A solder for relieving stress of heterogeneous joints, a preparation method and application thereof

Abstract

The present application relates to the technical field of brazing, in particular to a brazing filler metal for stress release of heterogeneous joint, a preparation method and application thereof. The brazing filler metal is a spherical composite brazing filler metal, comprising a buffer material, an active metal layer coated on at least part of the surface of the buffer material, and a brazing filler metal layer coated on the outer side of the active metal layer and the buffer material. The brazing filler metal is obtained by coating a solid active metal foil on the surface of the buffer material wire, plating through the molten brazing filler metal layer after cooling, and then cutting into wire segments and balling. The brazing filler metal can form a non-melting, discontinuous and uniformly distributed stress release intermediate layer in the longitudinal and transverse directions during brazing, which can effectively relieve stress concentration, and can also protect high active elements from oxidation, thereby significantly improving the shear strength of the heterogeneous joint.

Description

Technical Field

[0001] This invention relates to the field of brazing technology, and more specifically, to a brazing filler metal for relieving stress in heterogeneous joints, its preparation method, and its application. Background Technology

[0002] In the field of modern advanced manufacturing and materials joining, the demand for reliable connections between dissimilar materials (such as ceramics, carbon / carbon composites, diamond, and other non-metallic materials and metals) is increasing. To achieve effective connections between dissimilar materials, the industry widely uses solders containing highly reactive elements (such as Ti and Cr), such as AgCuTi, AgCuInTi, AgCuSnTi, and CuNiCr. However, the preparation and application of traditional active solders face multiple technical challenges: Active elements are highly susceptible to oxidation, exhibiting a strong affinity for oxygen. During melting in normal atmospheric conditions, they readily undergo severe oxidation, leading to deterioration of the solder composition and loss of activity. Therefore, to effectively protect these critical active elements, the industry often employs vacuum melting processes; however, this method involves significant equipment investment, high energy consumption, and complex processes, resulting in high solder manufacturing costs.

[0003] The addition of active elements severely deteriorates the plasticity of alloys, making traditional plastic processing methods such as rolling and drawing difficult to implement. Therefore, existing active brazing filler metals are mostly in the form of powder or amorphous foil. Among them, powder brazing filler metals can be prepared by atomization, have a large specific surface area, and are prone to oxygen absorption, resulting in a high oxygen content; amorphous foil is prepared by rapid solidification process, which is costly and has limitations in size and shape, making it unsuitable for large-scale applications. In addition, both of these forms of active brazing filler metals are difficult to automate due to their special morphology. To automate the process, powder brazing filler metals need to be further prepared into paste brazing filler metals, but paste brazing filler metals have a large amount of residual carbon after soldering due to the presence of organic solder paste, which affects the joint performance; amorphous foil is thin and has low strength, and mostly requires manual placement.

[0004] Due to the large differences in the coefficients of linear expansion of different base materials, large residual stresses appear in the welded joints. Some studies have tried to alleviate stress concentration by adding an intermediate layer (such as pure copper or nickel foil). However, these intermediate layers are mostly continuous structures, which have problems such as continuous stress transmission paths and local strain energy accumulation, and cannot fundamentally solve the risk of cracking. A few studies have used perforated intermediate layers to enhance stress dispersion, but their dispersion is limited and the stress relief effect still needs to be improved.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a brazing filler metal for relieving stress in heterogeneous joints. During brazing, this filler metal can form a non-melting, discontinuous, and uniformly distributed stress-relieving intermediate layer in both the longitudinal and transverse directions, which can effectively alleviate stress concentration and protect highly reactive elements from oxidation, thereby significantly improving joint strength.

[0007] A second objective of this invention is to provide a method for preparing a brazing filler metal that provides stress relief in heterogeneous joints as described above.

[0008] A third objective of this invention is to provide the application of the brazing filler metal described above, which provides stress relief in heterogeneous joints, in the brazing of heterogeneous joints.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A brazing filler metal for relieving stress in heterogeneous joints, the filler metal being a spherical composite filler metal comprising a buffer material, an active metal layer covering at least a portion of the surface of the buffer material, and a filler metal layer covering the active metal layer and the outside of the buffer material.

