Non-copper metal brazing and joining method

Abstract

To provide good brazing and joining for a non-copper metal.SOLUTION: A first member and a second member made of stainless steel and another non-copper metal are prepared, and an insert member made of alumina-dispersed reinforced copper or the like between both the members is prepared. The surfaces of the first and second members and the insert member are fine mirror-finished, and then using a BNi-6 brazing material which is a nickel alloy containing phosphorus of 11% but not copper, the first member, the brazing material, the insert member, the brazing material, and the second member are stacked in this order, and pressure is applied. In this state, heat treatment is performed at the heat treatment temperature of 960°C for 10 minutes. Then, after sufficient natural cooling, sudden cooling is performed using a nitrogen gas. Thus, non-copper metals can be brazed and joined well via the insert member.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for brazing non-copper-based metals together. [Background technology]

[0002] The inventors of the present application have been conducting extensive research into joining techniques for alumina dispersion strengthened copper, in which alumina is dispersed as an oxide, and have disclosed a technique that enables brazing joining. Patent Document 1 discloses a technique related to brazing between alumina dispersion strengthened copper alloys and between alumina dispersion strengthened copper and stainless steel. Patent Document 2 discloses a technique related to brazing between alumina dispersion strengthened copper and steel containing one or both of a ferrite phase and a martensite phase, or between alumina dispersion strengthened copper and iridium. Patent Document 3 discloses a technique related to brazing between copper and copper alloys other than alumina dispersion strengthened copper and oxygen-free copper, alumina dispersion strengthened copper, stainless steel, steel containing one or both of a ferrite phase and a martensite phase, tungsten, and iridium. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6528257 [Patent Document 2] Patent No. 6606661 [Patent Document 3] Patent No. 6852927 Summary of the Invention [Problem to be solved by the invention]

[0004] However, brazing joints between non-copper-based metals that do not contain copper have not been realized until now. In view of the above, an object of the present invention is to provide a brazing method for joining non-copper-based metals together. [Means for solving the problem]

[0005] The present invention provides A joining method for brazing a first member and a second member, both of which are made of a non-copper-based metal, comprising: (a) providing a phosphorus-containing, copper-free brazing filler metal; (b) preparing the first member, the second member, and an insert member, each of which is made of alumina dispersion strengthened copper, oxygen-free copper, tough pitch copper, or phosphorus deoxidized copper; (c) a joining step of laminating the first member, the brazing material, the insert member, the brazing material, and the second member in this order, heating them at a predetermined heat treatment temperature for a predetermined time, and then cooling them; The joining method may be such that the heat treatment temperature is set in a range lower than the melting point of the insert member and higher than the melting point of the insert member lowered by the eutectic reaction between phosphorus and copper.

[0006] In the present invention, an insert member made of any of alumina dispersion strengthened copper, oxygen-free copper, tough pitch copper, and phosphorus deoxidized copper (hereinafter, in this specification, they may be collectively referred to as "alumina dispersion strengthened copper, etc.") is interposed between non-copper-based metals. By doing so, the first member and the insert member are brazed together, and further the insert member and the second member are brazed together, thereby achieving brazed joining between non-copper-based metals as a whole.

[0007] As shown in Patent Documents 1 to 3, the inventors have previously conducted research into brazing using brazing filler metals that contain phosphorus but not copper, and have found that good brazing is possible between various metals. The principle behind this brazing is not entirely clear, but it is thought to be due to a eutectic reaction occurring between the phosphorus in the brazing filler metal and copper, which then diffuses into the joint. According to this principle, brazing cannot be performed between non-copper-based metals. However, as described above, by interposing an insert member between the first and second members made of a non-copper metal, it was possible to realize a joining method that uses brazing as a whole. The thickness of the insert member can be determined arbitrarily, but for example, by making the insert member thinner than one or both of the first and second members, the insert member cannot be clearly seen after joining, and the appearance can be such that the first and second members are substantially directly joined. The thickness of the insert member can be, for example, 2 mm or less, or 1 mm or less.

[0008] The joining method of the present invention is characterized by extremely high strength at the joint because it is achieved by diffusing the copper of the insert member. In addition, since the joint achieves a dense structure without voids, there is also the advantage that there is no need to worry about fluid leakage when used in piping, for example.

[0009] In the present invention, the phosphorus content of the brazing filler metal can be determined arbitrarily, but in the experiment, a nickel alloy with a phosphorus content of 11%, specifically BNi-6, was used. The copper of the first member may be, for example, oxygen-free copper, tough pitch copper, phosphorus-deoxidized copper, etc. The copper alloy may be a copper alloy mixed with other components such as zinc, tin, or silver. The heat treatment time can be experimentally determined based on the type of metal to be joined and the results of the joining. In the experiment, the time was set to 10 minutes, but it may be shorter. Furthermore, the shapes and dimensions of the first and second members are not important. The shape of the insert member can also be determined arbitrarily. However, from the viewpoint of achieving a strong bond, it is preferable that the shape of the insert member has an area that completely covers the bonded portion between the first and second members, and from the viewpoint of avoiding waste, it is preferable that the shape of the insert member be the same as the bonded portion.

