Ceramic sealed vacuum electrode and brazing method

Abstract

The application discloses a ceramic sealed vacuum electrode and a brazing method, and the ceramic sealed vacuum electrode comprises a conductive core column, a ceramic block, a first sleeve and a second sleeve which are sleeved on the conductive core column; the first sleeve and the second sleeve are made of Kovar alloy; the ceramic block comprises a cylinder, a circular plate arranged at the upper end of the cylinder and an annular plate arranged at the middle part of the cylinder; the inner side surface of the first sleeve is respectively brazed and connected with the lower surface and the outer side surface of the circular plate; the inner side surface of the second sleeve is respectively brazed and connected with the lower surface and the outer side surface of the annular plate; the application has the characteristics that the La component segregation during smelting of AgCuTi active filler can be effectively avoided, the hard and brittle phase in the weld is effectively refined, the local stress concentration in the weld is avoided, the residual thermal stress of the weld is reduced, the shear strength of the weld is improved, and the reliability and stability of the ceramic sealed vacuum electrode are ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vacuum brazing, in particular to a ceramic sealed vacuum electrode and a brazing method. BACKGROUND

[0002] The ceramic sealed vacuum electrode is widely used in the fields of vacuum equipment, electron tubes, vacuum circuit breakers and nuclear industry, and is used to realize electric signal transmission in a vacuum environment while providing high reliable sealing.

[0003] The ceramic sealed vacuum electrode is usually connected by brazing, but because the thermal expansion coefficients of the insulating ceramic and the conductive core column are quite different, a large thermal stress is generated during brazing. The excessive thermal stress can cause cracks in the ceramic sealed vacuum electrode during service, resulting in poor sealing and affecting the reliability and service life of the equipment.

[0004] Currently, in order to reduce the residual thermal stress and ensure the sealing of the ceramic sealed vacuum electrode in a high temperature and high pressure environment, a particle phase with a thermal expansion coefficient between that of the filler metal and the ceramic base material is added to the filler metal to form a composite filler metal, thereby reducing the difference in thermal expansion coefficient between the overall filler metal and the ceramic base material and reducing the residual thermal stress. However, too much content of the particle phase can cause poor wettability of the composite filler metal, resulting in a decrease in the bonding strength of the brazing part of the ceramic sealed vacuum electrode.

[0005] The AgCuTi filler metal is modified by smelting with a rare earth element La to control the microstructure of the brazing alloy. However, the diffusion speed of the La element in the filler metal is slow, which can cause local excessive or insufficient La element, affecting the brazing performance of the filler metal. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art and provides a ceramic sealed vacuum electrode and a brazing method.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] A ceramic sealed vacuum electrode passes through a flange; the ceramic sealed vacuum electrode comprises a conductive core column, a ceramic block sleeved on the conductive core column, a first sleeve and a second sleeve; the first sleeve and the second sleeve are both made of Kovar alloy; the ceramic block comprises a cylinder, a circular plate arranged at the upper end of the cylinder and an annular plate arranged at the middle part of the cylinder, the inner side surface of the first sleeve is brazed to the lower surface and the outer side surface of the circular plate, and the inner side surface of the sleeve is brazed to the lower surface and the outer side surface of the annular plate; the flange is provided with a stepped hole, the outer side surface of the first sleeve is brazed to the upper part of the inner side surface of the stepped hole, and the outer side surface of the second sleeve is brazed to the lower part of the inner side surface of the stepped hole.

[0009] The first sleeve and the second sleeve are made of Kovar alloy material, the Kovar alloy has good thermal expansion matching performance, and can effectively relieve the residual stress between the flange and the ceramic block. The stepped hole plays a role in supporting the ceramic block through the unique stepped structure inside.

[0010] As preferred, the conductive core column is made of molybdenum, stainless steel or oxygen-free copper material.

[0011] As preferred, the ceramic block is made of Al2O3 or zirconia material.

[0012] As preferred, the brazing is Ag-based composite filler, which is composed of mixed filler and organic binder, the mass percentage of the mixed filler is 85%-90%, and the rest is organic binder.

[0013] The mixed filler is composed of rare earth element La powder and AgCuTi active filler, the mass percentage of the rare earth element La powder in the mixed filler is 0.5%-2.5%, and the rest is AgCuTi active filler; the mixed filler is obtained by mechanically ball-milling the rare earth element La powder and the AgCuTi active filler, and the Ag-based composite filler is obtained by mixing the mixed filler with the organic binder.

