Hard metal brazing method

Abstract

To achieve good hard metal brazing.SOLUTION: A first member containing any of alumina dispersion strengthening copper, oxygen-free copper, tough pitch copper, and phosphorus deoxidized copper and a second member containing a hard metal are prepared. After a surface to be joined is fine mirror-finished, a brazing material of BNi-6 which is a nickel alloy containing phosphorus of 11% but not copper is pitched to apply pressure. In this state, heat treatment is performed at a heat treatment temperature of 960°C for 10 minutes. Then, after sufficient natural cooling, sudden cooling is performed by using nitrogen gas. Thus, good brazing of any of the alumina dispersion strengthening copper, the oxygen-free copper, the tough pitch copper, and the phosphorus deoxidized copper with the hard metal can be achieved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for brazing cemented carbide. [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 for brazing alumina dispersion strengthened copper to alumina dispersion strengthened copper and alumina dispersion strengthened copper to stainless steel. Patent Document 2 discloses a technique for brazing alumina dispersion strengthened copper to steel containing one or both of a ferrite phase and a martensite phase, or to iridium. Patent Document 3 discloses a technique for brazing copper and copper alloys other than alumina dispersion strengthened copper to 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 between alumina dispersion strengthened copper and cemented carbide has not been realized until now, and similarly, brazing between oxygen-free copper, tough pitch copper, phosphorus deoxidized copper, or copper alloy and cemented carbide has not been realized. In view of the above, an object of the present invention is to provide a brazing technique for joining alumina dispersion strengthened copper or other copper metals to cemented carbide. [Means for solving the problem]

[0005] The present invention provides A joining method for brazing a first member made of any one of alumina dispersion strengthened copper, oxygen-free copper, tough pitch copper, and phosphorus deoxidized copper to a second member made of cemented carbide, comprising: (a) providing a phosphorus-containing, copper-free brazing filler metal; (b) a heat treatment step of sandwiching the brazing material between the first member and the second member and heating the brazing material at a predetermined heat treatment temperature for a predetermined time; (c) cooling the joined first and second members after the heat treatment step; A joining method in which the heat treatment temperature is set in a range lower than the melting point of the first member and higher than the melting point of the first member lowered by the eutectic reaction between phosphorus and copper.

[0006] The inventors conducted brazing experiments using a brazing filler metal containing phosphorus but not copper, and found that good brazing can be achieved by the above-mentioned process and heat treatment temperature. The principle behind this is not entirely clear, but in the present invention, it is believed that a eutectic reaction between phosphorus and copper occurs between the brazing filler metal and the first member, causing the first member to diffuse. Furthermore, the heat treatment temperature is lower than the melting point of the first member, and the first member melts only at the joining portion, which is also preferable for achieving good brazing joining of the first member and the second member.

[0007] The inventors have previously studied brazing of various materials using copper-free brazing filler metals, but whether diffusion of the first member occurs in the joint depends on the metal used as the second member. This time, they experimentally confirmed that effective brazing can be achieved even when a cemented carbide is used as the second member, which led to the present invention. Cemented carbide is a composite material made by sintering carbides of metals from groups IVa, Va, and VIa of the periodic table with iron-based metals such as Fe, Co, and Ni.

[0008] In the present invention, The cemented carbide is preferably a WC-Co alloy. Experiments have confirmed that good brazing joints can be achieved with WC-Co alloys. However, since the metallic properties of any cemented carbide are considered to be similar, any cemented carbide can be used as the second component in the present invention.

[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 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] In the present invention, The step (c) may be natural cooling.

[0020] 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.

[0021] The present invention is applicable not only to cases where there is one type of second member to be joined, but also to cases where there are multiple second members. The multiple second members may be made of different types of cemented carbide, or there may be a mixture of second members made of cemented carbide and second members made of metals other than cemented carbide. When there are multiple second members of different types, the order in which they are joined can be determined arbitrarily. for example, When there are a plurality of second members made of a plurality of types of metals, The first member may be joined to the second member made of a metal having a thermal expansion coefficient close to that of the first member.

