Zirconium alloy surface nanocrystallization and self low-temperature diffusion bonding method

Abstract

The invention provides a zirconium alloy surface nanocrystallization and self low-temperature diffusion bonding method, relates to the technical field of nuclear fuel element manufacturing, and solves the technical problems that existing zirconium low-temperature diffusion bonding can only realize connection of a certain small-size sample and a sample with a regular and flat surface and cannot be applied in an engineering manner. The method comprises the following steps that the surface roughness of the to-be-welded surface of the zirconium alloy is machined to be smaller than or equal to 1.6 micrometers; performing surface nanocrystallization treatment on the to-be-connected surface of the processed to-be-welded zirconium alloy test piece by adopting ultrasonic peening; the to-be-welded zirconium alloy test piece subjected to nanocrystallization treatment is accurately assembled and fixed through spot welding; and the assembled zirconium alloy test piece to be welded is subjected to diffusion bonding through a vacuum diffusion bonding technology. The machining difficulty of the to-be-welded test piece is reduced, and batch manufacturing can be achieved in the field of nuclear fuel element manufacturing; the method is suitable for processing complex structural members; and a product with high joint connection strength, uniform interface structure components and good corrosion resistance is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear fuel element manufacturing, and more particularly, to a method for surface nanocrystallization and self low-temperature diffusion bonding of zirconium alloy. Background Art

[0002] As a clean and efficient energy source, developing nuclear energy is an unswerving energy development strategy in China at present. Nuclear fuel elements are the core components of nuclear reactors and have an extremely important impact on the safety and reliability of reactors. The cladding is the first safety barrier of nuclear reactors. Due to its low thermal neutron absorption cross-section, good corrosion resistance, and moderate mechanical properties, zirconium alloy is the only fuel element cladding material currently used in water-cooled nuclear reactors. The research on its joining technology directly determines the feasibility of integrated manufacturing of fuel assemblies. Whether the joining weld is stable and reliable will directly affect the performance of the entire fuel assembly, and thus pose a potential hazard to the safe, stable, and reliable operation of nuclear reactors.

[0003] At present, many countries at home and abroad have systematically carried out research on zirconium alloy welding technology. The direct application objects mainly focus on zirconium alloy rod-shaped fuel elements, specifically involving vacuum electron beam welding (EBW), tungsten inert gas welding (TIG), pulsed laser welding (LBW), resistance pressure welding (RPW), etc. However, there are few reports on the diffusion bonding forming of fuel elements, and there is even a blank in the diffusion bonding of zirconium-based cladding fuel elements. However, with the requirements of high burnup, high safety, and high reliability of fuel elements in the development of nuclear energy technology, the inherent characteristics of traditional fusion welding methods, such as large control precision of penetration depth and difficulty in controlling deformation, can no longer effectively meet the existing needs.

[0004] With the development of emerging joining technologies, the vacuum diffusion bonding technology using solid-phase bonding at the microinterface, as a precision joining method, is very suitable for the rapid forming and integrated manufacturing of a large number of densely welded multi-layer stacked components. In order to effectively reduce the adverse effects on the microstructure and properties of components after heating, and at the same time effectively reduce the difficulty of controlling the overall structural deformation size of precision components, the self low-temperature diffusion bonding technology of zirconium alloy has gradually received attention and emphasis.

[0005] For example, the patents with publication number CN 114571055 A, "A method for realizing low-temperature diffusion connection of zirconium alloy itself by using Ti foil intermediate layer" and "A method for indirect diffusion connection of zirconium alloy by using Ti foil intermediate layer at low temperature" with publication number CN116060750A, propose to realize low-temperature diffusion connection of zirconium alloy itself by using Ti foil intermediate layer, and the patent with publication number CN116441697A, "A method for low-temperature diffusion connection of zirconium alloy" proposes to realize low-temperature diffusion connection of zirconium alloy itself by using Ni foil intermediate layer; the patent with publication number CN115283807A, "A method for low-temperature rapid discharge plasma diffusion connection of zirconium and its alloy", proposes to realize diffusion connection of zirconium alloy by using discharge plasma technology. In fact, in the service environment of corrosion, the interface of zirconium alloy diffusion connection joints with Ti, Ni and other intermediate layers will become the corrosion weak area and crack first; the discharge plasma technology is limited by the limitations of power supply, control and other equipment systems, and can only realize the connection of small zirconium alloy samples at present, and cannot be used in engineering for the time being. The patent with publication number CN110871321A "A nano-processing device and a method for low-temperature diffusion bonding of titanium and zirconium using the same" discloses a method of achieving surface nano-processing of zirconium alloy and titanium alloy by an ultrasonic vibration table, and then performing vacuum diffusion bonding; however, this method is limited by the limitations of the surface nano-processing device and can only achieve welding samples of a certain size (diameter ≤ 200mm, thickness ≤ 220mm) with regular and flat surfaces, and it is impossible to perform local nano-processing on the surfaces to be connected of large-area complex zirconium alloy components, and it still cannot be applied in engineering. Summary of the invention

