Heterogeneous material-brazed joint with brachistochrone structure and preparation method therefor

Abstract

Provided are a heterogeneous material-brazed joint with a brachistochrone structure and a preparation method therefor. The heterogeneous material-brazed joint with a brachistochrone structure comprises a first brazed base material (1) and a second brazed base material (2), wherein the wettability of the first brazed base material (1) for brazing filler metal is better than the wettability of the second brazed base material (2); a brachistochrone groove (21) is provided on a surface to be brazed of the second brazed base material (2). By means of constructing the structure of the brachistochrone groove (21) on the surface to be brazed of the second brazed base material (2) that is difficult to wet, the circulation speed of the brazing filler metal on the surface of the material that is difficult to wet is increased, such that the joint has a high brazing quality and few brazing seam defects, and the shear strength of the brazed joint can be significantly improved.

Description

A brazing joint with the fastest descent wire structure in heterogeneous materials and its preparation method

[0001] Cross-references to related applications

[0002] This disclosure claims priority to Chinese Patent Application No. 2024108048089, filed on June 21, 2024, entitled "A Brazing Fastest Descent Wire Structure Joint of Heterogeneous Materials and Its Preparation Method", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of material joining technology, and more specifically, to a brazing brazing fastest descent wire structure joint of heterogeneous materials and its preparation method. Background Technology

[0004] In the field of brazing technology, dissimilar materials typically refer to materials with significantly different physical and chemical properties, such as elastic modulus, coefficient of thermal expansion, and melting point, like ceramics and metals, ferrous and non-ferrous metals, and copper and stainless steel. Dissimilar material components greatly improve the flexibility of structural design due to the ability to combine the superior properties of different materials, meeting the functional and performance requirements of modern engineering structures, and possessing higher technical and economic value, thus having broad application prospects in various fields. Therefore, reliable connections between dissimilar materials are particularly important.

[0005] However, when joining dissimilar materials, the significant differences in their physical, chemical, and mechanical properties, metallurgical compatibility during welding, the formation of brittle compounds through interfacial reactions, and the differences in their coefficients of thermal expansion all greatly affect the joint performance. Therefore, joining dissimilar materials mainly presents the following problems and challenges:

[0006] 1. When joining dissimilar materials, the wettability differences are large, making it difficult to wet both materials simultaneously;

[0007] A conventional brazed joint consists of a set of roughly parallel planes. The filler metal flows within the weld formed by the two parallel planes. Due to the different wettability of the filler metal to the two materials, as well as the different fluidity and adhesion after melting, the filler metal often fails to contact the material on the difficult-to-wet side, resulting in defects and affecting product performance.

[0008] 2. During the interfacial reaction process, due to the large differences in chemical composition between heterogeneous materials, complex interfacial reactions and excessive generation of brittle interfacial compounds are likely to occur.

[0009] 3. The difference in thermal expansion coefficients between dissimilar materials results in significant residual stress at the interface, making it difficult to relieve joint stress and easily leading to post-weld cracks.

[0010] The aforementioned issues all affect the performance of brazed joints. Therefore, it is of great significance to provide a brazed joint made of dissimilar materials and its preparation method to achieve efficient and high-quality welding of dissimilar materials.

[0011] In view of this, this disclosure is hereby made.

[0012] Summary of the Invention

[0013] One object of this disclosure is to provide a brazing brazing fastest descent wire structure joint of dissimilar materials, wherein the joint has high brazing quality, few brazing defects, and high joint strength.

[0014] A brazing brazing line structure joint of dissimilar materials includes a first brazing substrate and a second brazing substrate. The first brazing substrate has better wettability to brazing filler metal than the second brazing substrate. The brazing surface of the second brazing substrate is provided with a brazing line groove. Each of the brazing line grooves is composed of two sets of symmetrically arranged brazing line surfaces. The inner surface curves of the brazing line surfaces conform to the brazing line equation: x = r(θ - sinθ); y = r(1 - cosθ).

[0015] Another objective of this disclosure is to provide a method for preparing a brazing brachistochrone joint of dissimilar materials as described above. By processing a brachistochrone groove on the surface of a difficult-to-wet material, the flow rate of the brazing filler metal on the surface of the difficult-to-wet material, the brazing rate, and the uniformity of residual stress distribution at the brazed joint are increased during brazing, thereby reducing brazing defects and improving joint strength.

