Low temperature joining of electrically conductive ceramics by field assisted flash brazing in air atmosphere

Abstract

The application relates to a low-temperature connecting method of electric field assisted flash soldering of conductive ceramics under an air atmosphere, and relates to a low-temperature connecting method of ceramics. The application aims at solving the problems of high connecting temperature, long connecting time and high environmental atmosphere requirement of the existing common ceramic connecting method. The method comprises the following steps: 1, pretreatment; 2, placing the pretreated soldering material sheet between two pieces of pretreated ceramics, setting electrodes connected with an external power supply on the upper and lower surfaces of the connecting piece, placing the connecting piece and the electrodes arranged on the surfaces between the upper and lower pressing heads of a connecting furnace, and applying uniaxial pressure; 3, adjusting the current value before connection, heating the connecting furnace to the connecting temperature, increasing the voltage until the ceramics are conductive, and then connecting under the specific current. The application is used for the low-temperature connection of electric field assisted flash soldering of conductive ceramics under an air atmosphere.

Description

TECHNICAL FIELD

[0001] The present application relates to a low-temperature connection method of ceramic. BACKGROUND

[0002] Ceramic materials have excellent performance and are widely used in many fields. For example, perovskite can be used in solid fuel cells, sensors and other fields; MAX phase has excellent performance of metal and ceramic, and has good wear resistance and high temperature chemical stability; silicon carbide ceramic has excellent performance such as high temperature resistance, wear resistance and corrosion resistance, and is widely used in aerospace, mechanical processing, clean energy and other fields. For example, silicon carbide can be used for manufacturing high-temperature components such as air engine flame tube and nozzle adjusting sheet, and for preparing grinding tools and abrasives. At the same time, due to the radiation resistance and high temperature chemical stability of silicon carbide, it is the preferred material for nuclear reactor cladding. However, due to the characteristics of high hardness and poor plasticity of ceramic materials, it is a great challenge to prepare ceramic into large and complex components, so the improvement of ceramic processing and manufacturing technology has become a research hotspot.

[0003] Welding is a commonly used material processing method, which can effectively connect different materials and different shapes of components into large and complex components. Common connection methods for silicon carbide ceramic include diffusion bonding and brazing. Since the internal C-Si bond of silicon carbide is stable and difficult to diffuse, diffusion bonding of silicon carbide ceramic usually requires the addition of an intermediate layer and connection under high temperature and high pressure. Since silicon carbide ceramic is difficult to be wetted by conventional filler metal, such as Ag-CuO filler metal commonly used in air reaction brazing, active filler metal that can react with silicon carbide, such as Ag-Cu-Ti, is usually selected for brazing of silicon carbide ceramic. However, since active filler metal is easily oxidized, brazing process needs to be carried out in a vacuum environment. The above commonly used connection methods usually require a vacuum environment, and the equipment cost is high and the connection time is long. SUMMARY

[0004] The present application aims to solve the problems of high connection temperature, long connection time and high environmental atmosphere requirement in the existing common ceramic connection method, and further provides a low-temperature connection method of electrically conductive ceramic by electric field assisted flash brazing in air atmosphere.

[0005] A low-temperature connection method of electrically conductive ceramic by electric field assisted flash brazing in air atmosphere, which is carried out according to the following steps:

[0006] I. The electrically conductive ceramic and the filler metal sheet are pretreated respectively to obtain pretreated ceramic and pretreated filler metal sheet;

[0007] II. Put the pretreated filler metal sheet between two pretreated ceramics to obtain a to-be-connected piece, and set electrodes connected with an external power source on the upper and lower surfaces of the to-be-connected piece, and place the to-be-connected piece and the electrodes on the upper and lower pressure heads of a connecting furnace and apply a uniaxial pressure;

[0008] III. Before connection, the current value is adjusted to 0.5A-12A, then the connecting furnace is heated to a connection temperature in an air atmosphere, and is kept at the connection temperature, then the external power source is started at the connection temperature, and the voltage value of the external electric field is increased at a constant rate until the ceramic is conductive, the voltage instantaneously decreases and tends to be stable, the current instantaneously rises to 0.5A-12A and tends to be stable, and the current is kept at 0.5A-12A for 1s-120s, and after the keeping is completed, the power source is cut off and cooled to obtain a ceramic connected piece.

