A method for realizing low-temperature diffusion bonding of zirconium and its alloys under the action of a constant-current electric field

Abstract

A method for realizing low-temperature diffusion bonding of zirconium and its alloys under the action of a constant-current electric field, which relates to the technical field of material bonding. The purpose of the present invention is to solve the problems existing in the direct diffusion bonding of current zirconium and its alloys, such as low joint strength at low bonding temperatures, reduction of base metal properties at high bonding temperatures, and large post-welding deformation. The present invention mainly promotes the closure of pores and atomic diffusion at the diffusion bonding interface by the electromigration effect under the action of a constant-current electric field. The constant-current electric field increases the vacancy concentration and high-temperature plasticity of zirconium and its alloys, thereby obtaining high-strength zirconium and its alloy joints at low temperatures. The present invention can obtain a method for realizing low-temperature diffusion bonding of zirconium and its alloys under the action of a constant-current electric field.

Description

Technical Field

[0001] The present invention relates to the technical field of material connection, and particularly relates to a method for realizing low-temperature diffusion connection of zirconium and its alloys under the action of a constant-current electric field. Background Art

[0002] Zirconium and its alloys have low thermal neutron absorption cross-sections, good corrosion resistance, moderate mechanical properties, and are easy to cold-work. Therefore, they are widely used in manufacturing key components such as fuel cladding, pressure tubes, vessel tubes, and channel key tubes of water-cooled reactors, and are known as "the first metal of the atomic age". Over the years, scholars at home and abroad have carried out a large number of studies on the fusion welding technology of zirconium and its alloys, specifically including vacuum electron beam welding, tungsten inert gas welding, and laser welding. However, when using the fusion welding method, the welding temperature often exceeds the melting point of the zirconium alloy. The high temperature will cause grain coarsening in the heat-affected zone of the base material and precipitation of second-phase brittle compounds, thereby reducing the mechanical properties of the base material. At the same time, it will also lead to problems such as excessive post-weld deformation.

[0003] As a precision joining method, the diffusion bonding technology has a lower temperature and better control of post-weld deformation compared to the fusion welding method. However, when the joining temperature is low, the bonding rate and strength of the zirconium and its alloy joints are low. If a high-strength joint is desired, the joining temperature needs to be further increased. However, too high a joining temperature will cause grain coarsening of the zirconium and its alloy base materials and precipitation of second-phase brittle compounds, affecting the properties of the base materials. At the same time, it will also lead to excessive post-weld deformation of the structural parts, making it difficult to meet the product precision requirements.

[0004] Therefore, at present, it is necessary to find a method for diffusion bonding of zirconium and its alloys with high strength and low deformation. Reducing the diffusion bonding temperature is an effective way. Currently, the methods for low-temperature diffusion bonding of zirconium and its alloys mainly include interlayer alloying, surface nanocrystallization, and hydrogen implantation treatment. Although interlayer alloying can reduce the joining temperature, it is easy to form corrosion galvanic cells between the dissimilar interface elements and Zr, making the corrosion resistance of the joint unable to meet the practical requirements. Nanocrystallization treatment of the surface of zirconium and its alloys by mechanical grinding or impact can reduce the joining temperature, but it is difficult to control the surface deformation of zirconium and its alloys after mechanical grinding or impact, and it cannot meet the requirements of precision joining. Hydrogen implantation treatment of zirconium and its alloys can also effectively reduce the joining temperature, but there is a risk of hydrogen embrittlement if dehydrogenation is not complete, and there are risks in practical applications. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems existing in the direct diffusion bonding of current zirconium and its alloys, such as low joint strength at low joining temperatures, and reduction of base material properties and large post-weld deformation at high joining temperatures, and to provide a method for realizing low-temperature diffusion bonding of zirconium and its alloys under the action of a constant-current electric field.