[0016] The method for preparing the brazing fastest descent wire structure joint of the heterogeneous materials includes the following steps:

[0017] S1. Machining the fastest descent groove on the surface to be brazed of the second brazing substrate;

[0018] S2. Place the brazing filler metal between the surfaces to be brazed of the first and second brazing substrates and braze them to obtain the desired result.

[0019] Compared with related technologies, the beneficial effects of this disclosure are as follows:

[0020] This disclosure constructs a rapid descent groove structure on the brazing surface of a second brazing substrate that is difficult to wet, enabling the brazing filler metal to cover the largest contact area in the shortest time during its flow on the surface of the difficult-to-wet material. This increases the flow rate of the brazing filler metal on the surface of the difficult-to-wet material, preventing the brazing seam from being blocked due to excessive flow rate on the surface of the easily wettable material, thus avoiding defects. It also improves the wettability of the brazing filler metal on the surface of the difficult-to-wet material, improves the uniformity of residual stress at the brazed joint, and avoids cracking caused by stress concentration. At the same time, it can also increase the contact area between the difficult-to-wet material and the brazing filler metal, increasing the brazing rate on the surface of the difficult-to-wet material. This results in high brazing quality, fewer brazing seam defects, and high connection strength in the prepared heterogeneous material brazed joint. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments or related technologies of this disclosure, the accompanying drawings used in the description of the specific embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 is a schematic diagram of the first interface structure of the first brazing substrate and the second brazing substrate of this disclosure;

[0023] Figure 2 is a schematic diagram of the second interface structure of the first brazing substrate and the second brazing substrate of this disclosure;

[0024] Figure 3 is a schematic diagram of the third interface structure of the first brazing substrate and the second brazing substrate of this disclosure;

[0025] Figure 4 is a schematic diagram of the structure of the second brazing substrate to be welded surface in one embodiment of the present disclosure;

[0026] Figure 5 is a schematic diagram of the grid texture structure on the surface of the first brazing substrate to be welded in one embodiment of the present disclosure;

[0027] Figure 6 is a schematic diagram of the interface structure of the first brazing substrate and the second brazing substrate in one embodiment of this disclosure;

[0028] Figure 7 is a schematic diagram of the interface structure of the first brazing substrate and the second brazing substrate in another embodiment of this disclosure;

[0029] Figure 8 is a physical electron microscope image of the brazed joint interface in one embodiment of this disclosure;

[0030] Figure 9 is a physical electron microscope image of the brazed joint interface in another embodiment of this disclosure;

[0031] Figure 10 is an electron microscope image of the brazed joint interface in another embodiment of this disclosure;

[0032] Figure 11 is a schematic diagram of the bonding interface of a brazed joint in one embodiment of this disclosure.

[0033] Figure label:

[0034] 1-First brazing substrate; 11-Grid pattern; 12-Rapid descent line protrusion; 2-Second brazing substrate; 21-Rapid descent line groove; 211-Storage tank. Detailed Implementation

[0035] The technical solutions of this disclosure 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 only some embodiments of this disclosure, not all embodiments, and are only used to illustrate this disclosure, and should not be regarded as limiting the scope of this disclosure. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure. 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.

[0036] As shown in Figures 1, 2, and 3, the first aspect of this disclosure provides a brazing brazing brachistochrone structure joint of dissimilar materials, including a first brazing substrate 1 and a second brazing substrate 2. The first brazing substrate 1 has better wettability to brazing filler metal than the second brazing substrate 2. The brazing surface of the second brazing substrate 2 is provided with a brachistochrone groove 21. Each brachistochrone groove 21 is composed of two sets of symmetrically arranged brachistochrone surfaces. The inner surface curve of the brachistochrone surface conforms to the brachistochrone equation: x = r(θ - sinθ); y = r(1 - cosθ).

[0037] As shown in Figure 1, the inner surface curve of the brachistochrone curve refers to the cross-sectional curve at the intersection of the plane perpendicular to the brazing surface of the second brazing substrate 2 and the extension direction of the brachistochrone groove 21 with the brachistochrone groove 21.

[0038] The brachistochrone (maximum descent curve) refers to the curve on a vertical plane between two fixed points A and B, where point A is not lower than point B, allowing a particle to slide from point A to point B at the fastest speed (the particle is only subject to gravity and has an initial velocity of zero). For brazed joints, the process of a droplet of molten solder moving along the brazed joint from one point to another also exhibits a brachistochrone. The brachistochrone can be expressed in parametric form as x = r(θ - sinθ); y = r(1 - cosθ), where r and θ are determined by the position of the endpoint. Therefore, for any two points with no initial velocity and subjected to a single force, there exists a set of brachistochrone curves.

