Preparation method of bionic gradient porous interlayer and method for assisting metal / ceramic low-stress brazing by bionic gradient porous interlayer

Abstract

The invention discloses preparation of a bionic gradient porous interlayer and a method for assisting metal / ceramic low-stress brazing by using the bionic gradient porous interlayer, and relates to the technical field of auxiliary brazing of interlayers. The method aims at solving the problems that an existing metal / ceramic brazed joint is large in residual stress and poor in reliability. According to the bionic gradient porous interlayer, in the stress transfer process, interlayer areas with different porosities at all positions have different stress slow release capacities, and the stress distribution state of a connector can be improved by optimizing the material structure at the specific position; and meanwhile, micro-plastic deformation can happen to the cracks during expansion to consume fracture energy, stress concentration of the connector during loading is relieved, instant failure of the connector is avoided, and meanwhile the strength and toughness of the brazed connector are improved. According to the preparation method of the bionic gradient porous intermediate layer and the method for assisting metal / ceramic low-stress brazing of the bionic gradient porous intermediate layer, the bionic gradient porous intermediate layer can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of intermediate layer auxiliary brazing, and in particular to a method for preparing a bionic gradient porous intermediate layer and assisting metal / ceramic low-stress brazing thereof. Background Art

[0002] During the brazing process of metal and ceramic dissimilar materials, due to the large difference in thermal expansion coefficients between metal, ceramic and brazing filler metal, large residual stress is easily generated in the metal / ceramic joint, which greatly reduces the reliability of the joint and even causes cracks. Therefore, relieving the residual stress of the metal / ceramic brazed joint is the key to achieving reliable joint connection.

[0003] At present, among the many methods to relieve the residual stress of brazed joints, adding a soft intermediate layer with good plasticity in the brazing seam is one of the more stable and efficient methods. The stress relief effect that can be achieved by changing the material or parameters of the soft intermediate layer is limited. Compared with the dense intermediate layer, the porous intermediate layer has a low yield strength and a long plastic deformation platform, and has better stress relief ability, but it is easy to be completely filled by the brazing metal, forming a dense structure in the metal / ceramic joint to limit its deformation ability. When the three-dimensional pore structure of the porous intermediate layer is retained in the joint, the low-porosity intermediate layer tends to be dense metal, and the joint has poor adaptability to residual stress; the high-porosity intermediate layer has a good residual stress relief effect, but due to its own mechanical properties, it is easy to become a weak link in the joint. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of large residual stress and poor reliability of existing metal / ceramic brazing joints, and to provide a method for preparing a bionic gradient porous intermediate layer and assisting metal / ceramic low stress brazing.

[0005] A method for preparing a bionic gradient porous intermediate layer is carried out according to the following steps:

[0006] Step S1:

[0007] First, the volume and porosity of the intermediate structure of the bionic gradient porous intermediate layer and the volume and porosity of the external structure are set, and the porosity of the external structure is ensured to be greater than that of the intermediate structure; then, the total mass of the metal wire of the intermediate structure is calculated according to the set volume, porosity and density of the metal wire of the intermediate structure, and similarly, the total mass of the metal wire of the external structure is calculated according to the set volume, porosity and density of the metal wire of the external structure;

[0008] According to the calculated total mass of the metal wires, a number of metal wires are weighed to form an intermediate structure and an external structure, the intermediate structure is placed at the center of the mold, and the annular external structure is arranged outside the intermediate structure, and it is ensured that the metal wires outside the intermediate structure are in full contact with the metal wires inside the external structure, so as to obtain a bionic gradient porous intermediate layer precursor with a gradient porosity distribution from inside to outside;

[0009] The calculation formula is: ε = (1-M / ρV) × 100%; ε represents the porosity of the intermediate structure or the external structure, M represents the total mass of the metal wire of the intermediate structure or the external structure, ρ represents the density of the metal wire, and V represents the volume of the intermediate structure or the external structure;

[0010] Step S2:

[0011] The mold containing the biomimetic gradient porous intermediate layer precursor in step S1 was fastened and placed in a vacuum furnace at a vacuum degree of 1×10 -3 Pa~8×10 -3 Pa, heated to 40% to 90% of the melting point of the metal wire, and then kept warm for 10 to 120 minutes until the metal wires are connected, and cooled to room temperature after the end of the heat preservation to obtain a bionic gradient porous intermediate layer with different porosities from the inside to the outside.