[0006] A method for realizing low-temperature diffusion bonding of zirconium and its alloys under the action of a constant-current electric field is carried out according to the following steps:

[0007] Step S1:

[0008] The surfaces to be joined of two pieces of metal to be welded are polished, buffed and cleaned in sequence to obtain two pieces of workpieces to be joined;

[0009] The metal to be welded is zirconium or zirconium alloy;

[0010] Step S2:

[0011] After drying the two workpieces to be joined obtained in Step S1, they are loaded into a graphite mold in a stacked manner with the surfaces to be joined, to obtain the assembled workpieces to be joined;

[0012] Step S3:

[0013] The assembled workpieces to be joined obtained in Step S2 are placed between two copper electrodes in a hot pressing furnace. After vacuum pumping, an inert gas is introduced, and then the temperature is raised to 500 - 700 °C, and it is kept warm for 5 - 40 min under the conditions of a temperature of 500 - 700 °C, applying pressure and applying a constant current of 400 - 800 A. After the heat preservation is completed, it is cooled to room temperature, and the low-temperature diffusion bonding of zirconium and its alloy is realized based on the action of a constant current electric field.

[0014] Principle of the present invention:

[0015] In the diffusion bonding process of the present invention, a constant current electric field is directly applied to the zirconium and its alloy joints as a heat source, without introducing foreign elements and without the need for destructive treatment of the zirconium and its alloy joint surfaces. In addition, the skin effect exists in the DC pulsed electric field and the AC electric field, resulting in uneven current distribution in the joint, which will cause differences in the performance of each region of the joint. In contrast, the constant current electric field does not have the skin effect, and the current can uniformly pass through the joint, and the performance of each region of the joint is close. At the same time, the skin effect will also increase the resistance of the joint, thereby increasing the resistive heat. That is, to reach the same temperature, the DC pulsed electric field and the AC electric field will require a smaller current, but this will weaken the promotion effect of the electric field on the diffusion bonding.

[0016] The present invention mainly promotes the closure of holes and atomic diffusion at the diffusion bonding interface by the electromigration effect under the action of a constant current electric field. The constant current electric field improves the vacancy concentration and high-temperature plasticity of zirconium and its alloy, so as to obtain high-strength zirconium and its alloy joints at low temperature.

[0017] Advantages of the present invention:

[0018] (1) Through the electromigration effect under a constant-current electric field, the present invention improves the vacancy concentration and high-temperature plasticity of zirconium and its alloys, jointly promoting the closure of pores and atomic diffusion at the diffusion bonding interface, thereby achieving the diffusion bonding of Zr-4 alloy under low-temperature conditions of 650°C to 700°C. Compared with a radiation heat source, the present invention can reduce the diffusion bonding temperature by more than 150°C. At the same time, the strength of the joint in the present invention can reach 369 MPa, which is higher than 90% of the strength of the base material, and the joint strength can reach 175% of the strength of the diffusion bonding joint under the same temperature with a radiation heat source.

[0019] (2) The present invention directly heats the joints of zirconium and its alloys using a constant-current electric field, with a heating rate as high as 200°C / min and a cooling rate as high as 50°C / min, which are much higher than the heating and cooling rates of a radiation heat source. Therefore, compared with the radiation heating used in conventional diffusion bonding, the present invention can significantly reduce the time required for diffusion bonding.

[0020] (3) The present invention applies a constant-current electric field during the diffusion bonding process, without introducing additional heterogeneous interface atomic layers, and will not cause excessive grain growth and precipitation of brittle phases. Therefore, it has less impact on the mechanical properties of the base material of zirconium and its alloys and the corrosion resistance of the joint.

[0021] (4) The present invention does not require destructive treatment of the surfaces of zirconium and its alloys to be joined, and can effectively reduce the post-welding deformation rate of the joint.

[0022] The present invention can obtain a method for realizing low-temperature diffusion bonding of zirconium and its alloys based on the action of a constant-current electric field. Description of the Drawings

[0023] Figure 1 It shows a schematic diagram of low-temperature diffusion bonding of zirconium and its alloys under the action of the constant-current electric field of the present invention;

[0024] Figure 2 It shows a schematic diagram of the relative positions of zirconium and its alloy blocks and the thermocouple temperature measurement positions in Examples 1-3 and Comparative Examples 1-3;

[0025] Figure 3 It shows a process curve diagram of the diffusion bonding process in Example 1 and Comparative Example 1;

[0026] Figure 4 It shows a microstructural diagram of the diffusion bonding joint of Zr-4 alloy with a connection temperature of 700°C and a holding time of 20 min under the action of a constant-current electric field in Example 1;

[0027] Figure 5 It shows a microstructural diagram of the diffusion bonding joint of Zr-4 alloy heated to a connection temperature of 700°C and a holding time of 20 min by a radiation heat source without the action of a constant-current electric field in Comparative Example 1;

