Method for realizing low-temperature diffusion bonding of zirconium and alloy thereof under action of constant-current electric field

Abstract

The invention discloses a method for realizing low-temperature diffusion bonding of zirconium and alloy thereof based on a constant-current electric field, and relates to the technical field of material bonding. The method aims at solving the problems that in current direct diffusion bonding of zirconium and zirconium alloy, the joint strength is low at the low bonding temperature, and base metal performance is reduced and post-welding deformation is large at the high bonding temperature. According to the method, hole closing and atomic diffusion at a diffusion connection interface are jointly promoted mainly through the electromigration effect under the action of the constant-current electric field, the vacancy concentration of zirconium and the alloy thereof improved by the constant-current electric field, and high-temperature plasticity, so that the high-strength zirconium and the alloy connector thereof are obtained at low temperature. The method for realizing low-temperature diffusion bonding of the zirconium and the zirconium alloy under the action of the constant-current electric field can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of material connection, and in particular 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-section, good corrosion resistance, moderate mechanical properties, and are easy to cold process. Therefore, they are widely used in the manufacture of key components such as fuel cladding, pressure tubes, container tubes and channel key tubes of water-cooled reactors, and are known as the "first metal of the atomic age". Over the years, domestic and foreign scholars have conducted a large number of studies on fusion welding technology of zirconium and its alloys, including vacuum electron beam welding, tungsten inert gas shielded welding and laser welding. However, when using fusion welding, the welding temperature often exceeds the melting point of zirconium alloy. High temperature will coarsen the grains in the heat-affected zone of the parent material and precipitate the second phase brittle compounds, thereby reducing the mechanical properties of the parent material, and will also lead to problems such as excessive deformation after welding.

[0003] As a precision connection method, diffusion bonding technology has a lower temperature and better control of post-welding deformation than fusion welding. However, when the connection temperature is low, the welding rate and joint strength of zirconium and its alloy joints are low. If you want to obtain high-strength joints, you need to further increase the connection temperature. However, too high a connection temperature will cause the coarsening of the zirconium and its alloy parent materials and the precipitation of second-phase brittle compounds, affecting the performance of the parent materials. It will also cause excessive deformation of the structural parts after welding, making it difficult to meet the product precision requirements.

[0004] Therefore, it is currently necessary to find a method for high-strength and low-deformation diffusion bonding of zirconium and its alloys, and lowering the diffusion bonding temperature is an effective way. At present, the methods for low-temperature diffusion bonding of zirconium and its alloys mainly include intermediate layer alloying, surface nano-sizing and hydrogen treatment. Although intermediate layer alloying can reduce the connection temperature, corrosion galvanic cells are easily formed between heterogeneous interface elements and Zr, making the corrosion resistance of the joint unable to meet practical needs. Nano-sizing the surface of zirconium and its alloys by mechanical grinding or impact can reduce the connection temperature, but the deformation of the surface of zirconium and its alloys after mechanical grinding or impact is difficult to control and cannot meet precision connection. Hydrogen treatment of zirconium and its alloys can also effectively reduce the connection temperature, but if the dehydrogenation is not thorough, there is a risk of hydrogen embrittlement, and there are risks in practical application. Summary of the invention

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

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

[0007] Step S1:

[0008] 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;

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

[0010] Step S2:

[0011] 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;

[0012] Step S3:

[0013] 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.

[0014] Principle of the present invention:

[0015] The present invention directly applies a constant current electric field as a heat source to the zirconium and its alloy joints during the diffusion connection process, without introducing heterogeneous elements and without the need for destructive treatment of the connection surface of zirconium and its alloys. In addition, the skin effect of the DC pulse electric field and the AC electric field causes uneven current distribution in the connection joint, which will lead to differences in performance in various areas of the joint. In contrast, there is no skin effect in the constant current electric field, and the current can pass through the connection joint evenly, and the performance of each area of ​​the joint is close. At the same time, the skin effect will also increase the resistance of the connection joint and thus increase the resistance heat, that is, a smaller current will be required for the DC pulse electric field and the AC electric field to reach the same temperature, but this will weaken the role of the electric field in promoting diffusion connection.

[0016] The present invention mainly uses 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, and jointly promotes the closure of holes and atomic diffusion at the diffusion connection interface, thereby obtaining a high-strength zirconium and its alloy joint at low temperature.

[0017] Beneficial effects of the present invention:

[0018] (1) The present invention uses 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 and promotes the closure of holes and atomic diffusion at the diffusion bonding interface, thereby achieving diffusion bonding of Zr-4 alloy at low temperatures of 650°C to 700°C. Compared with the 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 connection joint of the present invention can reach 369MPa, which is higher than 90% of the strength of the parent material, and the joint strength can reach 175% of the strength of the diffusion bonding joint at the same temperature of the radiation heat source.

[0019] (2) The present invention uses a constant current electric field to directly heat the zirconium and its alloy joints, with a heating rate of up to 200°C / min and a cooling rate of up to 50°C / min, which are much higher than the heating and cooling rates of the radiation heat source. Therefore, compared with the radiation heating used in conventional diffusion bonding, the present invention can greatly shorten the time required for diffusion bonding.

[0020] (3) The present invention adopts a method of applying a constant current electric field during the diffusion bonding process, which does not introduce an additional heterogeneous interface atomic layer and does not cause excessive grain growth and brittle phase precipitation. Therefore, it has little effect on the mechanical properties of zirconium and its alloy parent materials 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 connected, and can effectively reduce the deformation rate of the joint after welding.

[0022] The invention can obtain a method for realizing low-temperature diffusion connection of zirconium and its alloys under the action of a constant current electric field. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram showing low temperature diffusion connection of zirconium and its alloys under the action of a constant current electric field according to the present invention;

[0024] Figure 2 A schematic diagram showing the relative positions of zirconium and its alloy blocks and the temperature measurement positions of thermocouples in Examples 1-3 and Comparative Examples 1-3;

[0025] Figure 3 A process curve diagram showing the diffusion bonding process of Example 1 and Comparative Example 1;

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

[0027] Figure 5 The 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 bonding temperature of 700° C. and a holding time of 20 min without the action of a constant current electric field;

[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] Fig. 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 implementation method three: This implementation method is different from specific implementation methods one or two in that: in step S1, 200#, 400#, 1000#, 2000#, 3000#, 5000# and 7000# sandpaper are used in sequence for polishing.

[0043] The other steps are the same as those in the first or second embodiment.

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

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

[0046] Specific implementation method five: This implementation method is different from specific implementation methods one to four in that: ultrasonic cleaning is adopted in step S1, the washing liquid used is anhydrous ethanol, and the ultrasonic cleaning time is 5 to 30 minutes.

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

[0048] Specific embodiment six: The difference between this embodiment and specific embodiments one to five is that: in step S2, the two dried parts to be connected are placed in the center of the graphite mold, and the connection interface of the two parts to be connected is aligned with the temperature measuring hole of the graphite mold, and then the graphite mold is placed between two graphite columns, and a graphite press 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 presses are respectively in contact with the copper electrodes.

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

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

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

[0052] Specific embodiment eight: The difference between this embodiment and specific embodiments one to seven is that the heating rate in step S3 is 1 to 200° C. / min.

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

[0054] Specific embodiment 9: The difference between this embodiment and specific embodiments 1 to 8 is that the pressure applied in step S3 is 5 to 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] Fig. 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; Fig. 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.

Images