[0014] After the rare earth element La powder is added to the AgCuTi active filler, the La element forms fine nucleation points in the AgCuTi molten filler, improves the nucleation rate of intermetallic compounds, and inhibits their growth and coarsening; the addition of La element reduces the energy of interfacial reaction, and its strong reducing property helps to control the reaction rate of Cu element and Ti element; the La element can change the formation temperature and morphology of intermetallic compounds in the filler, so that it nucleates at a lower temperature and forms a finer particle structure.

[0015] The La element reacts with O2 in the AgCuTi active filler to reduce the oxidation of active element Ti; La reacts with O to form rare earth oxides, which act as nucleation points for the growth of Cu-Ti phase, promoting the non-uniform nucleation of Cu-Ti phase; the atomic radius of La element is larger than that of Cu element, and the solid solubility of La element in AgCuTi active filler is lower, so the La element and its compounds are distributed at the interface, which reduces the grain boundary energy and the driving force for grain growth, effectively prevents the growth of grains, and maintains the fine morphology of Cu-Ti phase grains; the dispersed hard and brittle phase not only improves the mechanical properties of the weld, but also makes the locally concentrated stress more uniformly distributed.

[0016] The application adds rare earth element La powder to AgCuTi active filler metal, mixes the two by mechanical ball milling, effectively avoids composition segregation of the rare earth element La during smelting, effectively refines the hard and brittle phase in the weld by the characteristics of the rare earth element La, avoids local stress concentration in the weld, and reduces the residual thermal stress of the weld.

[0017] As preferred, the mass percentage of Ti in the AgCuTi active filler metal is ≤5%, and the mass percentage of Ag in both Ag and Cu in the AgCuTi active filler metal is 68%-76%.

[0018] As preferred, the particle diameter of the AgCuTi active filler metal is 1-100 mu m, and the particle diameter of the rare earth element La powder is 10-100 mu m.

[0019] As preferred, the organic binder is composed of solvent, thickening agent, dispersant, antioxidant, thixotropic agent and corrosion inhibitor; the mass percentage of the solvent, thickening agent, dispersant, antioxidant, thixotropic agent and corrosion inhibitor in the organic binder is (55%-60%), (4%-8%), (20%-30%), (5%-10%), (1%-3%) and (1%-3%); the solvent, thickening agent, dispersant, antioxidant, thixotropic agent and corrosion inhibitor are added into a beaker in proportion, inert gas is introduced into the beaker, each component in the beaker is heated to 40-50 DEG C, and each component in the beaker is subjected to constant temperature water bath magnetic stirring for 50-60 min by using a tool to obtain the prepared organic binder.

[0020] A brazing method of a ceramic sealed vacuum electrode, the brazing process comprising the following steps:

[0021] Step 1, the ceramic block is sleeved outside the conductive core column, and the ceramic block and the conductive core column are connected in an interference fit; the ceramic block is used to ensure that the conductive core column is isolated from the external environment;

[0022] The Ag-based composite filler metal with a thickness of 0.4-0.6 mm is applied on the upper and lower parts of the ceramic block, and the first sleeve and the second sleeve are respectively sleeved on the upper and lower parts of the ceramic block;

[0023] Step 2, the Ag-based composite filler metal with a thickness of 0.4-0.6 mm is applied on the outside of the first sleeve and the second sleeve to obtain an assembly;

[0024] The stepped hole effectively prevents the flow loss of the Ag-based composite filler metal during the brazing process by the unique stepped structure inside, and plays a mechanical supporting role.

[0025] The assembly is inserted into the mounting hole provided on the flange from top to bottom, and the ceramic sealed vacuum electrode is assembled;

[0026] Step 3: Invert several assembled ceramic-sealed vacuum electrodes and place them into the vacuum brazing furnace, positioning the first sleeve below the second sleeve. Ensure the lower end of the conductive core of each ceramic-sealed vacuum electrode is in contact with the upper surface of the horizontally positioned graphite plate in the vacuum brazing furnace. Place a weight ring on the upper surface of the flange to press it down. Use the three-stage pump of the vacuum brazing furnace to evacuate the furnace, achieving a vacuum level of 5 × 10⁻⁶. -3 the following;

[0027] Step 4, Pre-welding heating:

[0028] The temperature inside the vacuum brazing furnace is raised from room temperature to T1, where T1 is in the range of 240℃-260℃, the heating rate is ≤10℃ / min, and the holding time is 30min-45min.

[0029] Heating to T1 can effectively remove low-temperature components of organic binders and moisture from the solder.

[0030] The temperature inside the vacuum brazing furnace is raised from T1 to T2, where T2 ranges from 580℃ to 620℃, the heating rate is ≤10℃ / min, and the holding time is 15min-30min.

