A dissimilar material brazed joint and a method of making the same

Abstract

The present application 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: S1. placing a porous metal mesh on the surface of a steel base to be welded for diffusion welding, so as to obtain the steel base with a surface configuration; S2. taking the configuration surface of the steel base as a welding surface, assembling the steel base with a surface configuration, a filler metal and a titanium base to be welded, and then performing vacuum brazing. The present application welds the porous metal mesh on the surface of the steel base to be welded through diffusion welding, forms a periodic heterogeneous microstructure surface on the steel base, customizes and constructs a non-continuous mismatching and multi-phase alternating interface structure, can cut off the continuous stress line of the joint, inhibit the rapid initiation and sharp expansion of cracks, and can realize the strong and tough brazing connection of titanium and steel.

Description

Technical Field

[0001] The present 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 important and irreplaceable 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's high weight 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 and speed response, as well as mechanical and corrosion resistance. They 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 significant engineering application value.

[0003] The physical and chemical properties of titanium and steel differ significantly. The stress concentration and brittle-hard intermetallic compounds formed in the joint pose huge challenges to the metallurgical connection of titanium / steel. There are three commonly used 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, there is limited room for improving the performance of titanium / steel joints. Titanium / steel pressure welding mainly focuses on diffusion welding, friction welding and explosion welding. The resulting joints are relatively strong, but additional high temperature or high pressure is required during welding, and the welding structure is extremely limited. Compared with the first two welding methods, brazing can heat the entire component and achieve synchronous contraction of the titanium and steel base materials by establishing a temperature gradient or adding constraints, thereby effectively alleviating or even eliminating residual stress in the joint. At the same time, the welded structure has strong adaptability and does not require pre- and post-weld heat treatment, making it one of the ideal means of connecting dissimilar metals.

[0004] However, during the titanium / steel brazing process, the brazing seam exhibits zoning and stratification, generating a brittle, hard FeTi / Fe2Ti reaction layer with a continuous, straight interface on the steel side. This creates continuous stress lines, leading to rapid crack initiation and rapid expansion, severely weakening the joint's strength and toughness. Simply manipulating the brazing filler metal composition and brazing process is unlikely to fundamentally resolve the common problem of the formation of a straight, mismatched FeTi / Fe2Ti interface in titanium / steel brazed joints.

[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 brazing joint, so as to solve the technical problem that the heterogeneous material brazing joint has continuous mismatch interface failure after brazing, which seriously weakens the joint strength and toughness.

[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, can overcome the problems of rapid cracking and rapid crack expansion of the joint, 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 adopted:

[0009] A method for preparing a brazed joint of heterogeneous materials 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 bonding includes a first stage, a second stage, and a third stage. In the first stage, the temperature is raised to the first temperature at a rate of 8-12°C / min and kept at that temperature for 5-10 minutes. In the second stage, the temperature is raised to the second temperature at a rate of 3-10°C / min and kept at that temperature for 25-40 minutes. In the third stage, the temperature is lowered to the third temperature at a rate of 8-12°C / min and kept at that 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 brazing degree 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 3-10 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 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 sandpaper polishing, alcohol wiping and air drying; and / or the chemical cleaning includes pickling, water rinsing, alcohol wiping and air drying.

[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 of copper-steel and nickel-steel. Based on the localized metallurgical reaction of the lattice porous composite intermediate layer, Ti-Cu(Ni), Fe-Cu(Ni), Ti-Fe, and Ti-Fe-Cu(Ni) multi-products are generated, and a customized discontinuous 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 realize the strengthened and toughened brazing connection of titanium / steel.

[0031] (2) The present invention reveals the mechanism of the shape-controlled interface structure to enhance and toughen the titanium / steel brazing joint, 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 embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

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

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

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

[0037] Figure 4 1 is the joint strength curve of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of the present invention;

[0038] Figure 5 These are the joint strength curves of Example 2, Comparative Example 4, and Comparative Example 5. 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. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are 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 brazing joint of heterogeneous materials, comprising the following steps:

[0041] S1. The porous metal mesh is placed on the surface of the steel substrate to be welded and diffusion welded 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 flat interfaces will be generated on the steel side, forming continuous stress lines, which will cause rapid crack expansion and seriously weaken the strength and toughness of the joint. To address the above problems, the present invention welds a porous metal mesh to the surface of the steel substrate to be welded by diffusion welding, forming a periodic heterogeneous microstructure surface on the steel substrate, and then customizes the metallurgical reaction during 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 microstructured surface on a steel substrate through diffusion welding. The process is simple and easy to operate. A single diffusion welding process can construct a large-area microstructured surface, making it suitable for the rapid construction of microstructured surfaces on large workpieces. Although metal powder laser cladding can also construct heterogeneous microstructured surfaces on steel substrates and sever continuous stress lines, laser cladding requires multiple repeated cladding operations to achieve the desired configuration, which cannot be achieved with a single cladding process. Furthermore, large-area cladding cannot be achieved simultaneously, requiring point-by-point or line-by-line cladding, which is inefficient. For large workpieces with large surfaces to be processed, laser cladding is difficult to achieve.

[0045] The working principle of the present invention is that the metal mesh and the steel substrate are tightly connected through atomic diffusion, forming a barrier 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 arrangement of the metal mesh 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 hard reaction layer with a continuous flat interface, thereby forming a continuous stress line. Therefore, the overall effect is not ideal. Similarly, it is 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 will flow to each other in the molten state, and will still generate a FeTi, Fe2Ti brittle hard reaction layer with a continuous flat interface 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, and 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, and 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 value consisting of any two value points.

[0048] In some specific embodiments of the present invention, the mesh size 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 consisting 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 generally refers to the side length.