[0010] Preferably, the buffer material includes any one of Cu, Mo, Nb, and Ni.

[0011] Preferably, the active metal layer comprises a Ti layer and / or a Cr layer.

[0012] Preferably, the solder layer includes at least one of AgCu solder, AgCuIn solder, AgCuSn solder, and CuNi solder.

[0013] Preferably, the shape of the cushioning material includes at least one of a cylinder and a cuboid; When the cushioning material is cylindrical, the diameter of the cylinder is 0.1-0.22 mm, and the length is 0.8-1.2 times the diameter. When the cushioning material is in the shape of a cuboid, one side of the cuboid has a length of 0.1-0.22 mm, and the ratio of the length of the remaining side to that side is 0.8-1.2. Preferably, the thickness of the active metal layer is 0.001-0.04 mm.

[0014] The method for preparing the brazing filler metal for relieving stress in heterogeneous joints as described in any of the foregoing embodiments includes the following steps: S1. Take a filamentous buffer material and an active metal foil, apply flux paste to one side of the active metal foil, and make the side coated with the flux paste contact the buffer material. Composite the active metal foil onto the surface of the buffer material to obtain a first composite filament. S2. Cool the first composite wire, then pass it through molten solder layer metal to plate the solder layer metal onto the surface of the first composite wire to obtain the second composite wire; S3. Peel and draw the second composite yarn to obtain the third composite yarn; S4. The third composite wire is cut into wire segments, and the wire segments are laser sintered on a vibrating bed covered with CaF2 powder. The outer layer of solder metal melts and forms solder balls under the action of surface tension.

[0015] Preferably, the filamentous cushioning material includes any one of Cu filament, Mo filament, Nb filament, and Ni filament.

[0016] Preferably, the active metal foil includes Ti foil and / or Cr foil.

[0017] Preferably, the solder layer liquid metal includes at least one of AgCu solder, AgCuIn solder, AgCuSn solder, and CuNi solder.

[0018] Preferably, the end face of the filamentous cushioning material is circular with a diameter of 0.1-0.22 mm, and the length of the filament segment is 0.8-1.2 times the diameter of the end face of the filamentous cushioning material.

[0019] Preferably, the end face of the filamentous cushioning material is rectangular, one side of the rectangle is 0.1-0.22 mm long, and the remaining side lengths of the rectangle and the length of the filament segment are each independently 0.8-1.2 times the side length.

[0020] Preferably, the thickness of the active metal foil is 0.001-0.04 mm.

[0021] Preferably, the diameter D of the third composite filament satisfies either the first condition or the second condition; The first condition is: The end face of the filamentous cushioning material is circular, where d is the diameter of the end face of the filamentous cushioning material in mm. l The length of the wire segment is in mm; The second condition is: The end face of the filamentous cushioning material is square, where L1 is the side length of the end face of the filamentous cushioning material in mm, and L2 is the length of the filament segment in mm.

[0022] Preferably, in step S2, the first composite wire is cooled by passing through dry ice or liquid nitrogen before passing through the molten solder layer.

[0023] Application of the brazing filler metal for relieving stress in heterogeneous joints as described in any of the foregoing embodiments in the brazing of heterogeneous joints.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The brazing filler metal of the present invention is spherical, which facilitates automated material placement and is beneficial to automated brazing production. Furthermore, the buffer material is encapsulated inside the spherical brazing filler metal. By brazing multiple brazing filler metal balls densely arranged between the base material to be brazed, multiple discontinuous and uniformly distributed stress-relieving intermediate layers can be formed in the brazing seam. Compared with continuous intermediate layers, the discontinuous structure artificially introduces controllable voids. These areas allow for greater local plastic deformation, and the material is more likely to yield and flow around the voids, absorbing strain energy. The stress direction can be redistributed, and the stress flow lines will bypass the discrete intermediate layer "islands", avoiding concentration at the interface and better relieving stress.