[0031] T2 is selected based on the melting point of the organic binder in the brazing filler metal to ensure that the organic binder is completely removed at this temperature, thus avoiding affecting the vacuum level during subsequent brazing.

[0032] The temperature inside the vacuum brazing furnace is raised from T2 to T3, with T3 ranging from 740℃ to 760℃, a heating rate of ≤5℃ / min, and a holding time of 15min to 30min.

[0033] Increasing the temperature to T3 ensures that the ceramic-sealed vacuum electrode is heated evenly as it approaches the melting point of the brazing filler metal, thus preparing it for subsequent brazing.

[0034] Step 5, perform brazing:

[0035] The temperature inside the vacuum brazing furnace is raised from T3 to T4, with T4 ranging from 870℃ to 900℃. The heating rate is ≤3℃ / min, and the holding time is 10min-20min, at which point the Ag-based composite brazing filler metal melts.

[0036] The holding time can be determined based on the amount of material fed into the furnace. Too long a holding time can easily result in an excessively thick reaction layer on the ceramic side, while too short a holding time is not conducive to sufficient wetting of the brazing filler metal, both of which will reduce the bonding strength.

[0037] Step 6, Cooling down:

[0038] The temperature inside the vacuum brazing furnace is reduced from T4 to T5, with T5 ranging from 810℃ to 820℃ and a cooling rate of 15℃ / min to 20℃ / min. Ag-based composite brazing filler metal is used to weld the first sleeve to the circular plate and the upper part of the stepped hole, respectively. Ag-based composite brazing filler metal is used to weld the second sleeve to the annular plate and the lower part of the stepped hole, respectively.

[0039] Allow the temperature inside the vacuum brazing furnace to cool from T5 to room temperature, then open the vacuum brazing furnace and remove each ceramic sealed vacuum electrode.

[0040] Initially, rapid cooling is used, at which point the brazing filler metal is still in a liquid state, and the shrinkage of the brazed parts is not constrained. This is also to avoid excessive reaction between the brazing filler metal and the various components.

[0041] The temperature inside the vacuum brazing furnace is cooled from T5 to room temperature along with the furnace. The vacuum brazing furnace is then opened, and each ceramic sealed vacuum electrode is removed. The purpose of slow cooling is to minimize the residual stress generated by brazing.

[0042] Preferably, a conductive core pretreatment step is included before step 1:

[0043] Step 9-1: Using hot extrusion, a silver-copper alloy sheet is coated onto the conductive core. The silver-copper alloy sheet and the conductive core are heated to 780℃-800℃, and the silver-copper alloy sheet and the conductive core are combined using an extruder, so that the silver-copper alloy sheet is uniformly coated on the surface of the conductive core. After cooling and shaping, the coated composite conductive core is obtained. The composite conductive core is then drawn and annealed to ensure a stable bond between the silver-copper alloy sheet and the conductive core, ultimately obtaining a conductive core with a silver-copper coating.

[0044] Preferably, step 9-1 is followed by the following steps:

[0045] A Ti metal film was formed on the surface of a conductive core using a magnetron sputtering apparatus.

[0046] The Ti metal film ensures a reliable bond between the conductive core and the ceramic block, and enables the ceramic block to be wetted during brazing.

[0047] The conductive core was placed in the sputtering chamber of the magnetron sputtering instrument, and the Ti metal target was fixed on the target holder inside the sputtering chamber. The sputtering chamber was evacuated to 1.0 × 10⁻⁶. -3 Below Pa, the substrate temperature on the sample turntable is raised to 300℃-400℃ by heating the substrate. Argon gas is introduced into the sputtering chamber, and the argon gas flow rate is controlled at 25sccm-30sccm. The bias voltage is adjusted to 500V-550V, and the Ti metal target is pre-sputtered for 40min-50min to remove the oxide layer on the surface of the Ti metal target. Removing the oxide layer can ensure the purity and quality of the Ti metal film.

[0048] Adjust the substrate bias voltage to 90V-110V, control the argon flow rate to 15sccm-20sccm, and increase the gas pressure in the sputtering chamber to 2.0Pa-2.5Pa. This raises the target voltage of the Ti metal target to 280V-300V for glow discharge, ionizing the argon gas and generating argon ions. These argon ions bombard the Ti metal target, causing sputtering of the Ti metal target atoms. Adjust the working gas pressure in the sputtering chamber to 0.6Pa-0.8Pa and perform pre-sputtering for 15min-20min. After the target voltage and current of the Ti metal target stabilize, control the rotation speed of the sample turntable to 10r / min-12r / min, and adjust the target voltage and current of the Ti metal target to achieve a power of 260W-270W. Continue sputtering for 30min-40min to form a Ti metal film on the surface of the conductive core.

