Preparation of a bionic gradient porous intermediate layer and its auxiliary metal / ceramic low-stress brazing method

Abstract

A method for preparing a bionic gradient porous intermediate layer and assisting low-stress brazing of metal / ceramic materials, relates to the technical field of intermediate layer assisting brazing. The purpose of the present invention is to solve the problems of large residual stress and poor reliability in existing metal / ceramic brazing joints. During the stress transfer process of the bionic gradient porous intermediate layer of the present invention, the intermediate layer regions with different porosity at various positions have different stress relief capabilities. 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 fracture energy, relieve stress concentration of the joint during loading, avoid instantaneous failure of the joint, and improve the strength and toughness of the brazed joint. The present invention can obtain a method for preparing a bionic gradient porous intermediate layer and assisting low-stress brazing of metal / ceramic materials.

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 dissimilar metal-ceramic joints, large residual stresses are easily generated in the metal / ceramic joint due to the large differences in thermal expansion coefficients between the metal, ceramic, and brazing filler metal. This can significantly reduce joint reliability and even lead to cracks. Therefore, alleviating residual stress in metal / ceramic brazed joints is key to achieving reliable joint connections.

[0003] Among the many methods currently available for relieving residual stress in brazed joints, adding a soft interlayer with good plasticity to 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 interlayer is limited. Compared with dense interlayers, porous interlayers have lower yield strength and a longer plastic deformation platform, resulting in better stress relief capabilities. However, they are easily completely filled with brazing filler metal, forming a dense structure in the metal / ceramic joint that limits its deformation capacity. When the three-dimensional pore structure of the porous interlayer is retained in the joint, the low-porosity interlayer tends to be dense metal, resulting in poor adaptability to residual stress in the joint. High-porosity interlayers have a good residual stress relief effect, but due to their inherent mechanical properties, they can easily 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 biomimetic 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 biomimetic gradient porous intermediate layer, as well as the volume and porosity of the outer structure, are set, and the porosity of the outer structure is ensured to be greater than that of the intermediate structure. Then, based on the set volume, porosity, and density of the metal wires of the intermediate structure, the total mass of the metal wires of the intermediate structure is calculated. Similarly, based on the set volume, porosity, and density of the metal wires of the outer structure, the total mass of the metal wires of the outer structure is calculated.

[0008] According to the calculated total mass of the metal wires, several metal wires are weighed to form the intermediate structure and the outer structure, the intermediate structure is placed at the center of the mold, and the annular outer structure is arranged outside the intermediate structure, ensuring that the metal wires outside the intermediate structure are in full contact with the metal wires inside the outer structure, thereby obtaining a biomimetic gradient porous intermediate layer precursor with a gradient porosity distribution from the inside to the 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 wires of the intermediate structure or the external structure, ρ represents the density of the metal wires, 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, 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 biomimetic 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 biomimetic gradient porous intermediate layer, the metal foil, the brazing material foil and the ceramic material are stacked in order from top to bottom to obtain an assembly to be welded;

[0015] Step 2:

[0016] Place the assembly to be soldered obtained in step 1 in a brazing furnace and place it in a vacuum furnace at a temperature of 1×10 -3 Pa~8×10 -3 Under the conditions of Pa, the components to be welded are heated to 20 to 150°C higher than the melting point of the brazing material, and then brazing is performed for 1 to 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 enables a single material to produce multiple advantages, combining the characteristics of light weight, high strength and high toughness. This has important guiding significance for the design and preparation of a bionic gradient porous intermediate layer that can both relieve the residual stress of metal / ceramic joints and improve the mechanical properties of the joints.

[0019] Based on this, the bionic gradient porous interlayer of the present invention is based on the gradient structure of bamboo wall structures in nature, which have both high strength and high toughness. Metal wires of different masses are pressed and sintered in a concentric arrangement to form a bionic gradient porous interlayer with different porosity distributions in the radial direction. This gradient structure can improve stress distribution. The stress peak in the central area of ​​the ceramic in the metal / ceramic brazed joint is small and distributed over a wide range. The internal high-density interlayer provides a larger bonding area, which can improve the strength and rigidity of the joint and prevent the interlayer itself from becoming the weak link of the joint. The low-density interlayer in the outer area has better deformation capacity and can effectively alleviate the phenomenon of high and concentrated stress at the edge of the ceramic substrate in the metal / ceramic brazed joint, ultimately effectively alleviating the residual stress in the joint and simultaneously improving the strength of the brazed joint.