[0025] (2) The present invention places highly active elements (such as Ti foil) in the form of solid foil inside the inactive or low-activity brazing layer. The active elements are in solid state and physically isolated and protected by the brazing layer throughout the entire preparation and subsequent plastic processing. No expensive vacuum melting is required. Composite processing can be completed in a protective atmosphere or even a controlled atmosphere, which greatly reduces the cost. During brazing, the active metal layer and the brazing layer react in situ to generate the required active brazing material to achieve welding.

[0026] (3) The spherical composite brazing filler metal provided by the present invention has active elements existing as independent solid phases, which do not participate in the plastic deformation of the brazing filler metal layer alloy, thus significantly improving the processing performance. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 The morphological diagrams of the composite brazing filler metal before and after laser heating provided in the embodiments of the present invention (taking square wire as an example); Figure 2 This is an assembly diagram of a heterogeneous joint during welding of a spherical composite brazing filler metal provided in an embodiment of the present invention. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0030] A first aspect of the present invention provides a brazing filler metal for relieving stress in heterogeneous joints. The brazing filler metal is a spherical composite brazing filler metal, comprising a buffer material, an active metal layer covering at least a portion of the surface of the buffer material, and a brazing filler metal layer covering the outside of the active metal layer and the buffer material.

[0031] This invention provides a spherical composite brazing filler metal. An outer layer of inactive or low-activity brazing filler metal completely encapsulates an inner layer of highly active elements and a buffer material. This protects the active elements from oxidation, and the melting temperature of the buffer material is higher than the liquidus of the outer brazing filler metal and the temperature at which the outer brazing filler metal reacts in situ with the active metal layer to generate the active brazing filler metal. During brazing, multiple brazing filler spheres are densely packed and laid flat between the base materials to be brazed. The outer brazing filler metal and the intermediate active metal layer react in situ to generate the active brazing filler metal, achieving effective connection of dissimilar materials. The inner buffer material does not melt during brazing, forming multiple discontinuous, uniformly distributed stress-relieving intermediate layers in the brazing seam. Compared to continuous intermediate layers, the discontinuous structure artificially introduces controllable voids. These regions allow for greater local plastic deformation, and the material is more likely to yield and flow around the voids, absorbing strain energy. This allows for stress redistribution, and stress flow lines bypass the discrete intermediate layers. The "island" design avoids stress concentration at the interface, thus better mitigating stress. Furthermore, the close arrangement of spherical brazing filler metal facilitates automated material placement. The relative size of the spherical filler metal and the buffer material allows for reasonable control of the buffer material's dispersion, enabling automated placement and facilitating automated brazing production. In contrast, filamentous buffer materials require manual placement due to the need to control the wire arrangement direction and spacing, hindering automated production. Moreover, directly arranging filamentous buffer materials results in limited dispersion and poor buffering effect. Dispersing the filamentous buffer material further leads to significant differences in dispersion between the longitudinal and transverse directions due to its longitudinal continuity. Compared to filamentous buffer materials with large differences in dispersion between the longitudinal and transverse directions, a close arrangement of multiple brazing filler metal spheres internally coated with buffer material results in comparable dispersion in both the longitudinal and transverse directions, leading to a more uniform distribution, better stress mitigation, and higher joint strength after brazing.

[0032] In some specific embodiments of the present invention, the buffer material includes any one of Cu, Mo, Nb, and Ni; the buffer material has a high melting point and does not melt during brazing, and can form an intermediate layer in the brazing seam to relieve stress.

[0033] In some specific embodiments of the present invention, the active metal layer includes a Ti layer and / or a Cr layer.

[0034] The outer solder layer can be adapted to the type of base material being soldered. In some specific embodiments of the present invention, the solder layer includes at least one of AgCu solder, AgCuIn solder, AgCuSn solder, and CuNi solder.