[0028] Figure 6 The SEM image of the Zr-4 alloy diffusion bonded joint in Example 2 with a connection temperature of 650° C. and a holding time of 40 min under a constant current electric field is shown;

[0029] Figure 7 The SEM image of the Zr-4 alloy diffusion bonded joint heated to a connection temperature of 800°C and a holding time of 40 minutes by a radiation heat source without a constant current electric field in Comparative Example 2 is shown;

[0030] Figure 8 The SEM image of the Zr-4 alloy diffusion bonded joint in Example 3 with a connection temperature of 700°C and a holding time of 1 min under the action of a constant current electric field;

[0031] Figure 9 The SEM image of the Zr-4 alloy diffusion bonded joint in Comparative Example 3 with a connection temperature of 700°C and a holding time of 1 min under the discharge plasma diffusion bonding. DETAILED DESCRIPTION

[0032] Specific implementation method 1: This implementation method is based on a method for achieving low-temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field, and is carried out in the following steps:

[0033] Step S1:

[0034] Grinding, polishing and cleaning the surfaces of the two pieces of metal to be welded to be connected in sequence to obtain two pieces to be connected;

[0035] The metal to be welded is zirconium or a zirconium alloy;

[0036] Step S2:

[0037] After drying the two pieces to be connected obtained in step S1, they are placed in a graphite mold in a manner of stacking the surfaces to be connected, to obtain assembled pieces to be connected;

[0038] Step S3:

[0039] The assembled parts to be connected obtained in step S2 are placed between two copper electrodes in a hot pressing furnace, and an inert gas is introduced after vacuuming. The temperature is then raised to 500-700°C, and the parts are kept warm for 5-40 minutes at a temperature of 500-700°C, under pressure and a constant current of 400-800A. After the insulation is completed, the parts are cooled to room temperature to complete the low-temperature diffusion connection of zirconium and its alloys under the action of a constant current electric field.

[0040] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that the metal to be welded in step S1 is Zr-4 alloy.

[0041] The other steps are the same as those in the first specific implementation.

[0042] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that in step S1, sandpapers of 200#, 400#, 1000#, 2000#, 3000#, 5000# and 7000# are successively used for polishing.

[0043] Other steps are the same as those in Specific Embodiment 1 or 2.

[0044] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is that in step S1, a polishing agent with a particle size of 0.1 - 1.0 μm is used to polish the surface to be joined of the metal to be welded for 5 - 30 minutes.

[0045] Other steps are the same as those in Specific Embodiments 1 to 3.

[0046] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is that in step S1, ultrasonic cleaning is adopted, the cleaning liquid used is absolute ethanol, and the ultrasonic cleaning time is 5 - 30 minutes.

[0047] Other steps are the same as those in Specific Embodiments 1 to 4.

[0048] Specific Embodiment 6: The difference between this embodiment and one of Specific Embodiments 1 to 5 is that in step S2, the two pieces of workpieces to be joined after drying are placed in the exact center of the graphite mold, and the joining interfaces of the two pieces of workpieces are aligned with the temperature measuring holes of the graphite mold. Then, the graphite mold is placed between two graphite columns, and graphite pressing heads are placed outside the two graphite columns to obtain the assembled workpieces to be joined; in step S3, the assembled workpieces to be joined are placed between two copper electrodes in the hot pressing furnace, and the two graphite pressing heads are respectively in contact with the copper electrodes.

[0049] Other steps are the same as those in Specific Embodiments 1 to 5.

[0050] Specific Embodiment 7: The difference between this embodiment and one of Specific Embodiments 1 to 6 is that in step S3, after evacuating to 0 - 1000 Pa, high-purity argon gas at 0.01 - 1 standard atmospheric pressure is introduced.

[0051] Other steps are the same as those in Specific Embodiments 1 to 6.

[0052] Specific Embodiment 8: The difference between this embodiment and one of Specific Embodiments 1 to 7 is that in step S3, the heating rate is 1 - 200 °C / min.

[0053] Other steps are the same as those in Specific Embodiments 1 to 7.

[0054] Specific Embodiment 9: The difference between this embodiment and one of Specific Embodiments 1 to 8 is that in step S3, the applied pressure is 5 - 30 MPa.