[0020] Beneficial effects of the present invention:

[0021] (1) The bionic gradient porous interlayer of the present invention combines the advantages of 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 longer plastic deformation platform, which is conducive to alleviating the residual stress of the joint through micro-plastic deformation and has excellent strain tolerance in the joint. Compared with the porous interlayer without gradient, the bionic gradient porous interlayer optimizes the porosity distribution at specific locations, avoiding the interlayer itself from becoming a weak link in the joint, thereby improving the mechanical properties of the joint.

[0022] (2) Metal foil is added between the bionic gradient porous intermediate layer and the solder foils on both sides of the present invention, which prevents the solder metal from completely penetrating into the three-dimensional pore structure of the intermediate layer to form a dense structure and limit the deformation ability of the intermediate layer during the brazing process. The retention of the three-dimensional pore structure of the intermediate layer in the brazed joint is beneficial to reducing the probability of cracks in the ceramic and improving the stress relief ability 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 areas 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, thereby alleviating the stress concentration of the joint during loading, avoiding instantaneous failure of the joint, and improving the strength and toughness of the brazed joint.

[0024] (4) By applying the bionic gradient porous intermediate layer of the present invention, the Y2O3-MgO composite ceramic and TC4 alloy material are brazed together 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 pattern 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. By controlling the filling quality of the metal wires at different positions, bionic gradient porous intermediate layers with different structural design parameters can be prepared. 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 microstructure 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 embodiment 1: This embodiment provides a method for preparing a biomimetic 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 biomimetic gradient porous intermediate layer, as well as the volume and porosity of the outer structure, are set, and the porosity of the outer structure is ensured to be greater than that of the intermediate structure. Then, based on the set volume, porosity, and density of the metal wires of the intermediate structure, the total mass of the metal wires of the intermediate structure is calculated. Similarly, based on the set volume, porosity, and density of the metal wires of the outer structure, the total mass of the metal wires of the outer structure is calculated.

[0033] According to the calculated total mass of the metal wires, several metal wires are weighed to form the intermediate structure and the outer structure, the intermediate structure is placed at the center of the mold, and the annular outer structure is arranged outside the intermediate structure, ensuring that the metal wires outside the intermediate structure are in full contact with the metal wires inside the outer structure, thereby obtaining a biomimetic gradient porous intermediate layer precursor with a gradient porosity distribution from the inside to the 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 wires of the intermediate structure or the external structure, ρ represents the density of the metal wires, 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, 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 embodiment 2: The difference between this embodiment and specific embodiment 1 is that: in step S1, the thickness t of the intermediate structure and the outer structure are both 0.2mm~5mm, and the shape of the intermediate structure and the outer 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 embodiment.

[0039] Specific embodiment three: The difference between this embodiment and specific embodiment 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 after cleaning, the water is blown dry to obtain the pretreated metal wire.

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

[0041] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the metal wire 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 embodiment 5: This embodiment differs from specific embodiments 1 to 4 in 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 embodiment 6: The difference between this embodiment and specific embodiments 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 embodiment seven: This embodiment uses a biomimetic gradient porous intermediate layer prepared by the above method to assist metal / ceramic low-stress brazing, and is carried out in the following steps:

[0048] Step 1:

[0049] The metal to be welded, the brazing material foil, the metal foil, the biomimetic gradient porous intermediate layer, the metal foil, the brazing material foil and the ceramic material are stacked in order from top to bottom to obtain an assembly to be welded;

[0050] Step 2:

[0051] Place the assembly to be soldered obtained in step 1 in a brazing furnace and place it in a vacuum furnace at a temperature of 1×10 -3 Pa~8×10 -3 Under the conditions of Pa, the components to be welded are heated to 20 to 150°C higher than the melting point of the brazing material, and then brazing is performed for 1 to 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: This embodiment differs from specific embodiment seven in that the metal to be welded in step one 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.

[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 the seventh or eighth embodiment.

