Heterogeneous material brazed joint and preparation method thereof

Abstract

The invention relates to the technical field of brazing, in particular to a heterogeneous material brazing joint and a preparation method thereof. The preparation method comprises the following steps that S1, a porous metal net is placed on the surface of a to-be-welded steel substrate for diffusion welding, and the steel substrate with the surface configuration is obtained; and S2, the configuration face of the steel base body serves as a face to be welded, the steel base body with the surface configuration is assembled with brazing filler metal and a titanium base body to be welded, and then vacuum brazing is conducted. According to the method, the porous metal net is welded to the surface of the steel substrate to be welded through diffusion welding, a periodic heterogeneous microstructure surface is formed on the steel substrate, a discontinuous mismatched and multi-phase alternating interface structure is constructed in a customized mode, a continuous stress line of a connector can be cut off, rapid initiation and rapid expansion of cracks are restrained, and strengthening and toughening brazing connection of titanium and steel can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of brazing, and in particular to a heterogeneous material brazing joint and a preparation method thereof. Background Art

[0002] The rapid development of modern science and technology has put forward new and higher requirements for the performance of materials. Homogeneous materials with single performance can no longer meet the high-performance requirements of complex service environments. Heterogeneous metal components, due to their special composite structure, have highlighted an irreplaceable and important role in high-tech fields with harsh working conditions. Titanium and steel are both corrosion-resistant, and titanium has a high specific strength, while steel has an outstanding cost-effectiveness. As a typical representative of heterogeneous metal composite components, titanium / steel composite components can simultaneously overcome the disadvantages of titanium processing difficulties and steel mass in manufacturing and application, thereby giving full play to the structural and physical and chemical performance advantages of the two materials, such as lightweight structure, speed response, mechanics and corrosion resistance, etc., which can help reduce the weight of aerospace vehicle rudders and wings, and are also indispensable electrode materials for energy and chemical reactors. Therefore, achieving high-quality, efficient and reliable connection of titanium / steel heterogeneous metals has great engineering application value.

[0003] The physical and chemical properties of titanium and steel are significantly different. The stress concentration and brittle intermetallic compounds formed in the joint make the titanium / steel metallurgical connection face great challenges. There are three common methods for welding titanium / steel, namely fusion welding, pressure welding and brazing. When using fusion welding, copper-based welding wire is the main welding material, but due to the low strength and poor corrosion resistance of the copper matrix, the performance improvement space of titanium / steel joints is limited. Titanium / steel pressure welding mainly focuses on diffusion welding, friction welding and explosion welding. The resulting joint strength is relatively high, but additional high temperature or high pressure is required during welding, and the welding structure form is greatly limited. Compared with the first two types of welding methods, brazing can heat the entire component, and can achieve synchronous contraction of the two parent materials of titanium and steel by establishing a temperature gradient or adding constraints, thereby effectively alleviating or even eliminating the residual stress of the joint. At the same time, the welding structure has strong adaptability and does not require pre- and post-weld heat treatment. It is one of the ideal means of connecting heterogeneous metals.

[0004] However, during the titanium / steel brazing process, the brazing seam of the joint will show the characteristics of partitioning and stratification, and a FeTi and Fe2Ti brittle reaction layer with a continuous straight interface will be generated on the steel side, forming a continuous stress line, which will lead to rapid crack initiation and rapid expansion, seriously weakening the strength and toughness of the joint. Simply regulating the brazing filler metal composition and brazing process is difficult to fundamentally solve the common problem of the formation of the FeTi / Fe2Ti straight mismatch interface in the titanium / steel brazed joint.

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

[0006] The first object of the present invention is to provide a method for preparing a heterogeneous material brazed joint, so as to solve the technical problem that continuous mismatch interface failure occurs after brazing of the heterogeneous material brazed joint, which seriously weakens the strength and toughness of the joint.