[0009] The beneficial effects of the present application are:

[0010] 1. The present application utilizes the conductive characteristics of silicon carbide, and adopts an electric field assisted flash brazing method in an air atmosphere, so that reliable connection of silicon carbide ceramics can be realized in a temperature range of 400-600℃. The electric field assisted local heating creates a high temperature environment for the connection interface, the interface is rapidly heated, and the interface temperature is higher than the melting point of the filler metal, so that the filler metal melts and chemically reacts with the silicon carbide base material to achieve good wetting, and the filler metal or the intermediate layer is basically not oxidized in the air atmosphere; the connection time is short (1s-120s), which can effectively inhibit the generation of harmful phases of the joint, the connection efficiency is high, and the joint strength is higher than that of a joint obtained by vacuum brazing of the same filler metal, so that low-temperature high-quality connection of silicon carbide ceramics is realized.

[0011] 2. The joint shear strength of the silicon carbide ceramic connected piece can reach 70MPa at the premise of keeping the connection temperature at 400℃, the current at 10A and the pressure at 0.4MPa by using Ag-Cu-Ti filler metal. According to reports, the joint strength of silicon carbide ceramics obtained by vacuum brazing of Ag-Cu-Ti filler metal is generally between 20-50MPa, so it can be seen that the flash brazing proposed in the present application greatly improves the joint strength, and low-temperature reliable connection of silicon carbide ceramics can be realized in an air atmosphere. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 It is a schematic diagram of the low-temperature connection method of electrically conductive ceramics by electric field assisted flash brazing in an air atmosphere for Example 1, 1 is an alumina upper and lower pressure head, 2 is a platinum sheet electrode, 3 is a filler metal sheet, 4 is a silicon carbide ceramic, 5 is a uniaxial pressure, 6 is a muffle furnace, 7 is a heating resistance wire, and 8 is an external power source.

[0013] Figure 2 It is a joint microstructure photo of a silicon carbide ceramic connected piece prepared in Example 2.

[0014] Figure 3 Joint microstructure photograph of the silicon carbide ceramic joint prepared for Example Three;

[0015] Figure 4 Joint microstructure photograph of the silicon carbide ceramic joint prepared for Example Four;

[0016] Figure 5 Joint microstructure photograph of the silicon carbide ceramic joint prepared for Example Five;

[0017] Figure 6 Joint microstructure photograph of the silicon carbide ceramic joint prepared for Example Six;

[0018] Figure 7 Joint microstructure photograph of the silicon carbide ceramic joint prepared for Example Seven;

[0019] Figure 8 Joint microstructure photograph of the silicon carbide ceramic joint prepared for Example Eight. DETAILED DESCRIPTION

[0020] Embodiment One: A low-temperature joining method of electrically conductive ceramic by electric field assisted flash brazing in air atmosphere, which is carried out according to the following steps:

[0021] I. Pretreat the electrically conductive ceramic and the brazing filler sheet respectively to obtain pretreated ceramic and pretreated brazing filler sheet;

[0022] II. Place the pretreated brazing filler sheet between two pieces of pretreated ceramic to obtain a piece to be joined, and set electrodes connected with an external power source on the upper and lower surfaces of the piece to be joined, and place the piece to be joined and the electrodes on the upper and lower pressing heads of a joining furnace and apply uniaxial pressure;

[0023] III. Before joining, adjust the current value to 0.5A-12A, then in air atmosphere, raise the temperature of the joining furnace to the joining temperature, and keep the temperature at the joining temperature, then at the joining temperature, start the external power source, and raise the voltage value of the external electric field at a constant rate until the ceramic conducts, the voltage instantaneously drops and tends to be stable, the current instantaneously rises to 0.5A-12A and tends to be stable, keep the temperature at 0.5A-12A for 1s-120s, after the temperature is kept, cut off the power supply and cool down to obtain a ceramic joint.