[0039] A conventional brazed joint consists of a set of roughly parallel planes, with the filler metal flowing within the weld formed by the two parallel planes. However, for dissimilar joints, the filler metal has different wettability, fluidity after melting, and adhesion to the two materials. This often results in the filler metal on the difficult-to-wet side not coming into contact with the material, causing defects and affecting product performance.

[0040] This disclosure improves the wettability of the brazing filler metal on the surface of the difficult-to-wet material by setting a brazing groove structure with the steepest descent line on the surface to be brazed, thereby adjusting the flow rate of the brazing filler metal in the brazed joint. This improves the uniformity of residual stress at the brazed joint and avoids cracks caused by stress concentration. By constructing the brazing groove structure on the surface of the difficult-to-wet material, the brazing filler metal can cover the largest contact area in the shortest time when flowing on the surface of the difficult-to-wet material, increasing the flow rate of the brazing filler metal on the surface of the difficult-to-wet material. This prevents the brazing filler metal from flowing too fast on the surface of the easily wettable material, which could cause defects by covering the brazed joint with the easily wettable material surface. At the same time, it can also increase the contact area between the difficult-to-wet material and the brazing filler metal, increase the brazing rate on the surface of the difficult-to-wet material, and thus improve the performance of the brazed joint of dissimilar materials.

[0041] The brazed joints of dissimilar materials provided in this disclosure have the advantages of high brazing quality, few brazed seam defects, and high connection strength, which are of great significance for the application of dissimilar material components.

[0042] As shown in Figure 4, in some specific embodiments of this disclosure, the second brazing substrate 2 has a plurality of parallel brazing grooves 21 arranged at the steepest descent line. Increasing the number of brazing grooves 21 while keeping the total length of the brazing seam constant can reduce brazing material consumption while maintaining the contact area between the brazing material and the difficult-to-wet material unchanged.

[0043] In some preferred embodiments, a plurality of steepest descent grooves 21 are evenly distributed on the surface to be brazed of the second brazing substrate 2 to improve the uniformity of the brazing filler metal and stress distribution.

[0044] In some specific embodiments of this disclosure, the vertical distance H and the horizontal distance L between the starting point and the ending point of the brachistochrone groove 21 on the inner surface of the brachistochrone groove satisfy the following relationship with the size d of the brazing filler metal agglomerates when the filler metal is melted: H≥8d, L≥8d.

[0045] Taking the starting point as the origin, the position of the termination point can be determined based on the vertical distance H and horizontal distance L between the starting and ending points of the brachistochrone curve, thus obtaining the values ​​of r and θ. The vertical distance H and horizontal distance L should not be less than 8 times the size of the agglomerates during brazing, which helps improve the connection strength of the brazed joint. If the brachistochrone groove 21 is too small, its effect on improving the connection strength is not significant; however, a larger groove is not necessarily better. If the size of the brachistochrone groove 21 is too large, the amount of brazing filler metal used will increase, leading to higher costs. In this disclosure... In some preferred embodiments, the vertical distance H and the horizontal distance L satisfy: 8d≤H≤15d, 8d≤L≤15d. Within this range, the joint performance is good and there is no waste of too much solder. For example, H can be any one value or a range of any two values ​​from 8d, 9d, 10d, 11d, 12d, 13d, 14d, and 15d, and L can be any one value or a range of any two values ​​from 8d, 9d, 10d, 11d, 12d, 13d, 14d, and 15d.

[0046] In some specific embodiments of this disclosure, the surface of the first brazing substrate 1 to be brazed is provided with a grid pattern 11;

[0047] Alternatively, the brazing surface of the first brazing substrate 1 is provided with a maximum rate of descent protrusion 12, which is adapted to the maximum rate of descent groove 21 and forms an engagement structure.

[0048] That is, in some embodiments of this disclosure, the geometry of the connection interface of the heterogeneous brazed joint can be: the brazed surface of the first brazed substrate 1 is a flat surface without processing, and the brazed surface of the second brazed substrate 2 is provided with a brazing groove 21 (as shown in Figure 3); or the brazed surface of the first brazed substrate 1 is a grid pattern 11, and the brazed surface of the second brazed substrate 2 is provided with a brazing groove 21 (as shown in Figure 1); or the brazed surface of the second brazed substrate 2 is provided with a brazing groove 21, and the brazed surface of the first brazed substrate 1 is provided with a brazing protrusion 12 that meshes with the brazing groove 21 (Figure 2).