[0007] The second purpose of the present invention is to provide a heterogeneous material brazing joint, which is made by the preparation method of the heterogeneous material brazing joint as described above, and can overcome the problems of rapid cracking of the joint and rapid crack expansion, and the obtained heterogeneous material brazing joint has high joint strength.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] A method for preparing a heterogeneous material brazing joint comprises the following steps:

[0010] S1. The porous metal mesh is placed on the surface of the steel substrate to be welded for diffusion welding to obtain the steel substrate having a surface configuration;

[0011] S2. Using the configuration surface of the steel substrate as the surface to be welded, assemble the steel substrate with the surface configuration with the brazing material and the titanium substrate to be welded and then perform vacuum brazing.

[0012] Preferably, the porous metal mesh comprises a copper mesh or a nickel mesh.

[0013] Preferably, the purity of the porous metal mesh is greater than 99%.

[0014] Preferably, the mesh size of the porous metal mesh is 100-350 meshes.

[0015] Preferably, the diffusion welding is performed in a vacuum chamber, and the vacuum degree in the vacuum chamber is 10 -3 -10 -4 Pa.

[0016] Preferably, during the diffusion welding process, the pressure applied to the surface of the workpiece to be welded is 4-10 MPa.

[0017] Preferably, the temperature control of the diffusion welding includes a first stage, a second stage and a third stage. In the first stage, the temperature is increased to the first temperature at a rate of 8-12°C / min and kept at the temperature for 5-10 minutes; in the second stage, the temperature is increased to the second temperature at a rate of 3-10°C / min and kept at the temperature for 25-40 minutes; in the third stage, the temperature is decreased to the third temperature at a rate of 8-12°C / min and kept at the temperature for 5-10 minutes;

[0018] When the porous metal mesh is a copper mesh, the first temperature is 550-600° C., the second temperature is 800-850° C., and the third temperature is 480-520° C.;

[0019] When the porous metal mesh is a nickel mesh, the first temperature is 750-800°C, the second temperature is 1020-1080°C, and the third temperature is 480-500°C.

[0020] Preferably, the steel matrix includes any one of 316L stainless steel, 316 stainless steel, and 304 stainless steel.

[0021] Preferably, the titanium matrix includes TC4 titanium alloy or TiAl alloy.

[0022] Preferably, the solder comprises a titanium-based solder.

[0023] Preferably, the vacuum degree of the vacuum brazing is ≤5×10 -3 Pa.

[0024] Preferably, the vacuum brazing comprises the following steps: heating to 750-800°C at a rate of 8-12°C / min, keeping warm for 3-10min, then heating to 920-980°C at a rate of 3-8°C / min, keeping warm for 10-40min, then cooling to 480-500°C at a rate of 8-12°C / min, keeping warm for 5-10min, and finally cooling with the furnace.

[0025] Preferably, before step S1, the method further includes a step of cleaning the steel substrate and the porous metal mesh; and before step S2, the method further includes a step of cleaning the titanium substrate.

[0026] Preferably, the cleaning comprises mechanical cleaning and / or chemical cleaning;

[0027] The mechanical cleaning includes sanding, alcohol wiping and blowing; and / or the chemical cleaning includes pickling, water rinsing, alcohol wiping and blowing.

[0028] A heterogeneous material brazing joint is prepared by using the preparation method of a heterogeneous material brazing joint described in any one of the aforementioned embodiments.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The present invention proposes a new idea for the directional design of the interface structure of heterogeneous metal brazing joints, and prepares two types of "steel matrix + porous metal mesh" periodic heterogeneous microstructure surfaces: copper-steel and nickel-steel. Based on the localized metallurgical reaction of the lattice porous composite intermediate layer, multi-products such as Ti-Cu (Ni), Fe-Cu (Ni), Ti-Fe, and Ti-Fe-Cu (Ni) are generated. A customized non-continuous mismatch and multi-phase alternating interface structure is constructed to cut off the continuous stress line of the joint, inhibit the rapid initiation and rapid expansion of cracks, and achieve a titanium / steel reinforced brazing connection.