[0055] The other steps are the same as those in Specific Embodiments 1 to 8.

[0056] Specific embodiment ten: The difference between this embodiment and specific embodiments one to nine is that the cooling rate in step S3 is 1 to 50° C. / min.

[0057] The other steps are the same as those in Specific Embodiments 1 to 9.

[0058] The following examples are used to verify the beneficial effects of the present invention:

[0059] Embodiment 1: A method for achieving low-temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field, which is carried out according to the following steps:

[0060] Step S1:

[0061] The surfaces of the two Zr-4 alloys to be connected were polished with 200#, 400#, 1000#, 2000#, 3000#, 5000# and 7000# sandpapers in turn, and then the surfaces of the metals to be welded were polished for 5 minutes with a polishing agent with a particle size of 0.5 μm, and then ultrasonically cleaned for 5 minutes with anhydrous ethanol as a washing liquid to obtain two pieces to be connected;

[0062] Step S2:

[0063] After drying the two pieces to be connected obtained in step S1, the two pieces to be connected are placed in the center of the graphite mold in a manner of stacking the surfaces to be connected, and the connection interface of the two pieces to be connected is aligned with the temperature measuring hole of the graphite mold so that the thermocouple can accurately measure the temperature; then the graphite mold is placed between the two graphite columns, and a graphite indenter is placed outside the two graphite columns to obtain the assembled pieces to be connected (such as Figure 1-2 shown);

[0064] Step S3:

[0065] The assembled parts to be connected obtained in step S2 are placed between two copper electrodes in a hot pressing furnace, and the two graphite pressure heads are in contact with the copper electrodes respectively; after the furnace chamber is evacuated to 0Pa, high-purity argon gas at 0.5 standard atmospheric pressure is introduced. A pressure of 20MPa is applied to the parts to be connected through the copper electrodes and a constant current is introduced, and the temperature is raised to 700℃ at a heating rate of 100℃ / min, and the temperature is kept at 700℃ for 20min. After the insulation is completed, it is cooled to room temperature at a cooling rate of 50℃ / min. The temperature is directly measured by the thermocouple on the connection interface. The size of the constant current electric field during the insulation stage is 580A, and the low-temperature diffusion connection of Zr-4 alloy is completed under the action of the constant current electric field.

[0066] Comparative Example 1: The method for direct diffusion bonding of zirconium alloy without radiant heat source heating under the action of constant current electric field in this comparative example is carried out according to the following steps:

[0067] Step S1:

[0068] The surfaces of the two Zr-4 alloys to be connected were polished with 200#, 400#, 1000#, 2000#, 3000#, 5000# and 7000# sandpapers in turn, and then the surfaces of the metals to be welded were polished for 5 minutes with a polishing agent with a particle size of 0.5 μm, and then ultrasonically cleaned for 5 minutes with anhydrous ethanol as a washing liquid to obtain two pieces to be connected;

[0069] Step S2:

[0070] After drying the two pieces to be connected obtained in step S1, the two pieces to be connected are placed in the center of the graphite mold in a manner of stacking the surfaces to be connected, and the connection interfaces of the two pieces to be connected are aligned with the temperature measuring holes of the graphite mold so that the thermocouple can accurately measure the temperature; then the graphite mold is placed between the two graphite columns, and a graphite indenter is placed outside the two graphite columns to obtain the assembled pieces to be connected;

[0071] Step S3:

[0072] The assembled parts to be connected obtained in step S2 are placed in a vacuum diffusion furnace for radiant heating for diffusion connection. The specific operation is as follows: the furnace chamber is first evacuated to 5×10 -3 Pa, apply 20MPa pressure to the parts to be connected, then heat up to 450℃ at a heating rate of 15℃ / min, then continue to heat up to 700℃ at a heating rate of 10℃ / min, and keep it at 700℃ for 20min. After the insulation, cool it to room temperature at a cooling rate of 10℃ / min.

[0073] Figure 3 The process curve diagram of the diffusion bonding process of Example 1 and Comparative Example 1 is shown; Figure 3 As shown, by comparing the test data of Example 1 and Comparative Example 1, it can be seen that the total time required for diffusion connection can be greatly reduced under the action of a constant current electric field.

