A brazing process for connecting alumina ceramics and titanium metal using low-activated brazing filler metal

Abstract

The present invention relates to the field of brazing process technology, and in particular to a brazing process for connecting alumina ceramics and metallic titanium with a low-activated brazing filler metal. Its technical solution includes the following steps: magnetron sputtering titanium film is applied to the surface of the alumina ceramic to be welded, the sputtering power is 80-150W, the argon pressure is 0.5-1.5Pa, the film thickness is 0.5-5μm, and after the film is coated, it is annealed by an inert gas, the annealing temperature is 400-550℃, and the holding time is 10-30min; the surface of the metallic titanium substrate is laser microtextured to form a periodic groove structure with a depth of 10-50μm. The present invention solves the problems of poor wettability of the brazing filler metal and ceramics, low joint strength, and stress cracks in the joints, while also meeting the requirements that the radioactive substances generated by the brazing filler metal under irradiation conditions can be released in a relatively short time, greatly shortening the equipment maintenance cycle and increasing the service life of the equipment.

Description

Technical Field

[0001] The invention relates to the technical field of brazing processes, in particular to a brazing process for connecting alumina ceramics and metallic titanium using a low-activation brazing filler metal. Background Art

[0002] Alumina ceramics are inorganic, non-metallic materials with excellent mechanical properties, high-temperature resistance, corrosion resistance, and electrical insulation. They are widely used in high-tech fields such as aerospace, electronics, chemical equipment, and medical devices. Titanium, due to its high specific strength, excellent corrosion resistance, and biocompatibility, also plays an important role in aerospace, chemical engineering, marine engineering, and biomedicine. The combination of alumina ceramics and titanium combines the excellent properties of both materials and is widely used in high-temperature sensors, electronic packaging, chemical reactors, and medical implants.

[0003] Due to the significant differences in physical, chemical and thermal properties between alumina ceramics and titanium metal, including large differences in thermal expansion coefficients, poor wettability, and the easy formation of brittle compounds at the bonding interface, traditional mechanical bonding or direct fusion welding is difficult to achieve a reliable connection between the two. These problems limit the application of alumina ceramics and titanium metal in complex working conditions with higher requirements. As an efficient connection method, brazing has become a research hotspot for achieving reliable connection between alumina ceramics and titanium metal due to its advantages such as relatively low operating temperature, simple process and stable joint performance. By selecting appropriate brazing filler metals and optimizing process parameters, brazing can overcome the wettability barriers between ceramics and metals and form a high-strength metallurgical bond. The connection process of alumina ceramic materials mainly needs to solve two problems: one is the wettability problem of the connection interface; the other is the stress buffering problem of the joint.

[0004] The accelerating tube is a key component of an accelerator. It accelerates electrons injected from the electron gun to high energies under the influence of a microwave electric field, ultimately striking a target to produce high-energy X-rays. Therefore, its operating environment is susceptible to radiation exposure. Currently, brazing of alumina ceramics primarily utilizes active brazing materials, such as Ag- and Cu-based brazing materials. However, Ag- and Cu-based brazing materials are highly activated elements and, upon irradiation, can generate radioactive substances, increasing equipment maintenance cycles and reducing service life.

[0005] In summary, the present application proposes a brazing process for connecting alumina ceramic and titanium metal using a low-activation brazing filler metal. Summary of the Invention

[0006] The purpose of the present invention is to address the problem that in the background technology, the brazing connection of alumina ceramics mainly adopts active brazing materials such as Ag-based brazing materials and Cu-based brazing materials to achieve the connection, which will produce radioactive substances after irradiation, increase the equipment maintenance cycle and reduce the service life. A brazing process for connecting alumina ceramics and metal titanium using low-activated brazing materials is proposed.

[0007] The technical solution of the present invention is a brazing process for connecting alumina ceramic and titanium metal using a low-activation brazing filler metal, comprising the following steps:

[0008] S1. Magnetron sputtering titanium coating is performed on the surface of the alumina ceramic to be welded. The sputtering power is 80-150W, the argon pressure is 0.5-1.5Pa, and the film thickness is 0.5-5μm. After coating, the film is annealed in an inert gas at a temperature of 400-550°C and a holding time of 10-30 minutes.