[0035] In some specific embodiments of the present invention, the shape of the cushioning material includes at least one of a cylinder and a cuboid. When the buffer material is cylindrical, the diameter of the cylinder is 0.1-0.22 mm, for example, it can be any single value or a range of any two values ​​from 0.1 mm, 0.12 mm, 0.15 mm, 0.18 mm, 0.2 mm, and 0.22 mm; the length is 0.8-1.2 times the diameter, for example, it can be any single value or a range of any two values ​​from 0.8 times, 0.9 times, 1.0 times, 1.1 times, and 1.2 times. Controlling the diameter and length is to control the thickness of the non-melting stress-relieving intermediate layer in the brazed seam after brazing. Controlling the relative size of the diameter and length is to reduce the influence of different internal non-melting buffer material arrangement directions on the weld seam during subsequent brazing ball arrangement. The closer the length and diameter are, the smaller the influence and the better the effect. When the buffer material is a cuboid (including cubes), one side of the cuboid has a length of 0.1-0.22 mm. For example, it can be any single value or a range of any two values ​​from 0.1 mm, 0.12 mm, 0.15 mm, 0.18 mm, 0.2 mm, and 0.22 mm. The ratio of the remaining side lengths to this side length is 0.8-1.2. For example, it can be any single value or a range of any two values ​​from 0.8, 0.9, 1.0, 1.1, and 1.2. Controlling the side lengths is to control the thickness of the non-melting stress-relieving intermediate layer in the brazed seam after brazing. Controlling the ratio of each side length is to reduce the influence of different orientations of the internal non-melting buffer material on the weld when the brazing filler balls are arranged. The closer the side lengths are, the smaller the influence and the better the effect. When all side lengths are equal, the buffer material is a cube, which is a special type of cuboid. The influence of different orientations of the buffer material on the weld is even smaller, and the stress relief effect is better.

[0036] In some specific embodiments of the present invention, the thickness of the active metal layer is 0.001-0.04 mm, for example, it can be any one value or a range of any two values ​​among 0.001 mm, 0.005 mm, 0.008 mm, 0.01 mm, 0.02 mm, 0.03 mm, and 0.04 mm.

[0037] A second aspect of the present invention provides a method for preparing a brazing filler metal for relieving stress in heterogeneous joints as described in any of the foregoing embodiments, comprising the following steps: S1. Take a filamentous buffer material and an active metal foil, apply flux paste to one side of the active metal foil, and make the side with flux paste in contact with the buffer material. Composite the active metal foil onto the surface of the buffer material to obtain the first composite filament. S2. Cool the first composite wire, then pass it through molten solder layer metal to plate the solder layer metal onto the surface of the first composite wire to obtain the second composite wire; S3. Peel and draw the second composite yarn to obtain the third composite yarn; S4. The third composite wire is cut into wire segments, which are then laser-sintered on a vibrating bed covered with CaF2 powder. The outer layer of brazing filler metal melts and forms brazing filler balls under the action of surface tension.

[0038] This invention involves pre-coating an active metal foil in solid form onto the surface of a buffer material. During the plating of the solder metal layer, a solder metal liquid without active elements is used. This process can be carried out under atmospheric conditions with flux, making it simple, easy to implement, and significantly reducing costs. Furthermore, because the active elements exist as an independent solid phase and do not participate in the plastic deformation of the outer solder metal layer, processing performance is significantly improved, and the solder layer is less prone to cracking during subsequent peeling and drawing processes. Moreover, the solder layer is less likely to shatter and splatter when cutting into wire segments, ensuring dimensional stability. The prepared solder ball's outer inactive or low-activity solder layer completely encapsulates the inner active metal foil layer, preventing oxidation of active elements during storage and effectively improving the solder's storage stability. During brazing, the intermediate active metal layer reacts in situ with the outer inactive or low-activity solder layer to generate the required active solder, achieving effective connection of heterogeneous materials. The internal buffer material forms multiple non-melting, discontinuous stress-relieving intermediate layers during brazing, effectively alleviating stress and improving joint strength.