[0006] The present invention provides a method for zirconium alloy surface nano-crystallization and self-low temperature diffusion connection, so as to solve the technical problem that the existing zirconium low temperature diffusion connection can only be realized on the connection of certain small size samples and samples with regular and flat surfaces, and cannot be applied in engineering.

[0007] The embodiments of the present invention are implemented by the following technical solutions:

[0008] A method for surface nano-crystallization and low-temperature diffusion bonding of zirconium alloys, comprising the following steps:

[0009] S1: Specimen processing: The surface roughness of the zirconium alloy to be welded is processed to ≤1.6μm, and the surface is cleaned;

[0010] S2: Nano-treatment of the surface to be connected: using ultrasonic impact to perform surface nano-treatment on the surface to be connected of the processed zirconium alloy specimens to be welded; the ultrasonic impact process has an ultrasonic frequency range of 15kHz to 30kHz and an amplitude of 15μm to 20μm;

[0011] S3: Specimen assembly: The zirconium alloy specimens to be welded after nanocrystallization treatment are precisely assembled, and the assembled zirconium alloy specimens to be welded are fixed by spot welding.

[0012] S4: Diffusion bonding of specimens: The assembled zirconium alloy specimens to be welded are placed on the working platform of a vacuum diffusion welding machine, and diffusion bonding is carried out using a vacuum diffusion bonding process.

[0013] Preferably, the surface to be treated of the zirconium alloy specimens to be welded is at least one of a plane, a curved surface, and a special-shaped surface.

[0014] Preferably, in step S2, the ultrasonic impact device is installed on a moving mechanism to adjust the treatment position. After the zirconium alloy specimens to be welded are fixed and constrained, the surface to be welded is subjected to repeated ultrasonic impacts to obtain zirconium alloy specimens with nanocrystalline grains on the surface to be welded.

[0015] Preferably, in step S2, the reciprocating moving speed of the ultrasonic impact device is 5 mm - 10 mm / min.

[0016] Preferably, in step S3, the zirconium alloy specimens to be welded need to be surface cleaned before assembly.

[0017] The surface cleaning methods in step S1 and step S3 include the following steps: pickling, ultrasonic water washing, deionized water rinsing, and drying; the pickling is carried out by ultrasonic cleaning with an acidic cleaning agent at room temperature for 2 min.

[0018] Preferably, the acidic cleaning agent includes 35% - 45% HNO3 and 2% - 10% HF, and the balance is H2O.

[0019] Preferably, in step S4, a positioning mechanism is used to achieve precise assembly of the zirconium alloy specimens to be welded, and the misalignment amount of the upper and lower welding interface regions after assembly is < 0.3 mm.

[0020] Preferably, in step S4, the spot welding fixing method is one of TIG spot welding and laser spot welding.

[0021] Preferably, in step S4, the temperature of the vacuum diffusion bonding process is 650 °C

[0022] - 750 °C, the pressure per unit area of diffusion bonding is 10 MPa - 20 MPa, and the heat preservation time is 60 min - 120 min.

[0023] Preferably, in step S4, the vacuum diffusion bonding includes the following steps:

[0024] Place the zirconium alloy specimen to be welded, which has been precisely assembled and spot welded, on the working platform of the vacuum diffusion welding machine. Close the furnace door and evacuate. When the vacuum degree > 1×10 -2 Pa, raise the temperature in three stages; for the first stage of temperature rise, heat from room temperature to 400°C in 15 min - 25 min and hold at 400°C for 60 min; for the second stage of temperature rise, heat from 400°C to 600°C in 15 min - 25 min and hold at 600°C for 30 min; for the third stage of temperature rise, heat from 600°C to 750°C in 10 min - 20 min. After heating to 750°C, apply a pressure of 10 MPa and hold for 30 min, and then cool to room temperature with the furnace.