[0049] In industrial production, the conductive core and the ceramic block are often connected by an interference fit, and then a brazing filler metal is applied to the connection point on the upper surface for vacuum brazing to achieve a seal.

[0050] This invention employs a coating, heating, and drawing process to connect the silver-copper alloy layer to the conductive core through metallic bonding. Subsequently, a Ti metal film is grown in situ on the outer side of the conductive core using a magnetron sputtering coating process. Compared with existing technologies, the connection between the conductive core and the silver-copper alloy layer in this invention is more robust. Furthermore, during the brazing process, the Ti metal film on the surface of the conductive core reacts with the ceramic block first. Ti can wet the ceramic phase, enhancing the bonding force between the conductive core and the ceramic block, thus ensuring a sealed, stable, and reliable connection between the conductive core and the ceramic block.

[0051] Therefore, the present invention has the following beneficial effects:

[0052] It effectively avoids La component segregation during AgCuTi active brazing filler metal melting, and utilizes the characteristics of rare earth element La to effectively refine the hard and brittle phase in the weld, avoids local stress concentration in the weld, reduces the residual thermal stress of the weld of ceramic sealed vacuum electrode, improves the shear strength of the weld, and ensures the reliability and stability of ceramic sealed vacuum electrode. Attached Figure Description

[0053] Figure 1 This is a cross-sectional view of one embodiment of the present invention;

[0054] Figure 2 This is a SEM image of the weld seam of Embodiment 1, Embodiment 4, Embodiment 5 and Comparative Example 2 of the present invention;

[0055] Figure 3 This is a SEM image of the weld seam in Embodiment 5 of the present invention. Detailed Implementation

[0056] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0057] Example 1

[0058] The wide-range ionization vacuum gauge tube in the vacuum equipment includes a cathode, an anode, a collecting electrode, and a flange. This invention is used to braze the collecting electrode and the flange. The collecting electrode is the ceramic sealed vacuum electrode in this invention.

[0059] like Figure 1 The illustrated embodiment is a ceramic-sealed vacuum electrode that passes through a flange 6 made of Al2O3 ceramic material. The ceramic-sealed vacuum electrode includes a conductive core 4 made of 316 stainless steel, an Al2O3 ceramic block, a first sleeve 1, and a second sleeve 3 fitted onto the conductive core 4. Both the first and second sleeves are made of Kovar alloy. The Al2O3 ceramic block includes a cylinder 21, a circular plate 22 at the upper end of the cylinder, and an annular plate 23 in the middle of the cylinder. The inner side of the first sleeve is brazed to the lower surface and outer side of the circular plate, respectively. The inner side of the second sleeve is brazed to the lower surface and outer side of the annular plate, respectively. The flange has a stepped hole 61. The outer side of the first sleeve is brazed to the upper part of the inner side of the stepped hole, and the outer side of the second sleeve is brazed to the lower part of the inner side of the stepped hole.

[0060] The brazing uses Ag-based composite brazing alloy, which is composed of a mixed brazing alloy and an organic binder. The mixed brazing alloy accounts for 85% of the mass, and the remainder is the organic binder.

[0061] The mixed solder is composed of rare earth element La powder and AgCuTi active solder. The mass percentage of rare earth element La powder in the mixed solder is 0.5%, and the balance is AgCuTi active solder. The rare earth element La powder and AgCuTi active solder are mechanically ball-milled and mixed to obtain the mixed solder. The mixed solder is then mixed with an organic binder to obtain the prepared Ag-based composite solder.

[0062] The mass percentage of Ti in AgCuTi active solder is 3%; the mass percentage of Ag in AgCuTi active solder is 72% and the mass percentage of Cu is 28%.

[0063] The AgCuTi active solder has a particle diameter of 80 μm, and the rare earth element La powder has a particle diameter of 850 μm.

[0064] The organic binder is composed of solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor. The mass percentages of the solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor in the organic binder are 58%, 8%, 20%, 10%, 1%, and 3%, respectively. The solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor are added to a beaker in the specified proportions. An inert gas is introduced into the beaker, and the components in the beaker are heated to 45°C. The components in the beaker are then magnetically stirred in a constant-temperature water bath for 55 minutes using a tool to obtain the prepared organic binder.