[0010] In the present invention, the non-copper metal means a metal that does not contain copper. The first and second members may be made of the same type of non-copper metal, or may be made of different types. It is preferable that the melting point of the non-copper metal is higher than the heat treatment temperature, which can prevent the first and second members from being deformed during the joining process.

[0011] In view of the above, in the present invention, The first and second members are preferably made of stainless steel, steel containing one or both of a ferrite phase and a martensite phase, tungsten, iridium, or a cemented carbide, respectively. However, it is not intended to be limited to these metals. Here, cemented carbide refers to a composite material in which carbides of metals from Groups IVa, Va, and VIa of the Periodic Table are sintered with iron-based metals such as Fe, Co, and Ni. Although the type of cemented carbide is not limited, it is preferable to use a WC-Co alloy, as experiments have confirmed that good brazing joints can be obtained with WC-Co alloys.

[0012] In the present invention, the first member, the insert member, and the second member may all be joined in one joining step, or may be joined in two separate steps.

[0013] Therefore, in the present invention, the first member and the second member are made of different types of metals, a difference in thermal expansion coefficient between the first member and the insert member is smaller than a difference in thermal expansion coefficient between the second member and the insert member; The step (c) (c1) a first joining step of laminating the first member, the brazing material, and the insert member in this order, heating them at a predetermined heat treatment temperature for a predetermined time, and then cooling them; (c2) The joining method may include a second joining step in which the brazing material and the second member are sequentially stacked on the insert member of the member obtained in the first joining step, heated at a predetermined heat treatment temperature for a predetermined time, and then cooled.

[0014] For example, if the first and second components are made of different materials, i.e., have different thermal expansion coefficients, and are subjected to heat treatment all at once, the difference in thermal expansion will cause different thermal expansions and thermal distortions at the first joint between the first component and the insert component and the second joint between the second component and the insert component, which may result in poor bonding at either the first or second joint. In contrast, in the above embodiment, the insert member is first joined to a first member having a similar thermal expansion coefficient, and then the joining member that joins the first member and the insert member is joined to the second member, thereby mitigating the above-mentioned disadvantages. However, with this method, the first member and the insert member are subjected to two heat treatments, which causes thermal distortion depending on the difference in thermal expansion coefficients between the first member and the insert member. The greater the difference in thermal expansion coefficients between the first member and the insert member, the greater the impact. Therefore, in the above-mentioned embodiment, the first member made of a material with a thermal expansion coefficient close to that of the insert member is first joined, thereby mitigating the impact of the two heating processes. By doing so, good brazing can be achieved even when the first member and the second member are made of different materials.

[0015] When the joining step is carried out in two stages as described above, a polishing step of refining the surface of the insert member to a microscopic finish may be provided between the first joining step and the second joining step. This can avoid problems such as deformation of the insert member during the first joining step, resulting in a poor joining surface with the second member. Furthermore, a step of thinning the insert member may be performed in conjunction with the micro-surface finishing process. This allows the first joining step to be performed using a thick insert member, which can prevent poor joining due to, for example, an insert member that is too thin.

[0016] In the present invention, The bonding method may be such that the heat treatment temperature is 960°C. However, the temperature is not limited to this.

[0017] In the present invention, (d) a step of finishing the surfaces of the first member and the second member to be joined to a microscopic surface prior to the heat treatment step; The brazing filler metal in the heat treatment step may have a thickness of 1 to 100 micrometers.

[0018] The surface finish and thickness of the brazing material can be determined arbitrarily, but it has been found that by setting them as described above, a brazing joint with excellent adhesion can be achieved. The thickness is preferably 38 to 76 micrometers, and more preferably about 38 micrometers.

[0019] In addition, in the present invention, In the heat treatment step, pressure may be applied to the first member and the second member in a direction in which they are joined together.

[0020] This makes it possible to further improve the adhesion of the bonded portion. The pressure can be applied in a variety of ways. For example, a hot press may be used, that is, a method in which the first and second members are sandwiched and pressed using a press machine installed in a heat treatment furnace. When using such a method, it is preferable to set the heat treatment process taking into account the heat capacity of the press machine. Another method is hot isostatic pressing (HIP), which applies pressure isotropically and is useful when joining is required in multiple directions.

[0021] The pressure can be applied, for example, by providing first and second end plates fastened to each other and a center plate disposed therebetween; the first end plate and the center plate sandwich the first member and the second member; An elastic body may be interposed between the second end plate and the central plate to apply pressure to the first and second members disposed between the first end plate and the central plate.

[0022] This method has the advantage that pressure can be applied relatively uniformly to the first and second members because pressure is applied via the plate-like first and second end plates and center plate. It also has the advantage that pressure can be applied relatively inexpensively and is relatively easy to apply because it does not require the use of special equipment, such as hot pressing or hot isostatic pressing. The material of the plate can be selected arbitrarily, but it is preferable to select a material with high rigidity. Although various elastic bodies can be selected, it is preferable that the elastic body be made of a material that can exert an elastic force during the heat treatment process, for example, a carbon spring can be used. The magnitude of the pressure can also be determined arbitrarily, but a pressure that provides a significant effect can be set to, for example, 0.54 MPa. In addition to the method using elastic force, a mode in which pressure is applied by placing a weight on a plate or member can also be used.

[0023] In addition, in the above embodiment, The first and second end plates and the central plate preferably have a thickness that ensures a substantially uniform pressure distribution across the first and second members.

