A low-creep zirconium alloy guide tube and its manufacturing method

Abstract

A low-creep zirconium alloy guide tube and its manufacturing method are disclosed, belonging to the nuclear power field. The manufacturing method of the low-creep zirconium alloy guide tube includes the following steps: argon ion etching is performed on the surface of the zirconium alloy tube; a Mo transition layer and a 5μm-30μm thick Cr coating are sequentially deposited using magnetron sputtering; subsequently, the Cr coating is laser remelted to form a 0.2μm-0.5μm fine-grained remelted layer on the surface of the Cr coating. This method can effectively improve the creep resistance of the zirconium alloy tube, reduce the creep rate of the zirconium alloy tube under high-temperature load conditions, and improve the service life and reliability of the zirconium alloy guide tube.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power, specifically relating to a low-creep zirconium alloy guide tube and its manufacturing method. Background Technology

[0002] Zirconium alloy is currently the most widely used structural material for pressurized water reactor fuel assembly guide tubes. During service, the guide tubes continuously bear axial and radial loads, requiring not only sufficient coolant flow in their structure but also providing insertion channels for control rods and buffering the impact of falling rods. Therefore, zirconium alloy guide tubes need to possess excellent mechanical properties, corrosion resistance, radiation resistance, and creep resistance at service temperatures. Excessive creep rates will affect the structural integrity and reliability of the fuel assembly, and may even lead to serious consequences such as premature deformation and failure of the fuel skeleton during its service life. With the development of civilian nuclear power technology, high burnup materials have become one of the development directions for nuclear fuel technology. However, the creep properties of current materials used in guide tube manufacturing, such as Zr-4, M5, Zirlo, and E635 alloys, are insufficient to meet the operational requirements of high burnup reactors exceeding 60 GWd / tU. The development cycle for new material systems is lengthy, making it difficult to meet the application needs of nuclear power plants in a timely manner. Therefore, providing a process method based on existing material systems that can improve the creep performance of zirconium alloy guide tubes has high practical value. Summary of the Invention

[0003] The purpose of this invention is to provide a method for manufacturing a low-creep zirconium alloy guide tube, thereby improving the creep resistance of the zirconium alloy guide tube. This invention also provides a low-creep zirconium alloy guide tube.

[0004] According to one embodiment of the present invention, a method for manufacturing a low-creep zirconium alloy guide tube is provided, the method comprising the following steps:

[0005] Step a): Provide a zirconium alloy tube and perform argon ion etching on the outer surface of the zirconium alloy tube;

[0006] Step b): A Mo transition layer is deposited on the outer surface of the zirconium alloy tube using a magnetron sputtering process;

[0007] Step c): A 5μm-30μm Cr coating is deposited on the surface of the Mo transition layer using a magnetron sputtering process;

[0008] Step d): The Cr coating is subjected to laser remelting to form a fine-grained remelted layer with a thickness of 0.2μm-0.5μm on the surface of the Cr coating.

[0009] This method effectively reduces the load on the zirconium alloy substrate by setting a Cr composite coating with good high-temperature mechanical properties on the surface of the zirconium alloy tube, thereby alleviating the creep tendency of the zirconium alloy tube under high-temperature load conditions; the Mo transition layer can block the interdiffusion between the Cr coating and the zirconium substrate and prevent the formation of brittle phases; by establishing a composite structure in the radial direction, the interface layer between different components can hinder the long-range diffusion of vacancies and further reduce the creep rate; and the fine-grained remelted layer formed by laser remelting can effectively hinder the diffusion of oxygen into the zirconium substrate and suppress diffusion creep and grain boundary slip.

[0010] Furthermore, in some embodiments, in step c), the Cr coating is given a (200) preferred orientation by controlling the deposition bias. The columnar Cr crystal structure with a (200) preferred orientation can effectively hinder dislocation movement and reduce the creep rate.

[0011] Furthermore, in some embodiments, in step c), the sputtering target purity is not less than 99.99%, the deposition bias voltage is -100V to -200V, the sputtering power is 800W to 1200W, the pulse frequency is 200Hz to 500Hz, and the deposition temperature is 400℃ to 500℃.

[0012] Furthermore, in some embodiments, in step b), the sputtering target has a purity of not less than 99.99%, the deposition temperature is 200℃-300℃, the sputtering power is 800W-1200W, and the pulse frequency is 200Hz-500Hz; the thickness of the Mo transition layer is 0.5μm-1.5μm.