[0049] As shown in Figure 5, in some specific embodiments of this disclosure, the grid pattern 11 on the surface of the first brazing substrate 1 is composed of crisscrossing grooves.

[0050] When the surface of the first brazing substrate 1 to be brazed has a grid pattern 11, the flow rate of the brazing filler metal on the surface of the easily wettable material can be reduced by the obstruction of the grid pattern 11, while the brazing groove 21 can increase the flow rate of the brazing filler metal on the surface of the difficult-to-wet material. The two work together to achieve the purpose of the brazing filler metal covering both surfaces to be brazed at the same time, reducing brazing defects. The groove in the grid pattern also has the function of storing excess brazing filler metal. The grid pattern can also increase the roughness of the material surface, increase the adhesion of the material surface to the brazing filler metal, and increase the contact area between the brazing filler metal and the material. This structure can significantly improve the strength of the brazed joint of dissimilar materials.

[0051] When the brazing surface of the first brazing substrate 1 has a brachistochrone protrusion 12 that meshes with the brachistochrone groove 21, the brachistochrone structure is recessed on the surface of the difficult-to-wet material, increasing the wetting angle and improving wettability. On the surface of the easily wettable material, the brachistochrone structure is protruding, decreasing the wetting angle and reducing the wetting speed. This structure forms a single brazing filler metal channel at the joint, allowing gas to escape spontaneously, significantly reducing porosity, and ensuring that impurities are arranged orderly to the outside of the brazing seam, thus improving joint strength. Furthermore, compared to a planar or grid-patterned surface on the easily wettable material, this structure can reduce the amount of brazing filler metal used, shorten the brazing time, and improve brazing efficiency.

[0052] In some specific embodiments of this disclosure, the surface structure of the first brazing substrate 1 and the second brazing substrate 2 is a micron-level geometry.

[0053] In some specific embodiments of this disclosure, a storage trough 211 is provided at the intersection of two symmetrically arranged brachistodescending curve surfaces in the brachistodescending groove 21. This storage trough is configured to store excess brazing filler metal, thereby increasing the contact area between the material and the brazing filler metal and improving the joint strength. The depth of the storage trough 211 is ≥r / 5, and the width of the storage trough 211 is ≥r / 5.

[0054] If the storage tank 211 is too small, the effect on improving shear strength will not be obvious; if it is too large, it will lead to a large amount of brazing filler metal, long brazing time, low efficiency, and high cost. In some preferred embodiments of this disclosure, the depth of the storage tank 211 is r / 5-3r, such as r / 5, r / 4, r / 2, r, 2r, 3r, etc., and the width of the storage tank 211 is r / 5-3r, such as r / 5, r / 4, r / 2, r, 2r, 3r, etc.

[0055] In some specific embodiments of this disclosure, the surface structure of the surface to be welded of the second brazing substrate 2 is such that each transition point is a rounded arc, which allows the brazing filler metal to flow smoothly. By forming various arched (brachial groove) and rounded arc structures on the surface, the residual stress generated during the brazing process can be evenly distributed, avoiding cracking caused by stress concentration.

[0056] In some specific embodiments of this disclosure, the first brazing substrate 1 includes any one of YG8 and TC4;

[0057] And / or, the second brazing substrate 2 includes any one of PCBN and alumina ceramic.

[0058] In some specific embodiments of this disclosure, the first brazing substrate 1 is YG8, and the second brazing substrate 2 is PCBN.

[0059] In some other embodiments of this disclosure, the first brazing substrate 1 is TC4, and the second brazing substrate 2 is alumina ceramic.

[0060] The second aspect of this disclosure provides a method for preparing a brazing fastest-decreasing wire structure joint of dissimilar materials according to any one of the foregoing embodiments, comprising the following steps:

[0061] S1. Machining the fastest descent groove on the surface to be brazed of the second brazing substrate;

[0062] S2. Place the brazing filler metal between the surfaces to be brazed of the first and second brazing substrates and braze them to obtain the desired result.

[0063] This disclosed method increases the flow rate of the brazing filler metal on the surface of the difficult-to-wet material by processing a groove with the fastest descent line on the surface to be brazed on the second brazing substrate that is difficult to wet. This avoids the defects caused by the brazing filler metal flowing too fast on the surface of the easy-to-wet material, increases the contact area between the difficult-to-wet material and the brazing filler metal, and improves the brazing rate of the material surface. This method can significantly improve the brazing quality of brazed joints of dissimilar materials and increase the joint strength.