[0024] This allows pressure to be applied uniformly to the first member and the second member, achieving uniform joining. The specific thicknesses of the first and second end plates and the center plate can be determined experimentally or analytically depending on the materials and the magnitude of the pressure. In order to achieve the above-mentioned uniform pressure distribution, it is preferable that the first and second end plates and the center plate have a mechanism that allows them to remain parallel to each other.

[0025] In the present invention, The step (c) may be natural cooling.

[0026] Because the heat treatment temperature is extremely high, the first and second members will cool naturally over a very long period of time, from several hours to 48 hours. This long cooling period has the advantage of alleviating the thermal stress caused by the heat treatment. The cooling time can be determined depending on the type of metal being joined. For example, it has been confirmed that a cooling time of around 8 hours is sufficient for metals with a thermal expansion coefficient relatively close to that of copper. After cooling by natural cooling to a temperature such as 100° C. at which the thermal expansion of both members is considered to have been sufficiently alleviated, forced cooling using a refrigerant may be performed.

[0027] The present invention can be applied to joining members of various shapes. As an example, One of the first member and the second member may be a sheet-like member with no rigidity, and the other may be a member shaped to reinforce the first member or the second member.

[0028] For example, tungsten, which is used to protect parts that become very hot, is generally provided as a very thin sheet material, which is often difficult to use as is. However, according to the above embodiment, the tungsten sheet material can be brazed to a component with a reinforcing shape, making it easy to handle. The reinforcing shape can be, for example, a plate material with a thickness that ensures sufficient rigidity.

[0029] The present invention does not necessarily have to include all of the various features described above, and the present invention may be configured by omitting or combining some of them as appropriate. Furthermore, the present invention may be configured not only as a joining method but also as a structure based on the joining method. [Brief explanation of the drawings]

[0030] [Figure 1]1 is a flowchart showing steps of a brazing process. [Figure 2] FIG. 10 is an explanatory diagram showing the influence of pressure applied during bonding. [Figure 3] FIG. 10 is an explanatory diagram showing the influence of the thickness of the brazing material. [Figure 4] FIG. 10 is an explanatory diagram showing the result of joining stainless steels together. [Figure 5] FIG. 10 is an explanatory diagram showing the analysis results of a joint. [Figure 6] FIG. 10 is an explanatory diagram showing an enlarged view of the analysis results of the joint. [Figure 7] FIG. 1 is an explanatory diagram showing the results of joining cemented carbide and stainless steel. [Figure 8] 1 is a flowchart showing the steps of a two-stage brazing process. [Figure 9] FIG. 1 is an explanatory diagram showing a process for joining tungsten and stainless steel. [Figure 10] FIG. 1 is an explanatory diagram showing the result of joining tungsten and stainless steel. DETAILED DESCRIPTION OF THE INVENTION

[0031] 1 is a flowchart showing the steps of the brazing process. In this process, first, the members to be joined are prepared (step S10). In this example, a first member and a second member made of a non-copper-based metal, and an insert member to be sandwiched between them, are prepared. The first and second members can be made of various materials, such as stainless steel, steel containing one or both of a ferrite phase and a martensite phase, tungsten, iridium, or cemented carbide. The insert member can be made of alumina dispersion strengthened copper, oxygen-free copper, tough pitch copper, or phosphorus deoxidized copper. The insert member is used to join the first and second members, and is therefore thinner than these members. The shapes of the first and second members are arbitrary, but the joining surfaces must be flat. The shape of the insert member can also be determined arbitrarily, but in this embodiment, in order to firmly braze the first and second members, it is preferable that the insert member has the same shape as the joining surfaces of the two members or a shape that can contact them over a larger area. It is also preferable that the surfaces of the insert member that contact the first and second members are flat.

[0032] Next, the joining surfaces are subjected to a micro-mirror finish (step S11). Generally, surface finishing is divided into stages of roughness, namely, coarse finish, medium finish, micro-mirror finish, and mirror finish, of which this is micro-mirror finish. The reason for using a micro-mirror finish is as follows: when performing brazing joining, if a mirror finish is used, the joining surfaces may become excessively smooth, and a strong joint may not be achieved. On the other hand, if the surface finish is rough, to put it in extreme terms, the components may be joined at points rather than at surfaces, and a strong joint may not be achieved either. After examining joining with various surface finishes, the inventors found that a micro-mirror finish is preferable.

[0033] Next, a brazing filler metal is prepared. In this example, BNi-6, a nickel alloy containing 11% phosphorus, is used. Various brazing filler metals can be selected as long as they contain phosphorus and do not contain copper. Then, a brazing filler metal is sandwiched between the first member and the insert member, and between the insert member and the second member, and pressure is applied (step S13). That is, pressure is applied to a state in which the first member, brazing filler metal, insert member, brazing filler metal, and second member are stacked in this order. The figure shows the method of applying pressure. In this example, three steel plates are prepared. From the bottom, they are referred to as the first end plate (or lower plate), the center plate (or middle plate), and the second end plate (or upper plate). A joining member is sandwiched between the first end plate and the center plate. A carbon spring is also sandwiched between the center plate and the second end plate. The first and second end plates are fastened with bolts. Using this structure, the elastic force of the carbon spring is applied to the joining members as pressure via the center plate. Another advantage is that pressure can be applied uniformly to the joining members while the first, second end plates, and center plate are kept parallel to each other. The pressure can be determined arbitrarily, but in this example, it was 0.54 MPa. The reason why a carbon spring is used in this embodiment is that a material that can withstand the heat treatment described below was selected, but other materials may also be used. Furthermore, the application of pressure is not necessarily required, and heat treatment may be carried out without applying pressure, although it is desirable to apply pressure in order to ensure airtightness of the joining surfaces.

