A gradient active composite filler for joining alumina to silicon carbide ceramics and method
By designing a gradient active composite solder, the stress concentration problem caused by the difference in thermal expansion coefficients in the connection between alumina and silicon carbide ceramics was solved, achieving high-strength chemical bonding at low temperatures and improving the connection strength and toughness.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JUNYUAN ELECTRONIC TECHNOLOGY (HAINING) CO LTD
- Filing Date
- 2026-01-31
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies cannot effectively coordinate the difference in thermal expansion coefficients between alumina and silicon carbide ceramics, resulting in the concentration of residual thermal stress during connection, and traditional brazing filler metals are difficult to achieve high-strength chemical bonding at low temperatures.
A gradient active composite brazing filler metal is used, including a SiC side bonding layer, an intermediate gradient buffer layer, and an Al2O3 side bonding layer. The active elements are designed to match the two ceramics respectively, and low-temperature connection is achieved by vacuum brazing to generate a strong and tough interface reaction layer.
Achieving high-strength metallurgical-chemical bonding between alumina and silicon carbide ceramics at low temperatures avoids damage to the properties of the base material, stabilizes the shear strength at 90–120 MPa, and effectively alleviates thermal stress.
Abstract
Description
Technical Field
[0001] This invention relates to the field of ceramic brazing technology, and in particular to a gradient active composite brazing filler metal and method for joining alumina and silicon carbide ceramics. Background Technology
[0002] Both alumina ceramics and silicon carbide ceramics are essential materials for extreme environments (high temperature, corrosion, radiation, and abrasion). Alumina ceramics possess excellent electrical insulation, chemical stability, and low cost; while silicon carbide ceramics offer higher thermal conductivity, thermal shock resistance, strength, and resistance to neutron radiation. Reliably connecting these two ceramics to form multifunctional integrated components (such as integrated insulation-thermal conductivity components and wear-resistant-corrosion-resistant composite structures) is urgently needed in fields such as aerospace thermal protection systems, first-wall materials for nuclear fusion reactors, and heat dissipation substrates for high-power electronic devices.
[0003] However, achieving a reliable connection between these two ceramics presents significant challenges, primarily for the following reasons:
[0004] The physical properties are severely mismatched: the coefficients of thermal expansion (CTE) of the two materials differ significantly. Alumina (approximately 7.0-8.0 × 10⁻⁶) -6 The CTE of / K is silicon carbide (approximately 4.0-4.5 × 10⁻⁶). -6 The residual thermal stress is nearly 1.8 times that of K. During the cooling process after the connection, huge residual thermal stress will be generated, which can easily cause cracks at the interface or inside the brittle ceramic, leading to connection failure.
[0005] The chemical properties and bonding mechanisms differ: Alumina is an ionic crystal with a surface rich in oxygen, readily reacting with active metals such as Ti and Zr to form compounds like titanium / zirconium aluminates for bonding. Silicon carbide, on the other hand, is a covalent crystal with extremely strong chemical inertness; traditional solders have poor wettability against it, requiring the reaction of elements like Cr, Ti, and V to form silicides / carbides for bonding. A single active solder system cannot simultaneously optimize the interfacial reaction with both ceramics.
[0006] Risk of damage from high-temperature bonding: To promote interfacial reactions, traditional methods often use bonding temperatures above 1000°C. This temperature is close to or exceeds the resintering or creep temperature of some alumina ceramics, which may lead to performance degradation; at the same time, high temperatures will exacerbate thermal stress.
[0007] In existing technologies, direct diffusion welding requires extremely high temperatures and pressures, making it difficult to implement practically. While commonly used active metal brazing (such as Ag-Cu-Ti brazing filler metal) can connect alumina, its wetting and bonding strength with SiC is often insufficient, and a single layer of brazing filler metal cannot alleviate the enormous thermal stress. Some studies have also used physical vapor deposition (PVD) or slurry sintering to prepare metal interlayers (such as Mo and W), but these processes are complex, and the interfacial bonding strength between the metal and ceramic is limited.
[0008] Therefore, developing a specialized composite solder that can actively coordinate thermal stress and form high-strength chemical bonds with alumina and silicon carbide respectively is the core breakthrough for achieving high-performance bonding of these two key ceramic materials. Summary of the Invention
[0009] The technical problem to be solved by the present invention is to provide a gradient active composite solder and method for bonding alumina and silicon carbide ceramics, so as to solve the problems mentioned in the background art.
