Connection method of hot-end ceramic and cold-end metal and connection joint

Abstract

The invention relates to the technical field of welding, in particular to a hot end ceramic and cold end metal connecting method and a connecting joint. The connecting method of the hot-end ceramic and the cold-end metal comprises the steps that a low-thermal-conductivity brazing filler metal system is prepared; a porous three-dimensional framework is soaked in the low-thermal-conductivity brazing filler metal system, and a connecting middle layer is obtained; a ceramic layer, the connecting middle layer and a metal layer are sequentially stacked and assembled, and a to-be-welded connecting body is obtained; and the to-be-welded connector is subjected to vacuum brazing, and a connection joint of the hot-end ceramic and the cold-end metal is obtained. The problems that when ceramic and metal are welded, a connector is poor in heat insulation performance and low in connection strength can be solved.

Description

Technical Field

[0001] This invention relates to the field of welding technology, specifically to a method and joint for connecting a hot-end ceramic and a cold-end metal. Background Technology

[0002] In the aerospace field, especially in advanced fighter jets, to achieve greater power and lower energy consumption, the airframe is generally made of metallic materials such as titanium alloys, with the highest operating temperature inside or on the surface of the airframe being only 300 to 400°C. However, for the nozzle structure, which directly contacts the high-temperature heat flow, the maximum temperature can reach over 1000°C, far exceeding the service temperature of titanium alloys. Therefore, the material for this part of the structure is usually SiC. f / SiC (silicon carbide fiber reinforced silicon carbide composite ceramic) with an external heat-insulating coating to alleviate the high temperature caused by heat transfer.

[0003] In extreme service environments, due to the significant temperature difference between the metal substrate and the ceramic material, it is essential to ensure good thermal insulation performance at their joints. Currently, metal substrates such as titanium alloys are generally connected to ceramic materials via direct brazing, typically using Ag / Cu-based brazing filler metals. However, Ag has a thermal conductivity of 419 W / mK, and Cu has a thermal conductivity of 377 W / mK; both are good conductors of heat and offer virtually no thermal insulation. This results in joints prone to heat transfer at high temperatures, potentially leading to failure of the base material on one side. Furthermore, SiC... f / SiC is prone to cracking during welding. The wide heat-affected zone during welding can easily lead to localized thermal stress concentration, thereby increasing the risk of cracking and resulting in lower connection strength of the joint. Summary of the Invention

[0004] The present invention aims to solve the problems of poor thermal insulation performance and low connection strength of the joint after ceramic and metal welding.

[0005] To address the aforementioned problems, as a first aspect, the present invention provides a method for connecting a hot-end ceramic and a cold-end metal, comprising: Preparation of low thermal conductivity solder systems; A porous three-dimensional skeleton is immersed in the low thermal conductivity solder system to obtain a connection intermediate layer; The ceramic layer, the connecting intermediate layer, and the metal layer are stacked and assembled in sequence to obtain the connector to be welded. The components to be welded are vacuum brazed to obtain a joint between the hot-end ceramic and the cold-end metal.

[0006] Optionally, the low thermal conductivity solder system comprises the following elements by mass percentage: 30% to 40% Ti, 30% to 40% Zr, 10% to 20% Cu, 5% to 10% Ni, and 4% to 10% Nb.

[0007] Optionally, the porous three-dimensional skeleton comprises foamed metal and / or foamed ceramic.

[0008] Optionally, the foamed metal is foamed titanium, and the foamed ceramic is foamed silicon carbide.

[0009] Optionally, the step of immersing the porous three-dimensional skeleton in the low thermal conductivity solder system to obtain the connection intermediate layer includes: immersing the porous three-dimensional skeleton in the low thermal conductivity solder system using a vacuum pressure impregnation method to obtain the connection intermediate layer.

[0010] Optionally, the ceramic layer is made of silicon carbide fiber-reinforced silicon carbide composite ceramic, and the metal layer is made of titanium alloy.

[0011] Optionally, the melting point range of the low thermal conductivity solder system is 750 to 850°C.