[0034] Next, the bonded members are heat-treated while the pressure is still applied (step S14). The heat-treatment sequence is shown in the figure. Phase A is the temperature-raising phase for preheating. The temperature should be raised quickly to the target preheat temperature. Phase B is a preheating phase. In this example, the preheating was performed at 860°C for 60 minutes. The preheating temperature and time may be determined based on the furnace equipment used for the heat treatment, the dimensions of the members to be joined, the temperature of the heat treatment, etc. Phase C is a temperature-raising phase up to the heat treatment temperature. The temperature should be raised quickly to the target heat treatment temperature. Phase D is the heat treatment phase. In this example, heat treatment was performed at 960°C for 10 minutes. The heat treatment temperature of 960°C can be determined as follows. The insert member in this example is either alumina dispersion strengthened copper, oxygen-free copper, tough pitch copper, or phosphorus deoxidized copper. To avoid melting of the member, the heat treatment temperature must be lower than the melting point of the insert member (e.g., 1085°C for alumina dispersion strengthened copper). In this example, the principle behind the brazing joint is believed to be that the melting point of the insert member is lowered by the eutectic reaction between phosphorus and copper contained in the brazing filler metal, resulting in melting of the outermost surface of the joining member. Therefore, the heat treatment temperature must be higher than the melting point of the insert member during the eutectic reaction. In this example, 960°C was selected as the heat treatment temperature from within this temperature range. The heat treatment time can also be determined arbitrarily. In this example, 10 minutes was used, but brazing joints can also be achieved in as little as 2 to 3 minutes. Phase E is the cooling phase. In this phase, the parts are gradually cooled over a long period of time to relieve thermal stress. In this example, the parts were naturally cooled to approximately 100°C in a furnace over approximately 8 hours. The cooling time can be determined arbitrarily within a range of several hours to 48 hours, taking into account the quality of the materials to be joined. Phase F is a rapid cooling phase. Since it is determined that the thermal expansion of both components has been sufficiently alleviated by the cooling in Phase E, the components may be rapidly cooled thereafter. In this example, cooling was performed using nitrogen gas to prevent oxidation of the components. The rapid cooling phase is not necessarily required, and cooling in Phase E may be continued until the components reach room temperature. The brazing joint of this embodiment is achieved through the above steps.

[0035] In this example, both the heat treatment and cooling were vacuum heat treatment and cooling in a vacuum. The vacuum referred to here means a state in which the pressure inside the furnace is sufficiently reduced by evacuating with a vacuum pump, and is not limited to a complete vacuum. It can also be called an extremely low pressure. By creating a vacuum or extremely low pressure in this way, oxidation of the joining members can be suppressed. However, the heat treatment and cooling may also be performed under atmospheric pressure.

[0036] Next, the effects of pressure and the thickness of the brazing filler metal will be explained based on the results of an experiment in which both the first and second members were made of GlidCop (registered trademark), an alumina dispersion strengthened copper material, and BNi-6 was used as the brazing filler metal. FIG. 2 is an explanatory diagram showing the effect of pressure applied during bonding. FIG. 2(a) shows the shapes of the members to be joined. Member A is an alumina dispersion strengthened copper member, more specifically, a GlidCop (registered trademark) member, with the flow path shown in the figure cut into it. Member B is a plate-shaped GlidCop (registered trademark) member that covers the flow path. The periphery of the flow path forms the joint between members A and B. Figures 2(b1) and 2(b2) show the state when pressure is applied to the components. The lower and upper plates are fastened with bolts, and there is a connecting member between the lower and middle plates, and a carbon spring is sandwiched between the middle and upper plates. The elastic modulus of the carbon spring is also the same. The difference is that the thickness of each plate in Figure 2(b2) is about 2.5 to 3.5 times that of Figure 2(b1). Figures 2(c1) and 2(c2) show the results of ultrasonic testing corresponding to Figures 2(b1) and 2(b2), respectively. The area around the flow path is shown as seen from above. In Figure 2(c1), numerous streaky patterns can be seen around the flow path. These represent areas of poor bonding where parts A and B are not sufficiently bonded. On the other hand, no such poor bonding is visible in Figure 2(c2). In Figures 2(b1) and 2(b2), the pressure applied by the carbon springs is the same, so the pressure on the components should be equal. However, in Figure 2(b2), where each plate is thick, the pressure is applied uniformly, whereas in Figure 2(b1), where each plate is thin, the pressure is uneven. Therefore, it is preferable that the thickness of the plates used to apply pressure is sufficiently thick. The specific thickness is considered to be preferable so that deflection due to pressure is sufficiently suppressed. This can be determined experimentally by bonding various thicknesses and checking for bond failure, as shown in Figures 2(b1) and 2(b2). Here, results for two thicknesses are shown; however, by conducting experiments with more thicknesses, it is possible to determine the thickness necessary to avoid bond failure.

