Ceramic-metal material composite brazing method with in-situ synthesis reaction

Abstract

The invention relates to the field of ceramic materials, and discloses a ceramic-metal material composite brazing method with an in-situ synthesis reaction, which comprises the following steps: pretreating a ceramic surface and a metal surface to be welded; brazing filler metal is preset between the welding faces of the to-be-welded ceramic and the to-be-welded metal, and the brazing filler metal is AgCuTi welding flux added with amorphous boron powder; in the vacuum brazing process, the Ti element and boron powder are subjected to an in-situ reaction, and a TiB ceramic reinforced phase is generated. The technical problem of joint cracking caused by low interface bonding strength and mismatched thermal expansion coefficients in traditional ceramic-metal connection is solved. According to the method, the mixed powder intermediate layer containing the active elements is preset on the to-be-connected interface of the ceramic and the metal, the intermediate layer is induced to be subjected to the in-situ chemical reaction through heating, the composite reaction product with high strength and gradient thermal expansion performance is generated, and metallurgical bonding and stress buffering integration of the ceramic and the metal is achieved; the mechanical property and the service stability of the joint are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials and discloses a method for brazing ceramic-metal composite materials with in-situ self-generated reaction. Background Technology

[0002] Ceramic materials possess excellent properties such as high temperature resistance, corrosion resistance, and insulation / high thermal conductivity, while metallic materials exhibit high toughness and high electrical conductivity. The composite bonding of these two materials is urgently needed in high-end manufacturing. However, the coefficients of thermal expansion (CTE) of ceramics and metals differ significantly (e.g., alumina ceramics). ,Stainless steel During the connection process, thermal stress concentration is easily generated, leading to joint cracking and insufficient tensile strength (usually <90MPa); interface gaps are easily formed, resulting in poor airtightness (usually only...). This cannot meet the high reliability requirements of scenarios such as ceramic encapsulation shells and sealed vacuum electronic devices.

[0003] The existing technology has the following drawbacks:

[0004] 1. Thermal stress problem: The lack of effective thermal expansion matching design makes direct brazing prone to cold cracking of the joint, and the strength decreases by more than 20% after thermal cycling (-55℃~150℃);

[0005] 2. Weak interfacial bonding: The interfacial transition layer is thin and uneven, with low tensile strength;

[0006] 3. Insufficient air tightness: Uneven brazing filler metal distribution and high interfacial porosity (>0.5%) fail to meet requirements. The following high sealing requirements;

[0007] 4. Poor process stability: The control of ceramic surface treatment and brazing parameters is not precise, and the joint qualification rate is less than 80% during mass production.

[0008] Therefore, there is an urgent need to develop a ceramic-metal bonding process that can simultaneously address "thermal stress control, interface strengthening, and high airtightness assurance" to meet the stringent requirements of high-end fields. Summary of the Invention

[0009] The present invention aims to provide a ceramic-metal composite brazing method with in-situ self-generated reaction that achieves metallurgical bonding and stress buffering between ceramics and metals, significantly improving the mechanical properties and service stability of the joint.

[0010] To achieve the above objectives, the present invention adopts the following specific technical solution:

[0011] A method for brazing ceramic-metal composite materials with in-situ self-generated reaction includes the following steps:

[0012] Pre-treat the ceramic and metal surfaces to be welded;

[0013] A pre-placed brazing filler metal is placed between the ceramic and metal surfaces to be soldered. The brazing filler metal is AgCuTi brazing filler metal with amorphous boron powder added. The brazing filler metal can be solder paste or foil.

[0014] During vacuum brazing, Ti elements react in situ with boron powder to generate TiB ceramic reinforcing phase.

[0015] Furthermore, the pretreatment process for the ceramic surface to be welded includes: polishing the ceramic surface to a smooth finish, with a surface roughness Ra≤1.6μm and a flatness ≤0.09mm; and ultrasonically cleaning with acetone and alcohol solvents respectively to remove oil stains.

[0016] Furthermore, the ceramic is either alumina ceramic or silicon carbide ceramic.

[0017] Furthermore, the pretreatment process for the metal surface to be welded includes: grinding the metal surface to remove the oxide layer, with a roughness Ra≤1.6μm and a flatness ≤0.09mm; and ultrasonically cleaning the surface with 10% hydrochloric acid, deionized water, and acetone to remove oil stains.

[0018] Furthermore, the metal is one of titanium alloy, Kovar alloy, oxygen-free copper, or stainless steel.