[0012] Optionally, when vacuum brazing the connector to be welded, the temperature is first raised to the welding temperature and held at that temperature, and then lowered to room temperature, wherein the welding temperature is 900 to 950°C.

[0013] Optionally, when the joint to be welded is vacuum brazed, the heating rate is 10 to 20°C / min, the cooling rate is 5 to 10°C / min, and the holding time is 10 to 20 min.

[0014] As a second aspect, the present invention provides a connecting joint between a hot-end ceramic and a cold-end metal, the connecting joint being prepared by the connecting method of the hot-end ceramic and the cold-end metal as described in the first aspect.

[0015] The advantages of this invention compared to related technologies include: This invention adds a porous three-dimensional framework as a connecting intermediate layer between the hot-end ceramic and the cold-end metal. On the one hand, the porous three-dimensional framework enriches the contact interface in the weld, hindering the heat conduction behavior of the joint and thus improving the overall thermal resistance of the joint. At the same time, the porous structure has a certain degree of plasticity, which can absorb some thermal stress. On the other hand, to overcome the low strength of the porous three-dimensional framework, this invention pre-impregnates the porous three-dimensional framework with a liquid brazing filler system, allowing the brazing filler to fill the pores of the porous three-dimensional framework, greatly improving the connection strength and making the connecting intermediate layer less prone to fracture failure.

[0016] Furthermore, compared to welding methods using brazing filler metal coating or directly using brazing filler metal foil, the absence of a connecting interlayer limits the weld thickness to less than 1 mm. Moreover, once a single connecting interlayer reaches a certain thickness, the brazing filler metal cannot fully penetrate during brazing, leading to the interlayer's susceptibility to breakage under stress. This invention utilizes a pre-impregnation method to ensure the brazing filler metal fully wets the porous three-dimensional framework, thereby allowing for adjustable connecting interlayer thickness. This also provides greater optimization potential for the thermal resistance of the joint. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the connection process between the hot-end ceramic and the cold-end metal in an embodiment of the present invention. Figure 2 The DSC curve of the low thermal conductivity solder system in Example 1 is shown. Figure 3 This is a scanning electron microscope image of the weld structure of the connecting joint in Example 1. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0019] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit this application. The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0020] SiC fSiC (silicon carbide fiber-reinforced silicon carbide composite ceramic) is a novel composite ceramic material with advantages such as high high-temperature strength, low density, strong oxidation and creep resistance, and good thermal stability, making it suitable for high-end fields such as aerospace and nuclear energy. However, this composite ceramic material has poor processing performance and is difficult to directly process into complex components, requiring bonding with other materials (such as metals) for application. In related technologies, SiC... f SiC materials are typically joined to metal materials using brazing; however, SiC... f The temperature tolerance of SiC materials differs significantly from that of metallic materials. Therefore, in order to ensure the performance of the materials at both ends of the joint, there is an urgent need to provide a high-insulation connection method.

[0021] Therefore, one embodiment of the present invention provides a method for connecting hot-end ceramic and cold-end metal, referring to... Figure 1 This includes the following steps: Step (1): Prepare a low thermal conductivity solder system.

[0022] Step (2): Immerse the porous three-dimensional skeleton in a low thermal conductivity solder system to obtain the connection intermediate layer.

[0023] Step (3): Stack and assemble the ceramic layer, the connecting intermediate layer and the metal layer in sequence to obtain the connector to be welded.

[0024] Step (4): Vacuum brazing is performed on the bodies to be welded to obtain a connection joint between the hot-end ceramic and the cold-end metal.

[0025] In this embodiment of the invention, a porous three-dimensional skeleton is added as a connecting intermediate layer in the weld between the hot-end ceramic and the cold-end metal. On the one hand, the porous three-dimensional skeleton can enrich the contact interface in the weld, hinder the heat conduction behavior of the joint, thereby improving the overall thermal resistance of the joint. At the same time, the porous structure has a certain degree of plasticity and can absorb some thermal stress. On the other hand, to overcome the defect of low strength of the porous three-dimensional skeleton, this invention pre-impregnates the porous three-dimensional skeleton in a low thermal conductivity solder system, so that the solder fills the pores of the porous three-dimensional skeleton, which greatly improves the connection strength and makes the connecting intermediate layer less prone to fracture failure.