[0064] In some specific embodiments of this disclosure, step S1 further includes processing a grid pattern or a steepest descent line protrusion on the surface to be brazed of the first brazing substrate.

[0065] Processing a grid pattern on the surface to be brazed on the first brazing substrate can reduce the flow rate of the brazing filler metal on the surface of the easily wettable material, reduce the difference in the flow rate of the brazing filler metal on the surfaces of the two materials, so that the brazing filler metal can cover both materials at the same time, reduce brazing defects, increase the contact area between the brazing filler metal and the brazing substrate and the roughness of the brazing substrate, increase the brazing rate, and improve the joint strength.

[0066] Processing a brachistochrone protrusion on the surface of the first brazing substrate that meshes with the brachistochrone groove can also improve joint strength. Although the mesh pattern is superior in terms of joint strength improvement, the brachistochrone protrusion can reduce the amount of brazing filler metal, shorten the brazing time, and improve brazing efficiency compared to the mesh pattern structure.

[0067] In some specific embodiments of this disclosure, in step S1, the processing methods for the first brazing substrate and the brazing surfaces of the second brazing substrate include slow wire cutting and / or short pulse laser cutting.

[0068] In some specific embodiments of this disclosure, before step S1, a pretreatment step is included for the brazing surfaces of the first brazing substrate and the second brazing substrate. The pretreatment method includes: sandblasting and / or sandpaper polishing of the brazing surfaces, ultrasonic cleaning, and drying.

[0069] In some specific embodiments of this disclosure, ultrasonic cleaning is performed in acetone for a time of 10-20 min, for example, any one value or a range of any two values ​​from 10 min, 12 min, 14 min, 15 min, 16 min, 18 min, to 20 min.

[0070] In some specific embodiments of this disclosure, the brazing method includes vacuum brazing and / or induction brazing.

[0071] In some specific embodiments of this disclosure, the first brazing substrate is YG8, the second brazing substrate is PCBN, the brazing filler metal is CuSnTi, the brazing temperature is 800-1000℃, for example, any one value or a range of any two values ​​among 800℃, 850℃, 900℃, 950℃, and 1000℃, and the heating rate is 1-20℃ / min, for example, any one value or a range of any two values ​​among 1℃ / min, 3℃ / min, 5℃ / min, 7℃ / min, 10℃ / min, 12℃ / min, 14℃ / min, 16℃ / min, 18℃ / min, and 20℃ / min.

[0072] In some specific embodiments of this disclosure, the first brazing substrate is TC4, the second brazing substrate is alumina ceramic, the brazing filler metal is TiZrCuNi, the brazing temperature is 950-1000℃, for example, any one value or any two values ​​from 950℃, 980℃, and 1000℃, and the heating rate is 1-20℃ / min, for example, any one value or any two values ​​from 1℃ / min, 3℃ / min, 5℃ / min, 7℃ / min, 10℃ / min, 12℃ / min, 14℃ / min, 16℃ / min, 18℃ / min, and 20℃ / min.

[0073] The following detailed description of some embodiments of this disclosure is provided in conjunction with specific examples. Unless otherwise specified, all raw materials used in the embodiments can be commercially available.

[0074] In one possible implementation, a slow wire EDM machine is used to fabricate the geometry described in this disclosure on the PCBN / YG8 brazing joint, with the interface structure shown in Figure 6, and brazing is performed using CuSnTi solder.

[0075] Step 11: Pre-treat the surfaces of PCBN and YG8 to be soldered. The surfaces of the materials to be soldered are sandblasted, then ultrasonically cleaned in acetone for 15 minutes, and finally air-dried.

[0076] Step 12: The PCBN soldering surface is machined using a slow wire EDM machine. The brachistochrone formula described in this disclosure is imported into CAD drawing software. Literature review indicates that commercial CuSnTi solder agglomerates into particles approximately 2-3 μm in size during melting. Taking the starting point θ as 0°, the ending point θ as 120°, and r as 20 μm, the vertical distance between the starting and ending points is 30 μm, and the horizontal distance is 25 μm. Within this brachistochrone range, the particles formed during solder agglomeration can be considered point masses. The two segments of the brachistochrone surface are connected by a 20 μm deep and 20 μm wide storage tank, and the machine automatically processes the solder according to the CAD drawings and program.