[0009] S2. The surface of the titanium substrate is laser microtextured to form a periodic groove structure with a depth of 10-50 μm, and then the oxide film is removed by ultrasonic cleaning with a mixed solution of hydrofluoric acid and nitric acid;

[0010] S3 using aluminum-based low activation solder, which has a composition of Al 96.8-97.65wt.%, Mg 2.2-2.8wt.%, Cr0.15-0.35wt.%, purity ≥ 99%, and the solder is preformed into a foil with a thickness of 0.02-0.5mm;

[0011] S4. The coated alumina ceramic, the titanium substrate and the brazing material foil are assembled in sequence to form a laminated structure of alumina ceramic / brazing material / titanium substrate / brazing material / alumina ceramic, and a preload pressure of 0.5-2MPa is applied;

[0012] S5. Perform a gradient temperature increase in a vacuum brazing furnace: in the first stage, increase the temperature to 300-400°C at a rate of 10-15°C / min and hold for 10-20 minutes to eliminate interfacial stress; in the second stage, increase the temperature to 690-790°C at a rate of 5-8°C / min and hold for 2-60 minutes, with a vacuum degree ≤1×10-3Pa; in the third stage, slowly cool the temperature to below 200°C at a rate of 3-5°C / min and then cool in the furnace.

[0013] Optionally, the protective gas for the inert gas annealing treatment in step S1 is argon or helium, the gas flow rate is 20-50 sccm, and the grain size of the film layer after annealing is 50-200 nm.

[0014] Optionally, in step S2, the groove pitch of the laser microtexturing is 50-150 μm, and the ratio of groove width to depth is 1:1.5-1:3.

[0015] Optionally, in step S3, the surface of the solder foil is doped with 0.01-0.1 wt.% of rare earth element Y or Ce by ion implantation, with a doping depth of 0.1-0.5 μm.

[0016] Optionally, an alternating magnetic field is applied during the heat preservation stage in step S5, with a magnetic field strength of 50-200 mT and a frequency of 1-10 kHz.

[0017] Optionally, after the brazing is completed, the joint is subjected to aging treatment at an aging temperature of 150-250° C. for a holding time of 2-8 h, and then cooled to room temperature at a rate of ≤10° C. / min.

[0018] Optionally, the pre-tightening pressure in step S4 is achieved by a shape memory alloy fixture, and the fixture undergoes phase change and contraction at the brazing temperature, and the pressure is dynamically adjusted to ±5% of the set value.

[0019] Optionally, the microstructure of the aluminum-based low-activation solder is a nanocrystalline structure, the grain size is ≤100 nm, and Mg2Si and CrAl7 precipitated phases are evenly distributed at the grain boundaries.

[0020] Optionally, the volume ratio of the mixed solution in step S2 is hydrofluoric acid: nitric acid: deionized water = 1:3:6, the ultrasonic cleaning power is 200-400 W, and the time is 5-15 min.

[0021] Optionally, during the gradient heating stage, the interface temperature distribution is monitored in real time by infrared thermal imaging, the temperature uniformity deviation is ≤±5°C, and the heating rate is dynamically adjusted by a feedback system.

[0022] Compared with the prior art, this application has at least one of the following beneficial technical effects:

[0023] By magnetron sputtering titanium film on the surface of alumina ceramic to be welded, the wettability of ceramic and solder can be enhanced. After plating, inert gas annealing treatment refines the film grains, improves the stability and bonding strength of the film; the periodic groove structure formed by laser micro-texturing treatment on the surface of the metal titanium substrate increases the contact area with the solder, improves the mechanical interlocking effect, and enhances the connection strength.

[0024] The use of aluminum-based low-activation solder with specific composition, its nanocrystalline structure and uniformly distributed precipitation phase at the grain boundaries improve the strength, toughness and corrosion resistance of the solder; the surface of the solder foil is doped with rare earth elements Y or Ce to further improve the wettability, fluidity and interface reaction of the solder, thereby improving the joint performance.