[0026] Furthermore, compared to welding methods using brazing filler metal coating or directly using brazing filler metal foil, the absence of a connecting interlayer limits the weld thickness to below 1mm. Moreover, once a single connecting interlayer reaches a certain thickness, the brazing filler metal cannot fully penetrate during brazing, leading to the interlayer's susceptibility to breakage under stress. This embodiment utilizes pre-impregnation to ensure the brazing filler metal fully wets the porous three-dimensional framework, thereby allowing for adjustable connecting interlayer thickness. Preferably, it can be freely adjusted below 5mm, providing greater optimization potential for the thermal resistance of the joint.

[0027] For example, in the embodiments of the present invention, the material of the ceramic layer to be welded can be silicon carbide fiber reinforced silicon carbide composite ceramic, and the material of the metal layer can specifically be titanium alloy.

[0028] It should be noted that the low thermal conductivity solder system in this embodiment of the invention uses a low thermal conductivity element as the matrix, and is further optimized according to the application environment and joint design. Specifically, the low thermal conductivity solder system can be set according to the following conditions: thermal conductivity below 100 W / mK, good wetting with the base material and porous three-dimensional skeleton, and a coefficient of thermal expansion of less than 4 × 10⁻⁶ after mixing. -6 m / K to 7×10 -6 Between m / K. For example, low thermal conductivity elements can specifically be Ti (thermal conductivity 15 W / mK), Zr (thermal conductivity 23 W / mK), and Nb (thermal conductivity 54 W / mK), etc., and then optimized by adding other elements to lower the melting point or improve wettability. In some optional embodiments, the low thermal conductivity solder system may include the following elements in mass percentages: 30% to 40% Ti, 30% to 40% Zr, 10% to 20% Cu, 5% to 10% Ni, and 4% to 10% Nb. Of course, in other embodiments, similar elements such as V and Cr can be used to replace Ti, Zr, and Nb.

[0029] Furthermore, when immersing the porous three-dimensional skeleton in a low thermal conductivity brazing filler metal system, the low thermal conductivity brazing filler metal system can be heated to above its melting point temperature, causing it to melt and form a liquid brazing filler metal system. The porous three-dimensional skeleton is then immersed in this liquid brazing filler metal system. It should be noted that when designing the formulation of the low thermal conductivity brazing filler metal system, its melting point range can be controlled within 750 to 850°C, which is higher than the joint's service temperature but lower than the welding temperature and the phase transformation temperature of the titanium alloy. This ensures that the brazing process does not damage the base material and that the joint can operate stably.

[0030] In some alternative embodiments, the porous three-dimensional framework comprises foamed metal and / or foamed ceramic. Optionally, the foamed metal may be foamed titanium, and the foamed ceramic may be foamed silicon carbide.

[0031] By employing a porous three-dimensional framework made of the same material as the base metal, a significant portion of the connecting interlayer directly participates in the reaction during welding, resulting in a good bond with the brazing filler metal. Simultaneously, other phases are generated on the surface of the framework of the connecting interlayer to enrich the contact interface in the weld, such as Ti and Zr carbides and some micro-silicide phases. These not only help alleviate residual stress between other phases and SiC in the weld but also provide more contact interfaces or lattice mismatches to hinder heat transfer, thus improving the mechanical and thermal insulation properties of the joint.

[0032] In some alternative embodiments, a vacuum pressure impregnation method can be used to impregnate a porous three-dimensional framework in a low thermal conductivity solder system to obtain a bonding intermediate layer. The pressure impregnation process can promote a full bond between the solder and the porous three-dimensional framework.

[0033] In some optional embodiments, when vacuum brazing the joints to be welded, the temperature is first raised to the welding temperature and held at that temperature, and then cooled to room temperature. The heating rate can be 10 to 20 °C / min, the welding temperature range is 900 to 950 °C, the cooling rate can be 5 to 10 °C / min, and the holding time is 10 to 20 min.