[0031] (2) The present invention reveals the mechanism of the shape-controlled interface structure to enhance the toughness of titanium / steel brazing joints, which can enrich the welding metallurgy theory under the action of the composite intermediate layer, and its results can also be extended to other dissimilar metal welding fields.

[0032] (3) The method of the present invention is simple to operate and easy to implement. It can quickly construct heterogeneous microstructure surfaces of larger components and is convenient for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 Flow chart of Example 1 of the present invention: wherein (a) is a schematic diagram of the overlap between the steel substrate and the copper mesh, (b) is a schematic diagram of diffusion, (c) is a schematic diagram of brazing overlap, and (d) is a microscopic state diagram of the brazing joint;

[0035] Figure 2 The diffusion welding effect diagram of Example 1 of the present invention: (a) is a 2D effect diagram of diffusion welding, (b) is a 3D imaging diagram of diffusion welding, and (c) is a microscopic state diagram of the diffusion welding joint;

[0036] Figure 3 The diffusion welding effect diagram of Example 2 of the present invention: (a) is a 2D effect diagram of diffusion welding, (b) is a 3D imaging diagram of diffusion welding, and (c) is a microscopic state diagram of the diffusion welding joint;

[0037] Figure 4 The joint strength curves of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the present invention are shown;

[0038] Figure 5 The joint strength curves of Example 2, Comparative Example 4 and Comparative Example 5 are shown. DETAILED DESCRIPTION

[0039] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0040] like Figure 1 As shown, the first aspect of the present invention provides a method for preparing a heterogeneous material brazing joint, comprising the following steps:

[0041] S1. placing a porous metal mesh on the surface of a steel substrate to be welded for diffusion welding to obtain a steel substrate having a surface configuration;

[0042] S2. Using the configuration surface of the steel substrate as the surface to be welded, assemble the steel substrate with the surface configuration with the brazing material and the titanium substrate to be welded and then perform vacuum brazing.

[0043] When titanium and steel are directly brazed, the brazing seam will show the characteristics of zoning and stratification, and FeTi and Fe2Ti brittle reaction layers with continuous straight interfaces will be generated on the steel side, forming continuous stress lines, which will lead to rapid crack expansion and seriously weaken the strength and toughness of the joint. In view of the above problems, the present invention welds a porous metal mesh to the surface of a steel substrate to be welded by diffusion welding, forming a periodic heterogeneous microstructure surface on the steel substrate, and then customizes the metallurgical reaction in the brazing process to construct a discontinuous mismatch and multi-phase alternating interface structure, which can cut off the continuous stress lines of the joint, inhibit the rapid initiation and rapid expansion of cracks, and achieve a strengthened and toughened brazing connection between titanium and steel.

[0044] The present invention uses a metal mesh to prepare a periodic heterogeneous microstructure surface on the surface of a steel substrate by diffusion welding. The process is simple and easy to operate. A large-area microstructure surface can be constructed by diffusion welding once, and the surface can be applied to the rapid construction of a microstructure surface of a large workpiece. Although the metal powder laser cladding method can also construct a heterogeneous microstructure surface on a steel substrate and cut off continuous stress lines, the laser cladding method requires repeated cladding for multiple times to obtain the desired configuration, which cannot be achieved by one-time cladding, and large-area cladding cannot be achieved at the same time. Cladding needs to be performed point by point or line by line, which is inefficient. For large workpieces, the surface area to be processed is large, which is difficult to achieve by laser cladding.