[0039] If active solder containing active elements (such as AgCuTi) is directly used to form a molten plating solution, the active elements are easily oxidized. Under atmospheric conditions, when flux is applied, the active elements will oxidize and fail, making it difficult to achieve effective connection of heterogeneous joints. Although a protective atmosphere can prevent oxidation of active elements to some extent, some active elements will still be oxidized, resulting in reduced strength of the heterogeneous joint after brazing and higher costs. Furthermore, the plating process requires continuous feeding of the metal wire, making vacuum plating difficult. In addition, even if active solder containing active elements can be directly plated onto the surface of the buffer material, there is still the problem of poor machinability. Although the addition of active elements gives the solder excellent wetting and bonding capabilities, it also seriously damages the plasticity of the alloy. The active solder layer is prone to cracking during subsequent peeling and drawing processes, and during cutting, the outer active solder layer is prone to fragmentation and splashing, making it difficult to guarantee dimensional stability.

[0040] The purpose of pre-coating flux paste onto the active metal foil in step S1 of the method of this invention is to allow the flux to melt in the subsequent laser ball-forming process, ensuring that the interface between the active metal foil and the internal metal is not oxidized. The purpose of pre-cooling the first composite wire before passing through the molten solder layer in step S2 is, on the one hand, to prevent the thinner active metal foil layer from dissolving, and on the other hand, to allow more outer solder alloy to adhere. The purpose of peeling and drawing in step S3 is to obtain a suitable diameter, where the purpose of drawing is mainly to make the outer surface of the solder layer smooth without significantly changing the diameter of the composite wire. The role of CaF2 powder in step S4 is to protect the outer solder metal from oxidation and to make it easier to form balls. Under the short-term high temperature of the laser, the flux in step S1 begins to melt, protecting the interface between the active metal foil and the internal metal from oxidation. At the same time, the molten solder metal of the outer layer enters the gap of the intermediate layer, realizing the metallurgical bonding between the intermediate active metal foil and the internal metal. Figure 1 The diagram shows the structure of the wire segment before ball forming and the structure of the composite solder ball after ball forming, as provided in the embodiments of the present invention.

[0041] In some specific embodiments of the present invention, the filamentous buffer material includes any one of Cu filament, Mo filament, Nb filament, and Ni filament.

[0042] In some specific embodiments of the present invention, the active metal foil includes Ti foil and / or Cr foil.

[0043] In some specific embodiments of the present invention, the solder layer liquid metal includes at least one of AgCu solder, AgCuIn solder, AgCuSn solder, and CuNi solder.

[0044] In some specific embodiments of the present invention, the end face of the filamentous cushioning material is circular, and the diameter of the end face is 0.1-0.22 mm. For example, it can be any one value or a range of any two values ​​among 0.1 mm, 0.12 mm, 0.15 mm, 0.18 mm, 0.2 mm, and 0.22 mm. The length of the filament segment is 0.8-1.2 times the diameter of the end face of the filamentous cushioning material. For example, it can be any one value or a range of any two values ​​among 0.8 times, 0.9 times, 1.0 times, 1.1 times, and 1.2 times.

[0045] In some specific embodiments of the present invention, the end face of the filamentous cushioning material is rectangular, and one side of the rectangle is 0.1-0.22 mm in length. For example, it can be any one value or a range of any two values ​​among 0.1 mm, 0.12 mm, 0.15 mm, 0.18 mm, 0.2 mm, and 0.22 mm. The remaining side lengths of the rectangle and the length of the filament segment are each independently 0.8-1.2 times the side length. For example, it can be any one value or a range of any two values ​​among 0.8 times, 0.9 times, 1.0 times, 1.1 times, and 1.2 times the side length.

[0046] In some specific embodiments of the present invention, the thickness of the active metal foil is 0.001-0.04 mm, for example, it can be any one value or a range of any two values ​​among 0.001 mm, 0.005 mm, 0.008 mm, 0.01 mm, 0.02 mm, 0.03 mm, and 0.04 mm.