[0065] A brazing method for a ceramic sealed vacuum electrode, the brazing process comprising the following steps:

[0066] Before brazing, the surfaces of the Al2O3 ceramic block and the 316 stainless steel conductive core are polished step by step with sandpaper until they are free of scratches. Then, the Al2O3 ceramic block and the 316 stainless steel conductive core are ultrasonically cleaned in an alcohol solution and finally dried to obtain the surface-treated Al2O3 ceramic block and the 316 stainless steel conductive core.

[0067] Step 01: Using hot extrusion, the silver-copper alloy sheet 8 is coated onto the conductive core. The silver-copper alloy sheet and the conductive core are heated to 800°C, and the silver-copper alloy sheet and the conductive core are combined using an extruder, so that the silver-copper alloy sheet is uniformly coated on the surface of the conductive core. After cooling and shaping, the coated composite conductive core is obtained. The composite conductive core is then drawn and annealed to ensure that the silver-copper alloy sheet and the conductive core are stably bonded, and finally a conductive core with a silver-copper coating is obtained.

[0068] Step 02: A Ti metal film is formed on the surface of the conductive core using a magnetron sputtering apparatus.

[0069] The conductive core was placed in the sputtering chamber of the magnetron sputtering instrument, and the Ti metal target was fixed on the target holder inside the sputtering chamber. The sputtering chamber was evacuated to 1.0 × 10⁻⁶. -3 Below Pa, the temperature of the substrate on the sample turntable is raised to 350℃ by heating the substrate. Argon gas is introduced into the sputtering chamber, the argon gas flow rate is controlled at 30 sccm, the bias voltage is adjusted to 540V, and the Ti metal target is pre-sputtered for 50 minutes to remove the oxide layer on the surface of the Ti metal target.

[0070] The substrate bias voltage was adjusted to 100V, the argon flow rate was controlled to 18sccm, and the gas pressure in the sputtering chamber was increased to 2.3Pa. The voltage of the target holder for the Ti metal target was increased to 290V to perform glow discharge, which ionized the argon gas and generated argon ions. The argon ions bombarded the Ti metal target, causing the metal atoms of the Ti metal target to be sputtered. The working gas pressure in the sputtering chamber was adjusted to 0.7Pa, and pre-sputtering was performed for 18min. After the voltage and current of the Ti metal target holder stabilized, the rotation speed of the sample turntable was controlled to 11r / min, and the voltage and current of the Ti metal target holder were adjusted to achieve a power of 265W. Sputtering was continued for 30min to form a 0.8μm thick Ti metal film on the surface of the conductive core.

[0071] Step 1: Place the ceramic block over the outside of the conductive core post to make the ceramic block and the conductive core post an interference fit connection;

[0072] Apply Ag-based composite brazing filler metal 5 with a thickness of 0.5 mm to the upper and lower parts of the outer side of the ceramic block, and then fit the first sleeve and the second sleeve onto the upper and lower parts of the outer side of the ceramic block, respectively.

[0073] Step 2: Apply Ag-based composite brazing filler metal with a thickness of 0.55 mm to the outside of the first and second sleeves to obtain the assembly; insert the assembly into the mounting hole on the flange from top to bottom, and the ceramic sealed vacuum electrode assembly is completed.

[0074] Step 3: Invert multiple assembled ceramic-sealed vacuum electrodes and place them into the vacuum brazing furnace, positioning the first sleeve below the second sleeve. Ensure the lower end of the conductive core of each ceramic-sealed vacuum electrode is in contact with the upper surface of the horizontally positioned graphite plate in the vacuum brazing furnace. Place a weight ring on the upper surface of the flange to press it down. Use the three-stage pump of the vacuum brazing furnace to evacuate the furnace, achieving a vacuum level of 5 × 10⁻⁶. -3 the following;

[0075] Step 4, Pre-welding heating:

[0076] The temperature inside the vacuum brazing furnace is raised from room temperature to T1, where T1 is 250℃, the heating rate is ≤10℃ / min, and the holding time is 40min.

[0077] The temperature inside the vacuum brazing furnace is raised from T1 to T2, where T2 is in the range of 600℃, the heating rate is ≤10℃ / min, and the holding time is 25min.

[0078] The temperature inside the vacuum brazing furnace is raised from T2 to T3, where T3 is 750℃, the heating rate is ≤5℃ / min, and the holding time is 20min.

[0079] Step 5, perform brazing:

[0080] The temperature inside the vacuum brazing furnace is raised from T3 to T4, with T4 ranging from 880℃. The heating rate is ≤3℃ / min, and the temperature is held for 15min until the Ag-based composite brazing filler metal melts.