[0045] The working principle of the present invention is that the metal mesh and the steel substrate are tightly connected through atomic diffusion, and a barrier is formed on the surface of the steel substrate. The barrier can avoid the generation of FeTi, Fe2Ti brittle reaction layers with continuous straight interfaces on the surface of the steel substrate, thereby cutting off the continuous stress lines. It is difficult to achieve the above effect by directly placing the metal mesh and the brazing material between the steel substrate and the titanium substrate for brazing. Although the metal mesh is arranged between the parts to be welded can improve the strength of the brazed joint to a certain extent, the active intermediate layer will hinder the sufficient diffusion between the welding materials, which has a negative impact on the joint strength. In addition, the metal mesh and the steel substrate are not welded before brazing, and the molten brazing material will flow to the metal mesh during brazing. The metal mesh is difficult to play a barrier role between the titanium matrix and the steel matrix, and the steel matrix surface will still generate a FeTi, Fe2Ti brittle reaction layer with a continuous straight interface, thereby forming a continuous stress line, so the overall effect is not ideal; similarly, it is also difficult to achieve the above effect by using a brazing filler metal to braze the metal mesh on the steel matrix in advance to construct a microstructure surface, because when the titanium matrix is ​​subsequently brazed, the brazing filler metal between the metal mesh and the steel matrix will also melt, and the close connection between the steel matrix and the metal mesh will be destroyed. The brazing filler metal flows mutually in a molten state, and a FeTi, Fe2Ti brittle reaction layer with a continuous straight interface will still be generated on the steel matrix surface, thereby forming a continuous stress line. In the present invention, the metal mesh is pre-welded to the steel matrix surface by diffusion welding. When the titanium matrix is ​​subsequently brazed, only the brazing filler metal melts, and the close connection between the metal mesh and the steel matrix will not be destroyed. The metal mesh can form a discontinuous barrier on the steel matrix surface, thereby forming a discontinuous phase interface, which can cut off the continuous stress line and significantly improve the joint strength of the heterogeneous material brazing joint.

[0046] In some specific embodiments of the present invention, the porous metal mesh used includes a copper mesh or a nickel mesh. The copper mesh or the nickel mesh is used to construct a heterogeneous microstructure surface on the surface of the steel substrate, which can generate Ti-Cu (Ni), Fe-Cu (Ni), Ti-Fe, Ti-Fe-Cu (Ni) multi-products on the surface of the steel substrate, forming a discontinuous mismatch and multi-phase alternating interface structure, thereby cutting off the continuous stress line.

[0047] In some specific embodiments of the present invention, the purity of the porous metal mesh used is greater than 99%. For example, the purity can be any value among 99.1%, 99.3%, 99.5%, 99.7%, 99.9%, 99.99%, or a range consisting of any two values.

[0048] In some specific embodiments of the present invention, the mesh number of the porous metal mesh used is 100-350 mesh, for example, it can be any point value among 100 mesh, 150 mesh, 200 mesh, 250 mesh, 300 mesh, and 350 mesh, or a range value composed of any two point values; in some embodiments, the wire diameter of the 100-mesh porous metal mesh is 74 μm, and the pore size is 182 μm; the wire diameter of the 150-mesh porous metal mesh is 68 μm, and the pore size is 106 μm; the wire diameter of the 200-mesh porous metal mesh is 52 μm, and the pore size is 75 μm; the wire diameter of the 250-mesh porous metal mesh is 38 μm, and the pore size is 64 μm; the wire diameter of the 300-mesh porous metal mesh is 32 μm, and the pore size is 53 μm; the wire diameter of the 350-mesh porous metal mesh is 28 μm, and the pore size is 44 μm; when the mesh is a square hole, the pore size usually refers to the side length.

[0049] In some specific embodiments of the present invention, diffusion bonding is performed in a vacuum chamber, and the vacuum degree in the vacuum chamber (the reading displayed after the vacuum pump is evacuated) is 10 -4 -10 -3 Pa, for example, can be 10 -4 Pa, 2×10 -4 Pa, 5×10 -4 Pa, 8×10 -4 Pa, 10 -3 Pa, 10 -3 Any point value in Pa or the range of values ​​consisting of any two point values.

[0050] In some specific embodiments of the present invention, during the diffusion welding process, the pressure applied to the surface of the workpiece to be welded is 4-10MPa, for example, it can be any point value among 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa or a range value consisting of any two point values; if the pressure is too small, the atomic diffusion may not be sufficient during diffusion welding; if the pressure is too high, the metal mesh may be deformed, and the degree of deformation may be large.