[0047] In some specific embodiments of the present invention, the diameter D of the third composite filament satisfies either the first condition or the second condition; The first condition is: The end face of the filamentous cushioning material is circular, where d is the diameter of the end face of the filamentous cushioning material, in mm. l This refers to the length of the wire segment, in mm. The second condition is: The end face of the filamentous cushioning material is square, where L1 is the side length of the end face of the filamentous cushioning material in mm, and L2 is the length of the filament segment in mm.

[0048] Controlling the value of D serves two purposes: first, to achieve complete coverage; and second, to control the amount of solder used and the gap between the buffer materials. With a fixed amount of filamentous buffer material, if the value of D is too small, it is difficult to achieve complete coverage, and the gap is too small. If the value of D is too large, too much solder is used, and the gap between the buffer materials is too large. Controlling D within the above range can achieve a better coverage effect and higher welding strength.

[0049] In some specific embodiments of the present invention, the composite step in step S1 includes: wrapping an active metal foil around the outside of a filamentous buffer material, so that the side coated with flux is in contact with the filamentous buffer material, and using a wire drawing die to coat the surface of the filamentous buffer material with the active metal foil and achieve a preliminary mechanical bond. In the subsequent step S4, when forming balls, the molten brazing metal on the outer layer enters the gap, achieving a metallurgical bond between the active metal foil and the internal metal, which can compensate for the defect of the non-dense mechanical bonding interface in step S1.

[0050] In some specific embodiments of the present invention, in step S2, the first composite wire is cooled by using dry ice or liquid nitrogen. The method is as follows: before the first composite wire passes through the molten solder layer, it is cooled by passing through dry ice or liquid nitrogen.

[0051] A third aspect of the present invention provides the application of a brazing filler metal for relieving stress in heterogeneous joints as described in any of the foregoing embodiments in the brazing of heterogeneous joints; particularly in the brazing of non-metallic materials to metallic materials, for example, in the welding of diamond to metal, carbon / carbon composite materials to metal, carbon / silicon carbide composite materials to metal, or ceramics to metal. Heterogeneous joints brazed using the brazing filler metal for relieving stress in heterogeneous joints provided by the present invention exhibit high shear strength.

[0052] The present invention also provides a brazing method for heterogeneous joints, comprising the following steps: (1) Clean the surface of the composite brazing ball. The composite brazing ball is the brazing ball that provides stress relief for heterogeneous joints as described in any of the preceding embodiments. (2) Arrange multiple composite brazing filler balls closely on the surface of the base material B to be brazed, and then cover it with the base material A (assembly drawing as shown). Figure 2 As shown), the active metal layer in the middle reacts with the outer solder layer during the welding process, and finally generates the initially designed active solder composition in situ, and obtains a non-continuous stress-relieving intermediate layer.

[0053] In some specific embodiments of the present invention, the cleaning includes acid washing or cleaning with organic cleaning agents. The spherical composite brazing filler metal provided by the present invention has its internal interface completely protected by an external inactive or low-activity brazing filler metal layer, preventing oxidation of the weak areas of the bonding interface and making it easier to store and use. In addition, when it is cut before being spherically formed, the interface consists of three components: an inner metal layer, an active layer, and an outer brazing filler metal layer, which have a specific potential difference. After sintering into spheres, the outer layer is completely covered by metal, and there is no potential difference. During subsequent surface cleaning, the spherical composite brazing filler metal can avoid interface corrosion caused by the potential difference of heterogeneous materials during the cleaning process. At the same time, the regular spherical brazing filler metal is more suitable for use in automated brazing equipment.

[0054] In some specific embodiments of the present invention, the base material B includes any one of diamond, carbon / carbon composite material, carbon / silicon carbide composite material or ceramic; the base material A includes metal, which can be a pure metal (such as copper) or an alloy (such as a nickel-based alloy).