[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, with a cooling rate of 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 is carried out according to the following steps:

[0060] Step S1:

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

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

[0063] According to the above calculation results, 0.0564g of copper wire was weighed to form the intermediate structure and placed in the center of the mold. Another 0.0941g of copper wire was weighed to form the outer structure and placed outside the intermediate structure, ensuring that the metal wire outside the intermediate structure was in full contact with the metal wire inside the outer structure. This formed a gradient porosity distribution from the inside to the outside, thereby obtaining a biomimetic gradient porous intermediate 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 wires of the intermediate structure or the external structure, ρ represents the density of the metal wires, 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℃ at a heating rate of 10℃ / min, and kept at 900℃ for 60min. The metal wires were connected by die sintering. After the insulation, the material was cooled to room temperature at a cooling rate of 8℃ / 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 biomimetic 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 biomimetic gradient porous intermediate layer, the metal foil, the brazing material foil and the ceramic material are stacked in order from top to bottom to obtain an assembly to be welded;

[0071] Step 2:

[0072] The components to be welded obtained in step 1 are placed in a brazing furnace and the vacuum degree is 5×10 -3 Pa, the components to be welded are heated to 790℃ at a heating rate of 10℃ / min and brazed at 790℃ for 10min. After brazing, they are first cooled to 200℃ at a cooling rate of 5℃ / 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 materials to be welded are TC4 titanium alloy and Y2O3-MgO composite ceramic material respectively. The size of the TC4 titanium alloy is 15mm×10mm×3mm, and the size of the 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 the welded parts, which are then brazed together.

[0078] The brazing process parameters are as follows: the vacuum brazing furnace is evacuated to a vacuum degree of not less than 5×10 -3 Pa, then heated to 790℃ at a heating rate of 10℃ / min, brazing time was 10min, cooled to 200℃~450℃ at a cooling rate of 5℃ / min after welding, and 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 of not less than 5×10 -3 Pa, then heated to 790℃ at a heating rate of 10℃ / min, brazing time was 10min, cooled to 200℃ at a cooling rate of 5℃ / min after welding, and 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 sequence 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 = 0.75 mm, intermediate layer non-gradient i.e. N = 0, total porosity ε = 10%, and total area is 5 mm × 5 mm rectangle), weigh 0.1505 g 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 of not less than 5×10 -3 Pa, then heated to 790℃ at a heating rate of 10℃ / min, brazing time was 10min, cooled to 200℃ at a cooling rate of 5℃ / min after welding, and finally turned off the heating and cooled to room temperature with the furnace.

[0088] Figure 2 The interface 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 intermediate layer realizes the preparation of the gradient pore structure, the solder is well combined with the intermediate layer and the solder does not completely fill the three-dimensional pores of the intermediate layer, thus retaining the porous structure in the joint. Figure 2 and Figure 3 The presence or absence of a gradient copper interlayer does not affect the interfacial structure of the brazed joint. The shear strength of the brazed joint without an interlayer is 37 MPa. Using a pure copper interlayer slightly improves this to 56 MPa. Using a uniform porous, non-gradient interlayer as an auxiliary brazing layer achieves a shear strength of 93 MPa. Adding a biomimetic gradient porous interlayer increases the room-temperature shear strength of the joint to 140 MPa, a 278% increase, effectively alleviating residual stress in the brazed joint.

Claims

1. A method for preparing a biomimetic 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 biomimetic gradient porous intermediate layer, as well as the volume and porosity of the outer structure, are set, and the porosity of the outer structure is ensured to be greater than that of the intermediate structure. Then, based on the set volume, porosity, and density of the metal wires of the intermediate structure, the total mass of the metal wires of the intermediate structure is calculated. Similarly, based on the set volume, porosity, and density of the metal wires of the outer structure, the total mass of the metal wires of the outer structure is calculated. According to the calculated total mass of the metal wires, several metal wires are weighed to form the intermediate structure and the outer structure, the intermediate structure is placed at the center of the mold, and the annular outer structure is arranged outside the intermediate structure, ensuring that the metal wires outside the intermediate structure are in full contact with the metal wires inside the outer structure, thereby obtaining a biomimetic gradient porous intermediate layer precursor with a gradient porosity distribution from the inside to the 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 wires of the intermediate structure or the external structure, ρ represents the density of the metal wires, 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, 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 sequence 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 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 using a biomimetic 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 biomimetic gradient porous intermediate layer, the metal foil, the brazing material foil and the ceramic material are stacked in order from top to bottom to obtain an assembly to be welded; Step 2: Place the assembly to be soldered obtained in step 1 in a brazing furnace and place it in a vacuum furnace at a temperature of 1×10 -3 Pa~8×10 -3 Under the conditions of Pa, the components to be welded are heated to 20 to 150°C higher than the melting point of the brazing material, and then brazing is performed for 1 to 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 utilizing a biomimetic 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 multiphase ceramic, an oxide ceramic or sapphire.

9. The method of utilizing 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 utilizing 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, the material is first cooled to 200°C to 450°C, and then cooled to room temperature, with a cooling rate of 1 to 10°C / min.

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