[0019] Furthermore, the average particle size of the amorphous boron powder is less than 45 μm, and the mass of the added amorphous boron powder is controlled at 0.01%-1% of the mass of the AgCuTi solder. The boron is uniformly dispersed in the AgCuTi solder by adding it through mechanical alloying or uniform mixing during smelting.

[0020] Furthermore, the brazing filler metal is solder paste, which is applied to the ceramic and metal surfaces of the two parts to be welded, respectively, covering the entire area. The coating thickness is uniformly controlled at 0.08-0.15mm, and the gap between the two parts to be welded before applying the brazing filler metal is controlled at 0.05-0.15mm.

[0021] Furthermore, the brazing filler metal is a foil-shaped sheet that is machined to match the shape of the ceramic and metal surfaces to be welded. The foil-shaped sheet is flatly clamped on the ceramic and metal surfaces to be welded. The gap control requirement is that the brazing gap between the two parts to be welded before clamping the foil-shaped sheet is controlled at 0.05-0.18mm.

[0022] Furthermore, graphite clamps are used to assemble the workpieces to be welded and the brazing filler metal in a vacuum furnace, and pressure is applied to the graphite clamps.

[0023] Furthermore, the vacuum level of the vacuum furnace used for vacuum brazing needs to reach [a certain level]. Pa~ Pa, the specific parameters of the brazing process are as follows: braze at 800~950℃ for 10~20min, with a heating rate of 5~10℃ / min; the cooling process is divided into two stages, the first stage is to rapidly drop to below 770℃ at a cooling rate of 10℃ / min, and the second stage is to cool to room temperature with the furnace.

[0024] The present invention has the following beneficial effects:

[0025] This invention discloses a ceramic-metal composite brazing process with in-situ self-generated reaction, aiming to solve the technical pain points of traditional ceramic-metal connections, such as low interfacial bonding strength, joint cracking due to mismatched coefficients of thermal expansion, and the need for complex prefabrication in the connection process. This method pre-places a mixed powder intermediate layer containing active elements at the ceramic-metal interface, and utilizes heating to induce an in-situ chemical reaction in the intermediate layer, generating a composite reaction product with both high strength and gradient thermal expansion properties. This achieves integrated metallurgical bonding and stress buffering between the ceramic and metal, significantly improving the mechanical properties and service stability of the joint. It is suitable for dissimilar connections between structural ceramics such as alumina and silicon carbide and metallic materials such as titanium alloys and stainless steel, and can be widely applied in high-end manufacturing fields such as aerospace, energy equipment, and precision machinery.

[0026] This invention is based on the AgCuTi+B active solder system. During the brazing process, by controlling the reaction conditions, ceramic reinforcing phases such as TiB whiskers are generated in situ within the solder. These whiskers can improve the microstructure of the joint, enhance its strength and toughness, and alleviate stress within the joint. The innovation lies in achieving optimization of the joint's microstructure and performance improvement through in-situ self-generation reaction.

[0027] This invention achieves highly reliable bonding between structural ceramics such as alumina and silicon carbide and metallic materials such as titanium alloys and stainless steel; the welding process further enhances the bonding effect between the ceramics and metals, resulting in a seal with an airtightness of up to 1.0 × 10⁻⁶. -9 With a strength of Pa·m3 / s or higher, it meets the standard requirements for ceramic encapsulation shells and sealed vacuum electronic devices, and its tensile strength can reach 120 MPa or higher.

[0028] This invention addresses the challenge of joining various combinations of ceramics and metals. By improving the interface through surface treatment and refining parameters to refine the process, it solves problems such as excessive differences in expansion coefficients. The graphite mold used in this invention is simple and efficient, effectively fixing the workpiece and brazing filler metal, limiting part warping, and offering a simple tooling process with a high yield. By applying pressure, it effectively mitigates the phenomenon of brazing filler metal "flow" causing localized material shortages.

[0029] The process used in this invention is highly stable, requires minimal investment, and involves simple and efficient equipment. Precise parameter control results in a batch production pass rate of >80%, effectively improving production efficiency. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart of the ceramic-metal composite brazing method disclosed in this invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0033] It should be noted that similar reference numerals or letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0035] like Figure 1 The method for brazing ceramic-metal composite materials with in-situ self-generated reaction, as shown, includes the following steps:

[0036] Pre-treat the ceramic and metal surfaces to be welded;

[0037] A pre-placed brazing filler metal is placed between the ceramic and metal surfaces to be soldered. The brazing filler metal is AgCuTi brazing filler metal with amorphous boron powder added. The brazing filler metal can be solder paste or foil.