[0010] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:
[0011] This invention discloses a gradient active composite solder for bonding alumina and silicon carbide ceramics, wherein the gradient active composite solder comprises, in sequence:
[0012] SiC side bonding layer: Its thickness is 30-70μm, and its composition is Ag-(35-50)Cu-(8-15)Cr-(2-5)Si (wt%). The Cr reacts with SiC to form a continuous Cr-Si compound layer, which is bonded to SiC ceramic with high strength. The pre-added Si element is used to suppress excessive decomposition of SiC during brazing and to adjust the morphology of interface reaction products.
[0013] Intermediate gradient buffer layer: Its thickness is 30-80μm, and its composition is Ag-(20-40)Cu-(2-8)Ti-(1-4)Mo (wt%). Ti is the active element, and Mo is the element that strengthens and regulates the coefficient of thermal expansion. Its coefficient of thermal expansion is designed to be between that of the SiC side bonding layer and the Al2O3 side bonding layer, so as to play a stress buffering role. Mo is dispersed in the form of fine particles to improve the high temperature strength of the brazing seam.
[0014] Al2O3 side bonding layer: Its thickness is 20-50μm, and its composition is Ag-(20-30)Cu-(1-3)Ti-(1-3)Hf (wt%). It contains strong oxide active elements Ti and Hf. The two work together to reduce and wet the Al2O3 ceramic surface, forming a strong (Ti,Hf)-O compound reaction layer. The Hf in it can also refine the interfacial reaction products to improve the interfacial toughness.
[0015] Another aspect of the present invention discloses a method for joining alumina ceramics and silicon carbide ceramics using the aforementioned gradient active composite solder, the method comprising the following steps:
[0016] Step S1: Ceramic surface pretreatment and preparation of gradient active composite solder
[0017] The alumina ceramic and silicon carbide ceramic surfaces to be soldered are precision polished, then ultrasonically cleaned in acetone and ethanol in sequence, dried, and prepared with gradient active composite solder.
[0018] Step S2: Assemble the brazing filler metal and the workpiece
[0019] The prepared gradient active composite solder is placed between the alumina ceramic and silicon carbide ceramic surfaces to be soldered, with the SiC side bonding layer facing the silicon carbide ceramic and the Al2O3 side bonding layer facing the alumina ceramic to form an assembly. Slight pressure is applied to ensure that each layer is in close contact.
[0020] Step S3: Vacuum brazing connection
[0021] Place the assembly in a vacuum brazing furnace, evacuate the furnace, and heat it according to the following procedure:
[0022] Increase the temperature to 500-550℃ at a rate of 10-15℃ / min and hold for 10 minutes to completely remove the adsorbed gas;
[0023] Increase the temperature to 860-920℃ at a rate of 5-8℃ / min, and hold for 8-20 minutes;
[0024] After the heat preservation is completed, a staged slow cooling method is adopted: first, the temperature is slowly cooled to 700℃ at 3-5℃ / min, then cooled to 400℃ at 5-8℃ / min, and then cooled to room temperature with the furnace.
[0025] Preferably, in step S1, the alumina ceramic surface to be soldered and the silicon carbide ceramic surface to be soldered are precision polished until Ra is less than or equal to 0.1 μm.
[0026] Preferably, in step S2, the applied slight pressure is 5 to 15 kPa.
[0027] Preferably, in step S3, the vacuum brazing furnace is evacuated to a vacuum level of less than or equal to 5 × 10⁻⁶. -3 Pa.
[0028] The above technical solution has the following beneficial effects:
[0029] The three-layered gradient active composite brazing filler metal of this application forms a continuous gradient transition from a low coefficient of thermal expansion (SiC side bonding layer) to a high coefficient of thermal expansion (Al2O3 side bonding layer), which effectively avoids stress concentration caused by abrupt changes in the coefficient of thermal expansion; the Mo particles in the intermediate gradient buffer layer further enhance the creep resistance of the brazing seam and can relax some stress during high and low temperature cycling.
[0030] This application presents a gradient active composite solder with a dedicated active system designed for two types of ceramics. The SiC side is mainly composed of Cr-Si, forming a strong and tough silicide reaction layer; the Al2O3 side is mainly composed of Ti-Hf, forming a stable oxide reaction layer. Both interfaces achieve atomic-scale chemical bonding, and the reaction layer is continuous, with a moderate thickness, and the room temperature shear strength is stable at 90-120 MPa.