[0077] Step 13: Use a slow wire EDM machine to process the YG8 surface to be welded. First, cut grooves 20μm wide and 20μm deep every 20μm in the transverse direction. Then, rotate the YG8 sample 90° and cut grooves 20μm wide and 20μm deep every 20μm in the longitudinal direction to form a grid pattern.

[0078] Step 14: Pre-coat the surfaces of the two materials to be soldered with CuSnTi solder, place the furnace in a vacuum brazing furnace, and control the vacuum level to 1×10⁻⁶. -3 Pa is heated to 900°C at a heating rate of 10°C / min, held for 2 min, and then cooled to 400°C at a rate of 10°C / s. The result is a brazed joint.

[0079] Step 15: After brazing is completed, the shear strength of the brazed joint is tested using a universal testing machine. The results show that the shear strength of the welded joint manufactured using the structure of this embodiment reaches 269 MPa.

[0080] Alternatively, unlike the above implementation, the soldering surfaces of PCBN and YG8 can be further processed without additional processing, consisting only of steps 11, 14, and 15 in the above implementation. After brazing, the joint strength is tested, and its shear strength is 147 MPa. The strength is increased by 83% by using steps 11-15 compared to using only steps 11, 14, and 15.

[0081] In some embodiments, unlike steps 11-15 above, a short-pulse laser is used to process the PCBN surface to be soldered to achieve finer processing dimensions. The process parameters are: laser power 300W, frequency 1000KHz, scanning speed 40mm / s, and the dimensions of the processed material reservoir are depth × width = 4 × 4μm. The solder joint strength is 207MPa, which is 41% higher than steps 11, 14, and 15, and 23% lower than steps 11-15. The optimal soldering time is 2 minutes, unchanged from steps 11-15, and the solder consumption is reduced by 10% compared to steps 11-15.

[0082] In some embodiments, the difference from steps 11-15 above is that the dimensions of the processed storage tank are depth × width = 60 × 60 μm. The weld joint strength is 298 MPa, an increase of 10.8% compared to steps 11-15; however, the welding time reaches 4 minutes, a 100% increase, and the brazing filler metal consumption increases by 82%.

[0083] In another possible implementation, a pulsed laser and a slow wire EDM machine are used to fabricate the geometry described in this disclosure on the Al2O3 and TC4 brazed joint, with the interface structure shown in Figure 7. Commercial TiZrCuNi brazing filler metal is used for brazing.

[0084] Step 21: Pre-treat the surfaces of the alumina ceramic and TC4 titanium alloy to be welded. The pre-treatment involves sanding and polishing the surfaces of the materials to be welded, then ultrasonically cleaning them in acetone for 15 minutes, and finally air-drying them.

[0085] Step 22: Machining the Al2O3 and TC4 surfaces to be welded using a pulsed laser and a slow wire EDM machine respectively, and importing the brachistochrone formula described in this disclosure into CAD drawing software. The starting point θ is set to 0°, the ending point θ angle to be 180°, and the r value to be 30μm. At this point, the vertical distance between the starting and ending points of the brachistochrone is 60μm, and the horizontal distance is 94.25μm. After generating the left-side brachistochrone, the right-side brachistochrone is mirrored, with a 30μm interval between every two closed brachistochrone segments. A raised area is machined on the easily wetted TC4 side, and a recessed surface to be welded is machined on the Al2O3 side, automatically processed by the equipment according to the CAD drawings and program.

[0086] Step 23: Pre-coat the surfaces of the two materials to be soldered with TiZrCuNi solder, place them in a vacuum brazing furnace, and control the vacuum level to 1×10⁻⁶. -3 Pa is heated to 950°C at a heating rate of 10°C / min, held for 15 min, and then cooled to 300°C at a rate of 10°C / s. The brazed joint is then obtained by cooling it in the furnace.

[0087] Step 24: After brazing, the shear strength of the joint was tested using a universal testing machine. The results showed that the welded joint manufactured using the structure of this embodiment had a shear strength of 60 MPa, which is 50% higher than that of the welded joint without special treatment.

[0088] Alternatively, unlike the above implementation, the surfaces to be brazed of Al2O3 and TC4 may not require additional processing. The process may consist only of steps 21, 23, and 24 in the above implementation. After brazing, the joint strength is tested, and its shear strength is 40 MPa.