[0049] In some specific embodiments of the present invention, the 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 4-10 MPa, for example, it can be any point value among 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa or a range value consisting of any two point values; if the pressure is too small, the atomic diffusion during diffusion welding may not be sufficient; 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 end of the third stage, the temperature is cooled to room temperature with the furnace; in some embodiments, typically but not limitatively, 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 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 value points, and the holding time can be any value among 25min, 30min, 35min, 40min, or a range value composed of any two value points; the cooling rate of the third stage can be any value among 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, or a range value composed of any two value points, and the holding time can be any value among 5min, 6min, 7min, 8min, 9min, 10min, or a range value composed of any two value points.

[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 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 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 interfaces 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, the step of cleaning the steel substrate and the porous metal mesh is further included; before step S2, the step of cleaning the titanium substrate is further included.

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

[0062] Mechanical cleaning includes sanding, wiping with alcohol, and drying. The roughness after sanding is Ra1.6-6.4μm. After sanding, the surface of the workpiece to be welded is wiped clean with alcohol and dried. And / or, chemical cleaning includes pickling, rinsing with water, wiping with alcohol, and drying. The acid used for pickling can be 10% sulfuric acid solution or 10%-15% hydrochloric acid solution. The pickling time is 5-10 minutes. After pickling, rinse with clean water, then wipe clean with alcohol and 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 according to any one of the aforementioned embodiments.

[0064] The following describes some embodiments of the present invention in detail with reference to specific application examples. Unless otherwise specified, the raw materials used in the examples can be purchased from the market.

[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 surfaces of the 316 stainless steel and TC4 titanium alloy to achieve a surface roughness of Ra2.5μm. After polishing, wipe with alcohol and blow dry. In addition, use 10% by volume sulfuric acid solution to pickle the copper mesh for 5 minutes. After pickling, rinse with clean water, wipe the surface of the copper mesh clean 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 As shown in (b), 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. The first stage is to heat up to 600℃ at a rate of 10℃ / min, and then keep warm for 5min. The second stage is to heat up to 800℃ at a rate of 5℃ / min, and then keep warm for 40min. The third stage is to cool down to 500℃ at a rate of 10℃ / min, and then keep warm for 5min. After the end of the third stage of heat preservation, the weldment is cooled to room temperature with the furnace. The diffusion welding effect is as follows Figure 2 As shown, the steel substrate and the copper mesh are tightly connected.

[0068] (3) The steel substrate to be welded with the surface configuration, Ti-24Zr-40Cu-10Ni titanium-based brazing filler metal, and TC4 titanium alloy are welded according to the following method: Figure 1(c) The scheme shown in the figure is assembled and then vacuum brazing is performed. 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 5 minutes. In the second stage, the temperature is increased to 950℃ 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.

[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 surfaces of the 304 stainless steel and TiAl alloy to achieve a surface roughness of Ra2.5μm. After polishing, wipe with alcohol and blow dry. In addition, use 15% by volume hydrochloric acid solution to pickle the nickel mesh for 5 minutes. After pickling, rinse with clean water, wipe the surface of the nickel mesh clean 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 to heat up to 800℃ at a rate of 10℃ / min, and then keep warm for 5min. The second stage is to heat up to 1080℃ at a rate of 10℃ / min, and then keep warm for 40min. The third stage is to cool down to 500℃ at a rate of 10℃ / min, and then keep warm for 5min. After the end of 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 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 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, except that: Ti-24Zr-40Cu-10Ni (wt.%) titanium-based brazing filler metal is first used, and the brazing conditions in Example 1 are adopted to braze a 100-mesh copper mesh (purity >99.9%, wire diameter 74 μm, pore size 182 μm) to a steel substrate, and then the steel substrate brazed with the copper mesh is vacuum brazed with the titanium alloy. 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 onto the steel substrate, and the steel substrate and the titanium substrate are directly vacuum brazed. The other conditions are the same as those of 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 using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. 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 deviate from the essence of the corresponding technical solutions within 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. The configuration surface of the steel substrate is the surface to be welded, the steel substrate having a surface configuration and the brazing filler metal and the titanium substrate to be welded are assembled and vacuum brazed; The porous metal mesh comprises a copper mesh or a nickel mesh; the purity of the porous metal mesh is greater than 99%; the mesh number of the porous metal mesh is 100-350 mesh; During the diffusion welding process, the pressure applied to the surface of the workpiece to be welded is 4-10 MPa; The temperature control of the diffusion welding process includes a first stage, a second stage, and a third stage. In the first stage, the temperature is raised to the first temperature at a rate of 8-12°C / min and kept at this temperature for 5-10 minutes. In the second stage, the temperature is raised to the second temperature at a rate of 3-10°C / min and kept at this temperature for 25-40 minutes. In the third stage, the temperature is lowered to the third temperature at a rate of 8-12°C / min and kept at this temperature for 5-10 minutes. 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.; The steel substrate includes any one of 316L stainless steel, 316 stainless steel, and 304 stainless steel; the titanium substrate includes TC4 titanium alloy or TiAl alloy; the brazing filler metal includes titanium-based brazing filler metal; the vacuum degree of the vacuum brazing is ≤5×10 -3 Pa.

2. 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.

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

4. The method for preparing a heterogeneous material brazing joint according to claim 1, wherein: 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.

5. The method for preparing a heterogeneous material brazing joint according to claim 4, characterized in that: The cleaning includes mechanical cleaning and / or chemical cleaning; The mechanical cleaning includes sandpaper polishing, alcohol wiping and air drying; and / or the chemical cleaning includes pickling, water rinsing, alcohol wiping and air drying.

6. 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 5.

Images