[0074] Figure 4 The microstructure diagram of the Zr-4 alloy diffusion bonded joint in Example 1 with a connection temperature of 700°C and a holding time of 20 min under the action of a constant current electric field is shown; Figure 4 As shown, in this embodiment, applying a constant current electric field can make the diffusion bonding joint completely welded, without obvious holes, and no weld can be observed. The shear strength of the joint at room temperature is 338 MPa.

[0075] Figure 5The microstructure diagram of the Zr-4 alloy diffusion bonded joint in Comparative Example 1 is shown in which the radiant heat source is heated to a connection temperature of 700°C and a holding time of 20 minutes without the action of a constant current electric field; Figure 5 As shown, in Comparative Example 1, when no constant current electric field was applied, an obvious weld could be observed, and the shear strength of the joint at room temperature was 193 MPa; while applying a constant current electric field at the same temperature could increase the shear strength of the diffusion bonded joints of zirconium and its alloys by 75%, proving that the constant current electric field promotes the diffusion bonding of zirconium and its alloys.

[0076] Embodiment 2: A method for achieving low-temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field, which is carried out according to the following steps:

[0077] Step S1:

[0078] The surfaces of the two Zr-4 alloys to be connected were polished with 200#, 400#, 1000#, 2000#, 3000#, 5000# and 7000# sandpapers in turn, and then the surfaces of the metals to be welded were polished for 5 minutes with a polishing agent with a particle size of 0.5 μm, and then ultrasonically cleaned for 5 minutes with anhydrous ethanol as a washing liquid to obtain two pieces to be connected;

[0079] Step S2:

[0080] After drying the two pieces to be connected obtained in step S1, the two pieces to be connected are placed in the center of the graphite mold in a manner of stacking the surfaces to be connected, and the connection interfaces of the two pieces to be connected are aligned with the temperature measuring holes of the graphite mold so that the thermocouple can accurately measure the temperature; then the graphite mold is placed between the two graphite columns, and a graphite indenter is placed outside the two graphite columns to obtain the assembled pieces to be connected;

[0081] Step S3:

[0082] The assembled parts to be connected obtained in step S2 are placed between two copper electrodes in a hot press furnace, and the two graphite pressure heads are in contact with the copper electrodes respectively; after the furnace chamber is evacuated to 0Pa, high-purity argon gas at 0.5 standard atmospheric pressure is introduced. A pressure of 20MPa is applied to the parts to be connected through the copper electrodes and a constant current is introduced, and the temperature is raised to 650℃ at a heating rate of 100℃ / min, and the temperature is kept at 650℃ for 40min. After the insulation is completed, it is cooled to room temperature at a cooling rate of 50℃ / min. The temperature is directly measured by the thermocouple on the connection interface. The size of the constant current electric field during the insulation stage is 540A, and the low-temperature diffusion connection of Zr-4 alloy is completed under the action of the constant current electric field.

[0083] Comparative Example 2: The method for direct diffusion bonding of zirconium alloy without radiant heat source heating under the action of constant current electric field in this comparative example is carried out according to the following steps:

[0084] Step S1:

[0085] The surfaces of the two Zr-4 alloys to be connected were polished with 200#, 400#, 1000#, 2000#, 3000#, 5000# and 7000# sandpapers in turn, and then the surfaces of the metals to be welded were polished for 5 minutes with a polishing agent with a particle size of 0.5 μm, and then ultrasonically cleaned for 5 minutes with anhydrous ethanol as a washing liquid to obtain two pieces to be connected;

[0086] Step S2:

[0087] After drying the two pieces to be connected obtained in step S1, the two pieces to be connected are placed in the center of the graphite mold in a manner of stacking the surfaces to be connected, and the connection interfaces of the two pieces to be connected are aligned with the temperature measuring holes of the graphite mold so that the thermocouple can accurately measure the temperature; then the graphite mold is placed between the two graphite columns, and a graphite indenter is placed outside the two graphite columns to obtain the assembled pieces to be connected;

[0088] Step S3:

[0089] The assembled parts to be connected obtained in step S2 are placed in a vacuum diffusion furnace for radiant heating for diffusion connection. The specific operation is as follows: the furnace chamber is first evacuated to 5×10 -3 Pa, apply 20MPa pressure to the parts to be connected, then heat up to 450℃ at a heating rate of 15℃ / min, then continue to heat up to 800℃ at a heating rate of 10℃ / min, and keep it at 800℃ for 40min. After the insulation, cool it to room temperature at a cooling rate of 10℃ / min.