[0051] In some specific embodiments of the present invention, the temperature control of the diffusion welding includes a first stage, a second stage and a third stage. In the first stage, the temperature is increased to the first temperature at a rate of 8-12°C / min and kept warm for 5-10min; in the second stage, the temperature is increased to the second temperature at a rate of 3-10°C / min and kept warm for 25-40min; in the third stage, the temperature is reduced to the third temperature at a rate of 8-12°C / min and kept warm for 5-10min. After the third stage is finished, the temperature is cooled to room temperature with the furnace; in some embodiments, typically but not limiting, for example, the heating rate of the first stage can be any point value of 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min or a range value composed of any two point values, and the holding time can be 5min, 6min, 7min, 8min, 9min, The temperature rise rate of the second stage can be any point value among 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or a range value composed of any two point values, and the holding time can be any point value among 25min, 30min, 35min, 40min, or a range value composed of any two point values; the cooling rate of the third stage can be any point value among 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, or a range value composed of any two point values, and the holding time can be any point value among 5min, 6min, 7min, 8min, 9min, 10min, or a range value composed of any two point values.

[0052] When the porous metal mesh used is a copper mesh, the first temperature is 550-600°C, for example, it can be any point value among 550°C, 560°C, 570°C, 580°C, 590°C, and 600°C, or a range value consisting of any two point values; the second temperature is 800-850°C, for example, it can be any point value among 800°C, 810°C, 820°C, 830°C, 840°C, and 850°C, or a range value consisting of any two point values; the third temperature is 480-520°C, for example, it can be any point value among 480°C, 490°C, 500°C, 510°C, and 520°C, or a range value consisting of any two point values.

[0053] When the porous metal mesh used is a nickel mesh, the first temperature is 750-800°C, for example, it can be any point value among 750°C, 760°C, 770°C, 780°C, 790°C, and 800°C, or a range value consisting of any two point values; the second temperature is 1020-1080°C, for example, it can be any point value among 1020°C, 1040°C, 1060°C, and 1080°C, or a range value consisting of any two point values; the third temperature is 480-500°C, for example, it can be any point value among 480°C, 485°C, 490°C, 495°C, and 500°C, or a range value consisting of any two point values.

[0054] In some specific embodiments of the present invention, the steel substrate used includes any one of 316L stainless steel, 316 stainless steel, and 304 stainless steel.

[0055] In some specific embodiments of the present invention, the titanium matrix used includes TC4 titanium alloy (Ti6Al4V, wt.%) or TiAl alloy (such as Ti-48Al-2Cr-2Nb, at.%).

[0056] In some specific embodiments of the present invention, the brazing filler metal used for vacuum brazing includes a titanium-based brazing filler metal, for example, Ti-24Zr-40Cu-10Ni (wt.%).

[0057] In some specific embodiments of the present invention, in step S2, the assembly includes: assembling a steel substrate with a surface configuration, a solder and a titanium substrate from bottom to top, wherein the configured surface of the steel substrate is the surface to be welded; and designing a pressing piece on the titanium substrate to make the interface to be welded in close contact.

[0058] In some specific embodiments of the present invention, the vacuum degree of the vacuum brazing is ≤5×10 -3 Pa.

[0059] In some specific embodiments of the present invention, vacuum brazing includes the following steps: heating to 750-800°C at a rate of 8-12°C / min, keeping warm for 3-10 minutes, then heating to 920-980°C at a rate of 3-8°C / min, keeping warm for 10-40 minutes, then cooling to 480-500°C at a rate of 8-12°C / min, keeping warm for 5-10 minutes, and then cooling the weldment to room temperature with the furnace.

[0060] In some specific embodiments of the present invention, before step S1, a step of cleaning the steel substrate and the porous metal mesh is also included; before step S2, a step of cleaning the titanium substrate is also included.