[0024] The specific measures for adjusting the current before welding in the step III of the embodiment are as follows: adjust the current to the required current value by using a precision resistor, and the selected resistance specification is 10Ω-30Ω, 2500W-8000W.

[0025] The third step of the embodiment increases the voltage value of the external electric field at a constant rate until the sample is turned on. The sample is turned on mainly in the form of an instantaneous drop in voltage and an instantaneous rise in current, and both show a nonlinear negative correlation trend in the change stage, and then the voltage and current tend to be stable. The current value after turning on is a previously set value, and the time the sample is turned on to the power off is the connection time, which is 1s-120s.

[0026] In the third step of the embodiment, the filler metal or the intermediate layer does not melt, and the filler metal or the intermediate layer does not substantially oxidize during the heating process of the connecting furnace. The connection temperature is lower than the temperature required for conventional brazing or diffusion bonding.

[0027] In the third step of the embodiment, the size of the filler metal sheet is greater than that of the silicon carbide surface to be connected, so as to avoid incomplete brazing during the connection process.

[0028] The embodiment has low requirements for equipment and low equipment cost. Common box furnaces and tube furnaces can be used for connection, and the modified heating table can also be used.

[0029] The embodiment can use various forms of external electric fields, such as alternating current power supply, direct current power supply, and pulse power supply.

[0030] The embodiment is suitable for ceramic materials that have been surface treated. Common surface treatments for ceramics include surface metallization treatment, surface laser grooving treatment, and surface modification (physical coating, chemical coating, and precipitation reaction).

[0031] The embodiment has the following beneficial effects:

[0032] 1. The embodiment uses the electrical conductivity of silicon carbide and adopts the method of electric field assisted flash brazing in air atmosphere to achieve reliable connection of silicon carbide ceramics in the temperature range of 400-600°C. The auxiliary local heating of the electric field creates a high-temperature environment for the connection interface, the interface temperature is higher than the melting point of the filler metal, the filler metal melts and chemically reacts with the silicon carbide base material to achieve good wetting. The filler metal or the intermediate layer does not substantially oxidize in air atmosphere; the connection time is short (1s-120s), which can effectively inhibit the formation of harmful phases in the joint, the connection efficiency is high, and the joint strength is higher than that of the same filler metal vacuum brazing joint, achieving low-temperature high-quality connection of silicon carbide ceramics.

[0033] 2、Under the premise of keeping the connecting temperature at 400℃, the current at 10A, and the pressure at 0.4MPa, the highest shear strength of the silicon carbide ceramic connecting joint using Ag-Cu-Ti filler metal can reach 70MPa. According to the reports, the joint strength of silicon carbide ceramic brazed by Ag-Cu-Ti filler metal in vacuum is generally between 20MPa and 50MPa. Therefore, the flash brazing proposed in the embodiment greatly improves the joint strength, and can realize the reliable low-temperature connection of silicon carbide ceramic in air atmosphere.

[0034] Embodiment two: Different from the embodiment one, the step one is that the conductive ceramic is pretreated according to the following steps: cutting the conductive ceramic, then polishing the surface to be connected of the cut ceramic in turn by 1200#, 1500# and 2000# diamond grinding disc, and then ultrasonic cleaning with anhydrous ethanol or acetone for 1min to 5min and drying; the step one is that the filler metal sheet is pretreated according to the following steps: cutting the filler metal sheet, and then ultrasonic cleaning with anhydrous ethanol or acetone for 1min to 5min and drying. The others are the same as the embodiment one.

[0035] Embodiment three: Different from the embodiment one or two, the conductive ceramic in the step one is silicon carbide ceramic, perovskite ceramic, spinel ceramic, MAX phase ceramic, ion conductor ceramic or fiber reinforced ceramic matrix composite. The others are the same as the embodiment one or two.