[0025] With this technical solution, by machining the surface roughness of the surface to be welded to ≤1.6 μm, the flatness and smoothness of the surface are ensured, providing a good foundation for subsequent nanometer treatment; the cleaning method of pickling, ultrasonic water washing, deionized water rinsing and drying is adopted to thoroughly remove the oil stains and oxides on the surface, ensuring the cleanliness of the welding surface. Ultrasonic impact is used to perform nanometer treatment on the zirconium alloy surface, which can effectively refine the surface grains and form a nanoscale grain structure. The ultrasonic impact device is installed on the moving mechanism, which can achieve precise adjustment of the treatment position to process special-shaped surfaces and curved surfaces, ensuring the stability and efficiency of the treatment process and the uniformity and consistency of the surface treatment.

[0026] The positioning component is used to achieve the precise assembly of the zirconium alloy specimen to be welded, improving the accuracy and reliability of the connection. The assembled specimen is spot welded and fixed by TIG spot welding or laser spot welding methods to ensure the stability and unchanged position of the specimen during the diffusion connection process. The vacuum diffusion connection process temperature is 650°C - 750°C, ensuring the diffusion connection of zirconium alloy at low temperature and reducing the influence of high temperature on the material properties. The pressure per unit area of diffusion connection is 10 MPa - 20 MPa, ensuring the close contact and diffusion effect of the connection interface, improving the connection strength and quality; the method of raising the temperature in three stages is adopted to gradually increase the temperature, avoiding the adverse effects of sudden temperature changes on the material and ensuring the stability and safety of the connection process.

[0027] This method can be applied to zirconium alloy parts with different shapes and structures, having wide applicability. The combination of the ultrasonic impact device and the moving mechanism improves the automation degree of the processing process, making it suitable for industrial production. Vacuum diffusion bonding is carried out in a vacuum environment, avoiding the influence of oxygen and other impurities in the air on the welding interface, and improving the quality and safety of the bonding. The method of stepwise heating avoids damage to the material caused by sudden temperature changes, ensuring the safety of the bonding process. Surface nanocrystallization treatment improves the activity of the zirconium alloy surface, promotes the progress of diffusion bonding, and increases the bonding strength of the bonding interface. The precise control of temperature, pressure, and holding time ensures the high quality and high reliability of diffusion bonding. The use of low-temperature diffusion bonding technology reduces energy consumption and material loss, and lowers the production cost. With a high degree of automation and simple operation, it improves production efficiency and reduces labor costs.

[0028] The present invention reduces the processing difficulty of the specimens to be welded. For complex structural components, it can effectively inhibit the adverse effects of the diffusion bonding thermal cycle process on the microstructure and properties of zirconium alloy, achieve good bonding of the interfaces to be joined at low temperature, obtain products with high joint connection strength, uniform interface tissue composition, and good corrosion resistance, and the process flow is standardized and effective, with strong executability and repeatability, enabling batch manufacturing in the field of nuclear fuel element manufacturing.

[0029] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0030] 1. The present invention reduces the processing difficulty of the specimens to be welded and enables batch manufacturing in the field of nuclear fuel element manufacturing;

[0031] 2. The present invention is applicable to the processing of complex structural components;

[0032] 3. The present invention obtains products with high joint connection strength, uniform interface tissue composition, and good corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is the process flow diagram of the method for zirconium alloy surface nanocrystallization and self low-temperature diffusion bonding provided in Embodiment 1 of the present invention;

[0035] Figure 2Schematic diagram of ultrasonic impact nanocrystallization for the zirconium alloy surface nanocrystallization and self-low-temperature diffusion bonding method provided in Embodiment 1 of the present invention;

[0036] Figure 3 Interface microstructure diagram of the zirconium alloy surface nanocrystallization and self-low-temperature diffusion bonding method provided in Embodiment 1 of the present invention;

[0037] Figure 4 Fracture morphology diagram of the zirconium alloy surface nanocrystallization and self-low-temperature diffusion bonding method provided in Embodiment 1 of the present invention;

[0038] Figure 5 Corrosion sample diagram of the welded part of the zirconium alloy surface nanocrystallization and self-low-temperature diffusion bonding method provided in Embodiment 1 of the present invention;

[0039] Icon: 1. Moving mechanism; 2. Ultrasonic impact execution device; 3. Zirconium alloy specimen to be welded; 4. Positioning mechanism; 5. Working platform. Detailed implementation manners

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those conditions not specified in the embodiments, they shall be carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0041] Embodiment 1

[0042] A zirconium alloy surface nanocrystallization and self-low-temperature diffusion bonding method includes the following steps:

[0043] S1: Specimen processing: The surface roughness of the surface to be welded of the zirconium alloy is processed to ≤1.6 μm, and surface cleaning is performed;