[0090] Figure 6 The SEM image of the Zr-4 alloy diffusion bonded joint in Example 2 with a connection temperature of 650°C and a holding time of 40 min under a constant current electric field is shown; Figure 6 As shown, no obvious welds and holes were observed in the joints in this embodiment, proving that good bonding was achieved, and the shear strength of the joint at room temperature reached 369 MPa.

[0091] Figure 7 The SEM image of the Zr-4 alloy diffusion bonded joint in Comparative Example 2 is shown in which the radiant heat source is heated to a connection temperature of 800°C and a holding time of 40 minutes without the action of a constant current electric field; Figure 7As shown, no obvious welds and holes were observed in the joints in Comparative Example 2, and the joint shear strength was 321 MPa. Under the same connection pressure and connection time, the shear strength of the joint at a connection temperature of 650°C under the application of a constant current electric field was still higher than the shear strength of the joint at a connection temperature of 800°C under the application of no DC electric field, indicating that the application of a constant current electric field can reduce the diffusion connection temperature of zirconium and its alloys by more than 150°C, further proving that the constant current electric field promotes the diffusion connection of zirconium and its alloys.

[0092] Embodiment 3: A method for realizing low temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field, which is carried out according to the following steps:

[0093] Step S1:

[0094] The surfaces of the two Zr-4 alloys to be connected were polished with 200#, 400#, 1000#, 2000#, 3000#, 5000# and 7000# sandpapers in turn, and then the surfaces of the metals to be welded were polished for 5 minutes with a polishing agent with a particle size of 0.5 μm, and then ultrasonically cleaned for 5 minutes with anhydrous ethanol as a washing liquid to obtain two pieces to be connected;

[0095] Step S2:

[0096] After drying the two pieces to be connected obtained in step S1, the two pieces to be connected are placed in the center of the graphite mold in a manner of stacking the surfaces to be connected, and the connection interfaces of the two pieces to be connected are aligned with the temperature measuring holes of the graphite mold so that the thermocouple can accurately measure the temperature; then the graphite mold is placed between the two graphite columns, and a graphite indenter is placed outside the two graphite columns to obtain the assembled pieces to be connected;

[0097] Step S3:

[0098] The assembled parts to be connected obtained in step S2 are placed between two copper electrodes in a hot pressing furnace, and the two graphite pressure heads are in contact with the copper electrodes respectively; after the furnace chamber is evacuated to 0Pa, high-purity argon gas at 0.5 standard atmospheric pressure is introduced. A pressure of 20MPa is applied to the parts to be connected through the copper electrodes and a constant current is introduced, and the temperature is raised to 700℃ at a heating rate of 100℃ / min, and kept at 700℃ for 1min. After the insulation is completed, it is cooled to room temperature at a cooling rate of 100℃ / min. The temperature is directly measured by the thermocouple on the connection interface. The size of the constant current electric field during the insulation stage is 580A, and the low-temperature diffusion connection of Zr-4 alloy is completed under the action of the constant current electric field.

[0099] Comparative Example 3: A method for discharge plasma diffusion bonding, which is carried out according to the following steps:

[0100] Step S1:

[0101] The surfaces of the two Zr-4 alloys to be connected were polished with 200#, 400#, 1000#, 2000#, 3000#, 5000# and 7000# sandpapers in turn, and then the surfaces of the metals to be welded were polished for 5 minutes with a polishing agent with a particle size of 0.5 μm, and then ultrasonically cleaned for 5 minutes with anhydrous ethanol as a washing liquid to obtain two pieces to be connected;

[0102] Step S2:

[0103] After drying the two pieces to be connected obtained in step S1, the two pieces to be connected are placed in the center of the graphite mold in a manner of stacking the surfaces to be connected, and the connection interfaces of the two pieces to be connected are aligned with the temperature measuring holes of the graphite mold so that the thermocouple can accurately measure the temperature; then the graphite mold is placed between the two graphite columns, and a graphite indenter is placed outside the two graphite columns to obtain the assembled pieces to be connected;

[0104] Step S3:

[0105] Put the assembled parts to be connected obtained in step S2 into a spark plasma sintering furnace, evacuate the furnace chamber to 0Pa, and then introduce high-purity argon gas at 0.5 standard atmospheric pressure. Apply a pressure of 20MPa and pass a DC pulse current, heat up to 700℃ at a heating rate of 100℃ / min, and keep it at 700℃ for 1min. After the insulation is completed, cool it to room temperature at a cooling rate of 100℃ / min. The temperature is directly measured by a thermocouple on the connection interface. The spark plasma diffusion connection is completed.