[0012] A method for low-stress brazing of metal / ceramic assisted by a bionic gradient porous intermediate layer prepared by the above method is carried out in the following steps:

[0013] Step 1:

[0014] The metal to be welded, the brazing material foil, the metal foil, the bionic gradient porous intermediate layer, the metal foil, the brazing material foil and the ceramic material are stacked in sequence from top to bottom to obtain a component to be welded;

[0015] Step 2:

[0016] The assembly to be soldered obtained in step 1 is placed in a brazing furnace and the vacuum degree is 1×10 -3 Pa~8×10 -3 Under the condition of Pa, the components to be welded are heated to 20-150°C higher than the melting point of the brazing material, and then brazing is performed for 1-30 minutes; after brazing, the components are cooled to room temperature to complete the low-stress brazing of metal / ceramic assisted by the bionic gradient porous intermediate layer.

[0017] Principle of the present invention:

[0018] Inspired by natural biomaterials, the bamboo wall structure exhibits different local properties in the radial direction. The gradient distribution of fiber density in the radial direction makes a single material produce multiple advantages, and it has the characteristics of light weight, high strength and high toughness. It has important guiding significance for the design and preparation of a bionic gradient porous intermediate layer that can relieve the residual stress of metal / ceramic joints and improve the mechanical properties of the joints.

[0019] Based on this, the bionic gradient porous intermediate layer of the present invention is based on the gradient structure of the bamboo wall structure with both high strength and high toughness in nature. Metal wires of different masses are pressed and sintered in the form of concentric arrangement to form a bionic gradient porous intermediate layer with different porosity distribution in the radial direction. This gradient structure can improve stress distribution. The stress peak value of the central area of ​​the ceramic in the metal / ceramic brazed joint is small and the distribution range is wide. The internal design of the high-density intermediate layer obtains a larger bonding area, which can improve the strength and rigidity of the joint and avoid the intermediate layer itself from becoming the weak link of the joint; while the low-density intermediate layer in the external area has a better deformation ability, which can effectively alleviate the phenomenon of large and concentrated stress at the edge of the ceramic matrix in the metal / ceramic brazed joint, and finally effectively alleviate the residual stress of the joint and simultaneously improve the strength of the brazed joint.

[0020] Beneficial effects of the present invention:

[0021] (1) The bionic gradient porous interlayer of the present invention has the advantages of both high-density and low-density porous interlayers. Compared with dense metals of the same material, the bionic gradient porous interlayer has a lower yield strength and a long plastic deformation platform, which is conducive to relieving the residual stress of the joint through micro-plastic deformation and has excellent strain accommodation capacity in the joint; compared with the porous interlayer without gradient, the bionic gradient porous interlayer optimizes the porosity distribution at a specific position, thereby avoiding the interlayer itself from becoming a weak link in the joint and improving the mechanical properties of the joint.

[0022] (2) Metal foil is added between the bionic gradient porous middle layer and the solder foils on both sides of the present invention, which prevents the solder metal from completely penetrating into the three-dimensional hole structure of the middle layer to form a dense structure to limit the deformation capacity of the middle layer during the brazing process. The retention of the three-dimensional hole structure of the middle layer in the brazed joint is beneficial to reducing the probability of cracks in the ceramic and improving the stress relief capacity of the joint.