[0034] Another embodiment of the present invention provides a connecting joint between a hot-end ceramic and a cold-end metal, which is manufactured using the method described above for connecting the hot-end ceramic and the cold-end metal. Specifically, the connecting joint includes a ceramic layer, a connecting intermediate layer, and a metal layer arranged sequentially.

[0035] The present invention will be described in detail below through specific embodiments and comparative examples: Example 1 A low thermal conductivity solder system was prepared according to the following elemental ratios: Ti: 35.0%, Zr: 35.0%, Cu: 16%, Ni: 10%, Nb: 4%. The DSC curve of the low thermal conductivity solder system in this embodiment is shown below. Figure 2 As shown, by Figure 2 It is known that the melting point of this solder system is approximately 840℃. Then, foamed silicon carbide is used as a porous three-dimensional framework and impregnated into the low thermal conductivity solder system using a vacuum pressure impregnation method for 30 minutes. After cooling and solidification, a connection intermediate layer is obtained. Subsequently, SiC... f After cutting the SiC, TC4, and connecting intermediate layers, they were sanded smooth using 80-grit, 200-grit, 400-grit, and 1000-grit sandpaper, respectively. Then, according to the SiC... f SiC, the intermediate bonding layer, and TC4 are stacked sequentially and then assembled into a graphite mold to form the weld joint. Finally, the weld joint is placed in a vacuum brazing furnace and brazed at 10°C. -6 Under a vacuum of bar, the temperature is increased to 940°C at a heating rate of 10°C / min, held for 10 minutes, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the connecting joint.

[0036] The scanning electron microscope image of the weld microstructure of the connection joint prepared in this embodiment is as follows: Figure 3 As shown, where Figure 3 (a) Connecting the intermediate layer to SiC f Scanning electron microscope image between the / SiC side. Figure 3 (b) is a scanning electron microscope image showing the connection between the intermediate layer and the TC4 side. From Figure 3As can be seen, the connecting intermediate layer exists in the form of a skeleton and can form a good bond with the brazing filler metal. More importantly, a bonding layer is also formed on the surface of the skeleton of the connecting intermediate layer, which makes a good contribution to both the mechanical and thermal properties of the joint.

[0037] Furthermore, mechanical tests were conducted on the joint using an electronic universal testing machine. The results showed that the shear strength of the joint at room temperature was 22.56 MPa, and the high-temperature shear strength at 500℃ reached 25.39 MPa. The increase in high-temperature shear strength was due to the relief of residual stress caused by shrinkage recovery during reheating. Thermal performance tests were performed on the joint using a laser thermal conductivity meter. The calculated room temperature thermal conductivity at the weld joint was only 1.87 W / mK, and the high-temperature thermal conductivity at 500℃ was only 2.62 W / mK.

[0038] Example 2 A low thermal conductivity solder system was prepared according to the following elemental ratios: V: 10%, Cu: 55%, Ni: 25%, Cr: 10%. Then, titanium foam was used as a porous three-dimensional framework, impregnated in the low thermal conductivity solder system, and impregnated for 1 hour. After cooling and solidification, a bonding intermediate layer was obtained. Subsequently, SiC... f After cutting the SiC, TC4, and connecting intermediate layers, they were sanded smooth using 80-grit, 200-grit, 400-grit, and 1000-grit sandpaper, respectively. Then, according to the SiC... f SiC, the intermediate bonding layer, and TC4 are stacked sequentially and then assembled into a graphite mold to form the weld joint. Finally, the weld joint is placed in a vacuum brazing furnace and brazed at 10°C. -6 Under a vacuum of bar, the temperature is increased to 930°C at a heating rate of 15°C / min, held for 20 minutes, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the connecting joint.

[0039] Mechanical tests were conducted on the joint using an electronic universal testing machine. The results showed that the shear strength of the joint at room temperature was 25.95 MPa, and the high-temperature shear strength at 500℃ reached 32.42 MPa. Thermal performance tests were performed on the joint using a laser thermal conductivity meter. The calculated room temperature thermal conductivity at the weld joint was only 2.14 W / mK, and the high-temperature thermal conductivity at 500℃ was only 2.88 W / mK.