[0038] During vacuum brazing, Ti elements react in situ with boron powder to generate TiB ceramic reinforcing phase.

[0039] AgCuTi+B active brazing filler metal can induce in-situ growth of TiB whiskers and other ceramic reinforcing phases during brazing by controlling reaction conditions and brazing process curves. Amorphous boron powder with an average particle size of less than 45 μm is preferred, and its addition amount is controlled at 0.01%-1%. It is added through mechanical alloying or uniform mixing during smelting to ensure uniform dispersion of boron in the matrix and avoid agglomeration that could affect the strengthening effect. Furthermore, boron can moderately reduce the excessive fluidity of the brazing filler metal, minimizing overflow during brazing.

[0040] This invention utilizes in-situ chemical reactions for self-reinforcement during the brazing process. Under the high-temperature environment of vacuum brazing (typically 850-950℃), the Ti element in the brazing filler metal reacts in-situ with added amorphous boron powder to generate a TiB ceramic reinforcing phase, as shown in the reaction equation: Ti + B → TiB. TiB whiskers, as a high-hardness, high-modulus ceramic phase, are uniformly dispersed in the brazing matrix. On one hand, they hinder dislocation movement through "dispersion strengthening" and "grain boundary pinning" effects, significantly improving the shear strength and wear resistance of the joint. On the other hand, the tight interfacial bonding between TiB and the AgCuTi brazing filler metal matrix effectively alleviates the difference in thermal expansion coefficients between alumina ceramic and metal, reducing thermal stress concentration and thus extending the thermal cycle life of the joint.

[0041] Preferably, the pretreatment process for the ceramic surface to be welded includes: polishing the ceramic surface to a smooth finish, with a surface roughness Ra ≤ 1.6 μm and a flatness ≤ 0.09 mm; and ultrasonically cleaning with acetone and alcohol solvents respectively to remove oil stains, thus completing the treatment and cleaning of the ceramic surface. The surface treatment and cleaning of the metal parts are then completed.

[0042] Preferably, the ceramic is either alumina ceramic or silicon carbide ceramic.

[0043] Preferably, the process of pre-treating the metal surface to be welded includes: grinding the metal surface to remove the oxide layer, with a roughness Ra≤1.6μm and a flatness ≤0.09mm; and ultrasonically cleaning the surface with 10% hydrochloric acid, deionized water and acetone respectively to remove oil stains.

[0044] Preferably, the metal is one of titanium alloy, Kovar alloy, oxygen-free copper, or stainless steel.

[0045] Preferably, the average particle size of the amorphous boron powder is less than 45 μm, and the mass of the added amorphous boron powder is controlled at 0.01%-1% of the mass of the AgCuTi solder. The boron is uniformly dispersed in the AgCuTi solder by adding it through mechanical alloying or uniform mixing during smelting.

[0046] Preferably, the brazing filler metal is solder paste, which is applied to the ceramic and metal surfaces of the two parts to be welded, respectively, covering the entire area. The coating thickness is uniformly controlled at 0.08-0.15mm, and the gap between the two parts to be welded before applying the brazing filler metal is controlled at 0.05-0.15mm to ensure that the solder can completely cover the welding surface after melting.

[0047] Preferably, the brazing filler metal is a foil-shaped sheet processed to match the shape of the ceramic and metal surfaces to be welded. The foil-shaped sheet is flatly clamped on the ceramic and metal surfaces to be welded. The gap control requirement is that the brazing gap between the two parts to be welded is controlled at 0.05-0.18mm before clamping the foil-shaped sheet.

[0048] Specifically, for the foil welding sheet assembly process: a sandwich-type precision positioning method is adopted. This involves pre-processing the foil welding sheet into a shape that matches the welding surface according to the dimensions of the welding surfaces of the parts to be welded, leaving a small edge allowance if necessary. Then, the cut welding sheet is flatly clamped between the metallized welding surfaces of the two parts to be welded, ensuring complete contact between the welding sheet and both welding surfaces without wrinkles, warping, or misalignment. Gap control requirements: The brazing gap between the two parts to be welded must be strictly controlled within 0.05-0.18mm before clamping the foil welding sheet.

[0049] Preferably, a graphite clamp is used to assemble the workpiece and brazing filler metal in a vacuum furnace, and pressure is applied to the graphite clamp.