[0037] Figure 3 is an explanatory diagram showing the effect of brazing filler metal thickness. The brazing filler metal thickness refers to the thickness of the brazing filler metal layer interposed between two components. The left column in Figure 3 shows the results when the brazing filler metal thickness was 38 micrometers, and the right column shows the results when the brazing filler metal thickness was 76 micrometers. Figures 3(a1) and 3(a2) show the joined components as viewed from directly above. In this example, two rectangular components of a uniform thickness are joined, with a rectangular window formed in the center of the upper component. Both components are made of GlidCop (registered trademark). As shown in Figures 3(a1) and 3(a2), it can be seen that the brazing filler metal slightly protrudes from the joining surface to the inside of the window, with the thicker brazing filler metal in Figure 3(c2) protruding more. Figures 3(b1) and 3(b2) show the joined components viewed from the side. It can be seen that the discolored area is larger in Figure 3(b2), where the brazing filler metal is thicker. Figures 3(c1) and 3(c2) show the window area viewed from an oblique angle. It can be seen that a larger amount of brazing filler metal is protruding from the thicker brazing filler metal in Figure 3(c2). Figures 3(d1) and 3(d2) show the results of ultrasonic testing. It can be seen that the brazing filler metal has protruded inside the rectangular frame corresponding to the window. Furthermore, in Figure 3(d2), where the brazing filler metal is thick, many streaky areas of poor bonding can be seen around the window, but in Figure 3(d1), where the brazing filler metal is thin, no such poor bonding can be seen. From the above, it can be seen that a thicker brazing filler metal is not necessarily better. The appropriate brazing filler metal thickness is thought to be determined depending on the level of surface finish. In the case of a micro-mirror finish, 38 micrometers is preferable to 76 micrometers. In this example, results are shown for two thickness levels, but it is possible to determine the appropriate brazing filler metal thickness by performing joining and inspection at multiple thickness levels. In addition, in this example, the presence or absence of joining defects is inspected using ultrasonic flaw detection, but the mechanical strength of the joint may also be measured at the same time. 2 and 3 show the results of an experiment using GlidCop®, but it can be said that the effects of pressure and brazing material thickness are similar between various materials, such as non-copper metals.

[0038] As a first example, joining of the same kind of non-copper metals will be described below. FIG. 4 is an explanatory diagram showing the results of joining stainless steel pieces together. FIG. 4(a) shows a schematic diagram of the joined state. In the first example, an insert member 12 made of alumina dispersion strengthened copper is interposed between a first member 11 and a second member 13 made of stainless steel. Any stainless steel can be used, but in this example, SUS316L was used. GlidCop (registered trademark) was used as the alumina dispersion strengthened copper. Because the insert member 12 is used to join the first member 11 and the second member 13 rather than being an inherent member, its thickness t2 is desirably set to be sufficiently thinner than the thicknesses of the first member 11 and the second member 13. On the other hand, the thicknesses of the first member 11 and the second member 13 may be thinner than t2. In this example, the first member 11 and the second member 13 are test pieces with a thickness of approximately 10 mm, and the thickness t2 of the insert member 12 is set to 2 mm or less. In this example, the first member 11 and the insert member 12 are brazed together, and the insert member 12 and the second member 13 are brazed together, thereby joining the first member 11 and the second member 13 as a whole. Therefore, the insert member 12 needs to have a thickness that enables such brazing. The lower limit of the thickness of the insert member 12 can be determined by experiment or the like within a range in which such a joining is possible.

[0039] During brazing, as shown in the figure, the first member 11, brazing material, insert member 12, brazing material, and second member 13 are stacked in this order, and then heat treatment is performed. BNi-6 can be used as the brazing material. The thicknesses t1 and t3 of the brazing material can be determined arbitrarily, but are preferably in the range of 1 to 100 micrometers, for example. Considering the results shown in FIG. 3, the thicknesses t1 and t3 of the brazing material are more preferably 38 to 76 micrometers, and even more preferably about 38 micrometers. The thicknesses t1 and t3 of the brazing material do not need to be the same and may be different thicknesses.

[0040] An electron microscope photograph of the joined cross section is shown in Figure 4(b). The first component 11 corresponds to the area indicated by arrow e, the insert component 12 corresponds to the area indicated by arrow c, and the second component 13 corresponds to the area indicated by arrow a. The brazing filler metal corresponds to the area between the second component 13 and the insert component 12, and the area between the first component 13 and the insert component 12, as indicated by arrows b and d, but cannot be seen because it melts during the heat treatment. In the example of Figure 4(b), the area corresponding to the insert member 12 can also be seen, but if the thickness of the insert member 12 is made thinner, it is possible to achieve an appearance in which the insert member 12 is not substantially present. Fig. 4(c) shows an enlarged electron microscope photograph of region A of the joint in Fig. 4(b). From this photograph, it can be seen that the first member 11, the insert member 12, and the second member 13 are brazed together very tightly.