[0036] Embodiment four: Different from the embodiment one to three, the filler metal sheet in the step one is Ag-Cu-Ti filler metal, TiZrNiCu filler metal, CuTi filler metal, TiNi filler metal, Si-Ti filler metal, nickel-based filler metal, high-entropy alloy filler metal, glass filler metal, composite filler metal filled with particle reinforced phase, composite filler metal filled with metal mesh, nickel foam or pure Ni interlayer. The others are the same as the embodiment one to three.

[0037] Embodiment five: Different from the embodiment one to four, the electrode in the step two is platinum sheet. The others are the same as the embodiment one to four.

[0038] Embodiment six: Different from the embodiment one to five, the uniaxial pressure applied in the step two is ≤5MPa. The others are the same as the embodiment one to five.

[0039] Embodiment seven: Different from the embodiment one to six, the area of the pretreated filler metal sheet in the step two is greater than the surface to be connected. The others are the same as the embodiment one to six.

[0040] Eighth Embodiment: The eighth embodiment differs from one of the first through seventh embodiments in that in step three, the external electric field voltage value is increased at a constant rate of 1 V / s to 5 V / s until the ceramic is turned on. The other aspects are the same as the first through seventh embodiments.

[0041] Ninth Embodiment: The ninth embodiment differs from one of the first through eighth embodiments in that in step three, the connection temperature is 400°C to 600°C. The other aspects are the same as the first through eighth embodiments.

[0042] Tenth Embodiment: The tenth embodiment differs from one of the first through ninth embodiments in that in step three, the connection furnace is heated to a connection temperature of 400°C to 600°C at an air atmosphere and a heating rate of 5°C / min to 15°C / min, and is held at the connection temperature of 400°C to 600°C for 1 min to 5 min. The other aspects are the same as the first through ninth embodiments.

[0043] The beneficial effects of the present application are verified by the following examples:

[0044] Example One, in combination Figure 1 Specific description:

[0045] A low-temperature connection method of electric field-assisted flash brazing of conductive ceramic under an air atmosphere, which is performed according to the following steps:

[0046] I. The silicon carbide ceramic and the brazing sheet are pretreated respectively to obtain pretreated ceramic and pretreated brazing sheet;

[0047] II. The pretreated brazing sheet is placed between two pieces of pretreated ceramic to obtain a piece to be connected, electrodes connected to an external power source are arranged on the upper and lower surfaces of the piece to be connected, the piece to be connected and the electrodes arranged on the surfaces are placed between the upper and lower pressing heads of a muffle furnace, and a uniaxial pressure is applied;

[0048] III. Before connection, the current value is adjusted to 10 A, then the muffle furnace is heated to a connection temperature of 400°C at an air atmosphere and a heating rate of 10°C / min, and is held at the connection temperature of 400°C for 5 min, then at the connection temperature of 400°C, the external power source is started, the external electric field voltage value is increased at a constant rate of 2 V / s until the ceramic is turned on, the voltage instantaneously decreases and tends to be stable, the current instantaneously increases to 10 A and tends to be stable, under the condition of a current of 10 A, the holding time is 120 s, after the holding is completed, the power source is turned off and cooled to obtain a silicon carbide ceramic connection piece.

[0049] In step one, the pretreatment of the silicon carbide ceramic is performed according to the following steps: cutting the silicon carbide ceramic, cutting the silicon carbide into 5×5×3 mm 3 and 5×10×3 mm3 Two pieces of each of two sizes, 5 x 5 x 3 mm 3 Two pieces of each of two sizes, 5 x 5 x 3 mm 3 Two pieces of each of two sizes, 5 x 5 x 3 mm 3 Two pieces of each of two sizes, 5 x 5 x 3 mm 2 Two pieces of each of two sizes, 5 x 5 x 3 mm

[0050] The filler metal sheet in step one is Ag-Cu-Ti (Cu content is 28 wt.%, Ti content is 4 wt.%), and the thickness is 100 μm.

[0051] The electrode in step two is a platinum sheet.

[0052] The uniaxial pressure applied in step two is 0.4 MPa.

[0053] The external power source in step two is a direct current stabilized power source, and the power source specification is 0-150 V, 3000 W.

[0054] The current value is adjusted to 10 A by using a precision resistor, and the selected resistance specification is 20 Ω, 5000 W.