[0106] Figure 8 The SEM image of the Zr-4 alloy diffusion bonded joint in Example 3 with a connection temperature of 700°C and a holding time of 1 min under a constant current electric field is shown; Figure 8 As shown in the figure, no obvious welds or holes are observed in the joints. The room temperature joint shear strength is 287MPa.

[0107] Figure 9 The SEM image of the Zr-4 alloy diffusion bonded joint in Comparative Example 3 with a connection temperature of 700°C and a holding time of 1 min under the discharge plasma diffusion bonding method is shown; Figure 9 As shown, some tiny holes can be observed at the weld in Comparative Example 3. The room temperature joint shear strength is 246Mpa.

[0108] In summary, compared with the discharge plasma diffusion connection method in Comparative Example 3 under the same connection parameters, the method for realizing low-temperature diffusion connection of zirconium and its alloys under the action of a constant current electric field in Example 3 can increase the shear strength of the diffusion connection joint by 17%, which is a significant improvement.

Claims

1. A method for achieving low-temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field, characterized in that The method proceeds as follows: Step S1: Grinding, polishing and cleaning the surfaces of the two pieces of metal to be welded to be connected in sequence to obtain two pieces to be connected; The metal to be welded is zirconium or a zirconium alloy; Step S2: After drying the two pieces to be connected obtained in step S1, they are placed in a graphite mold in a manner of stacking the surfaces to be connected, to obtain assembled pieces to be connected; Step S3: The assembled parts to be connected obtained in step S2 are placed between two copper electrodes in a hot pressing furnace, and an inert gas is introduced after vacuuming. The temperature is then raised to 500-700°C, and the parts are kept warm for 5-40 minutes at a temperature of 500-700°C, under pressure and a constant current of 400-800A. After the insulation is completed, the parts are cooled to room temperature to complete the low-temperature diffusion connection of zirconium and its alloys under the action of a constant current electric field.

2. A method for achieving low temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field according to claim 1, characterized in that The metal to be welded in step S1 is Zr-4 alloy.

3. The method for realizing low temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field according to claim 1, characterized in that In step S1, 200#, 400#, 1000#, 2000#, 3000#, 5000# and 7000# sandpaper are used for grinding in sequence.

4. The method for realizing low temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field according to claim 1, characterized in that In step S1, the surface of the metal to be welded to be connected is polished for 5 to 30 minutes using a polishing agent with a particle size of 0.1 to 1.0 μm.

5. The method for realizing low temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field according to claim 1, characterized in that In step S1, ultrasonic cleaning is performed, the washing liquid used is anhydrous ethanol, and the ultrasonic cleaning time is 5 to 30 minutes.

6. The method for realizing low temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field according to claim 1, characterized in that In step S2, the two dried parts to be connected are placed in the center of the graphite mold, and the connection interfaces of the two parts to be connected are aligned with the temperature measuring holes of the graphite mold, and then the graphite mold is placed between the two graphite columns, and a graphite press head is placed on the outside of the two graphite columns to obtain the assembled parts to be connected; in step S3, the assembled parts to be connected are placed between two copper electrodes in a hot pressing furnace, and the two graphite press heads are respectively in contact with the copper electrodes.

7. The method for realizing low temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field according to claim 1, characterized in that After the vacuum is evacuated to 0-1000 Pa in step S3, high-purity argon gas at 0.01-1 standard atmospheric pressure is introduced.

8. The method for realizing low temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field according to claim 1, characterized in that The heating rate in step S3 is 1-200° C. / min.

9. The method for realizing low temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field according to claim 1, characterized in that The pressure applied in step S3 is 5 to 30 MPa.

10. The method for realizing low temperature diffusion bonding of zirconium and its alloys under the action of a constant current electric field according to claim 1, characterized in that The cooling rate in step S3 is 1-50°C / min.

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