[0050] Specifically, a custom-designed graphite clamp is developed based on the sample shape. Made of high-purity graphite, it is used to limit and position the workpiece during subsequent thermal deformation, preventing displacement of the ceramic and metal due to melting of the brazing filler metal. After assembling the workpiece, brazing filler metal, and graphite clamp, the parts are placed in a vacuum furnace, and a certain pressure is applied to the graphite clamp. The appropriate pressure, approximately 1-5 kPa, is selected based on the welding surface area and weld size. The graphite clamp is a complete set that holds the ceramic, brazing sheet, and metal together as a single unit, serving a limiting function.

[0051] Preferably, the vacuum level of the vacuum furnace used for vacuum brazing needs to reach [a certain level]. Pa~ Pa, the specific parameters of the brazing process are as follows: braze at 800~950℃ for 10~20min, with a heating rate of 5~10℃ / min; the cooling process is divided into two stages, the first stage is to rapidly drop to below 770℃ at a cooling rate of 10℃ / min, and the second stage is to cool to room temperature with the furnace.

[0052] The cooling process is divided into two stages. In the first stage, the temperature is rapidly reduced to below 770℃ at a rate of 10℃ / min. The core purpose of this stage is to quickly fix the weld shape while the brazing filler metal still maintains a certain fluidity and can fully fill the weld gap, thus preventing the brazing filler metal from being lost or segregated due to prolonged high temperatures. Then, in the second stage, the furnace is cooled to room temperature. This slow cooling effectively reduces the thermal stress caused by the difference in thermal expansion between the metal and the ceramic.

[0053] At high temperatures, the viscosity of the brazing filler metal drops sharply, potentially causing localized material shortages due to "flow." Precise control of brazing process parameters, filler metal composition design, and applied pressure is crucial for preventing this phenomenon and effectively improving the tensile strength and airtightness of the joint. The brazing process parameters are summarized below:

[0054] The optimal brazing temperature is 800–900℃, and the brazing time is 10–20 minutes. If the temperature is too low, the filler metal will not melt completely and will not be able to wet the base metal surface, resulting in a "false weld" or insufficient filling of the gap; if the temperature is too high, the filler metal will be lost, resulting in a reduction in joint strength.

[0055] The preferred type of solder is foil or solder paste to avoid a sharp drop in solder viscosity, which could cause localized material shortages due to "flow".

[0056] It is preferable to use clamps to assemble the ceramics and metals to be welded, so as to meet the requirements of workpiece limitation and positioning during the thermal deformation process.

[0057] The surfaces to be welded need to be wetted at the interface, and the brazing filler metal should not produce any spherical particles after welding.

[0058] Welding pressure 1-5 kPa, adaptability of brazing filler metal viscosity / flowability / gap size.

[0059] Example 1: Connection between alumina ceramic shell and TC4 titanium alloy

[0060] Pre-treatment of the surface to be welded:

[0061] Alumina ceramic housing: dimensions 30mm×40mm×30mm; roughness Ra≤1.6μm, flatness≤0.09mm; titanium alloy parts: flatness≤0.05mm. Ultrasonic cleaning was performed using hydrochloric acid, deionized water, and acetone solvents, respectively.

[0062] Solder: AgCuTi+B foil solder sheet, 0.2mm thick. Cut pre-formed sheets and leave 1-2mm margin at the edges to avoid insufficient solder overflow.

[0063] Brazing parameters: Vacuum degree 3.2×10 -3Pa, applied pressure 3.5 kPa, custom graphite fixture, room temperature → 600℃ (10℃ / min) → 840℃ (5℃ / min), hold for 15 min → 770℃ (10℃ / min) → room temperature (3.5℃ / min).

[0064] Helium mass spectrometry leak detection and airtightness test were performed on the parts; airtightness test: air pressure 500 kPa, inflation time: 10 s, pressure holding time: 5 s, test time: 15 s, leakage value: <200 Pa.

[0065] The tensile strength, airtightness, and leakage value of the final parts are shown in Table 1.

[0066] Example 2: Connection between alumina ceramic tube and Kovar alloy

[0067] Pre-treatment of the surface to be welded:

[0068] Alumina ceramic tube: diameter 25 mm, height 77 mm; end face roughness Ra ≤ 1.6 μm.

[0069] Flatness ≤ 0.05 mm, Kovar alloy: flatness ≤ 0.05 mm. Ultrasonic cleaning was performed using hydrochloric acid, deionized water, and acetone solvents, respectively.