[0025] The gradient heating method can effectively eliminate interface stress and avoid problems such as material deformation and cracking caused by rapid temperature changes; applying an alternating magnetic field during the insulation stage can promote the diffusion of solder atoms, improve the uniformity of the joint structure, and enhance the joint strength and density; using infrared thermal imaging to monitor the interface temperature distribution in real time and dynamically adjust the heating rate to ensure temperature uniformity and improve the stability of brazing quality.

[0026] The pre-tightening pressure is achieved by using a shape memory alloy fixture, and the pressure can be dynamically adjusted according to demand at the brazing temperature to ensure stable pressure during the brazing process, ensure close contact between the brazing material and the base material, and improve the connection quality.

[0027] The present invention proposes a brazing method for alumina ceramics and titanium metal suitable for reducing the radioactive activity of an accelerating tube. The method solves the problems of poor wettability between the brazing material and the ceramic, low joint strength, and stress cracks in the joints. At the same time, the radioactive substances generated by the brazing material under irradiation conditions can be decontrolled in a relatively short time, thereby greatly shortening the equipment maintenance cycle and increasing the equipment service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart of a brazing process for joining alumina ceramic and titanium metal using a low-activation brazing filler metal;

[0029] Figure 2 This is a microstructure morphology of the interface of the joint between alumina ceramic and titanium metal brazed using low-activation brazing filler metal in Example 1;

[0030] Figure 3 This is a microstructural morphology of the interface of the joint between alumina ceramic and titanium metal brazed using low-activation brazing filler metal in Example 2;

[0031] Figure 4 This is a microstructure morphology of the interface of the joint between alumina ceramic and titanium metal brazed using low-activation brazing filler metal in Example 3;

[0032] Figure 5 This is the microstructure morphology of the interface of the alumina ceramic and metal titanium joint brazed using low-activation brazing filler metal in Example 4. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0034] Example 1

[0035] like Figure 1 As shown, a brazing process for connecting alumina ceramic and titanium metal using a low-activation brazing filler metal comprises the following steps:

[0036] S1. Magnetron sputtering titanium coating was applied to the surface of the alumina ceramic to be welded. The sputtering power was 80 W, the argon pressure was 0.5 Pa, and the film thickness was 0.5 μm. After coating, the film was annealed at an inert gas temperature of 400°C for 10 minutes. The shielding gas for the inert gas annealing was helium at a flow rate of 20 sccm. The grain size of the film after annealing was 50 nm.

[0037] S2. Laser microtexturing the surface of a titanium substrate to form a periodic groove structure with a depth of 10 μm. The oxide film was then removed by ultrasonic cleaning using a mixture of hydrofluoric acid and nitric acid. The groove spacing for laser microtexturing was 50 μm, and the groove width-to-depth ratio was 1:1.5. The volume ratio of the mixed solution was hydrofluoric acid: nitric acid: deionized water = 1:3:6. The ultrasonic cleaning power was 200 W for 5 minutes.

[0038] S3. An aluminum-based low-activation solder with a composition of 96.8 wt.% Al, 2.2 wt.% Mg, and 0.15 wt.% Cr, all with a purity of ≥99%, was preformed into a 0.02 mm thick foil. The solder foil surface was doped with 0.01 wt.% of the rare earth element Y by ion implantation to a doping depth of 0.1 μm. The microstructure of the aluminum-based low-activation solder was a nanocrystalline structure with a grain size of ≤100 nm, and Mg2Si and CrAl7 precipitates were uniformly distributed at the grain boundaries.

[0039] S4. Assemble the coated alumina ceramic, titanium substrate, and brazing filler metal foil in sequence to form a laminated structure of alumina ceramic / brazing filler metal / titanium substrate / brazing filler metal / alumina ceramic. Apply a preload pressure of 0.5 MPa. This preload pressure is achieved using a shape memory alloy fixture. The fixture undergoes phase change and contraction at the brazing temperature, dynamically adjusting the pressure to ±5% of the set value.