[0089] In some embodiments, the difference from steps 11-15 above is that the shape of the joint interface is as shown in Figure 3, the surface to be soldered of YG8 is not processed, the surface to be soldered of PCBN is processed with the steepest descent groove, and the other parameters are the same as in steps 11-15 above. The shear strength of the prepared brazed joint is 173 MPa, which is 17.7% higher than in steps 11, 14 and 15 above, and 35.7% lower than in steps 11-15 above.

[0090] In some embodiments, the difference from steps 11-15 above is that the shape of the joint interface is as shown in Figure 2, and the actual object is shown in Figure 8. The brazing surface of YG8 is processed with a ramp rate of descent protrusion, and the brazing surface of PCBN is processed with a ramp rate of descent groove. The other parameters are the same as in steps 11-15 above. The shear strength of the prepared brazed joint is 192 MPa, which is 30.6% higher than in steps 11, 14 and 15 above, and 28.6% lower than in steps 11-15 above. However, the brazing time is 1 minute, which is 100% faster than in steps 11-15 above, and the amount of brazing filler metal used is reduced by 72% compared with steps 11-15 above.

[0091] In some embodiments, unlike the previous embodiment, an additional 20μm × 20μm material storage groove is machined within the groove of the fastest descent line on the surface of the PCBN to be soldered, as shown in Figure 9. The remaining parameters are the same as in the previous embodiment. The shear strength of the prepared brazed joint is 213MPa, an improvement of 11% compared to the previous embodiment. The soldering time is 1.2 min, a 20% increase compared to the previous embodiment, and the amount of solder used is increased by 14% compared to the previous embodiment.

[0092] In some embodiments, unlike steps 11-15 above, a material storage tank is not machined within the groove for the steepest descent line on the surface of the PCBN to be soldered, as shown in Figure 10. The remaining parameters are the same as in steps 11-15. The shear strength of the prepared brazed joint is 247 MPa, a decrease of 8% compared to steps 11-15. The soldering time is 1.6 min, a 20% reduction compared to steps 11-15, and the amount of solder used is reduced by 20% compared to steps 11-15.

[0093] In another possible implementation, a CNC lathe is used to manufacture the geometry described herein on the end faces of a stainless steel tube with an inner diameter of 30 mm and a wall thickness of 6 mm, and a copper tube with a wall thickness of 5 mm. Welding is performed using induction heating, as shown in Figure 11.

[0094] Step 31: Based on the copper tube wall thickness of 5mm, confirm the dimensions of the brachistochrone curve. Take the starting point θ as 0°, the ending point θ as 180°, and the r value as 1.5mm. At this time, the horizontal distance between the starting and ending points of the brachistochrone curve is 4.71mm, and the vertical distance is 3mm.

[0095] Step 32: Using a CNC machine tool, starting from a point on the outer diameter of the stainless steel tube, rotate and machine a concave surface in the direction of the inner hole using the steepest descent curve confirmed in Step 31, and machine a horizontal platform in the direction of the inner hole at the end point of the curve.

[0096] Step 33: Using a CNC machine tool, starting from a point on the outer diameter of the copper tube, rotate and machine a convex surface in the outer circumferential direction using the steepest descent curve confirmed in Step 31, and machine a horizontal platform in the direction of the inner hole.

[0097] Step 34: Place the stainless steel tube at the bottom with the concave side facing up, and the copper tube with the convex side facing down, connecting the two tubes. Fit the flux-cored silver solder ring (brand: Zhengzhou Machinery Research Institute Co., Ltd., grade: Ag25CuZn) onto the joint.

[0098] Step 35: Use a high-frequency induction heating device with a heating power of 20KW. Place the two tubes described in step 34 in the induction heating coil for heating. When the heating time is 4s, it can be observed that the solder flows out from the inside of the brazing seam, indicating that the brazing has been completed.

[0099] Optionally, unlike the above implementation, the brazing seam joint surface of the stainless steel tube and the copper tube end face is a plane, and the other conditions are the same as in Example 9. The brazing time is 7s, which is 75% slower than steps 11-15 above. The brazing seam structure of the fastest descent wire structure can significantly shorten the brazing time and improve the brazing efficiency.

