JPS6235868B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for joining metals, and in particular to a method for joining metals suitable for bond welding or butt welding of heat-resistant alloys, thin plates or pipes made of different materials that are difficult to fusion weld, respectively. .

Conventionally, typical examples of joining methods for members that are difficult to fusion-weld include brazing and fusion-diffusion joining. The basic bonding equipment for both methods is the same, and there are two methods for bonding the members: one in vacuum and one in inert gas.
FIG. 1 shows a bonding apparatus in vacuum.

In the joining procedure of the brazing method, as shown in FIG. After evacuating the inside of the vacuum chamber 1 with a vacuum pump 6, it is heated with a high frequency induction coil 7 under low pressure to melt only the brazing material and join. Note that 8, 9, 10, and 12 in the figure indicate a thermocouple, a high-frequency power source, a current control circuit, and a pressurizing shaft, respectively. The joining mechanism at this time is as shown in Figure 2A, when the brazing filler metal 12 is in the molten state (2), the base material (joining member)
The surface of the brazing material 13 reacts with the brazing material 12 and slightly melts to form a molten layer 14. At the same time, the brazing filler metal element diffuses into the base material to form a diffusion layer 15, and the bonding progresses (3). However, because the composition of the brazing filler metal is significantly different from that of the base metal, and because high pressure cannot be applied and the molten layer of the filler metal cannot be thinned, the bonding time is only a few hours, making the joint part the same as the base metal. I can't. Therefore, the bonding layer 16 is inferior to the base material in mechanical and physical properties, which is a disadvantage of the brazing method.

Next, the melt diffusion bonding method is a method proposed by U.S. Pat. Other than that, the procedure is the same as the brazing method. The bonding mechanism is as shown in Figure 2B.
When 7 is in the molten state (2), the melting point lowering element in the insert material diffuses into the base material (joining member) 13 to form a diffusion layer 15 and the joining progresses. During bonding, the molten layer solidifies isothermally, but ultimately the bonding is completed when the bonded area becomes homogeneous with the base material. Therefore, with this joining method, a high-quality joint with properties comparable to that of the base material can be obtained. However, with this joining method, the joining temperature is high, close to the melting point of the base material, so depending on the material, the base material may deteriorate significantly, and the liquid phase cannot be forcibly discharged because high pressure cannot be applied. There are problems such as initial impurities remaining as they are and a long time required for bonding.

Furthermore, a problem common to both bonding methods is that since the bonding is performed by heating the entire product in a furnace, product dimensions are limited, and a sound bond cannot be obtained in the atmosphere.

The purpose of the present invention is to lower the temperature of the base metal during joining of heat-resistant superalloys and dissimilar metals, which are difficult to weld by general fusion welding, to join in a short time in the atmosphere, and to improve the mechanical and physical properties of the joint. An object of the present invention is to provide a method for joining metals that can have properties equivalent to those of the base metal.

The present inventors have found that by increasing the electrical resistance of the bonding interface to more than several times the specific resistance of the base metal, and by applying a large current for a short time that heat diffusion cannot sufficiently proceed, the heat is concentrated only at the bonding interface. Even if the temperature of the bonding interface is around the melting point of the base material under appropriate bonding conditions, the temperature of the bonding member located several hundred μm or more away from the bonding interface will be 1/2 of the melting point. It has been found that bonding using a thin molten layer is possible because it is possible to form a steep temperature distribution that is less than or equal to 100%.

The present invention has been made based on such knowledge. The present invention provides an alloy with a composition close to that of the base material,
Alternatively, an insert material made of a metal that can form a sound alloy with the base metal is inserted into the gap between the two base materials to be joined, and a heating process is performed in which the insert material is heated with electricity while applying pressure, and the temperature at the joining interface is is detected, and when the detected temperature reaches the melting point of the base material, the applied current is reduced, and the bonding interface temperature is maintained at a value lower than the melting point of the base material and higher than the melting point of the insert material, and diffusion processing is performed. This metal joining method is characterized by comprising a treatment step and an extrusion step of extruding the melt at the joining interface between the two base materials to the outside of the joint.