[0055] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0056] Example 1 This embodiment provides a spherical composite solder, the preparation method of which includes the following steps: S1. A circular copper wire with a diameter of 0.1 mm is used as a buffer material. Silver flux paste is evenly brushed onto one side of the Ti foil to ensure that the interface between the Ti foil and the internal metal is not oxidized during the subsequent laser sintering process. The Ti foil coated with flux is used to wrap the internal copper wire, and the Ti foil is composited onto the surface of the Cu wire through a wire drawing die. The two are mechanically bonded to obtain the first composite wire. The thickness of the Ti foil is 0.001 mm. S2. The first composite wire is first passed through dry ice to cool down, and then through molten AgCu solder (Ag71-Cu29) alloy at a speed of 30m / min to obtain a composite material with a surface coated with low-melting solder, thus obtaining the second composite wire; S3. Peel and draw the second composite filament to obtain the third composite filament with a diameter of 0.14 mm; S4. Cut the third composite wire into segments with a length of 0.1 mm; perform laser sintering on the segments on a vibrating bed covered with CaF2 powder, melting the outer low-melting alloy and forming brazing filler balls under the action of surface tension.

[0057] Example 2 Example 2 is similar to Example 1, except that the internal buffer material is changed to a square copper wire with a square end face and a side length of 0.1 mm, the Ti foil thickness is 0.003 mm, and the diameter of the third composite wire is 0.19 mm; all other process conditions are the same as in Example 1.

[0058] Example 3 Example 3 is similar to Example 1, except that the internal buffer material is a copper wire with a diameter of 0.1 mm and the wire length is still 0.1 mm. The only difference is that the thickness of the Ti foil in step S1 is 0.04 mm and the diameter of the third composite wire obtained in step S3 is 0.63 mm. All other process conditions are the same as in Example 1.

[0059] Example 4 Example 4 is similar to Example 1, except that the internal buffer material is a copper wire with a diameter of 0.1 mm and the wire length is still 0.1 mm. The only difference is that the thickness of the Ti foil in step S1 is 0.015 mm and the diameter of the third composite wire obtained in step S3 is 0.39 mm. All other process conditions are the same as in Example 1.

[0060] Application Example 1 The process of brazing C / C composite material and Ni-based superalloy GH4099 using the brazing filler ball prepared in Example 1 includes the following steps: (1) Perform surface pickling on the brazing filler balls; (2) The obtained composite brazing balls are laid flat and closely arranged on the surface of the C / C composite material to be brazed, and then GH4099 is covered on it. The welding temperature is 850℃ and the holding time is 20min to obtain the C / C-GH4099 joint. The brazing seam contains a non-continuous stress-relieving intermediate layer.

[0061] Application Example 2 The C / C composite material and Ni-based superalloy GH4099 were brazed using the brazing filler ball prepared in Example 2, and the welding method was the same as in Application Example 1.

[0062] Application Example 3 The brazing filler balls prepared in Example 1 were used to braze CVD diamond and copper. The welding method was similar to that in Application Example 1, except that the base material was different.

[0063] Application Example 4 The brazing filler balls prepared in Example 3 were used to braze CVD diamond and copper. The welding method was similar to that in Application Example 3, except that the brazing filler balls used were different.

[0064] Application Example 5 The brazing filler balls prepared in Example 4 were used to braze CVD diamond and copper. The welding method was similar to that in Application Example 3, except that the brazing filler balls used were different.

[0065] Comparative Example 1 Comparative Example 1 is similar to Application Example 3, except that Ag-28Cu-2Ti active powder and a certain amount of terpineol are mixed into a paste and uniformly applied to both sides of the intermediate Cu layer (copper foil with through holes). The coating thickness is about 0.3 mm. CVD diamond-Cu joints are brazed. The intermediate layer is Cu (thickness 0.1 mm, area consistent with the surface to be brazed). Holes with a diameter of 1 mm are opened on the surface of the Cu layer, and the center distance between the holes is 3 mm.

[0066] Comparative Example 2 Comparative Example 2 is similar to Application Example 3, except that Ag-28Cu-2Ti active powder and a certain amount of terpineol are mixed into a paste and uniformly applied to the CVD diamond and Cu surfaces to be brazed. The coating thickness is about 0.15 mm. The CVD diamond-Cu joint is brazed. The intermediate layer is a non-melting copper wire with a diameter of 0.1 mm. Its length is consistent with the length of the surface to be brazed. The wires are closely arranged (the stress relief layer is not continuous as a whole, but the dispersion is not large).