[0023] (3) During the stress transfer process, the bionic gradient porous intermediate layer of the present invention has different stress relief capabilities in the intermediate layer regions with different porosities at different positions. Optimizing the material structure at specific positions can improve the stress distribution state of the joint. At the same time, micro-plastic deformation will occur when the crack expands to consume the fracture energy, relieve the stress concentration of the joint during loading, avoid instantaneous failure of the joint, and at the same time improve the strength and toughness of the brazed joint.

[0024] (4) The bionic gradient porous intermediate layer of the present invention is used to braze the Y2O3-MgO composite ceramic and TC4 alloy material using AgCuInTi brazing filler metal. The shear strength of the brazed joint reaches 140 MPa, which is 278% higher than that of the joint directly brazed without an intermediate layer, and the fracture behavior mode of the joint is changed.

[0025] (5) The bionic gradient porous intermediate layer of the present invention is sintered by metal wires with good plasticity. The bionic gradient porous intermediate layer with different structural design parameters can be prepared by controlling the filling quality of the metal wires at different positions. The preparation method is simple and flexible.

[0026] The invention can obtain a method for preparing a bionic gradient porous intermediate layer and assisting metal / ceramic low-stress brazing thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram showing the gradient pore structure of bamboo wall in nature;

[0028] Figure 2 The interface structure morphology of the bionic gradient porous intermediate layer assisted brazing joint in Example 1 is shown;

[0029] Figure 3 The figure shows the interface structure morphology of the pure copper intermediate layer auxiliary brazing joint in comparative example 2. DETAILED DESCRIPTION

[0030] Specific implementation method 1: This implementation method is a method for preparing a bionic gradient porous intermediate layer, which is carried out according to the following steps:

[0031] Step S1:

[0032] First, the volume and porosity of the intermediate structure of the bionic gradient porous intermediate layer and the volume and porosity of the external structure are set, and the porosity of the external structure is ensured to be greater than that of the intermediate structure; then, the total mass of the metal wire of the intermediate structure is calculated according to the set volume, porosity and density of the metal wire of the intermediate structure, and similarly, the total mass of the metal wire of the external structure is calculated according to the set volume, porosity and density of the metal wire of the external structure;

[0033] According to the calculated total mass of the metal wires, a number of metal wires are weighed to form an intermediate structure and an external structure, the intermediate structure is placed at the center of the mold, and the annular external structure is arranged outside the intermediate structure, and it is ensured that the metal wires outside the intermediate structure are in full contact with the metal wires inside the external structure, so as to obtain a bionic gradient porous intermediate layer precursor with a gradient porosity distribution from inside to outside;

[0034] The calculation formula is: ε = (1-M / ρV) × 100%; ε represents the porosity of the intermediate structure or the external structure, M represents the total mass of the metal wire of the intermediate structure or the external structure, ρ represents the density of the metal wire, and V represents the volume of the intermediate structure or the external structure;

[0035] Step S2:

[0036] The mold containing the biomimetic gradient porous intermediate layer precursor in step S1 was fastened and placed in a vacuum furnace at a vacuum degree of 1×10 -3 Pa~8×10 -3 Pa, heated to 40% to 90% of the melting point of the metal wire, and then kept warm for 10 to 120 minutes until the metal wires are connected, and cooled to room temperature after the end of the heat preservation to obtain a bionic gradient porous intermediate layer with different porosities from the inside to the outside.

[0037] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that: in step S1, the thickness t of the intermediate structure and the external structure are both 0.2mm~5mm, and the shape of the intermediate structure and the external structure is circular or rectangular; the diameter d of the metal wire is 0.03mm~0.5mm; the porosity of the bionic gradient porous intermediate layer precursor is 5%~80%.

[0038] The other steps are the same as those in the first specific implementation.

[0039] Specific implementation method three: The difference between this implementation method and specific implementation method one or two is that the metal wire described in step S1 is pretreated according to the following steps: the cut metal wire is placed in acetone solution, 0.5-1.0 mol / L hydrochloric acid solution and deionized water in turn for ultrasonic cleaning, and the water is blown dry after cleaning to obtain the pretreated metal wire.