[0041] Figure 5 is an explanatory diagram showing the analysis results of the joint. Figure 5(a) is the same electron microscope photograph as Figure 4(c), and is an enlarged photograph of a partial region of the joint. Figure 5(b) is a mapping image of the iron component distribution measured in the region shown in Figure 5(a). In the image, the part corresponding to the insert member 12 is black, indicating that almost no iron was detected. The parts corresponding to the first member 11 and the second member 13 are gray, indicating that iron components were detected. Figure 5(c) shows the same copper distribution measurement. In the figure, the part corresponding to the insert member 12 is gray, indicating that copper was detected. The parts corresponding to the first member 11 and the second member 13 are black, indicating that no copper was detected. Figure 5(d) shows the nickel component distribution measured in the region shown in Figure 5(a), and Figure 5(e) shows the phosphorus component distribution measured in the same region. It can be seen that nickel and phosphorus were detected at the boundaries between the insert member 12 and the first member 11 and the second member 13, respectively.

[0042] The results of a further enlarged component analysis of the region AA shown in FIG. 5(a), ie, the boundary portion between the insert member 12 and the second member 13, are shown below. Figure 6 is an explanatory diagram showing an enlarged view of the analysis results of the joint. Figure 6(a) is an enlarged photograph of region AA in Figure 5(a). Figure 6(b) shows the iron detection results for that region, and Figure 6(c) shows the copper detection results. In both images, it can be seen that the undetected region (black region) and the detected region (gray region) are not clearly separated, but rather there is a gradual change in the boundary between them. This indicates that the copper component of the insert member 12 has diffused into the second member 13, or that components such as iron of the second member 13 have diffused into the insert member 12. Figure 6(d) shows the detection results for nickel at the joint, and Figure 6(e) shows the detection results for phosphorus at the joint. Nickel and phosphorus were also detected at the boundary between the insert member 12 and the second member 13, and it can be seen that they also change gradually in a gradational manner. This indicates that the nickel and phosphorus contained in the brazing filler metal are also diffusing into the insert member 12 and the second member 13.

[0043] As confirmed above, it can be seen that brazing can be achieved between the stainless steel first member 11 and second member 13 by interposing the alumina dispersion strengthened copper insert member 12 between them. In other words, brazing is achieved between the first member and the insert member 12, and brazing is also achieved between the second member 13 and the insert member 12, thereby achieving brazing of the first member 11 and the second member 13 as a whole. As shown in Figures 5 and 6, brazing is a very strong joint because it is a joint that is formed by the diffusion of metal components (especially copper components).

[0044] In the first example, alumina dispersion strengthened copper was used as the insert member 12. As can be seen in Figures 5 and 6, this brazing is thought to be due to the copper melting and diffusing at the joint due to a eutectic reaction between the phosphorus contained in the brazing material and the copper contained in the first member. Therefore, as already confirmed in Patent Documents 1 to 3 by the same inventor, it is believed that similar results to those of the first embodiment can be obtained even if oxygen-free copper, tough pitch copper, or phosphorus-deoxidized copper other than alumina dispersion strengthened copper is used as the insert member 12.

[0045] As a second embodiment, joining of different non-copper metals will be described below. FIG. 7 is an explanatory diagram showing the results of joining cemented carbide and stainless steel. The joining state is shown schematically in Figure 7(a). In the second example, a first member 11a made of stainless steel and a second member 13a made of cemented carbide are used, with an insert member 12a made of alumina dispersion strengthened copper interposed between them. The stainless steel and alumina dispersion strengthened copper are the same materials as in the first example, and a WC-Co alloy is used as the cemented carbide. The thickness t12 of the insert member 12a can also be determined arbitrarily, as in the first example, but here it is set to 2 mm or less. In brazing, the first member 11a, the brazing material, the insert member 12a, the brazing material, and the second member 13a are stacked in this order, and then heat treated as shown in the figure. The brazing material used is BNi-6, and its thicknesses t11 and t13 are the same as those in the first example.

[0046] 7(b) shows a cross section of the joined parts. The first member 11a corresponds to the area indicated by arrow e, the insert member 12a corresponds to the area indicated by arrow c, and the second member 13a corresponds to the area indicated by arrow a. As indicated by arrows b and d, the brazing filler metal corresponds to the boundary L1 between the second member 13a and the insert member 12a and the boundary L2 between the first member 11a and the insert member 12a, but cannot be seen because it melts during heat treatment. The shading pattern appearing in the cemented carbide region is an external appearance that is influenced by the melting of the brazing material, and is unrelated to the internal bonding state.

[0047] Figure 7(c) shows the results of an ultrasonic flaw detection test of the boundary L1 between the second member 13a and the insert member 12a. The test was performed in the direction of arrow V in Figure 7(b). The white rectangular area A1 near the center is the edge of the bonded interface. Furthermore, the slightly shaded rectangular area A2 near the center indicates the area that is well bonded. The ultrasonic flaw detection test confirmed that the area A2 near the center of the bond is well bonded with sufficient uniformity and no bonding defects.

[0048] FIG. 7(d) shows the results of ultrasonic testing of the boundary L2 between the first member 11a and the insert member 12a. The white rectangular area A3 near the center is the edge of the bonded interface. Furthermore, the slightly shaded rectangular area A4 near the center indicates a portion where the bond is slightly defective (note that the display is reversed from FIG. 7(c)). That is, the ultrasonic testing results showed that the peripheral portion of the bond was well brazed, while a slight bond defect was confirmed in the area A3 near the center. However, because the bond defect in area A4 was only confirmed by the ultrasonic testing and was only small in area, the bonded portion between the first member 11a and the insert member 12a maintained a bond strength sufficient for practical use.