[0040] S5. Perform a gradient heating process in a vacuum brazing furnace: first, increase the temperature to 300°C at a rate of 10°C / min and hold for 10-20 minutes to eliminate interfacial stress; second, increase the temperature to 690°C at a rate of 5°C / min and hold for 2 minutes, with a vacuum degree ≤1×10-3Pa; third, slowly cool the temperature to below 200°C at a rate of 3°C / min and then cool with the furnace. During the holding period, apply an alternating magnetic field with a magnetic field strength of 50mT and a frequency of 1kHz.

[0041] After brazing, the joint is aged at 150°C for 2 hours and then cooled to room temperature at a rate of ≤10°C / min. Figure 2 As shown, there are no cracks;

[0042] During the gradient heating stage, the interface temperature distribution is monitored in real time by infrared thermal imaging, with the temperature uniformity deviation ≤±5°C, and the heating rate is dynamically adjusted through the feedback system.

[0043] In the process of gradient temperature rise in vacuum brazing furnace, an adaptive control algorithm is introduced, as follows:

[0044] Data acquisition: Use an infrared thermal imager to collect interface temperature distribution data at a frequency of once per second to obtain temperature values ​​at multiple temperature measurement points.

[0045] Comparison and judgment: The collected temperature of each temperature measurement point is compared with the preset temperature uniformity deviation range (≤±5℃). If the temperature of a certain point deviates from the set temperature by more than 5℃, the adjustment mechanism is triggered.

[0046] Adjustment Strategy: When the temperature is above the set point, the PID control algorithm proportionally reduces the heating element power based on the degree of deviation. For example, for every 1°C deviation, the power is reduced by 5%. When the temperature is below the set point, the heating element power is proportionally increased. For example, for every 1°C deviation, the power is increased by 5%. Furthermore, the heating time is dynamically adjusted according to the different stages of the heating process. In the first stage, the heating rate is 10°C / min. If the temperature deviation is large, the heating time of that stage is appropriately shortened or extended based on the power adjustment, with each adjustment step being 1 minute. The system continuously monitors and adjusts to ensure precise temperature control throughout the entire gradient heating process.

[0047] Example 2

[0048] like Figure 1 As shown, a brazing process for connecting alumina ceramic and titanium metal using a low-activation brazing filler metal comprises the following steps:

[0049] S1. Magnetron sputtering titanium coating was applied to the surface of the alumina ceramic to be welded. The sputtering power was 150 W, the argon pressure was 1.5 Pa, and the film thickness was 5 μm. After coating, the film was annealed in an inert gas atmosphere at 550°C for 30 minutes. The shielding gas during the inert gas annealing was argon at a flow rate of 50 sccm. The grain size of the film after annealing was 200 nm.

[0050] S2. Laser microtexturing the surface of a titanium substrate to form a periodic groove structure with a depth of 50 μm. The oxide film was then removed by ultrasonic cleaning using a mixture of hydrofluoric acid and nitric acid. The groove spacing for laser microtexturing was 150 μm, and the groove width-to-depth ratio was 1:3. The volume ratio of the mixed solution was hydrofluoric acid: nitric acid: deionized water = 1:3:6. The ultrasonic cleaning power was 400 W, and the cleaning time was 15 minutes.

[0051] S3. An aluminum-based low-activation solder with a composition of 97.65 wt.% Al, 2.8 wt.% Mg, and 0.35 wt.% Cr, all with a purity of ≥99%, was prefabricated into a 0.5 mm thick foil. The solder foil surface was doped with 0.1 wt.% of the rare earth element Ce by ion implantation to a doping depth of 0.1-0.5 μm. The microstructure of the aluminum-based low-activation solder was nanocrystalline with a grain size of ≤100 nm, and Mg2Si and CrAl7 precipitates were uniformly distributed at the grain boundaries.

[0052] S4. Assemble the coated alumina ceramic, titanium substrate, and brazing filler metal foil in sequence to form a laminated structure of alumina ceramic / brazing filler metal / titanium substrate / brazing filler metal / alumina ceramic. Apply a preload pressure of 2 MPa using a shape memory alloy fixture. The fixture undergoes phase change and contraction at the brazing temperature, dynamically adjusting the pressure to ±5% of the set value.