[0081] Step 6, Cooling down:

[0082] The temperature inside the vacuum brazing furnace is reduced from T4 to T5, with T5 ranging from 815℃ and a cooling rate of 18℃ / min. Ag-based composite brazing filler metal is used to weld the first sleeve to the circular plate and the upper part of the stepped hole, respectively. Ag-based composite brazing filler metal is used to weld the second sleeve to the annular plate and the lower part of the stepped hole, respectively.

[0083] Allow the temperature inside the vacuum brazing furnace to cool from T5 to room temperature, then open the vacuum brazing furnace and remove each ceramic sealed vacuum electrode.

[0084] Example 2

[0085] The mass percentages of solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor in the organic binder of Example 2 are 59%, 5%, 25%, 8%, 2%, and 1%, respectively.

[0086] Sputtering was performed continuously for 35 minutes to form a 1.2 μm thick Ti metal film on the surface of the conductive core.

[0087] The other structures and methods in Example 2 are the same as those in Example 1;

[0088] Example 3

[0089] The mass percentages of solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor in the organic binder in Example 3 are 60%, 5%, 22%, 9%, 2%, and 2%, respectively.

[0090] A 1.5 μm thick Ti metal film was formed on the surface of the conductive core by continuous sputtering for 40 min.

[0091] The other structures and methods in Example 3 are the same as those in Example 1;

[0092] Example 4

[0093] In Example 4, the mass percentage of the Ag-based composite solder was 90%, and the mass percentage of rare earth element La powder in the solder was 1.5%.

[0094] The mass percentages of solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor in the organic binder are: 59%, 4%, 30%, 5%, 1%, and 1%, respectively.

[0095] Sputtering was performed continuously for 30 minutes to form a 0.8 μm thick Ti metal film on the surface of the conductive core.

[0096] The other structures and methods in Example 4 are the same as those in Example 1;

[0097] Example 5

[0098] In Example 5, the mass percentage of the Ag-based composite solder was 88%, and the mass percentage of rare earth element La powder in the solder was 2.5%.

[0099] The mass percentages of solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor in the organic binder are: 58%, 6%, 25%, 8%, 2%, and 1%, respectively.

[0100] Sputtering was performed continuously for 30 minutes to form a 0.8 μm thick Ti metal film on the surface of the conductive core.

[0101] The other structures and methods in Example 5 are the same as those in Example 1;

[0102] Comparative Example 1

[0103] An Al2O3 ceramic block and a 316 stainless steel conductive core were brazed together using AgCuTi active solder. The AgCuTi active solder used was (AgCu)97Ti3, and the AgCu was Ag72Cu28.

[0104] Comparative Example 2

[0105] A 0.5 mm thick layer of AgCuTi active solder was applied to the upper and lower outer surfaces of the ceramic block. The first and second sleeves were then fitted onto the upper and lower outer surfaces of the ceramic block, respectively. A 0.55 mm thick layer of AgCuTi active solder was then applied to the outer surfaces of the first and second sleeves to obtain the assembly. The assembly was then vacuum brazed. The AgCuTi active solder used was (AgCu)97Ti3, and the AgCu used was Ag72Cu28.

[0106] Performance testing

[0107] 1. The ceramic sealed vacuum electrodes obtained in Examples 1-3 and Comparative Example 1 were placed on a universal testing machine to test the shear strength of the weld between the Al2O3 ceramic block and the 316 stainless steel conductive core. The results are shown in Table 1:

[0108] Weld Shear strength / MPa Example 1 177.83 Example 2 208.64 Example 3 189.58 Comparative Example 1 150.85

[0109] Table 1

[0110] It can be seen that the shear strength of the welds in Examples 1-3 is better than that in Comparative Example 1. As the thickness of the Ti metal film increases, the shear strength of the weld shows a trend of first increasing and then decreasing. Among them, when the thickness of the Ti metal film is 1.2 μm, the shear strength of the weld is as high as 208.64 MPa.

[0111] The ceramic sealed vacuum electrodes obtained in Examples 1, 4, 5, and Comparative Example 2 were placed on a universal testing machine to test the shear strength of the weld between the outer side of the Al2O3 ceramic block and the first sleeve. The ceramic sealed vacuum electrodes were placed on a nanoindenter to detect the welds between the outer side of the Al2O3 ceramic block and the first and second sleeves. The residual stress of the welds was calculated according to the Suresh model. The results are shown in Table 2.

[0112]

[0113]

[0114] Table 2

[0115] It can be seen that the shear strength of the welds in Examples 1, 4 and 5 is better than that in Comparative Example 2. With the increase of rare earth element La content, the shear strength of the weld shows a gradual increasing trend, while the residual stress shows a gradual decreasing trend. Among them, when the La content is 2.5%, the shear strength of the weld is as high as 199.25 MPa, and the residual stress value is 0.42 GPa.