[0049] 7, it was confirmed that a generally satisfactory brazing joint was achieved overall even when different non-copper metals, such as alumina dispersion strengthened copper for the insert member 12a, stainless steel for the first member 11a, and cemented carbide WC-Co alloy for the second member 13a, were used. The principle behind the overall brazing is thought to be that, as in the first example, copper melts and diffuses in the joint due to a eutectic reaction between phosphorus contained in the brazing filler metal and copper contained in the insert member 12a.

[0050] Although brazing with cemented carbide had not been confirmed previously, the results of Fig. 7 confirmed that good brazing can also be achieved with cemented carbide. Brazing is achieved by either melting and diffusion of copper or the anchor effect of molten copper conforming to the irregularities on the surface of the materials to be joined, and it is considered that the cemented carbide of the second member 13a is sufficient as long as it can accept the diffused copper or the copper that conforms to the anchor effect. From this perspective, it is considered that there is no difference between WC-Co based cemented carbide and other cemented carbide, and therefore, based on the results of Fig. 7, it is considered that good brazing can be achieved not only with WC-Co based cemented carbide but also with cemented carbide in general. Furthermore, according to the results of Figure 7, there is no effect of one member interfering with the brazing between the first member 11a and the insert member 12a or the brazing between the second member 13a and the insert member 12a, so different types of non-copper-based metals can be selected arbitrarily for the first member 11a and the second member 12a.

[0051] However, in the second example (FIG. 7), as shown in FIG. 7(d), some bonding defects were observed in some places, and a method for improving this will be investigated. The reason for this poor bonding is thought to be as follows: When the first and second members are made of different materials, their thermal expansion coefficients are different, so if they are heat-treated together at once, the difference in thermal expansion will cause different thermal strains at the first bonding region between the first member and the insert member and the second bonding region between the second member and the insert member, which can result in poor bonding at either the first bonding region or the second bonding region. Therefore, it is believed that the above-mentioned adverse effects can be alleviated by performing brazing in two stages, such as first joining a member with a thermal expansion coefficient close to that of the insert member, and then joining the other member.

[0052] The two-stage brazing process will now be explained. Here, of the first and second components, the one with a thermal expansion coefficient closer to that of the insert component will be referred to as the first component. In the case of the cemented carbide and stainless steel shown in Figure 7, the stainless steel has a thermal expansion coefficient closer to that of the alumina dispersion strengthened copper that makes up the insert component, so the stainless steel will be the first component and the cemented carbide will be the second component.

[0053] FIG. 8 is a flowchart showing the steps of a two-stage brazing process. First, the first member, brazing material, and insert member are stacked together to carry out the first joining process (step S20). The stacked state is shown schematically in the figure. The hatched portion is the brazing material. The joining process itself can be carried out using the steps shown in FIG.

[0054] Next, the surface of the insert member is subjected to a micro-mirror finish (step S21). This is because the heating in the first joining process may roughen the surface of the insert member, which may cause problems when joining it to the second member. In the example shown in the figure, the top surface of the insert member is subjected to a micro-mirror finish. This makes it possible to join the second member well to the top surface of the insert member. However, the micro-mirror finish is not essential, and may be omitted if the top surface of the insert member is in a sufficiently good condition for joining after the first joining process.

[0055] It is also possible to adjust the thickness of the insert member in conjunction with the surface finishing of the insert member. In this way, for example, the insert member can be prepared to be thicker during the first joining process, and after the first joining process is completed, the insert member can be made sufficiently thin, leaving a thickness necessary for subsequent joining with the second member, taking into account the copper diffusion state.

[0056] Next, the brazing material and the second component are layered on the insert component, and a second joining process is performed (step S22). The brazing material and the second component are layered on top of the already joined first component and insert component. The joining process itself can be performed using the steps shown in FIG. 1. Because the first component and the insert component are already joined, the influence of the difference in thermal expansion coefficients between the first component and the insert component on the joint during the second joining process is thought to be reduced compared to when the first component and the second component are joined simultaneously. Therefore, by performing this two-stage brazing process, it is possible to reduce joining defects caused by the difference in thermal expansion coefficients, as shown in FIG. 7(d).

[0057] Hereinafter, as a third embodiment, an example of joining a stainless steel reinforcing material to a tungsten sheet material will be described. This corresponds to the brazing joining of dissimilar non-copper materials shown in the second embodiment, but is a more practical example. That is, tungsten is sometimes used to improve the heat resistance of high-temperature parts, but it is generally supplied in the form of a very thin sheet with no rigidity, making it difficult to use. Therefore, if a reinforcing material could be brazed to the back of the sheet-shaped tungsten, it would be easier to handle. In the third example, a stainless steel plate is used as such a reinforcing material.