[0053] S5. Perform a gradient heating process in a vacuum brazing furnace: in the first stage, heat to 400°C at a rate of 15°C / min and hold for 20 minutes to eliminate interfacial stress; in the second stage, heat to 790°C at a rate of 8°C / min and hold for 60 minutes, with a vacuum degree ≤1×10-3Pa; in the third stage, slowly cool to below 200°C at a rate of 5°C / min and then cool with the furnace. During the holding stage, apply an alternating magnetic field with a magnetic field strength of 200 mT and a frequency of 10 kHz.

[0054] After brazing, the joint is aged at 250℃ for 8 hours, and then cooled to room temperature at a rate of ≤10℃ / min. Figure 3 As shown, there are no cracks;

[0055] During the gradient heating stage, the interface temperature distribution is monitored in real time by infrared thermal imaging, with the temperature uniformity deviation ≤±5°C, and the heating rate is dynamically adjusted through the feedback system.

[0056] An adaptive control algorithm is introduced to perform gradient temperature rise in a vacuum brazing furnace, as follows:

[0057] Data acquisition: Use an infrared thermal imager to collect interface temperature distribution data at a frequency of once per second to obtain temperature values ​​at multiple temperature measurement points.

[0058] Comparison and judgment: The collected temperature of each temperature measurement point is compared with the preset temperature uniformity deviation range (≤±5℃). If the temperature of a certain point deviates from the set temperature by more than 5℃, the adjustment mechanism is triggered.

[0059] Adjustment Strategy: When the temperature is above the set point, the PID control algorithm proportionally reduces the heating element power based on the degree of deviation. For example, for every 1°C deviation, the power is reduced by 5%. When the temperature is below the set point, the heating element power is proportionally increased. For example, for every 1°C deviation, the power is increased by 5%. Furthermore, the heating time is dynamically adjusted according to the different heating stages. In the first stage, the heating rate is 15°C / min. If the temperature deviation is large, the heating time of that stage is appropriately shortened or extended based on the power adjustment, with each adjustment step being 3 minutes. The system continuously monitors and adjusts to ensure precise temperature control throughout the entire gradient heating process.

[0060] Example 3

[0061] like Figure 1As shown, a brazing process for connecting alumina ceramic and titanium metal using a low-activation brazing filler metal comprises the following steps:

[0062] S1. Magnetron sputtering titanium film was applied to the surface of the alumina ceramic to be welded. The sputtering power was 100 W, the argon pressure was 1 Pa, and the film thickness was 2 μm. After coating, the film was annealed in an inert gas atmosphere at 450°C for 20 minutes. The shielding gas during the inert gas annealing was argon at a flow rate of 35 sccm. The grain size of the film after annealing was 100 nm.

[0063] S2. Laser microtexturing the surface of a titanium substrate to form a periodic groove structure with a depth of 30 μm. The oxide film was then removed by ultrasonic cleaning using a mixture of hydrofluoric acid and nitric acid. The groove spacing for laser microtexturing was 100 μm, and the groove width-to-depth ratio was 1:2. The volume ratio of the mixed solution was hydrofluoric acid: nitric acid: deionized water = 1:3:6. The ultrasonic cleaning power was 300 W, and the cleaning time was 10 min.

[0064] S3. An aluminum-based low-activation solder with a composition of 97.2 wt.% Al, 2.5 wt.% Mg, and 0.25 wt.% Cr, all with a purity of ≥99%, was preformed into a 0.2 mm thick foil. The solder foil surface was doped with 0.05 wt.% of the rare earth element Y by ion implantation to a doping depth of 0.3 μm. The microstructure of the aluminum-based low-activation solder was a nanocrystalline structure with a grain size of ≤100 nm, and Mg2Si and CrAl7 precipitates were uniformly distributed at the grain boundaries.