[0031] The main connection temperature when the two ceramics are joined is controlled below 920℃, which is far below the sintering temperature of both, thus avoiding damage to the microstructure of the base material. Detailed Implementation
[0032] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0033] This application addresses the challenges of thermal stress mismatch and interfacial reaction coordination in heterojunctions of alumina and silicon carbide ceramics by providing a gradient active composite brazing filler metal and a method for vacuum joining using this metal. Through a unique composition and structural design, the gradient active composite brazing filler metal achieves a continuous transition in the coefficient of thermal expansion from the silicon carbide side to the alumina side, actively mitigating and dispersing residual stress during the joint. It ensures that both sides of the filler metal are rich in active elements most compatible with the corresponding ceramics, achieving a high-strength metallurgical-chemical bond at the interface. This enables high-quality joining at relatively low joining temperatures, avoiding damage to the base material properties.
[0034] Example 1
[0035] A gradient-active composite solder for joining alumina ceramics and silicon carbide ceramics:
[0036] The solder has a three-layer foil composite structure, consisting of a SiC side bonding layer, an intermediate gradient buffer layer, and an Al2O3 side bonding layer, as detailed below:
[0037] SiC side bonding layer: Its thickness is 30-70μm, and its composition is Ag-(35-50)Cu-(8-15)Cr-(2-5)Si (wt%). The core active elements of this layer are Cr and Si. Cr reacts with SiC to form a continuous Cr-Si compound layer, such as Cr3Si2 and CrSi2, which is bonded to SiC ceramic with high strength. The pre-added Si element is used to suppress excessive decomposition of SiC during brazing and to adjust the morphology of the interface reaction products.
[0038] Specifically, the thickness of the SiC side bonding layer is 30μm or 70μm, or it can be 50μm. The composition of the SiC side bonding layer is Ag-(35-50)Cu-(8-15)Cr-(2-5)Si (wt%), which specifically includes: 35-50 wt% Cu, 8-15 wt% Cr, 2-5 wt% Si, and the remainder is Ag.
[0039] Intermediate gradient buffer layer: Its thickness is 30-80μm, and its composition is Ag-(20-40)Cu-(2-8)Ti-(1-4)Mo (wt%). This layer is a functional gradient layer, in which Ti is the active element and Mo is the element that strengthens and regulates the coefficient of thermal expansion. Its coefficient of thermal expansion is designed to be between that of the SiC side bonding layer and the Al2O3 side bonding layer, which plays a stress buffering role. Mo is dispersed in the form of fine particles, which can pin dislocations to improve the high temperature strength of the brazing seam.
[0040] Specifically, the thickness of the intermediate gradient buffer layer is 30μm, 80μm, or even 55μm. The composition of the intermediate gradient buffer layer is Ag-(20-40)Cu-(2-8)Ti-(1-4)Mo (wt%), specifically including: 20-40 wt% Cu, 2-8 wt% Ti, and 1-4 wt% Mo. The sum of the mass percentages (wt%) of Ag, Cu, Ti, and Mo is 100 wt%, with the remainder being Ag. The thermal expansion coefficient of the intermediate gradient buffer layer is designed to be between that of the SiC side bonding layer and the Al2O3 side bonding layer, thus playing a stress buffering role.
[0041] Al2O3 side bonding layer: Its thickness is 20-50μm, and its composition is Ag-(20-30)Cu-(1-3)Ti-(1-3)Hf (wt%). It contains strong oxide active elements Ti and Hf. The two work together to reduce and wet the Al2O3 ceramic surface, forming a strong (Ti,Hf)-O compound reaction layer. The Hf in it can also refine the interfacial reaction products to improve the interfacial toughness.
[0042] Specifically, the thickness of the Al2O3 side bonding layer is 20μm, 50μm, or 35μm. The composition of the Al2O3 side bonding layer is Ag-(20-30)Cu-(1-3)Ti-(1-3)Hf (wt%), which specifically includes: 20-30 wt% Cu, 1-3 wt% Ti, and 1-3 wt% Hf (hafnium) elements, with the sum of the four being 100 wt%. The remainder is Ag elements. The strong oxide active elements Ti and Hf work synergistically to form a strong (Ti,Hf)-O compound reaction layer.