[0058] Figure 9 is an illustration of the tungsten to stainless steel joining process, which follows the two-stage brazing process (see Figure 8). As shown in Figure 9(a), first, a stainless steel reinforcing material with a thermal expansion coefficient close to that of the alumina dispersion strengthened copper insert material is brazed to the stainless steel plate material as the first member, and then the brazing material and the alumina dispersion strengthened copper insert material are layered on top of each other, and heated to perform the first joining process. Figure 9(b) shows the result of the first joining process, where the insert member is joined to the top surface of the stainless steel. Next, as shown in Figure 9(c), the upper surface of the insert member is subjected to a micro-mirror finish. At the same time, a process for adjusting the thickness may be carried out. Then, as shown in FIG. 9(d), a brazing material and a tungsten sheet as the second member are laminated on the upper surface of the insert member, and heated to perform a second joining process. 9(e) shows the state after the second joining process is completed, where the stainless steel and tungsten are joined together via the insert member made of alumina dispersion strengthened copper.

[0059] Figure 10 is an explanatory diagram showing the results of joining tungsten and stainless steel. Figure 10(a) shows a schematic diagram of the joined test piece. A square test piece measuring 40 mm on each side was used. The joining condition was confirmed at the BB cross section approximately 5 mm from one side of this piece. Figure 10(b) shows the joining state of the B-B cross section. As shown in the upper photograph, a uniform joining is apparent throughout the entire surface. The lower photograph shows an enlarged cross section of regions B1 and B2 near both ends of the B-B cross section. From the top, the tungsten, alumina dispersion strengthened copper, and stainless steel layers can be seen. It can also be seen that the boundaries between these layers are not clearly defined, but rather have a slightly blurred gradation. The joining area where the gradation is particularly strong is the interface between the alumina dispersion strengthened copper and stainless steel. This interface is primarily joined by diffusion between the two materials. At the interface between the tungsten and alumina dispersion strengthened copper, where the gradation is weak, the joining is primarily achieved by the anchor effect, where the molten copper conforms to the irregularities on the tungsten surface. This confirms that joining by diffusion or the anchor effect occurs at the boundary between each layer, resulting in good brazing.

[0060] According to the above-described embodiments, the use of an insert member allows for good brazing of the first and second members made of non-copper-based metals. This also applies when the first and second members are made of different materials.

[0061] It is not necessary to have all of the various features described above, and some may be omitted or combined as appropriate. The present invention can be applied to various non-copper metals that can be brazed, regardless of the materials shown in the examples. For example, in addition to stainless steel, cemented carbide, and tungsten, steel containing either or both of a ferrite phase and a martensite phase, and iridium can be used. [Industrial Applicability]

[0062] The present invention can be used for brazing non-copper-based metals together. [Explanation of symbols]

[0063] 11, 11a First member 12, 12a Insert member 13, 13a Second member

Claims

1. A joining method for brazing a first member and a second member, both of which are made of a non-copper-based metal, comprising: (a) providing a phosphorus-containing, copper-free brazing filler metal; (b) preparing the first member, the second member, and an insert member, each of which is made of alumina dispersion strengthened copper, oxygen-free copper, tough pitch copper, or phosphorus deoxidized copper; (c) a joining step of laminating the first member, the brazing filler metal, the insert member, the brazing filler metal, and the second member in this order, heating them at a predetermined heat treatment temperature for a predetermined time, and then cooling them; A joining method in which the heat treatment temperature is set in a range lower than the melting point of the insert member and higher than the melting point of the insert member lowered by the eutectic reaction between phosphorus and copper.

2. The joining method according to claim 1, A joining method, wherein the first member and the second member are each made of any one of stainless steel, steel containing one or both of a ferrite phase and a martensite phase, tungsten, iridium, or cemented carbide.

3. The joining method according to claim 1, the first member and the second member are made of different types of metals, a difference in thermal expansion coefficient between the first member and the insert member is smaller than a difference in thermal expansion coefficient between the second member and the insert member; The step (c) (c1) a first joining step of stacking the first member, the brazing material, and the insert member in this order, heating them at a predetermined heat treatment temperature for a predetermined time, and then cooling them; (c2) A joining method comprising a second joining step of stacking the brazing material and the second member in that order on the insert member of the member obtained in the first joining step, heating at a predetermined heat treatment temperature for a predetermined time, and then cooling.

4. The joining method according to claim 1, The heat treatment temperature is 960°C.

5. The joining method according to claim 1 or 2, (d) a step of finishing the surfaces of the first member and the second member to be joined to a microscopic surface prior to the heat treatment step; The brazing material in the heat treatment step has a thickness of 1 to 100 micrometers.

6. The joining method according to claim 1, A joining method in which pressure is applied to the first member and the second member in a direction in which they are joined together in the heat treatment step.

7. The joining method according to claim 6, providing first and second end plates fastened to each other and a center plate disposed therebetween; the first end plate and the center plate sandwich the first member and the second member; A joining method in which pressure is applied to the first and second members arranged between the first end plate and the center plate by interposing an elastic body between the second end plate and the center plate.

8. The joining method according to claim 6, A joining method in which the first and second end plates and the center plate have thicknesses that result in a substantially uniform pressure distribution on the first and second members.

9. The joining method according to claim 1, The joining method in which the step (c) is natural cooling.

10. The joining method according to claim 1, A joining method in which one of the first member and the second member is a sheet-like member with no rigidity, and the other is a member shaped to reinforce the first member.

Images