[0065] S4. Assemble the coated alumina ceramic, titanium substrate, and brazing filler metal foil in sequence to form a laminated structure of alumina ceramic / brazing filler metal / titanium substrate / brazing filler metal / alumina ceramic. Apply a preload pressure of 1 MPa using a shape memory alloy fixture. The fixture undergoes phase change and contraction at the brazing temperature, dynamically adjusting the pressure to ±5% of the set value.

[0066] S5. Perform a gradient heating process in a vacuum brazing furnace: in the first stage, heat the sample to 350°C at a rate of 12°C / min and hold it for 15 minutes to eliminate interfacial stress; in the second stage, heat the sample to 750°C at a rate of 6°C / min and hold it for 30 minutes, with a vacuum degree ≤1×10-3Pa; in the third stage, slowly cool the sample to below 200°C at a rate of 4°C / min and then cool it with the furnace. During the holding stage, apply an alternating magnetic field with a magnetic field strength of 100 mT and a frequency of 5 kHz.

[0067] After brazing, the joint was aged at 200°C for 5 hours, and then cooled to room temperature at a rate of ≤10°C / min to obtain the brazed alumina ceramic / titanium sample. Figure 4Shown is the microstructure morphology of the alumina ceramic / metal titanium sample, which has no cracks.

[0068] During the gradient heating stage, the interface temperature distribution is monitored in real time by infrared thermal imaging, with the temperature uniformity deviation ≤±5°C, and the heating rate is dynamically adjusted through the feedback system.

[0069] In this process of gradient heating, an adaptive control algorithm is introduced, as follows:

[0070] Data acquisition: Use an infrared thermal imager to collect interface temperature distribution data at a frequency of once per second to obtain temperature values ​​at multiple temperature measurement points.

[0071] Comparison and judgment: The collected temperature of each temperature measurement point is compared with the preset temperature uniformity deviation range (≤±5℃). If the temperature of a certain point deviates from the set temperature by more than 5℃, the adjustment mechanism is triggered.

[0072] Adjustment Strategy: When the temperature is above the set point, the PID control algorithm proportionally reduces the heating element power based on the degree of deviation. For example, for every 1°C deviation, the power is reduced by 5%. When the temperature is below the set point, the heating element power is proportionally increased. For example, for every 1°C deviation, the power is increased by 5%. Furthermore, the heating time is dynamically adjusted according to the different heating stages. In the first stage, the heating rate is 12°C / min. If the temperature deviation is large, the heating time of that stage is appropriately shortened or extended based on the power adjustment, with each adjustment step being 2 minutes. The system continuously monitors and adjusts to ensure precise temperature control throughout the entire gradient heating process.

[0073] Example 4

[0074] like Figure 1 As shown, a brazing process for connecting alumina ceramic and titanium metal using a low-activation brazing filler metal comprises the following steps:

[0075] S1. Magnetron sputtering titanium coating was applied to the surface of the alumina ceramic to be welded. The sputtering power was 120 W, the argon pressure was 1.3 Pa, and the film thickness was 4.5 μm. After coating, the film was annealed in an inert gas atmosphere at 520°C for 28 minutes. The shielding gas used in the inert gas annealing was argon at a flow rate of 45 sccm. The grain size of the film after annealing was 180 nm.

[0076] S2. Laser microtexturing the surface of a titanium substrate to form a periodic groove structure with a depth of 45 μm. The oxide film was then removed by ultrasonic cleaning using a mixture of hydrofluoric acid and nitric acid. The groove spacing for the laser microtexturing was 140 μm, and the groove width-to-depth ratio was 1:2.5. The volume ratio of the mixed solution was hydrofluoric acid: nitric acid: deionized water = 1:3:6. The ultrasonic cleaning power was 350 W, and the cleaning time was 13 minutes.

[0077] S3. An aluminum-based low-activation solder with a composition of 97.45 wt.% Al, 2.6 wt.% Mg, and 0.20 wt.% Cr, all with a purity of ≥99%, was prefabricated into a 0.45 mm thick foil. The solder foil surface was doped with 0.09 wt.% of the rare earth element Y by ion implantation to a doping depth of 0.2 μm. The microstructure of the aluminum-based low-activation solder was nanocrystalline with a grain size of ≤100 nm, and Mg2Si and CrAl7 precipitates were uniformly distributed at the grain boundaries.