[0043] Example 2
[0044] A method for joining alumina and silicon carbide ceramics using the above-mentioned gradient composite solder specifically includes the following steps:
[0045] Surface pretreatment:
[0046] The alumina ceramic and silicon carbide ceramic surfaces to be soldered are precision polished to a surface roughness (Ra) of less than or equal to 0.1 μm. Then, they are ultrasonically cleaned in acetone and ethanol in sequence, and dried after cleaning. Specifically, the soldering surface is the side that will be in contact with the gradient active composite solder. Both soldering surfaces are polished to a surface roughness (Ra) of less than or equal to 0.1 μm, such as Ra of 0.08 μm. After polishing, they are ultrasonically cleaned in acetone and ethanol in sequence, and dried for later use.
[0047] Brazing filler metal and workpiece assembly:
[0048] Assemble the alumina ceramic soldering surface, the gradient active composite solder, and the silicon carbide ceramic soldering surface. Position the gradient active composite solder between the alumina ceramic soldering surface and the silicon carbide ceramic soldering surface, with the SiC side bonding layer of the gradient active composite solder facing and contacting the silicon carbide ceramic soldering surface, and the Al2O3 side bonding layer facing and contacting the alumina ceramic soldering surface. After assembly, an assembly is formed. During the assembly process, a pressure of 5 to 15 kPa can be applied to ensure tight contact between the layers, specifically 5 kPa or 15 kPa.
[0049] Vacuum brazing connection:
[0050] The assembly was placed in a vacuum brazing furnace, and the furnace was evacuated to a pressure of less than or equal to 5 × 10⁻⁶. -3 Pa, then heat and braze according to the following procedure:
[0051] First, raise the temperature to 500-550℃ at a rate of 10-15℃ / min and hold for 10 minutes to completely remove the adsorbed gas. Specifically, raise the temperature in the vacuum brazing furnace to 500℃ or 550℃ at a rate of 10℃ / min or 15℃ / min and hold for 10 minutes after raising the temperature.
[0052] Then raise the temperature to 860-920℃ at a rate of 5-8℃ / min and hold for 8-20 minutes. Specifically, raise the temperature to 860-920℃ at a rate of 5-8℃ / min, or raise the temperature to 880-900℃. In other words, continue to raise the temperature to 860℃ or 920℃ at a rate of 5℃ / min or 8℃ / min, or raise the temperature in the vacuum brazing furnace to 880℃ or 900℃, and hold for 8 minutes or 20 minutes after raising the temperature.
[0053] After the above heat preservation is completed, a staged slow cooling is adopted: first, the temperature is slowly cooled to 700°C at a cooling rate of 3-5°C / min, then cooled to 400°C at a cooling rate of 5-8°C / min, and then cooled to room temperature with the furnace. This cooling system can release thermal stress to the greatest extent. Specifically, the temperature in the vacuum brazing furnace is first slowly cooled to 700°C at a cooling rate of 3°C / min or 5°C / min, then cooled to 400°C at a cooling rate of 5°C / min or 8°C / min, and finally cooled to room temperature with the furnace to complete the vacuum brazing of alumina ceramics and silicon carbide ceramics.
[0054] Example 3
[0055] Base material: 99% alumina ceramic sheet and reaction sintered silicon carbide ceramic sheet, both with the same dimensions, with length, width and height of 10mm, 10mm and 5mm respectively;
[0056] The gradient-active composite brazing filler metal was prepared using a vacuum melting-rapid solidification method to fabricate a three-layer alloy foil. The gradient-active composite brazing filler metal specifically includes:
[0057] SiC side bonding layer: Ag-45Cu-10Cr-3Si, thickness 50μm;
[0058] Intermediate gradient buffer layer: Ag-30Cu-5Ti-2Mo, thickness 60μm;
[0059] Al2O3 side bonding layer: Ag-25Cu-2Ti-2Hf, thickness 30μm;
[0060] The total thickness of the gradient active composite solder is 140 μm.
[0061] The bonding process between alumina ceramics and silicon carbide ceramics includes the following steps:
[0062] The surfaces of alumina ceramics and silicon carbide ceramics to be welded are polished to Ra 0.08μm, ultrasonically cleaned, and then dried for later use.
[0063] Assemble the layers sequentially and apply a pressure of 10 kPa.
[0064] Inside the vacuum furnace, a vacuum of 3×10⁻⁶ was created. -3 Pa. Increase the temperature to 520℃ at 12℃ / min and hold for 10 min, then increase the temperature to 890℃ at 6℃ / min and hold for 15 min.