[0044] S2: Nanocrystallization treatment of the surface to be bonded: The surface to be welded of the processed zirconium alloy specimen 3 is subjected to surface nanocrystallization treatment by ultrasonic impact; the ultrasonic frequency range of the ultrasonic impact process is 20 kHz, and the amplitude is 18 μm;

[0045] S3: Specimen assembly: The processed zirconium alloy specimen 3 to be welded is precisely assembled, and the assembled zirconium alloy specimen 3 to be welded is spot welded and fixed;

[0046] S4: Specimen diffusion bonding: The assembled zirconium alloy specimen 3 to be welded is placed on the working platform 5 of a vacuum diffusion welding machine, and diffusion bonding is performed using a vacuum diffusion bonding process.

[0047] In this embodiment, in the step S2, the ultrasonic impact device is installed on the moving mechanism 1 to adjust the processing position. After the zirconium alloy specimen 3 to be welded is fixed and constrained, the surface to be welded is subjected to repeated ultrasonic impacts to obtain the zirconium alloy specimen 3 with nanocrystalline grains on the surface to be welded.

[0048] In this embodiment, in the step S2, the reciprocating moving speed of the ultrasonic impact device is 5 mm / min.

[0049] In this embodiment, in the step S3, before assembling the zirconium alloy specimen 3 to be welded, the surface of the zirconium alloy specimen 3 to be welded needs to be cleaned;

[0050] The surface cleaning method in the steps S1 and S3 includes the following steps: pickling, ultrasonic water washing, deionized water rinsing and drying; the pickling is carried out by ultrasonic cleaning with an acidic cleaning agent at room temperature for 2 min.

[0051] In this embodiment, the acidic cleaning agent includes 45% HNO3 and 10% HF, and the balance is 45% H2O.

[0052] In this embodiment, in the step S4, a positioning mechanism 4 is used to achieve the precise assembly of the zirconium alloy specimen 3 to be welded, and the misalignment amount of the upper and lower welding interfaces is <0.3 mm after assembly.

[0053] In this embodiment, in the step S4, the spot welding fixing method is TIG spot welding.

[0054] In this embodiment, in the step S4, the process temperature of the vacuum diffusion bonding is 650 °C to 750 °C, the pressure per unit area of the diffusion bonding is 10 MPa to 20 MPa, and the holding time is 60 min to 120 min.

[0055] In this embodiment, in the step S4, the vacuum diffusion bonding includes the following steps:

[0056] Place the precisely assembled and spot-welded zirconium alloy specimen 3 to be welded on the working platform 5 of the vacuum diffusion welding machine, close the furnace door and evacuate. When the vacuum degree is 1×10 -2 Pa, heat up in three stages; the first stage of heating is from room temperature to 400 °C in 25 min and hold at 400 °C for 60 min; the second stage of heating is from 400 °C to 600 °C in 25 min and hold at 600 °C for 30 min; the third stage of heating is from 600 °C to 750 °C in 20 min. After heating up to 750 °C, pressurize to 10 MPa and hold for 30 min, and then cool to room temperature with the furnace.

[0057] In this embodiment, the moving mechanism 1 is an industrial robot capable of three-axis movement, which facilitates the reciprocating movement of the ultrasonic execution device 2 and the lifting for special-shaped surfaces and curved surfaces.

[0058] As Figure 3-4 Shown are the interface microstructure diagram and fracture morphology diagram of the welded part in this embodiment; its grain boundaries are clear and narrow, which is beneficial to maintaining the purity of the grain boundaries; the connection between each grain is tight, without obvious gaps or signs of separation. Low-temperature connection can effectively achieve the tight bonding between grains.

[0059] Judging from the roughness of the fracture and the size distribution of the grains, the low-temperature connection of the present invention has relatively high strength.

[0060] Working principle and usage method: By processing the surface roughness of the surface to be welded to ≤1.6 μm, the flatness and smoothness of the surface are ensured, providing a good foundation for subsequent nanocrystallization treatment; the cleaning method of pickling, ultrasonic water washing, deionized water rinsing and drying is adopted to thoroughly remove the oil and oxides on the surface, ensuring the cleanliness of the welding surface. The surface of the zirconium alloy is subjected to nanocrystallization treatment by ultrasonic impact, which can effectively refine the surface grains and form a nanoscale grain structure. The ultrasonic impact execution device 2 is installed on the moving mechanism 1, which can achieve precise adjustment of the processing position to process special-shaped surfaces and curved surfaces, ensuring the stability and efficiency of the processing process, and ensuring the uniformity and consistency of the surface treatment.