In the present invention, the insert material inserted into the gap between the base materials to be joined in order to increase the electrical resistance of the joint interface can form an alloy having a composition close to that of the base materials or a healthy alloy layer with the base materials. These alloys or metals may be in the form of powder or foil. When the alloy or metal is in the form of powder, it has a high interfacial resistance and is particularly effective in the present invention, and when the alloy or metal is a foil, the bonding interface becomes two interfaces, resulting in a high interfacial resistance. In the case of powdered alloys or metals, it is desirable to uniformly place powder with a particle size of about 20 to 170 μm on the surface of the base material to be joined, and form one or two layers. By placing the powder in this manner, the interfacial resistance can be increased and concentrated heating can be performed efficiently.

Further, the melting point of the insert material may be equal to or lower than the melting point of the base material, or may be higher than the melting point of the base material.

When the melting point of the insert material is equal to or lower than the melting point of the base material, the insert material easily melts due to local heat generation at the bonding interface, and homogenization is facilitated by a thin molten layer. If the melting point of the insert material is higher than the melting point of the base material, the base material will melt due to local heat generation at the joint interface, and the molten layer of the insert material will be easily pushed out of the joint.
The bonding layer has a composition close to that of the base material. Examples of such a combination of base material and insert material include Inconel 625 as the heat-resistant superalloy, Ti or BNi-2 brazing material as the insert material,
In addition, IN-738 can be used as a heat-resistant superalloy, and BNi-2 brazing material can be used as an insert material.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

FIG. 5 shows an embodiment for joining block-like members. Moreover, FIG. 6 is a schematic diagram for explaining the joining process of FIG. 5. In FIG. 5, the bonding member 4 is pressurized by an electrode 20 with a metal powder 19 that forms a sound alloy layer with the base material and has a melting point lower than the melting point of the base material sandwiched at the bonding interface. The bonding current is supplied from the current control circuit 21 to the bonding member 4 via the transformer 22 and the electrode 20. The temperature of the bonding interface at this time is the temperature of the infrared lens 23.
Detected by an infrared condensing head 24, an optical fiber 25, and an infrared detection circuit 26,
A temperature determination circuit 27 determines the magnitude of the detected value,
Feedback is given to the junction current. As shown in FIG. 6A, the bonding process at this time is to first pressurize the bonding member 4 with an initial pressure _P1 , and then to apply a constant bonding current set to a very high value. At this time, the temperature at the interface rises rapidly, but after confirming by temperature detection that the interface temperature has reached the melting point of the base material, the bonding current is immediately controlled to lower the interface temperature. Thereafter, the bonding current is controlled so that the interface temperature is maintained at a constant temperature θc that is lower than the melting point of the base material θm and higher than the melting point of the insert material, and a predetermined time elapses while cooling the electrode 20 with the cooling water 28. After that, complete the entire process. FIG. 6B schematically shows the bonding state, electrical resistance distribution, and temperature distribution at each bonding point. At the start of energization (1), the electrical resistance of the bonding interface is much higher than that of the base material due to the metal powder 19. When a large current is applied in this state, only the interface is instantaneously heated intensively, resulting in the temperature distribution shown in (2). At this point, the interface between the insert material and the base material is completely melted (molten layer 29), and the unnecessary melt layer is discharged by the pressing force. At point (3), diffusion is in progress and the solid bonding layer is still completely distinguishable from the base material. At the point (4) when the diffusion process ends, the molten layer 2
8 disappears, a diffusion layer 30 is formed, and both members are completely integrated.

According to this example, the area near the bonding interface can be melted and bonded in a thin layer due to the concentrated heat generation at the interface, so even if there is an oxide film or dirt on the initial base material surface, these will be dispersed in the melt layer. Good bonding is possible, and therefore bonding in the atmosphere is possible.

Further, according to this embodiment, since the unnecessary melt layer can be discharged with a high pressure, the bonding layer can be made extremely thin, and the diffusion treatment time can be shortened to homogenize the bonded portion.