[0065] The temperature is lowered to 700℃ at a rate of 3℃ / min, then to 400℃ at a rate of 6℃ / min, and finally cooled in the furnace to complete the vacuum brazing connection.
[0066] Performance testing:
[0067] Room temperature shear strength: tested on a universal testing machine, with an average value of 112 MPa.
[0068] Interface analysis: SEM-EDS (SEM-EDS is an analytical technique that combines scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS)) shows that a continuous Cr-Si compound layer of about 1.5 μm thickness is formed at the interface between SiC ceramic and SiC side bonding layer; a (Ti,Hf)-O compound layer of about 2 μm thickness is formed at the interface between Al2O3 side bonding layer and Al2O3 ceramic; there is obvious interdiffusion of elements among the three brazing filler metals, realizing metallurgical bonding.
[0069] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.
Claims
1. A gradient-active composite solder for bonding alumina and silicon carbide ceramics, characterized in that, The complex gradient active composite solder comprises, in sequence: SiC side bonding layer: Its thickness is 30-70μm, and its composition is Ag-(35-50)Cu-(8-15)Cr-(2-5)Si. The Cr reacts with SiC to form a continuous Cr-Si compound layer, which is bonded to SiC ceramic with high strength. The pre-added Si element is used to suppress the excessive decomposition of SiC during the brazing process and to adjust the morphology of the interface reaction products. Intermediate gradient buffer layer: Its thickness is 30-80μm, and its composition is Ag-(20-40)Cu-(2-8)Ti-(1-4)Mo. Ti is the active element, and Mo is the element that strengthens and regulates the coefficient of thermal expansion. Its coefficient of thermal expansion is designed to be between that of the SiC side bonding layer and the Al2O3 side bonding layer, so as to play a stress buffering role. Mo is dispersed in the form of fine particles to improve the high temperature strength of the brazing seam. Al2O3 side bonding layer: Its thickness is 20-50μm, and its composition is Ag-(20-30)Cu-(1-3)Ti-(1-3)Hf. It contains strong oxide active elements Ti and Hf. The two work together to reduce and wet the Al2O3 ceramic surface, forming a strong (Ti,Hf)-O compound reaction layer. The Hf in it can also refine the interfacial reaction products to improve the interfacial toughness.
2. A method for joining alumina ceramics and silicon carbide ceramics using the gradient active composite solder as described in claim 1, characterized in that, The method includes the following steps: Step S1: Ceramic surface pretreatment and preparation of gradient active composite solder The alumina ceramic and silicon carbide ceramic surfaces to be soldered are precision polished, then ultrasonically cleaned in acetone and ethanol in sequence, dried, and prepared with gradient active composite solder. Step S2: Assembly of brazing filler metal and workpiece The prepared gradient active composite solder is placed between the alumina ceramic and silicon carbide ceramic surfaces to be soldered, with the SiC side bonding layer facing the silicon carbide ceramic and the Al2O3 side bonding layer facing the alumina ceramic to form an assembly. Slight pressure is applied to ensure that each layer is in close contact. Step S3: Vacuum brazing connection Place the assembly in a vacuum brazing furnace, evacuate the furnace, and heat it according to the following procedure: Increase the temperature to 500-550℃ at a rate of 10-15℃ / min and hold for 10 minutes to completely remove the adsorbed gas; Increase the temperature to 860-920℃ at a rate of 5-8℃ / min, and hold for 8-20 minutes; After the heat preservation is completed, a staged slow cooling method is adopted: first, the temperature is slowly cooled to 700℃ at 3-5℃ / min, then cooled to 400℃ at 5-8℃ / min, and then cooled to room temperature with the furnace.
3. The gradient active composite brazing filler metal and connection method for joining alumina and silicon carbide ceramics according to claim 1, characterized in that, In step S1, the alumina ceramic surface to be soldered and the silicon carbide ceramic surface to be soldered are precision polished until Ra is less than or equal to 0.1 μm.
4. The gradient active composite brazing filler metal and connection method for joining alumina and silicon carbide ceramics according to claim 1, characterized in that, In step S2, the applied slight pressure is 5 to 15 kPa.
5. The gradient active composite brazing filler metal and connection method for joining alumina and silicon carbide ceramics according to claim 1, characterized in that, In step S3, the vacuum brazing furnace is evacuated to a vacuum level of less than or equal to 5 × 10⁻⁶. -3 Pa.