[0070] Brazing filler metal: AgCuTi+B foil, 0.1mm thick, pre-cut sheet;

[0071] Brazing parameters: Vacuum degree Pa, apply pressure of 5 kPa, use a custom graphite core clamp, room temperature → 600℃ (8℃ / min) → 850℃ (5℃ / min), hold for 15 min → 770℃ (10℃ / min) → room temperature (3.5℃ / min);

[0072] Perform helium mass spectrometry leak detection and airtightness test on the parts; airtightness test: air pressure 500 kPa, inflation time: 10 s, pressure holding time: 10 s, test time: 10 s, leakage value: <100 Pa.

[0073] The tensile strength, airtightness, and leakage value of the final parts are shown in Table 1.

[0074] Table 1: Component Test Results

[0075]

[0076] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0077] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for brazing ceramic-metal composite materials with in-situ self-generated reaction, characterized in that, Includes the following steps: Pre-treat the ceramic and metal surfaces to be welded; The pre-placed brazing filler metal is placed between the ceramic and metal surfaces to be soldered. The brazing filler metal is AgCuTi brazing filler metal with amorphous boron powder added. The brazing filler metal can be solder paste or foil. During vacuum brazing, Ti elements react in situ with boron powder to generate TiB ceramic reinforcing phase.

2. The method for in-situ self-generated reaction of ceramic-metal composite brazing according to claim 1, characterized in that, The pretreatment process for the ceramic surface to be welded includes: polishing the ceramic surface to a smooth finish, with a surface roughness Ra≤1.6μm and a flatness ≤0.09mm; and ultrasonic cleaning with acetone and alcohol solvents to remove oil stains.

3. The method for in-situ self-generated reaction of ceramic-metal composite brazing according to claim 1, characterized in that, The ceramic is a type of alumina ceramic or silicon carbide ceramic.

4. The method for in-situ self-generated reaction of ceramic-metal composite brazing according to claim 1, characterized in that, The pretreatment process for the metal surface to be welded includes: grinding the metal surface to remove the oxide layer, with a roughness Ra≤1.6μm and a flatness ≤0.09mm; and ultrasonically cleaning the surface with 10% hydrochloric acid, deionized water and acetone to remove oil stains.

5. The method for in-situ self-generated reaction of ceramic-metal composite brazing according to claim 1, characterized in that, The metal is one of the following: titanium alloy, Kovar alloy, oxygen-free copper, or stainless steel.

6. The method for in-situ self-generated reaction of ceramic-metal composite brazing according to claim 1, characterized in that, The average particle size of amorphous boron powder is less than 45 μm. The mass of amorphous boron powder added is controlled at 0.01%-1% of the mass of AgCuTi solder. Boron is uniformly dispersed in AgCuTi solder by adding it through mechanical alloying or uniform mixing during smelting.

7. The method for in-situ self-generated reaction of ceramic-metal composite brazing according to claim 1, characterized in that, The solder is solder paste, which is applied to the ceramic and metal surfaces of the two parts to be soldered, respectively, covering the entire area. The coating thickness is uniformly controlled at 0.08-0.15mm, and the gap between the two parts to be soldered before applying the solder is controlled at 0.05-0.15mm.

8. The method for in-situ self-generated reaction of ceramic-metal composite brazing according to claim 1, characterized in that, The brazing filler metal is a foil-shaped piece that is machined to match the shape of the ceramic and metal surfaces to be welded. The foil-shaped piece is flatly sandwiched between the ceramic and metal surfaces to be welded. The gap control requirement is that the brazing gap between the two parts to be welded before the foil-shaped piece is sandwiched is controlled at 0.05-0.18mm.

9. The method for in-situ self-generated reaction of ceramic-metal composite brazing according to claim 1, characterized in that, The workpiece and brazing filler metal are assembled in a vacuum furnace using a graphite clamp, and pressure is applied to the graphite clamp.

10. The method for in-situ self-generated reaction of ceramic-metal composite brazing according to claim 1, characterized in that, The vacuum level of the vacuum furnace used for vacuum brazing needs to reach a certain level. Pa~ Pa, the specific parameters of the brazing process are as follows: braze at 800~950℃ for 10~20min, with a heating rate of 5~10℃ / min; the cooling process is divided into two stages, the first stage is to rapidly drop to below 770℃ at a cooling rate of 10℃ / min, and the second stage is to cool to room temperature with the furnace.

Images