[0022] When joining multiple types of metals to be joined sequentially, the first metal to be joined is subjected to repeated heat treatment. Thermal stress between the first and second members is caused by the difference in thermal expansion coefficients between the members, so by joining the members in order of their thermal expansion coefficients, as in the above embodiment, it is possible to alleviate the thermal stress caused by the repeated heat treatment.

[0023] It is not necessary to have all of the various features of the present invention 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]

[0024] [Figure 1] 1 is a flowchart showing steps of a brazing process. [Figure 2] FIG. 10 is an explanatory diagram showing a joining result. [Figure 3] FIG. 10 is an explanatory diagram showing the influence of pressure applied during bonding. [Figure 4]FIG. 10 is an explanatory diagram showing the influence of the thickness of the brazing material. DETAILED DESCRIPTION OF THE INVENTION

[0025] 1 is a flowchart showing the steps of a brazing process. In this process, first, the members to be joined are prepared (step S10). In this example, a first member made of alumina dispersion strengthened copper, oxygen-free copper, tough pitch copper, or phosphorus deoxidized copper, and a second member made of cemented carbide are prepared. The shapes of the members to be joined are arbitrary, but the joining surfaces must be flat. 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.

[0026] 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 components to be joined, and pressure is applied (step S13). The figure shows the method of applying pressure. In this example, three steel plates are prepared. From the bottom, they are referred to as a first end plate (or lower plate), a center plate (or middle plate), and a second end plate (or upper plate). The joining components are 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 components as pressure via the center plate. Another advantage is that pressure can be applied uniformly to the joining components 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.

[0027] 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 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 first 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 members, the heat treatment temperature must be lower than the melting point of the first member (for example, 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 first 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 members. Therefore, the heat treatment temperature needs to be higher than the melting point of the first 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, the heat treatment time was 10 minutes, 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.

[0028] 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.

[0029] The effects of the bonding in the examples will be explained below based on the experimental results. FIG. 2 is an explanatory diagram showing the joining result. Figure 2(a) shows the state before joining. Using BNi-6 as a brazing filler metal containing phosphorus but not copper, rectangular parallelepiped test pieces with a flat surface measuring approximately 20 to 30 mm on a side and a thickness of approximately 1 to 10 mm were joined together. In this example, GlidCop (registered trademark), an alumina dispersion strengthened copper, was used as the first member, and cemented carbide, specifically a WC-Co alloy, was used as the second member. Then, as shown in the figure, the brazing filler metal was sandwiched between the first and second members, and brazing was performed. The thickness t of the brazing filler metal was in the range of 1 to 100 micrometers.

[0030] Figure 2(b) shows the appearance after joining. The cemented carbide part corresponds to the area indicated by arrow a, and the alumina dispersion strengthened copper part corresponds to the area indicated by arrow c. The brazed part, where the two are joined, corresponds to the area indicated by arrow b (for reference, a dashed line has been added in Figure 2(b)), but after joining, the brazing filler melts and metal diffusion occurs between the alumina dispersion strengthened copper and the cemented carbide, making it impossible to clearly identify the joined part. 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.

[0031] Figure 2(c) shows the results of an ultrasonic flaw detection test of the joint. The test was conducted in the direction of arrow V in Figure 2(b). The white rectangular area A1 near the center is the edge of the joint interface. Furthermore, the slightly shaded rectangular area A2 near the center indicates the area that is well bonded. The results of the ultrasonic flaw detection confirm that area A2 near the center of the joint is well bonded with sufficient uniformity and no bonding defects.

[0032] 2, it was confirmed that a good brazing joint was achieved when alumina dispersion strengthened copper was used as the first member and a WC-Co based cemented carbide alloy was used as the second member. As described in Patent Documents 1 to 3 previously by the same inventor, this brazing is thought to be achieved by a eutectic reaction between the phosphorus contained in the brazing filler metal and the copper contained in the first member at the joint, causing the copper to melt and diffuse, and / or by an anchor effect in which the molten copper conforms to the irregularities on the surfaces of the materials to be joined. Therefore, it is believed that results similar to those shown in FIG. 2 can be obtained even when oxygen-free copper, tough pitch copper, or phosphorus-deoxidized copper other than alumina dispersion strengthened copper is used as the first member. Furthermore, brazing is achieved by either or both of the melting and diffusion of copper and the anchor effect of the molten copper conforming to the irregularities on the surface of the materials to be joined, and it is considered that the cemented carbide 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, according to the results of Figure 2, it is considered that similarly good brazing joints can be obtained not only with WC-Co based cemented carbide but also with cemented carbide in general.