[0116] like Figure 2 As shown, scanning electron microscopy was used to examine the weld between the Al2O3 ceramic block and the first sleeve of the ceramic sealed vacuum electrode in Examples 1, 4, 5, and Comparative Example 2. Figure 2 Figures (b)-(d) correspond to Examples 1, 4, and 5, respectively; Figure (a) corresponds to Example 2.

[0117] from Figure 2 As can be seen, with the increase of La content in Ag-based composite brazing filler metal, the Cu-Ti brittle phase in the weld is refined, the residual stress distribution in the weld is made more uniform, the concentration of local stress is reduced, and the mechanical properties of the weld are significantly improved.

[0118] like Figure 3 As shown, the weld of the ceramic sealed vacuum electrode in Example 5 was completely filled with brazing filler metal, and no pores or microcracks were observed. Combined with EDS and XRD analysis, it was determined that the weld of the ceramic sealed vacuum electrode included Ti3Cu3O, Ag(s,s), Cu(s,s), TiCu and TiFe2 phases.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A ceramic-sealed vacuum electrode, the ceramic-sealed vacuum electrode passing through a flange (6); characterized in that, The ceramic sealed vacuum electrode includes a conductive core column (4), a ceramic block sleeved on the conductive core column, a first sleeve (1), and a second sleeve (3); both the first sleeve and the second sleeve are made of Kovar alloy; the ceramic block includes a cylinder (21), a circular plate (22) located at the upper end of the cylinder, and an annular plate (23) located in the middle of the cylinder; the inner side of the first sleeve is brazed to the lower surface and the outer side of the circular plate, respectively, and the inner side of the second sleeve is brazed to the lower surface and the outer side of the annular plate, respectively; a stepped hole (61) is provided on the flange; the outer side of the first sleeve is brazed to the upper part of the inner side of the stepped hole, and the outer side of the second sleeve is brazed to the lower part of the inner side of the stepped hole; the brazing is done with Ag-based composite brazing alloy, which is composed of mixed brazing alloy and organic binder, with the mass percentage of mixed brazing alloy being 85%-90% and the remainder being organic binder; The mixed solder is composed of rare earth element La powder and AgCuTi active solder. The mass percentage of rare earth element La powder in the mixed solder is 0.5%-2.5%, and the balance is AgCuTi active solder. The rare earth element La powder and AgCuTi active solder are mechanically ball-milled and mixed to obtain the mixed solder. The mixed solder is then mixed with an organic binder to obtain the prepared Ag-based composite solder.

2. The ceramic sealed vacuum electrode according to claim 1, characterized in that, The conductive core is made of molybdenum, stainless steel, or oxygen-free copper.

3. The ceramic sealed vacuum electrode according to claim 1, characterized in that, The ceramic block is made of Al2O3 or zirconium oxide.

4. The ceramic sealed vacuum electrode according to claim 1, characterized in that, The mass percentage of Ti in the AgCuTi active solder is ≤5%, and the mass percentage of Ag in both Ag and Cu in the AgCuTi active solder is 68%-76%.

5. The ceramic sealed vacuum electrode according to claim 1, characterized in that, The AgCuTi active solder has a particle diameter of 1μm-100μm, and the rare earth element La powder has a particle diameter of 10μm-100μm.

6. The ceramic sealed vacuum electrode according to claim 1, 4, or 5, characterized in that, The organic binder is composed of solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor. The mass percentages of the solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor in the organic binder are (55%-60%), (4%-8%), (20%-30%), (5%-10%), (1%-3%), and (1%-3%), respectively. The solvent, thickener, dispersant, antioxidant, thixotropic agent, and corrosion inhibitor are added to a beaker in the specified proportions. An inert gas is introduced into the beaker, and the components in the beaker are heated to 40℃-50℃. The components in the beaker are then magnetically stirred in a constant-temperature water bath for 50-60 minutes to obtain the prepared organic binder.