[0055] Example Two: The difference between this example and Example One is that in step three, the current is 10 A, and the holding time is 90 s. The others are the same as in Example One.

[0056] Example Three: The difference between this example and Example One is that in step three, the current is 10 A, and the holding time is 60 s. The others are the same as in Example One.

[0057] Example Four: The difference between this example and Example One is that in step three, the current is 10 A, and the holding time is 30 s. The others are the same as in Example One.

[0058] Example Five: The difference between this example and Example One is that in step three, the current is 10 A, and the holding time is 1 s. The others are the same as in Example One.

[0059] Example Six: The difference between this example and Example One is that in step two, the uniaxial pressure applied is 0 MPa. The others are the same as in Example One.

[0060] That is, only the sample and the electrode sheet and the base material and the filler metal sheet are tightly attached by the self weight of the electrode sheet.

[0061] Example seven: the difference between this example and example one is that: in step three, the current value is adjusted to 0.6A before connection, then the muffle furnace is heated to the connection temperature of 400℃ under the condition of air atmosphere and the heating rate of 10℃ / min, and kept for 5min at the connection temperature of 400℃, then the external power supply is started at the connection temperature of 400℃, the external field voltage value is increased at a constant rate of 2V / s until the ceramic is turned on, the voltage drops instantaneously and tends to be stable, the current rises instantaneously to 0.6A and tends to be stable, and the current is kept at 0.6A for 120s, after the heat preservation is completed, the power is cut off and cooled, and the silicon carbide ceramic connector is obtained. The others are the same as example one.

[0062] Example eight: the difference between this example and example one is that: the filler metal sheet in step one is BNi-2, with a thickness of 30μm; in step three, the current is kept at 10A for 60s. The others are the same as example one.

[0063] Figure 2 The joint microstructure photo of the silicon carbide ceramic connector prepared in example two; as can be seen from the figure, under air atmosphere, when the connection temperature is 400℃, the joint microstructure is symmetrically distributed, the joint is dense, and no obvious defects are observed, and at the same time, it can also be found that there is a obvious reaction layer near the silicon carbide base material.

[0064] Figure 3 The joint microstructure photo of the silicon carbide ceramic connector prepared in example three; as can be seen from the figure, the joint is well bonded, and no obvious defects are observed, but it can be found that element segregation occurs in the weld.

[0065] Figure 4 The joint microstructure photo of the silicon carbide ceramic connector prepared in example four; as can be seen from the figure, the joint is tightly bonded, and no defects such as pores and cracks are observed.

[0066] Figure 5 The joint microstructure photo of the silicon carbide ceramic connector prepared in example five; as can be seen from the figure, when the current time is 1s, the obtained joint is well bonded, and no obvious defects are found, and on the side close to the base material, copper element segregation can be observed.

[0067] Figure 6 The joint microstructure photo of the silicon carbide ceramic connector prepared in example six; as can be seen from the figure, under the condition of no pressure, the size of the joint is obviously larger than that of the joint obtained under the condition of applying pressure, and the microstructure morphology and element distribution also differ. No obvious defects are observed in the joint, and the connection quality is good.

[0068] Figure 7The joint microstructure photo of the silicon carbide ceramic connector prepared in Example Seven; it can be seen from the figure that the silicon carbide ceramic can also achieve effective connection under the condition of a current of 0.6 A, but no obvious reaction layer is observed, and the microstructure and element distribution are different from those of Example Four and Example Six, and no obvious defects are observed in the joint.

[0069] Figure 8 The joint microstructure photo of the silicon carbide ceramic connector prepared in Example Eight; it can be seen from the figure that there is an obvious reaction layer at the interface, and a few small cavities can be observed.