In addition, according to this example, since the melt layer is forcibly discharged, the oxide film and impurities on the initial base material surface are simultaneously discharged, and the amount of these remaining in the bonding layer is reduced, so that the bonding layer is can improve the mechanical properties of

Next, FIG. 7 shows another embodiment of the present invention, in which
An example of bonding a grooved member and a thin plate member is shown. Further, FIG. 8 shows a time chart for explaining the bonding process of this embodiment. In FIG. 7, a thin plate member 31 and a grooved member 32 are set between electrodes 20 with metal powder 19 inserted at the bonding interface. Then, both joining members 31 and 32 are pressurized by the pressurizing device 33 via the pressurizing shaft 34. The junction current is transferred from the power supply 35 to the current control circuit 36 and the transformer 3.
7 to the electrode 20. At this time, the temperature of the bonding interface is determined by the small measurement hole 3 on the thin plate member 31 side.
8 and inserting an optical fiber head 39 therein, the infrared rays are detected by an infrared detection circuit 40.
In the figure, 41 is an insulating layer, and 42 is a support base. As shown in the time chart of FIG. 8, the welding process begins with application of a set large current _I1 while applying a high pressure _P1 . Next, it is determined whether the interface temperature has reached a predetermined maximum temperature θmax by comparing the output of the maximum temperature setting circuit 43 and the output of the infrared detection circuit 40, and the interface temperature is When θmax is reached, the pressurizing force is changed to P ₂ by the pressurizing control circuit 45. On the other hand, at the same time, the gate of the gate circuit 46 is opened, and the control of the junction current is started by the diffusion treatment temperature setting circuit 47 and the comparison circuit 48 so that the temperature of the junction interface becomes a constant temperature θconst. The diffusion treatment temperature θconst at this time is set to a temperature lower than the melting point θm ₁ of the base material and higher than the melting point θm ₂ of the inserted metal powder 19. θ
This is because if the cost is higher than θm ₁ , the base material may melt and be deformed by pressurization. This is because if θcost is lower than θm ₂ , the insert material will not melt and the diffusion process will not progress sufficiently. It is more desirable for the insert material to be in a liquid state during the diffusion treatment.

On the other hand, when the temperature reaches θmax, the pressurizing force is decreased from P ₁ to P ₂ as shown in FIG. This is due to the following reason. Although a high pressure force is required when extruding the insert material from the interface, a high pressure force is not required after the insert material is extruded. Furthermore, by lowering the pressing force, deformation of the base material can be further prevented.

Even if the melting point of the insert material is higher than that of the base material, the insert material melts at a temperature lower than the melting point of the base material due to the diffusion process between the base material and the insert material. , θcost θ
It can be maintained between m ₁ and θm ₂ .

According to this example, since a two-stage switching pressure mechanism is adopted that switches the pressure from P ₁ to P ₂ , the pressure during the diffusion treatment process can be set low, so that the diffusion treatment temperature θconst can be adjusted to Since the melting point of the base material is raised to near the melting point of the base material, which is higher than the melting point of the raw material, the diffusion rate of each element becomes faster and the diffusion process time can be shortened.

Note that gas turbine blades and the like require liquefaction treatment and aging treatment after joining, but in such a case, liquefaction treatment and aging treatment may be performed simultaneously during the diffusion treatment in the present invention.

Metals were actually joined using the apparatus shown in FIG. 7 above. The details are explained below. The situation when BNi-2 brazing filler metal powder with a melting point of 960℃ is inserted into the butt joint interface of stainless steel, and the welding is performed under the following conditions: current density 68A/mm ² , pressing force 4Kg/mm ² , and energization time 1 second. Observed with a high-speed camera. As a result, we confirmed a phenomenon in which molten brazing filler metal was extruded from the bonding interface when the bonded members were in a dark red color, i.e., at approximately 700°C. In other words, under these bonding conditions, the temperature at the bonding interface could be increased by at least 260°C compared to the base material temperature.