[0078] S4. Assemble the coated alumina ceramic, titanium substrate, and brazing filler metal foil in sequence to form a laminated structure of alumina ceramic / brazing filler metal / titanium substrate / brazing filler metal / alumina ceramic. Apply a preload pressure of 1.8 MPa. This preload pressure is achieved using a shape memory alloy fixture. The fixture undergoes phase change and contraction at the brazing temperature, dynamically adjusting the pressure to ±5% of the set value.

[0079] S5. Perform a gradient heating process in a vacuum brazing furnace: in the first stage, heat the material to 380°C at a rate of 13°C / min and hold it for 18 minutes to eliminate interfacial stress; in the second stage, heat the material to 720°C at a rate of 7°C / min and hold it for 40 minutes, with a vacuum degree ≤1×10-3Pa; in the third stage, slowly cool the material to below 200°C at a rate of 3.5°C / min and then cool it with the furnace. During the holding period, apply an alternating magnetic field with a magnetic field strength of 175mT and a frequency of 9kHz.

[0080] After brazing, the joint was aged at 220°C for 7 hours and then cooled to room temperature at a rate of ≤10°C / min. Figure 5 As shown, there are no cracks.

[0081] During the gradient heating stage, the interface temperature distribution is monitored in real time by infrared thermal imaging, with the temperature uniformity deviation ≤±5°C, and the heating rate is dynamically adjusted through the feedback system.

[0082] In the process of gradient temperature rise in vacuum brazing furnace, an adaptive control algorithm is introduced, as follows:

[0083] Data acquisition: Use an infrared thermal imager to collect interface temperature distribution data at a frequency of once per second to obtain temperature values ​​at multiple temperature measurement points.

[0084] Comparison and judgment: The collected temperature of each temperature measurement point is compared with the preset temperature uniformity deviation range (≤±5℃). If the temperature of a certain point deviates from the set temperature by more than 5℃, the adjustment mechanism is triggered.

[0085] Adjustment Strategy: When the temperature is above the set point, the PID control algorithm proportionally reduces the heating element power based on the degree of deviation. For example, for every 1°C deviation, the power is reduced by 5%. When the temperature is below the set point, the heating element power is proportionally increased. For example, for every 1°C deviation, the power is increased by 5%. Furthermore, the heating time is dynamically adjusted according to the different heating stages. In the first stage, the heating rate is 14°C / min. If the temperature deviation is large, the heating time of that stage is appropriately shortened or extended based on the power adjustment, with each adjustment step being 2.5 minutes. The system continuously monitors and adjusts to ensure precise temperature control throughout the entire gradient heating process.

[0086] This invention enhances the wettability of the alumina ceramic and the brazing material by magnetron sputtering a titanium film on the surface to be welded. Post-coating, inert gas annealing refines the film grains, improving its stability and bonding strength. Laser microtexturing of the titanium substrate creates a periodic groove structure that increases the contact area with the brazing material, enhancing mechanical interlocking and strengthening the connection. A specific aluminum-based low-activation brazing material with a nanocrystalline structure and uniformly distributed precipitates at the grain boundaries enhances its strength, toughness, and corrosion resistance. The brazing foil is doped with rare earth elements Y or Ce to further improve its wettability, fluidity, and interfacial reaction, ultimately enhancing joint performance.

[0087] It is worth noting that the gradient heating method can effectively eliminate interface stress and avoid problems such as material deformation and cracking caused by rapid temperature changes; applying an alternating magnetic field during the insulation stage can promote the diffusion of solder atoms, improve the uniformity of the joint structure, and enhance the strength and density of the joint; using infrared thermal imaging to monitor the interface temperature distribution in real time and dynamically adjust the heating rate to ensure temperature uniformity and improve the stability of brazing quality. The pre-tightening pressure is achieved by using shape memory alloy fixtures, and the pressure can be dynamically adjusted according to demand at the brazing temperature to ensure stable pressure during the brazing process, ensure close contact between the solder and the base material, and improve the connection quality. Aging treatment after brazing can eliminate residual stress, improve the joint structure and performance, and enhance the strength, hardness and corrosion resistance of the joint, so that the joint can meet the needs of more complex working conditions.