[0061] In some embodiments of the invention, cleaning comprises mechanical cleaning and / or chemical cleaning;

[0062] Mechanical cleaning includes sandpaper polishing, alcohol wiping and drying. The roughness after sandpaper polishing is Ra1.6-6.4μm. After polishing, the surface of the workpiece to be welded is wiped clean with alcohol and blown dry; and / or, chemical cleaning includes pickling, water rinsing, alcohol wiping and drying. The acid used for pickling can be 10% sulfuric acid solution or 10%-15% hydrochloric acid solution. The pickling time is 5-10min. After pickling, rinse with clean water, then wipe clean with alcohol and blow dry.

[0063] A second aspect of the present invention provides a heterogeneous material brazing joint, which is prepared by the method for preparing a heterogeneous material brazing joint described in any one of the aforementioned embodiments.

[0064] The following is a detailed description of some embodiments of the present invention in conjunction with specific application examples. The raw materials used in the examples can be purchased from the market unless otherwise specified.

[0065] Example 1

[0066] (1) Select 15mm×10mm×5mm 316 stainless steel, 5mm×5mm×5mm TC4 titanium alloy and 100-mesh copper mesh (purity>99.9%, wire diameter 74μm, pore size 182μm). Use metallographic sandpaper to polish the surface to be welded of 316 stainless steel and TC4 titanium alloy to make the surface roughness reach Ra2.5μm, wipe with alcohol after polishing and blow dry. In addition, use 10% sulfuric acid solution by volume to pickle the copper mesh for 5 minutes, rinse with clean water after pickling, wipe the surface of the copper mesh with alcohol and blow dry.

[0067] (2) Place the polished surface of 316 stainless steel and the copper mesh from bottom to top in the vacuum chamber of the diffusion furnace, overlapping as shown in the figure. Figure 1 (a) and Figure 1 (b) is shown, and diffusion welding is performed. The vacuum degree in the vacuum chamber is 10 -4 Pa, the pressure applied to the copper mesh is 6MPa, and mica is added between the copper mesh and the pressure piece to prevent the copper mesh from adhering to the pressure piece. The temperature control is divided into three stages. In the first stage, the temperature is increased to 600℃ at a rate of 10℃ / min, and then kept warm for 5min. In the second stage, the temperature is increased to 800℃ at a rate of 5℃ / min, and then kept warm for 40min. In the third stage, the temperature is reduced to 500℃ at a rate of 10℃ / min, and then kept warm for 5min. After the third stage of insulation, the weldment is cooled to room temperature with the furnace. The diffusion welding effect is as follows Figure 2 As shown, the steel substrate is tightly connected to the copper mesh.

[0068] (3) The steel substrate to be welded with a surface configuration, the Ti-24Zr-40Cu-10Ni titanium-based brazing filler metal, and the TC4 titanium alloy are Figure 1(c) The scheme shown in the figure is assembled and then vacuum brazed. A mica sheet is placed on the TC4 titanium alloy to ensure close contact between the interfaces to be welded. The vacuum degree of vacuum brazing is 10 -4 Pa, temperature control is divided into three stages. In the first stage, the temperature is increased to 800℃ at a rate of 10℃ / min, and then kept warm for 5min. In the second stage, the temperature is increased to 950℃ at a rate of 5℃ / min, and then kept warm for 10min. In the third stage, the temperature is reduced to 500℃ at a rate of 10℃ / min, and then kept warm for 5min. After the third stage, the weldment is cooled to room temperature along with the furnace temperature.

[0069] The schematic diagram of the joint structure after brazing is as follows Figure 1 As shown in (d), Ti-Cu, Fe-Cu, Ti-Fe, and Ti-Fe-Cu multi-products are generated on one side of the steel matrix, forming a discontinuous mismatch and multi-phase alternating interface structure, cutting off the continuous stress line of the joint, inhibiting the rapid initiation and rapid expansion of cracks, and improving the strength and toughness of the titanium / steel brazing joint.