Next, we turned to a heat-resistant superalloy (Inconel 625).
We tried joining by inserting BNi-2 brazing filler metal powder. As a result, the bonding layer thickness was 20 μm as shown in Figure 3.
It has become clear that the following joint can be obtained.
At this time, EPMA analysis revealed that a considerable amount of base metal elements had dissolved into the bonding layer. Moreover, the base material portion at this time had the same structure as the base material before bonding at a distance of 5 μm or more from the bonding layer. Also the fourth
The figure shows the joint shown in Figure 3 in a vacuum furnace at 100°C below the melting point of the base material.
A photograph of the structure obtained when the material was held at a high temperature of ℃ for 20 minutes is shown, and the structure is the same as the base material except for the size of the crystal grains, and it is clear that it can be homogenized in a short time. In this way, the temperature of the parts during bonding can be lowered, so high pressure can be applied without deforming the parts, so the thinner bonding layer allows for a shorter diffusion time to make the bonding layer homogeneous with the base material composition. Can be done.

As described above, according to the present invention, the insert material is inserted into the gap between the two base materials to be joined, and the insert material is heated with electricity while applying pressure, and the parts are joined by local heat generation at the joining interface. Since the temperature can be lowered and high pressure can be applied without causing deformation of the parts, sound bonding can be achieved with a thin bonding layer, and flux etc. is used to melt the parts surface at the bonding interface. Can be bonded in the atmosphere without any problems. Furthermore, since the process can be carried out in the atmosphere, the bonding apparatus can be simplified.

In addition, the present invention maintains the bonding interface temperature between the base materials at a value lower than the melting point of the base material and higher than the melting point of the insert material when performing the diffusion treatment after the electrical heating for the above-mentioned local heat generation treatment. , diffusion proceeds sufficiently without causing deformation of the base material, and the bonding interface between the base materials can be made uniform. Furthermore, since the bonding layer is thin, the diffusion treatment time can be shortened and production efficiency can be improved.

Furthermore, in the present invention, after the above-mentioned electrical heating for local heat generation, the melt at the joint interface between both members is pushed out of the joint, so even if the base material and the insert material are different materials, the joint layer will not overlap with the base material. The composition will be similar to that of the previous one, and the bonding strength will improve.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an apparatus for carrying out the conventional joining method, Fig. 2 A and B are schematic diagrams of the joining part in the conventional joining method, and Fig. 3 is a joint joined by the joining method according to the present invention. FIG. 4 is an optical photograph of the bonded portion after diffusion treatment, FIG. 5 and FIG. 7 are schematic diagrams of the apparatus for carrying out the bonding method according to the present invention,
Fig. 6A is a time chart showing the operation of the device shown in Fig. 5, Fig. 6B is a schematic diagram of the joint and a distribution diagram of electric resistance and temperature, and Fig. 8 shows the operation of the device shown in Fig. 7. It is a time chart. 4, 31, 32...Joining member, 19...Metal powder,
20... Electrode, 24... Infrared focusing head, 25... Optical fiber, 26, 40... Infrared detection circuit, 27
...Temperature judgment circuit, 22, 37...Transformer, 21,
36... Current control circuit, 33... Pressure device, 34... Pressure shaft, 38... Measurement hole, 39... Optical fiber head,
41... Insulating layer, 42... Support stand, 43... Maximum temperature setting circuit, 44, 48... Comparison circuit, 45... Pressure control circuit, 46... Gate circuit, 47... Diffusion treatment temperature setting circuit.

Claims (1)

[Scope of Claims] 1. An insert material made of an alloy having a composition close to that of the base material, or a metal that can form an integral alloy with the base material,
A heating step of inserting it into the gap between the two base materials to be joined and heating it with electricity while applying pressure, and detecting the temperature of the joining interface, and when the detected temperature reaches the melting point of the base materials, the above-mentioned a diffusion treatment step of reducing the applied current and maintaining the temperature of the bonding interface at a value lower than the melting point of the base material and greater than the melting point of the insert material for diffusion treatment; A metal joining method characterized by comprising an extrusion step of extruding. 2. The method of joining metals according to claim 1, wherein the pressing force is lowered when the detected temperature reaches the melting point of the base material. 3. The metal joining method according to claim 1 or 2, wherein the insert material is metal powder.