[0100] Although this disclosure 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 this disclosure 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 this disclosure; 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 this disclosure; therefore, this means that all such substitutions and modifications that fall within the scope of this disclosure are included in the appended claims. Industrial applicability

[0101] By employing the above scheme, a rapid descent groove structure is constructed on the brazing surface of the second brazing substrate that is difficult to wet. This allows the brazing filler metal to cover the largest contact area in the shortest time during its flow on the surface of the difficult-to-wet material, increasing the flow rate of the brazing filler metal on the surface of the difficult-to-wet material. This prevents the brazing filler metal from flowing too fast on the surface of the easily wettable material, which could cause the brazing seam to be blocked and result in defects. Furthermore, this scheme improves the wettability of the brazing filler metal on the surface of the difficult-to-wet material, improves the uniformity of residual stress at the brazed joint, and avoids cracking caused by stress concentration. Simultaneously, it increases the contact area between the difficult-to-wet material and the brazing filler metal, increasing the brazing rate on the surface of the difficult-to-wet material. This results in high-quality brazing of the heterogeneous material brazed joint, fewer brazing seam defects, and high connection strength.

Claims

1. A brazing joint structure for the fastest descent wire of dissimilar materials, characterized in that, It includes a first brazing substrate and a second brazing substrate. The first brazing substrate has better wettability to the brazing filler metal than the second brazing substrate. The brazing surface of the second brazing substrate is provided with a brachistochrone groove. Each of the brachistochrone grooves is composed of two sets of symmetrically arranged brachistochrone surfaces. The inner surface curve of the brachistochrone surface conforms to the brachistochrone equation: x = r(θ - sinθ); y = r(1 - cosθ).

2. The brazing fastest descent wire structure joint of dissimilar materials according to claim 1, characterized in that, The second brazing substrate has multiple parallel-arranged steepest descent grooves on the surface to be brazed.

3. The brazing fastest descent wire structure joint of dissimilar materials according to claim 2, characterized in that, The plurality of brachistochrone grooves are evenly distributed on the brazing surface of the second brazing substrate.

4. The brazing fastest descent wire structure joint of dissimilar materials according to claim 1, characterized in that, The vertical distance H and horizontal distance L between the start and end points of the brachistochrone groove on the inner surface of the brachistochrone groove satisfy the following relationship with the size d of the brazing filler metal agglomerates when the filler metal is melted: H≥8d, L≥8d.

5. The brazing fastest descent wire structure joint of dissimilar materials according to claim 1, characterized in that, The surface of the first brazing substrate to be brazed has a grid pattern; Alternatively, the brazing surface of the first brazing substrate is provided with a brachistochrone protrusion, which is adapted to the brachistochrone groove to form an engagement structure.

6. The brazing fastest descent wire structure joint of dissimilar materials according to claim 5, characterized in that, The grid pattern on the surface of the first brazing substrate is composed of crisscrossing grooves.

7. The brazing fastest descent wire structure joint of dissimilar materials according to any one of claims 1-6, characterized in that, It includes at least one of the following features a to b: a. A storage trough is provided at the intersection of two symmetrically arranged brachistochrone curved surfaces within the brachistochrone groove, wherein the depth of the storage trough is ≥r / 5 and the width of the storage trough is ≥r / 5; b. In the surface structure of the surface to be welded of the second brazing substrate, each transition point is a rounded arc.

8. The brazing fastest descent wire structure joint of dissimilar materials according to any one of claims 1-7, characterized in that, The first brazing substrate includes either YG8 or TC4; And / or, the second brazing substrate includes any one of PCBN and alumina ceramic.

9. The method for preparing a brazed brazing fastest-decreasing wire structure joint of dissimilar materials according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Machining the fastest descent groove on the surface to be brazed of the second brazing substrate; S2. Place the brazing filler metal between the surfaces to be brazed of the first and second brazing substrates and braze them to obtain the desired result.

10. The method for preparing a brazed joint with the fastest descent wire structure of dissimilar materials according to claim 9, characterized in that, Step S1 further includes processing a grid pattern or a steepest descent line protrusion on the surface to be brazed of the first brazing substrate.

11. The method for preparing a brazed joint with the fastest descent wire structure of dissimilar materials according to claim 10, characterized in that, In step S1, the processing method includes slow wire cutting and / or short pulse laser cutting.

12. The method for preparing a brazed joint with the fastest descent wire structure of dissimilar materials according to claim 9, characterized in that, Before step S1, the method further includes a pretreatment step for the brazing surfaces of the first brazing substrate and the second brazing substrate. The pretreatment method includes: sandblasting and / or sandpaper polishing of the brazing surfaces, ultrasonic cleaning, and drying.

13. The method for preparing a brazed joint with the fastest descent wire structure of dissimilar materials according to claim 9, characterized in that, In step S2, the brazing method includes vacuum brazing and / or induction brazing.

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