[0040] The other steps are the same as those in the first or second embodiment.

[0041] Specific implementation method 4: The difference between this implementation method and specific implementation methods 1 to 3 is that the metal wire described in step S1 is copper, nickel, gold, silver, aluminum or titanium.

[0042] The other steps are the same as those in Specific Embodiments 1 to 3.

[0043] Specific implementation method five: The difference between this implementation method and specific implementation methods one to four is that the mold is a graphite mold, a stainless steel mold or a high-temperature resistant alloy mold.

[0044] The other steps are the same as those in Specific Embodiments 1 to 4.

[0045] Specific implementation method 6: The difference between this implementation method and specific implementation methods 1 to 5 is that the heating rate in step S2 is 5°C / min to 20°C / min, and the cooling rate is 2°C / min to 15°C / min.

[0046] The other steps are the same as those in Specific Embodiments 1 to 5.

[0047] Specific implementation method 7: This implementation method uses a bionic gradient porous intermediate layer prepared by the above method to assist metal / ceramic low stress brazing, and is carried out according to the following steps:

[0048] Step 1:

[0049] The metal to be welded, the brazing material foil, the metal foil, the bionic gradient porous intermediate layer, the metal foil, the brazing material foil and the ceramic material are stacked in sequence from top to bottom to obtain a component to be welded;

[0050] Step 2:

[0051] The assembly to be soldered obtained in step 1 is placed in a brazing furnace and the vacuum degree is 1×10 -3 Pa~8×10 -3 Under the condition of Pa, the components to be welded are heated to 20-150°C higher than the melting point of the brazing material, and then brazing is performed for 1-30 minutes; after brazing, the components are cooled to room temperature to complete the low-stress brazing of metal / ceramic assisted by the bionic gradient porous intermediate layer.

[0052] Specific embodiment eight: The difference between this embodiment and specific embodiment seven is that the metal to be welded in step one is Ni-based alloy, Ti alloy, Zr alloy, Nb alloy or Fe-based alloy; the ceramic material is complex phase ceramic, oxide ceramic or sapphire.

[0053] The other steps are the same as those in the seventh embodiment.

[0054] Specific embodiment nine: The difference between this embodiment and specific embodiment seven or eight is that the solder foil described in step one is Ag-based solder, Cu-based solder, Ni-based solder, Ti-based solder or Zr-based solder; the metal foil is copper, nickel, gold, silver, aluminum or titanium.

[0055] The other steps are the same as those in Specific Embodiment 7 or 8.

[0056] Specific embodiment ten: The difference between this embodiment and specific embodiments seven to nine is that: the heating rate in step two is 1 to 15°C / min; after brazing, it is first cooled to 200°C to 450°C, and then cooled to room temperature, and the cooling rate is 1 to 10°C / min.

[0057] The other steps are the same as those in Specific Embodiments 7 to 9.

[0058] The following examples are used to verify the beneficial effects of the present invention:

[0059] Example 1: A method for preparing a biomimetic gradient porous intermediate layer, comprising the following steps:

[0060] Step S1:

[0061] The cut metal wire is sequentially placed in an acetone solution, a 0.5 mol / L hydrochloric acid solution and deionized water for ultrasonic cleaning to remove surface oil and oxides, and finally the water is blown dry to obtain a pretreated metal wire;

[0062] According to the preset parameters of the intermediate structure and the outer structure (intermediate layer thickness t=0.75 mm, the number of intermediate layer gradients N is 2, the total porosity ε=10%, the total area is a 5 mm×5 mm rectangle, the central area is a 2.5 mm×2.5 mm rectangle, and the difference in inner and outer porosity Δε=30%), the total mass of the metal wire of the intermediate structure and the outer structure is calculated respectively;

