, 2 ) copper-based alloys, the plate ( 3 ) made of superplastic material made of a superplastic CuZn38Ni15 alloy, the temperature between 500 ° C and 600 ° C and the time is selected between 60 minutes and 120 minutes. 13. The method according to claim 1, characterized in that for the two workpieces ( 1, 2 ) oxide ceramic, the plate ( 3 ) made of superplastic material of a superplastic TiAl6V4 alloy used, the temperature between 900 ° C and 930 ° C and the time is selected between 90 min and 120 min. 14. The method according to claim 1, characterized in that for the two workpieces ( 1, 2 ) non-oxide ceramic, the plate ( 3 ) made of superplastic material made of a superplastic ZrNb2.5 alloy, the temperature between 900 ° C and 1000 ° C and the time between 90 min and 120 min is selected. 15. The method according to claim 1, characterized in that aluminum alloys are used for the two workpieces ( 1, 2 ), the temperature is selected between 450 ° C and 530 ° C and the time between 10 min and 30 min. 16. The method according to claim 15, characterized in that superplastic material of a superplastic 7475-AlZnMg alloy is used for the plate ( 3 ). 17. The method according to claim 15, characterized in that a superplastic 8090-AlLi alloy is selected for the plate ( 3 ) made of superplastic material.