[0070] Example 2

[0071] (1) Select 15mm×10mm×5mm 304 stainless steel, 5mm×5mm×5mm TiAl alloy (Ti-48Al-2Cr-2Nb, at.%) and 150 mesh nickel mesh (purity>99.9%, wire diameter 68μm, pore size 106μm). Use metallographic sandpaper to polish the surface to be welded of 304 stainless steel and TiAl alloy to make the surface roughness reach Ra2.5μm. After polishing, wipe with alcohol and blow dry. In addition, use 15% hydrochloric acid solution by volume to pickle the nickel mesh for 5 minutes. After pickling, rinse with clean water, wipe the surface of the nickel mesh with alcohol and blow dry.

[0072] (2) Place the polished surface of 304 stainless steel and the nickel mesh from bottom to top in the vacuum chamber of the diffusion furnace for diffusion welding. The vacuum degree in the vacuum chamber is 10 -4 Pa, the pressure applied to the nickel mesh is 8MPa, and mica is added between the nickel mesh and the pressure piece to prevent the nickel mesh from adhering to the pressure piece. The temperature control is divided into three stages. The first stage is heated to 800℃ at a rate of 10℃ / min, and then kept warm for 5min. The second stage is heated to 1080℃ at a rate of 10℃ / min, and then kept warm for 40min. The third stage is cooled to 500℃ at a rate of 10℃ / min, and then kept warm for 5min. After the third stage of heat preservation, the welding is cooled to room temperature with the furnace. The diffusion welding effect is as follows Figure 3 As shown, the steel substrate and the nickel mesh are tightly connected.

[0073] (3) Assemble the steel substrate with surface configuration, the Ti-24Zr-40Cu-10Ni titanium-based brazing material, and the TiAl alloy from bottom to top and perform vacuum brazing. Place a mica sheet on the TiAl alloy to make the interface to be welded in close contact. The vacuum degree of vacuum brazing is 10 -4 Pa, temperature control is divided into three stages. In the first stage, the temperature is increased to 800℃ at a rate of 10℃ / min, and then kept warm for 5 minutes. In the second stage, the temperature is increased to 980℃ at a rate of 5℃ / min, and then kept warm for 10 minutes. In the third stage, the temperature is reduced to 500℃ at a rate of 10℃ / min, and then kept warm for 5 minutes. After the third stage, the weldment is cooled to room temperature along with the furnace temperature.

[0074] Comparative Example 1

[0075] Comparative Example 1 is similar to Example 1, except that the copper mesh is not diffusion-welded on the steel substrate, and the steel substrate and the titanium substrate are directly vacuum brazed. The other conditions are the same as those in Example 1.

[0076] Comparative Example 2

[0077] Comparative Example 2 is similar to Example 1, with the only difference being that the steel substrate and the copper mesh are not diffusion-welded in advance, and the copper mesh and the brazing material are directly placed between the steel substrate and the titanium alloy for vacuum brazing. The other conditions are the same as those in Example 1.

[0078] Comparative Example 3

[0079] Comparative Example 3 is similar to Example 1, with the only difference being that a 100-mesh copper mesh (purity > 99.9%, wire diameter 74 μm, pore size 182 μm) is brazed to a steel substrate using Ti-24Zr-40Cu-10Ni (wt.%) titanium-based brazing filler metal and the brazing conditions in Example 1, and then the steel substrate brazed with the copper mesh is vacuum brazed with the titanium alloy, and the remaining conditions are the same as in Example 1.

[0080] Comparative Example 4

[0081] Comparative Example 4 is similar to Example 2, except that the nickel mesh is not diffusion welded on the steel substrate, and the steel substrate and the titanium substrate are directly vacuum brazed. The other conditions are the same as those in Example 2.

[0082] Comparative Example 5

[0083] Comparative Example 5 is similar to Example 2, with the only difference being that the steel substrate and the nickel mesh are not diffusion welded in advance, and the nickel mesh and the brazing material are directly placed between the steel substrate and the titanium alloy for vacuum brazing. The other conditions are the same as those in Example 2.