7. A brazing method based on the ceramic sealed vacuum electrode of claim 1, characterized in that, The brazing process includes the following steps: Step 1: Place the ceramic block over the outside of the conductive core post to make the ceramic block and the conductive core post an interference fit connection; Apply Ag-based composite brazing filler metal (5) with a thickness of 0.4mm-0.6mm to the upper and lower parts of the outer side of the ceramic block, and then put the first sleeve and the second sleeve on the upper and lower parts of the outer side of the ceramic block, respectively. Step 2: Apply an Ag-based composite brazing filler metal with a thickness of 0.4mm-0.6mm to the outer sides of the first and second sleeves to obtain the assembly. Insert the assembly into the mounting hole on the flange from top to bottom, and the ceramic sealed vacuum electrode assembly is complete; Step 3: Invert several assembled ceramic-sealed vacuum electrodes and place them into the vacuum brazing furnace, positioning the first sleeve below the second sleeve. Ensure the lower end of the conductive core of each ceramic-sealed vacuum electrode is in contact with the upper surface of the horizontally positioned graphite plate in the vacuum brazing furnace. Place a weight ring on the upper surface of the flange to press it down. Use the three-stage pump of the vacuum brazing furnace to evacuate the furnace, achieving a vacuum level of 5 × 10⁻⁶. -3 the following; Step 4, Pre-welding heating: The temperature inside the vacuum brazing furnace is raised from room temperature to T1, where T1 is in the range of 240℃-260℃, the heating rate is ≤10℃ / min, and the holding time is 30min-45min. The temperature inside the vacuum brazing furnace is raised from T1 to T2, where T2 ranges from 580℃ to 620℃, the heating rate is ≤10℃ / min, and the holding time is 15min-30min. The temperature inside the vacuum brazing furnace is raised from T2 to T3, with T3 ranging from 740℃ to 760℃, a heating rate of ≤5℃ / min, and a holding time of 15min to 30min. Step 5, perform brazing: The temperature inside the vacuum brazing furnace is raised from T3 to T4, with T4 ranging from 870℃ to 900℃. The heating rate is ≤3℃ / min, and the holding time is 10min-20min, at which point the Ag-based composite brazing filler metal melts. Step 6, Cooling down: The temperature inside the vacuum brazing furnace is reduced from T4 to T5, with T5 ranging from 810℃ to 820℃ and a cooling rate of 15℃ / min to 20℃ / min. Ag-based composite brazing filler metal is used to weld the first sleeve to the circular plate and the upper part of the stepped hole, respectively. Ag-based composite brazing filler metal is used to weld the second sleeve to the annular plate and the lower part of the stepped hole, respectively. Allow the temperature inside the vacuum brazing furnace to cool from T5 to room temperature, then open the vacuum brazing furnace and remove each ceramic sealed vacuum electrode.

8. The brazing method for the ceramic sealed vacuum electrode according to claim 7, characterized in that, Step 1 is preceded by a conductive core pretreatment step: Step 9-1: The silver-copper alloy sheet (8) is coated onto the conductive core using hot extrusion. The silver-copper alloy sheet and the conductive core are heated to 780℃-800℃. The silver-copper alloy sheet and the conductive core are combined using an extruder, so that the silver-copper alloy sheet is uniformly coated on the surface of the conductive core. After cooling and shaping, the coated composite conductive core is obtained. The composite conductive core is then drawn and annealed to ensure that the silver-copper alloy sheet and the conductive core are stably combined, and finally a conductive core with a silver-copper coating is obtained.

9. The brazing method for the ceramic sealed vacuum electrode according to claim 8, characterized in that, Step 9-1 is followed by the following steps: A Ti metal film was formed on the surface of a conductive core using a magnetron sputtering apparatus (7): The conductive core was placed in the sputtering chamber of the magnetron sputtering instrument, and the Ti metal target was fixed on the target holder inside the sputtering chamber. The sputtering chamber was evacuated to 1.0 × 10⁻⁶. -3 Below Pa, the temperature of the substrate on the sample turntable is raised to 300℃-400℃ by heating the substrate. Argon gas is introduced into the sputtering chamber, and the argon gas flow rate is controlled at 25sccm-30sccm. The bias voltage is adjusted to 500V-550V, and the Ti metal target is pre-sputtered for 40min-50min to remove the oxide layer on the surface of the Ti metal target. Adjust the substrate bias voltage to 90V-110V, control the argon flow rate to 15sccm-20sccm, and increase the gas pressure in the sputtering chamber to 2.0Pa-2.5Pa. This raises the target voltage of the Ti metal target to 280V-300V for glow discharge, ionizing the argon gas and generating argon ions. These argon ions bombard the Ti metal target, causing sputtering of the Ti metal target atoms. Adjust the working gas pressure in the sputtering chamber to 0.6Pa-0.8Pa and perform pre-sputtering for 15min-20min. After the target voltage and current of the Ti metal target stabilize, control the rotation speed of the sample turntable to 10r / min-12r / min, and adjust the target voltage and current of the Ti metal target to achieve a power of 260W-270W. Continue sputtering for 30min-40min to form a Ti metal film on the surface of the conductive core.

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