[0061] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for surface nano-crystallization and low-temperature diffusion bonding of zirconium alloy, characterized in that: The steps include: S1: Specimen processing: The surface roughness of the zirconium alloy to be welded is processed to ≤1.6μm, and the surface is cleaned; S2: Nano-processing of the surface to be connected: using ultrasonic impact to perform surface nano-processing on the surface to be connected of the processed zirconium alloy specimen (3); the ultrasonic impact process has an ultrasonic frequency range of 15kHz to 30kHz and an amplitude of 15μm to 20μm; S3: assembling test pieces: accurately assembling the nano-treated zirconium alloy test pieces (3) to be welded, and spot welding and fixing the assembled zirconium alloy test pieces (3) to be welded; S4: Diffusion bonding of test pieces: The assembled zirconium alloy test pieces to be welded (3) are placed on a working platform (5) of a vacuum diffusion welding machine, and diffusion bonding is performed using a vacuum diffusion bonding process.

2. A method for surface nano-crystallization and self-low temperature diffusion bonding of zirconium alloy according to claim 1, characterized in that: The surface to be processed of the zirconium alloy test piece (3) to be welded is at least one of a flat surface, a curved surface and a special-shaped surface.

3. A method for surface nano-crystallization and self-low temperature diffusion bonding of zirconium alloy according to claim 1, characterized in that: In step S2, the ultrasonic impact device (2) is installed on the moving mechanism (1) to adjust the processing position, and after the zirconium alloy specimen (3) to be welded is fixed and constrained, the surface to be welded is subjected to reciprocating ultrasonic impacts to obtain the zirconium alloy specimen (3) to be welded with nano-grained surface.

4. A method for surface nano-crystallization and self-low temperature diffusion bonding of zirconium alloy according to claim 3, characterized in that: In step S2, the reciprocating movement speed of the ultrasonic impact device (2) is 5 mm to 10 mm / min.

5. A method for surface nano-crystallization and self-low temperature diffusion bonding of zirconium alloy according to any one of claims 1 to 4, characterized in that: In the step S3, the surface of the zirconium alloy test piece (3) to be welded needs to be cleaned before the zirconium alloy test piece (3) to be welded is assembled; The surface cleaning method in step S1 and step S3 includes the following steps: pickling, ultrasonic water washing, deionized water rinsing and drying; the pickling adopts an acidic cleaning agent to perform ultrasonic cleaning at room temperature for 2 minutes.

6. A method for surface nano-crystallization and self-low temperature diffusion bonding of zirconium alloy according to claim 5, characterized in that: The acid cleaning agent comprises 35% to 45% HNO3 and 2% to 10% HF, with the remainder being H2O.

7. A method for surface nano-crystallization and self-low temperature diffusion bonding of zirconium alloy according to any one of claims 1 to 4, characterized in that: In the step S4, a positioning mechanism (4) is used to achieve accurate assembly of the zirconium alloy test piece (3) to be welded, and after the interface to be welded is assembled, the misalignment between the upper and lower interface regions to be welded is less than 0.3 mm.

8. A method for surface nano-crystallization and self-low temperature diffusion bonding of zirconium alloy according to any one of claims 1 to 4, characterized in that: In the step S4, the spot welding fixing method is one of TIG spot welding and laser spot welding.

9. A method for surface nano-crystallization and self-low temperature diffusion bonding of zirconium alloy according to any one of claims 1 to 4, characterized in that: In the step S4, the vacuum diffusion bonding process temperature is 650° C. to 750° C., the diffusion bonding pressure per unit area is 10 MPa to 20 MPa, and the insulation time is 60 min to 120 min.

10. A method for surface nano-crystallization and self-low temperature diffusion bonding of zirconium alloy according to claim 9, characterized in that: In step S4, the vacuum diffusion connection includes the following steps: The zirconium alloy test piece (3) to be welded, which is precisely assembled and fixed by spot welding, is placed on the working platform (5) of the vacuum diffusion welding machine, and the furnace door is closed to evacuate the vacuum. When the vacuum degree is greater than 1×10 -2 Pa, the temperature is increased in three stages; the first stage is from room temperature to 400°C over 15min to 25min, and kept at 400°C for 60min; The second stage of heating is from 400°C to 600°C over 15min to 25min, and kept at 600°C for 30min; the third stage of heating is from 600°C to 750°C over 10min to 20min, and after heating to 750°C, it is pressurized to 10MPa and kept at this temperature for 30min, and then cooled to room temperature with the furnace.

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