[0033] Next, the effects of pressure and the thickness of the brazing filler metal will be described based on the results of an experiment in which GlidCop (registered trademark) was used for both the first and second members and BNi-6 was used as the brazing filler metal. FIG. 3 is an explanatory diagram showing the effect of pressure applied during bonding. Figure 3(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 3(b1) and 3(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 3(b2) is about 2.5 to 3.5 times that of Figure 3(b1). Figures 3(c1) and 3(c2) show the results of ultrasonic testing corresponding to Figures 3(b1) and 3(b2), respectively. The area around the flow path is shown as seen from above. In Figure 3(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, in Figure 3(c2), no such poor bonding is visible. In Figures 3(b1) and 3(b2), the pressure applied by the carbon springs is the same, so the pressure on the components should be equal. However, in Figure 3(b2), where the plates are thick, the pressure is applied uniformly, whereas in Figure 3(b1), where the plates are thin, the pressure is uneven. Therefore, it is preferable that the plates used to apply pressure are sufficiently thick. The specific thickness is considered to be sufficient to suppress deflection due to pressure. This can be determined experimentally by bonding plates of various thicknesses and checking for bond failure, as shown in Figures 3(b1) and 3(b2). While the results for two thicknesses are shown here, conducting experiments with more thicknesses will enable us to determine the thickness necessary to avoid bond failure.

[0034] Figure 4 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 4 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 4(a1) and 4(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 4(a1) and 4(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 4(c2) protruding more. Figures 4(b1) and 4(b2) show the joined components viewed from the side. It can be seen that the discolored area is larger in Figure 4(b2), where the brazing filler metal is thicker. Figures 4(c1) and 4(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 4(c2). Figures 4(d1) and 4(d2) show the results of ultrasonic testing. It can be seen that the brazing filler metal has protruded inside the rectangular frame that corresponds to the window. Furthermore, in Figure 4(d2), where the brazing filler metal is thick, many streaky areas of poor bonding can be seen around the window, but in Figure 4(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. 3 and 4 show the experimental results for GlidCop (registered trademark) alone, but the results for cemented carbide and alumina dispersion strengthened copper or the like are similar.

[0035] As described above, according to the brazing method of the embodiment, a good brazing joint can be achieved between a first member made of any of alumina dispersion strengthened copper, oxygen-free copper, tough pitch copper, and phosphorus deoxidized copper and a second member made of cemented carbide.

[0036] 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 is also applicable to brazing multiple materials. When brazing and joining component A made of alumina dispersion strengthened copper or the like, component B made of cemented carbide, and component C made of a material other than cemented carbide, it is preferable to first join components B and C, whichever has a thermal expansion coefficient similar to that of component A, and then join the other components. When repeatedly joining components in this manner, the components that have been joined will be exposed to a heat treatment environment again in order to join the next component. If the thermal expansion coefficients of the components differ significantly, repeated heat treatments will cause significant thermal stress. Joining components with similar thermal expansion coefficients first can avoid this problem and suppress the generation of thermal stress. [Industrial Applicability]

[0037] The present invention can be used for brazing cemented carbide.

Claims

1. A joining method for brazing a first member made of any one of alumina dispersion strengthened copper, oxygen-free copper, tough pitch copper, and phosphorus deoxidized copper to a second member made of cemented carbide, the method comprising: (a) providing a phosphorus-containing, copper-free brazing filler metal; (b) a heat treatment step of sandwiching the brazing material between the first member and the second member and heating the brazing material at a predetermined heat treatment temperature for a predetermined time; (c) cooling the joined first and second members after the heat treatment step; A joining method in which the heat treatment temperature is set in a range lower than the melting point of the first member and higher than the melting point of the first member lowered by the eutectic reaction between phosphorus and copper.

2. The joining method according to claim 1, The cemented carbide is a WC-Co alloy.

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

4. The joining method according to claim 1, (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.

5. 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.

6. The joining method according to claim 5, 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.

7. 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.

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

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