[0063] According to the above calculation results, 0.0564g of copper wire is weighed to form the middle structure and placed at the center of the mold, and 0.0941g of copper wire is weighed to form the outer structure and placed outside the middle structure, and the metal wire outside the middle structure is ensured to be in full contact with the metal wire inside the outer structure, so as to form a gradient porosity distribution from the inside to the outside, and obtain a bionic gradient porous middle layer precursor;

[0064] The calculation formula is: ε = (1-M / ρV) × 100%; ε represents the porosity of the intermediate structure or the external structure, M represents the total mass of the metal wire of the intermediate structure or the external structure, ρ represents the density of the metal wire, and V represents the volume of the intermediate structure or the external structure;

[0065] Step S2:

[0066] The mold containing the biomimetic gradient porous intermediate layer precursor in step S1 was fastened with bolts and placed in a vacuum furnace at a vacuum degree of 5×10 -3 Pa, heated to 900°C at a heating rate of 10°C / min, and kept at 900°C for 60 minutes. The metal wires were connected by die-cut sintering. After the insulation, the material was cooled to room temperature at a cooling rate of 8°C / min to obtain a bionic gradient porous intermediate layer with different porosities from the inside to the outside.

[0067] The diameter d of the copper wire is 80 μm.

[0068] A method for low-stress brazing of metal / ceramic assisted by a bionic gradient porous intermediate layer prepared by the above method is carried out in the following steps:

[0069] Step 1:

[0070] The metal to be welded, the brazing material foil, the metal foil, the bionic gradient porous intermediate layer, the metal foil, the brazing material foil and the ceramic material are stacked in sequence from top to bottom to obtain a component to be welded;

[0071] Step 2:

[0072] The assembly to be welded obtained in step 1 is placed in a brazing furnace and the vacuum degree is 5×10 -3 Pa, the components to be welded are heated to 790°C at a heating rate of 10°C / min, and brazed at 790°C for 10 minutes. After brazing, they are first cooled to 200°C at a cooling rate of 5°C / min, and then cooled to room temperature to complete the low-stress brazing of metal / ceramic assisted by the bionic gradient porous intermediate layer.

[0073] The solder foil is AgCuInTi solder and has a thickness of 100 μm.

[0074] The metal foil is a Cu foil with a thickness of 50 μm.

[0075] The metal and ceramic material to be welded are TC4 titanium alloy and Y2O3-MgO composite ceramic material respectively. The size of TC4 titanium alloy is 15mm×10mm×3mm, and the size of Y2O3-MgO composite ceramic material is 4mm×4mm×3mm.

[0076] Comparative Example 1: The method for brazing metal / ceramic is carried out according to the following steps:

[0077] A 100 μm thick AgCuInTi brazing filler metal foil is placed between the surfaces to be welded of the TC4 titanium alloy and the Y2O3-MgO composite ceramic material to obtain a welded part, which is then brazed together;

[0078] The brazing process parameters are as follows: the vacuum brazing furnace is evacuated to a vacuum degree not less than 5×10 -3 Pa, then heated to 790℃ at a heating rate of 10℃ / min, brazing time was 10min, after welding, cooled to 200℃~450℃ at a cooling rate of 5℃ / min, finally turned off heating and cooled to room temperature with the furnace.

[0079] Comparative Example 2: The method for brazing metal / ceramic is carried out according to the following steps:

[0080] The TC4 titanium alloy, the AgCuInTi solder foil, the pure copper intermediate layer, the AgCuInTi solder foil, and the Y2O3-MgO composite ceramic material are stacked in sequence from bottom to top to obtain an assembly to be welded; and then brazing connection is performed.

[0081] The size of the pure copper middle layer is 5mm×5mm×0.75mm, and the thickness of the AgCuInTi solder is 100μm.