[0070] The shear strength test was performed on the silicon carbide ceramic connectors prepared in Examples One to Five, Six and Eight under the condition of a shear speed of 0.05 mm / min; the shear strength of the silicon carbide ceramic connector prepared in Example One was 32 MPa, the shear strength of the silicon carbide ceramic connector prepared in Example Two was 53 MPa, the shear strength of the silicon carbide ceramic connector prepared in Example Three was 70 MPa, the shear strength of the silicon carbide ceramic connector prepared in Example Four was 43 MPa, the shear strength of the silicon carbide ceramic connector prepared in Example Five was 34 MPa, the shear strength of the silicon carbide ceramic connector prepared in Example Six was 30 MPa, and the shear strength of the silicon carbide ceramic connector prepared in Example Eight was 32 MPa. The test results showed that under the premise of maintaining the connection temperature at 400℃, the current at 10 A, and the pressure at 0.4 MPa, the joint shear strength showed a first increase and then a decrease with time, the best connection time was 60 s, and the joint shear strength was 70 MPa.

Claims

1. A low-temperature joining method for conductive ceramics by electric field-assisted flash brazing in an air atmosphere, characterized in that... It proceeds in the following steps:

1. The conductive ceramic and the solder sheet are pretreated separately to obtain the pretreated ceramic and the pretreated solder sheet.

2. Place the pretreated brazing filler metal sheet between two pretreated ceramic pieces to obtain the part to be connected. Electrodes connected to an external power supply are set on both the upper and lower surfaces of the part to be connected. Place the part to be connected and the electrodes on the surface between the upper and lower pressure heads of the connecting furnace and apply a uniaxial pressure of 0MPa~0.4MPa.

3. Before connection, adjust the current value to 0.5A~12A. Then, under air atmosphere and a heating rate of 5℃ / min~15℃ / min, heat the connection furnace to a connection temperature of 400℃~600℃. Hold the connection temperature at 400℃~600℃ for 1min~5min. Then, at a connection temperature of 400℃~600℃, turn on the external power supply and increase the external electric field voltage at a constant rate of 1V / s~5V / s until the ceramic conducts. The voltage drops instantly and tends to stabilize, while the current rises instantly to 0.5A~12A and tends to stabilize. Hold the connection at a current of 0.5A~12A for 1s~120s. After the holding period, turn off the power supply and cool the connection to obtain the ceramic connector.

2. The low-temperature joining method for electric field-assisted flash brazing of conductive ceramics in an air atmosphere according to claim 1, characterized in that... The pretreatment of conductive ceramics in step one is carried out in the following steps: cut the conductive ceramics, then grind the cut ceramics to be connected surfaces with diamond grinding discs of 1200#, 1500# and 2000# in sequence, then ultrasonically clean them with anhydrous ethanol or acetone for 1 min to 5 min and dry them; the pretreatment of brazing filler metal in step one is carried out in the following steps: cut the brazing filler metal, then ultrasonically clean it with anhydrous ethanol or acetone for 1 min to 5 min and dry it.

3. The low-temperature joining method for electric field-assisted flash brazing of conductive ceramics in an air atmosphere according to claim 2, characterized in that... The conductive ceramic mentioned in step one is silicon carbide ceramic, perovskite ceramic, spinel ceramic, MAX phase ceramic, ion conductor ceramic, or fiber-reinforced ceramic matrix composite material.

4. The low-temperature joining method for electric field-assisted flash brazing of conductive ceramics in an air atmosphere according to claim 2, characterized in that... The solder sheet mentioned in step one is Ag-Cu-Ti solder, TiZrNiCu solder, CuTi solder, TiNi solder, Si-Ti solder, nickel-based solder, high-entropy alloy solder, glass solder, composite solder with added particle reinforcement phase, composite solder with added metal mesh, nickel foam or pure Ni interlayer.

5. The low-temperature joining method for electric field-assisted flash brazing of conductive ceramics in an air atmosphere according to claim 1, characterized in that... The electrode mentioned in step two is a platinum sheet.

6. The low-temperature joining method for electric field-assisted flash brazing of conductive ceramics in an air atmosphere according to claim 1, characterized in that... In step two.

7. The low-temperature joining method for electric field-assisted flash brazing of conductive ceramics in an air atmosphere according to claim 1, characterized in that... In step two, the area of ​​the pre-treated brazing filler metal sheet is larger than the surface to be joined.

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