[0040] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example directly coats the SiC with a low thermal conductivity solder system. f On the welding surfaces of SiC and TC4, a coating with a thickness of 2 mm is applied, and then the layers are stacked and assembled into a connector to be welded. Subsequently, the connector to be welded is vacuum brazed, and the brazing process parameters are the same as in Example 1.

[0041] The thermal properties of the joint in this comparative example were tested using a laser thermal conductivity meter. The calculated room temperature thermal conductivity of the weld seam was 18.33 W / mK, and the high-temperature thermal conductivity at 500℃ was 25.62 W / mK. It is evident that the thermal conductivity of the joint is significantly improved without an intermediate connecting layer.

[0042] Comparative Example 2 The difference between this comparative example and Example 1 is that this comparative example directly coats the SiC with a low thermal conductivity solder system. f On the welding surfaces of SiC and TC4, an untreated porous three-dimensional framework is then clamped onto the SiC. f A weld joint is formed between the welding surfaces of SiC and TC4. The weld joint is then vacuum brazed, with the same brazing process parameters as in Example 1.

[0043] Mechanical tests were conducted on the joint in this comparative example using an electronic universal testing machine. The results showed that the shear strength of the joint at room temperature was only 8.21 MPa, and the high-temperature shear strength at 500℃ was only 12.33 MPa. It is evident that without impregnation treatment of the porous three-dimensional skeleton, the mechanical properties of the joint are poor, and the shear strength is significantly reduced.

[0044] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for connecting a hot-end ceramic to a cold-end metal, characterized in that, include: Preparation of low thermal conductivity solder systems; A porous three-dimensional skeleton is immersed in the low thermal conductivity solder system to obtain a connection intermediate layer; The ceramic layer, the connecting intermediate layer, and the metal layer are stacked and assembled sequentially to obtain the connector to be welded. The components to be welded are vacuum brazed to obtain a joint between the hot-end ceramic and the cold-end metal.

2. The method for connecting the hot-end ceramic and the cold-end metal according to claim 1, characterized in that, The low thermal conductivity solder system comprises the following elements in mass percentage: 30% to 40% Ti, 30% to 40% Zr, 10% to 20% Cu, 5% to 10% Ni and 4% to 10% Nb.

3. The method for connecting the hot-end ceramic and the cold-end metal according to claim 1, characterized in that, The porous three-dimensional framework comprises foamed metal and / or foamed ceramic.

4. The method for connecting the hot-end ceramic and the cold-end metal according to claim 3, characterized in that, The foamed metal is foamed titanium, and the foamed ceramic is foamed silicon carbide.

5. The method for connecting the hot-end ceramic and the cold-end metal according to claim 1, characterized in that, The step of immersing the porous three-dimensional skeleton in the low thermal conductivity solder system to obtain the connection intermediate layer includes: immersing the porous three-dimensional skeleton in the low thermal conductivity solder system using a vacuum pressure impregnation method to obtain the connection intermediate layer.

6. The method for connecting the hot-end ceramic and the cold-end metal according to claim 1, characterized in that, The ceramic layer is made of silicon carbide fiber-reinforced silicon carbide composite ceramic, and the metal layer is made of titanium alloy.

7. The method for connecting the hot-end ceramic and the cold-end metal according to claim 1, characterized in that, The melting point range of the low thermal conductivity solder system is 750 to 850°C.

8. The method for connecting the hot-end ceramic and the cold-end metal according to claim 1, characterized in that, When the joint to be welded is vacuum brazed, the temperature is first raised to the welding temperature and held at that temperature, and then lowered to room temperature, wherein the welding temperature is 900 to 950°C.

9. The method for connecting the hot-end ceramic and the cold-end metal according to claim 8, characterized in that, When the joints to be welded are vacuum brazed, the heating rate is 10 to 20°C / min, the cooling rate is 5 to 10°C / min, and the holding time is 10 to 20 min.

10. A connection joint between a hot-end ceramic and a cold-end metal, characterized in that, The connecting joint is prepared by the method of connecting the hot-end ceramic and the cold-end metal as described in any one of claims 1 to 9.

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