[0082] The brazing process parameters are as follows: the vacuum brazing furnace is evacuated to a vacuum degree not less than 5×10 -3 Pa, then heated to 790℃ at a heating rate of 10℃ / min, brazing time was 10min, after welding, cooled to 200℃ at a cooling rate of 5℃ / min, finally turned off the heating, and cooled to room temperature with the furnace.

[0083] Comparative Example 3: The method for brazing metal / ceramic is carried out according to the following steps:

[0084] The TC4 titanium alloy, AgCuInTi solder foil, Cu foil, uniform porous non-gradient intermediate layer, Cu foil, AgCuInTi solder foil, and Y2O3-MgO composite ceramic material are stacked in order from bottom to top to obtain an assembly to be welded; and then brazing connection is performed.

[0085] The thickness of the AgCuInTi solder is 100 μm, and the thickness of the Cu foil is 50 μm.

[0086] The preparation method of the uniform porous non-gradient intermediate layer is to calculate the required metal wire mass according to the preset structural parameters (intermediate layer thickness t=0.75mm, intermediate layer non-gradient i.e. N=0, total porosity ε=10%, total area is 5mm×5mm rectangle), weigh 0.1505g of copper wire and place it evenly in a mold to form a uniform porous non-gradient intermediate layer precursor, fasten the mold with bolts and place it in a vacuum furnace for heating and sintering to form a sintering neck between the copper wires to obtain a uniform porous non-gradient intermediate layer.

[0087] The brazing process parameters are as follows: the vacuum brazing furnace is evacuated to a vacuum degree not less than 5×10 -3 Pa, then heated to 790℃ at a heating rate of 10℃ / min, brazing time was 10min, after welding, cooled to 200℃ at a cooling rate of 5℃ / min, finally turned off the heating, and cooled to room temperature with the furnace.

[0088] Figure 2 The interface structure morphology of the bionic gradient porous intermediate layer assisted brazing joint in Example 1 is shown. Figure 3 The figure shows the interface structure morphology of the pure copper intermediate layer auxiliary brazing joint in comparative example 2.

[0089] like Figure 2 As shown in the figure, the interface morphology of the joint shows that the bionic gradient porous middle layer realizes the preparation of gradient pore structure, the solder is well combined with the middle layer and the solder does not completely fill the three-dimensional pores of the middle layer, thus retaining the porous structure in the joint. Figure 2 and Figure 3 It can be seen that the presence or absence of a gradient structure in the copper intermediate layer does not affect the interface structure of the brazed joint. The shear strength of the joint directly brazed without an intermediate layer is 37MPa, the joint strength with a pure copper intermediate layer is slightly improved to 56MPa, and the shear strength of the joint assisted by a uniform porous non-gradient intermediate layer reaches 93MPa. After adding a bionic gradient porous intermediate layer, the room temperature shear strength of the joint is as high as 140MPa, which is an increase of 278%, effectively alleviating the residual stress of the brazed joint.

Claims

1. A method for preparing a bionic gradient porous intermediate layer, characterized in that The preparation method is carried out according to the following steps: Step S1: First, the volume and porosity of the intermediate structure of the bionic gradient porous intermediate layer and the volume and porosity of the external structure are set, and the porosity of the external structure is ensured to be greater than that of the intermediate structure; then, the total mass of the metal wire of the intermediate structure is calculated according to the set volume, porosity and density of the metal wire of the intermediate structure, and similarly, the total mass of the metal wire of the external structure is calculated according to the set volume, porosity and density of the metal wire of the external structure; According to the calculated total mass of the metal wires, a number of metal wires are weighed to form an intermediate structure and an external structure, the intermediate structure is placed at the center of the mold, and the annular external structure is arranged outside the intermediate structure, and it is ensured that the metal wires outside the intermediate structure are in full contact with the metal wires inside the external structure, so as to obtain a bionic gradient porous intermediate layer precursor with a gradient porosity distribution from inside to outside; The calculation formula is: ε = (1-M / ρV) × 100%; ε represents the porosity of the intermediate structure or the external structure, M represents the total mass of the metal wire of the intermediate structure or the external structure, ρ represents the density of the metal wire, and V represents the volume of the intermediate structure or the external structure; Step S2: The mold containing the biomimetic gradient porous intermediate layer precursor in step S1 was fastened and placed in a vacuum furnace at a vacuum degree of 1×10 -3 Pa~8×10 -3 Pa, heated to 40% to 90% of the melting point of the metal wire, and then kept warm for 10 to 120 minutes until the metal wires are connected, and cooled to room temperature after the end of the heat preservation to obtain a bionic gradient porous intermediate layer with different porosities from the inside to the outside.