[0088] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant inspirations of the above embodiments, those skilled in the art may make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A brazing process for connecting alumina ceramics and titanium metal using low-activation brazing filler metal, characterized in that: The following steps are involved: S1. Magnetron sputtering titanium coating is performed on the surface of the alumina ceramic to be welded. The sputtering power is 80-150W, the argon pressure is 0.5-1.5Pa, and the film thickness is 0.5-5μm. After coating, the film is annealed in an inert gas at a temperature of 400-550°C and a holding time of 10-30 minutes. S2. The surface of the titanium substrate is laser microtextured to form a periodic groove structure with a depth of 10-50 μm, and then the oxide film is removed by ultrasonic cleaning with a mixed solution of hydrofluoric acid and nitric acid; S3 using aluminum-based low activation solder, which has a composition of Al 96.8-97.65wt.%, Mg 2.2-2.8wt.%, Cr 0.15-0.35wt.%, purity ≥ 99%, and the solder is preformed into a foil with a thickness of 0.02-0.5mm; S4. The coated alumina ceramic, the titanium substrate and the brazing material foil are assembled in sequence to form a laminated structure of alumina ceramic / brazing material / titanium substrate / brazing material / alumina ceramic, and a preload pressure of 0.5-2MPa is applied; S5. Perform a temperature ramp in a vacuum brazing furnace: first, increase the temperature to 300-400°C at a rate of 10-15°C / min and hold for 10-20 minutes to eliminate interfacial stress. In the second stage, the temperature is raised to 690-790℃ at 5-8℃ / min, kept at this temperature for 2-60min, and the vacuum degree is ≤1×10-3Pa; in the third stage, the temperature is slowly cooled to below 200℃ at 3-5℃ / min and then cooled with the furnace.

2. The brazing process according to claim 1, characterized in that The protective gas for the inert gas annealing treatment in step S1 is argon or helium, with a gas flow rate of 20-50 sccm. The grain size of the film layer after annealing is 50-200 nm.

3. The brazing process according to claim 1, characterized in that The groove pitch of the laser microtexturing in step S2 is 50-150 μm, and the ratio of groove width to depth is 1:1.5-1:

3.

4. The brazing process according to claim 1, characterized in that In step S3, the surface of the solder foil is doped with 0.01-0.1 wt.% of rare earth element Y or Ce by ion implantation, with a doping depth of 0.1-0.5 μm.

5. The brazing process according to claim 1, characterized in that In the step S5, an alternating magnetic field is applied during the heat preservation stage, with a magnetic field strength of 50-200 mT and a frequency of 1-10 kHz.

6. The brazing process according to claim 1, characterized in that: After the brazing is completed, the joint is subjected to aging treatment at a temperature of 150-250° C. for a holding time of 2-8 hours, and then cooled to room temperature at a rate of ≤10° C. / min.

7. The brazing process according to claim 1, characterized in that In step S4, the pre-tightening pressure is achieved by a shape memory alloy fixture. The fixture undergoes phase change and shrinkage at the brazing temperature, and the pressure is dynamically adjusted to ±5% of the set value.

8. The brazing process according to claim 1, characterized in that The microstructure of the aluminum-based low-activation solder is a nanocrystalline structure, the grain size is ≤100nm, and Mg2Si and CrAl7 precipitation phases are evenly distributed at the grain boundaries.

9. The brazing process according to claim 1, characterized in that: The volume ratio of the mixed solution in step S2 is hydrofluoric acid: nitric acid: deionized water = 1:3:6, the ultrasonic cleaning power is 200-400W, and the time is 5-15 minutes.

10. The brazing process according to claim 1, characterized in that: During the gradient heating stage, the interface temperature distribution is monitored in real time by infrared thermal imaging, the temperature uniformity deviation is ≤±5°C, and the heating rate is dynamically adjusted by a feedback system.

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