[0067] Comparative Example 3 Comparative Example 3 is similar to Application Example 3, except that Ag-28Cu-2Ti active powder and a certain amount of terpineol are mixed into a paste and uniformly applied to the CVD diamond and Cu surfaces to be soldered. The coating thickness is about 0.15 mm. The CVD diamond-Cu joint is directly brazed without a stress relief layer in between.

[0068] Comparative Example 4 Comparative Example 4 is similar to Application Example 3, except that the spherical solder used is prepared using a different process than the solder balls in Example 1. In this process, copper wire is directly passed through molten AgCuTi solder liquid (the composition of which is similar to that of Ag, Cu, and Ti in the finished solder balls in Example 1), and then the same process is used to form balls. The brazing filler balls prepared in this comparative example were used for direct brazing of CVD diamond-Cu joints.

[0069] Comparative Example 5 Comparative Example 5 is similar to Application Example 3, except that the spherical brazing filler metal used is prepared using a different process than that in Example 1. The process is that the copper wire with an outer Ti layer is not cooled down and is directly passed through the molten AgCu metal liquid, and then the same process is used to make spheres. The brazing filler balls prepared in this comparative example were used for direct brazing of CVD diamond-Cu joints.

[0070] Test case The shear strength of the heterogeneous joints at room temperature was tested in each application example and comparative example, according to GB / T11363-2008. The test results are shown in Table 1.

[0071] Table 1

[0072] As can be seen from the data in the table, the spherical composite brazing filler metal provided by this invention can significantly improve the bonding strength between C / C, C / SiC, CVD diamond and metal materials.

[0073] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a brazing filler metal for relieving stress in heterogeneous joints, characterized in that, Includes the following steps: S1. Take a filamentous buffer material and an active metal foil, apply flux paste to one side of the active metal foil, and bring the side coated with the flux paste into contact with the buffer material. Composite the active metal foil onto the surface of the buffer material to obtain a first composite filament; wherein, the filamentous buffer material includes any one of Cu filament, Mo filament, Nb filament, and Ni filament; the active metal foil includes Ti foil and / or Cr foil; the thickness of the active metal foil is 0.001-0.04 mm; S2. Cool the first composite wire and then pass it through molten solder layer metal to plate the solder layer metal onto the surface of the first composite wire to obtain a second composite wire; the solder layer metal includes at least one of AgCu solder, AgCuIn solder, AgCuSn solder, and CuNi solder. S3. Peel and draw the second composite yarn to obtain the third composite yarn; S4. The third composite filament is cut into segments, which are then laser-sintered on a vibrating bed covered with CaF2 powder. The outer brazing filler metal melts and forms brazing filler balls under surface tension. When the end face of the filamentous buffer material is circular, its end face diameter is 0.1-0.22 mm, and the length of the filament segment is 0.8-1.2 times the end face diameter of the filamentous buffer material. When the end face of the filamentous buffer material is rectangular, one side of the rectangle is 0.1-0.22 mm, and the remaining side lengths of the rectangle and the length of the filament segment are each independently 0.8-1.2 times that side length.

2. The method for preparing brazing filler metal for slow-release of stress in heterogeneous joints according to claim 1, characterized in that, The diameter D of the third composite filament satisfies either the first condition or the second condition; The first condition is: The end face of the filamentous cushioning material is circular, where d is the diameter of the end face of the filamentous cushioning material in mm. l The length of the wire segment is in mm; The second condition is: The end face of the filamentous cushioning material is square, where L1 is the side length of the end face of the filamentous cushioning material in mm, and L2 is the length of the filament segment in mm.

3. The method for preparing brazing filler metal for slow-release of stress in heterogeneous joints according to claim 1, characterized in that, In step S2, the first composite wire is cooled by passing through dry ice or liquid nitrogen before passing through the molten solder layer.

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