[0084] Test example

[0085] The joint strength of each embodiment and each comparative example was tested respectively. The joint strength and deformation of embodiment 1 and comparative examples 1-3 are shown in FIG. Figure 4 As shown, the joint strength and deformation of Example 2, Comparative Example 4 and Comparative Example 5 are as follows Figure 5 As shown, compared with Comparative Examples 1, 2 and 3, the joint strength of Example 1 is significantly improved; compared with Comparative Examples 4 and 5, the joint strength of Example 2 is also significantly improved.

[0086] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a brazed joint of heterogeneous materials, characterized in that: The following steps are involved: S1. The porous metal mesh is placed on the surface of the steel substrate to be welded for diffusion welding to obtain the steel substrate having a surface configuration; S2. Using the configuration surface of the steel substrate as the surface to be welded, assemble the steel substrate with the surface configuration with the brazing material and the titanium substrate to be welded and then perform vacuum brazing.

2. The method for preparing a heterogeneous material brazing joint according to claim 1, characterized in that: Contains at least one of the following characteristics: (1) The porous metal mesh comprises a copper mesh or a nickel mesh; (2) The purity of the porous metal mesh is greater than 99%; (3) The mesh size of the porous metal mesh is 100-350 meshes.

3. The method for preparing a heterogeneous material brazing joint according to claim 1, characterized in that: The diffusion welding is carried out in a vacuum chamber, and the vacuum degree in the vacuum chamber is 10 -3 -10 -4 Pa.

4. The method for preparing a heterogeneous material brazing joint according to claim 1, characterized in that: During the diffusion welding process, the pressure applied to the surface of the workpiece to be welded is 4-10 MPa.

5. The method for preparing a heterogeneous material brazing joint according to claim 1, characterized in that: The temperature control of the diffusion welding includes the first stage, the second stage and the third stage. The first stage is heated to the first temperature at a speed of 8-12°C / min and kept warm for 5-10min; the second stage is heated to the second temperature at a speed of 3-10°C / min and kept warm for 25-40min; the third stage is cooled to the third temperature at a speed of 8-12°C / min and kept warm for 5-10min. When the porous metal mesh is a copper mesh, the first temperature is 550-600° C., the second temperature is 800-850° C., and the third temperature is 480-520° C.; When the porous metal mesh is a nickel mesh, the first temperature is 750-800°C, the second temperature is 1020-1080°C, and the third temperature is 480-500°C.

6. The method for preparing a heterogeneous material brazing joint according to claim 1, characterized in that: Contains at least one of the following characteristics: (1) The steel substrate includes any one of 316L stainless steel, 316 stainless steel, and 304 stainless steel; (2) The titanium matrix comprises TC4 titanium alloy or TiAl alloy; (3) The solder includes a titanium-based solder; (4) The vacuum degree of the vacuum brazing is ≤5×10 -3 Pa.

7. The method for preparing a heterogeneous material brazing joint according to claim 1, characterized in that: The vacuum brazing comprises the following steps: heating to 750-800°C at a speed of 8-12°C / min, keeping the temperature for 3-10min, then heating to 920-980°C at a speed of 3-8°C / min, keeping the temperature for 10-40min, then cooling to 480-500°C at a speed of 8-12°C / min, keeping the temperature for 5-10min, and cooling.

8. The method for preparing a heterogeneous material brazing joint according to claim 1, characterized in that: Before step S1, the method further includes a step of cleaning the steel substrate and the porous metal mesh; before step S2, the method further includes a step of cleaning the titanium substrate.

9. The method for preparing a heterogeneous material brazing joint according to claim 8, characterized in that: The cleaning includes mechanical cleaning and / or chemical cleaning; The mechanical cleaning includes sanding, alcohol wiping and blowing; and / or the chemical cleaning includes pickling, water rinsing, alcohol wiping and blowing.

10. A brazing joint of heterogeneous materials, characterized in that: The brazing joint is prepared by the method for preparing a heterogeneous material brazing joint according to any one of claims 1 to 9.

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