2. The method for preparing a biomimetic gradient porous intermediate layer according to claim 1, characterized in that In step S1, the thickness t of the intermediate structure and the outer structure are both 0.2 mm to 5 mm, and the shapes of the intermediate structure and the outer structure are circular or rectangular; the diameter d of the metal wire is 0.03 mm to 0.5 mm; and the porosity of the bionic gradient porous intermediate layer precursor is 5% to 80%.

3. The method for preparing a biomimetic gradient porous intermediate layer according to claim 1 or 2, characterized in that The metal wire described in step S1 is pretreated according to the following steps: the cut metal wire is placed in acetone solution, 0.5-1.0 mol / L hydrochloric acid solution and deionized water in turn for ultrasonic cleaning, and the water is blown dry after cleaning to obtain the pretreated metal wire.

4. The method for preparing a biomimetic gradient porous intermediate layer according to claim 1 or 2, characterized in that The metal wire described in step S1 is copper, nickel, gold, silver, aluminum or titanium.

5. The method for preparing a biomimetic gradient porous intermediate layer according to claim 1, characterized in that The mold is a graphite mold, a stainless steel mold or a high temperature resistant alloy mold.

6. The method for preparing a biomimetic gradient porous intermediate layer according to claim 1, characterized in that In step S2, the heating rate is 5°C / min to 20°C / min, and the cooling rate is 2°C / min to 15°C / min.

7. A method for low-stress brazing of metal / ceramic assisted by a bionic gradient porous intermediate layer prepared by the method according to any one of claims 1 to 6, characterized in that The method proceeds as follows: Step 1: The metal to be welded, the brazing material foil, the metal foil, the bionic gradient porous intermediate layer, the metal foil, the brazing material foil and the ceramic material are stacked in sequence from top to bottom to obtain a component to be welded; Step 2: The assembly to be soldered obtained in step 1 is placed in a brazing furnace and the vacuum degree is 1×10 -3 Pa~8×10 -3 Under the condition of Pa, the components to be welded are heated to 20-150°C higher than the melting point of the brazing material, and then brazing is performed for 1-30 minutes; after brazing, the components are cooled to room temperature to complete the low-stress brazing of metal / ceramic assisted by the bionic gradient porous intermediate layer.

8. The method of using a bionic gradient porous intermediate layer to assist metal / ceramic low stress brazing according to claim 7, characterized in that The metal to be welded in step 1 is a Ni-based alloy, a Ti alloy, a Zr alloy, a Nb alloy or a Fe-based alloy; and the ceramic material is a composite ceramic, an oxide ceramic or sapphire.

9. The method of using a biomimetic gradient porous intermediate layer to assist metal / ceramic low stress brazing according to claim 7, characterized in that The solder foil described in step 1 is Ag-based solder, Cu-based solder, Ni-based solder, Ti-based solder or Zr-based solder; the metal foil is copper, nickel, gold, silver, aluminum or titanium.

10. The method of using a biomimetic gradient porous intermediate layer to assist metal / ceramic low stress brazing according to claim 7, characterized in that In step 2, the heating rate is 1 to 15°C / min; after brazing, it is first cooled to 200°C to 450°C, and then cooled to room temperature, and the cooling rate is 1 to 10°C / min.

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