[0013] Furthermore, in some embodiments, in step c), the average grain size of the Cr coating is 200nm-500nm.

[0014] Furthermore, in some embodiments, in step d), the laser remelting power is 200 W / mm². 2 -400W / mm 2 The scanning speed is 5mm / s-10mm / s, and the repetition frequency is 20Hz.

[0015] Furthermore, in some embodiments, step e) is included after step d): the zirconium alloy tube is subjected to rotary forging, wherein the feed rate is 10 mm / min-15 mm / min, the rotation speed is 500 r / min-600 r / min, and the contact pressure between the forging hammer and the zirconium alloy tube is 50-80 MPa.

[0016] According to another aspect of the present invention, a low-creep zirconium alloy guide tube is provided. The zirconium alloy guide tube includes a zirconium substrate. A Mo transition layer and a Cr coating are sequentially disposed on the surface of the zirconium substrate. The Cr coating includes a columnar crystal layer and a fine-grained remelted layer. The thickness of the Cr coating is 5 μm-30 μm, and the thickness of the fine-grained remelted layer is 0.2 μm-0.5 μm.

[0017] Furthermore, in some embodiments, the columnar crystal layer has a (200) preferred orientation.

[0018] Furthermore, in some embodiments, the thickness of the zirconium substrate is 100μm-900μm, the thickness of the Mo transition layer is 0.5μm-1.5μm, the average grain size of the columnar crystal layer is 200nm-500nm, and the average grain size of the fine-grained remelted layer does not exceed 100nm.

[0019] Furthermore, in some embodiments, the low-creep zirconium alloy guide tube is manufactured using the manufacturing method of the low-creep zirconium alloy guide tube provided in any of the foregoing embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a partial cross-sectional structure of a low-creep zirconium alloy guide tube in one embodiment;

[0021] Figure 2 This is a comparison chart of one embodiment and a pair of proportional creep rates.

[0022] Meaning of the reference numerals in the attached figures:

[0023] 1-Zirconium matrix; 2-Mo transition layer; 3-Cr coating; 4-Columnar crystal layer; 5-Fine-grained remelted layer.

[0024] The purpose of the above-described drawings is to provide a detailed description of the present invention so that those skilled in the art can understand the technical concept of the invention, and is not intended to limit the invention. For the sake of brevity, the above-described drawings only schematically depict the structures related to the technical features of the present invention, and do not depict the complete structure and all details strictly according to actual scale. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0026] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive, independent, or alternative embodiments. Those skilled in the art will understand that the embodiments herein can be combined with other embodiments without causing structural conflicts.

[0027] In this description, unless otherwise explicitly specified and limited, the technical terms "installation," "connection," "joining," etc., should be interpreted broadly, for example, referring to movable connections, fixed connections, or integration. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0028] In this description, terms such as "upper," "lower," "left," "right," "lateral," "longitudinal," "height," "length," and "width," which indicate orientation or positional relationships, are intended to accurately describe the embodiments and simplify the description, rather than limiting the parts or structures involved to have a specific orientation, or to be installed or operated in a specific orientation, and should not be construed as limiting the embodiments in this document.

[0029] In this description, terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating relative importance or limiting the number, specific order, or primary / secondary relationship of the described technical features. In this description, "multiple" means at least two.

[0030] Zirconium alloys have the advantages of low thermal neutron absorption cross section, low induced radioactivity, and good corrosion resistance below 600℃. They also have good radiation resistance and comprehensive mechanical properties, so they are widely used as structural materials for reactor fuel assemblies.

[0031] In fuel assemblies, the guide tube needs to transmit the axial load between the upper and lower tube seats, balance the force exerted by the fuel rods on the grid, provide axial positioning for the grid while bearing a certain amount of lateral load. Structurally, the guide tube needs to provide insertion channels for related functional components such as control rod assemblies, combustible poison assemblies, drag plug assemblies, and neutron source assemblies, ensuring sufficient coolant flow while buffering the impact load of falling rods. Therefore, the comprehensive performance requirements of the guide tube are particularly stringent. Currently, the structural materials used to manufacture guide tubes include Zr-4 alloy, M5 alloy, ZIRLO alloy, and E635 alloy. Among them, Zr-4 alloy has insufficient corrosion resistance under high burnup conditions above 48 GWd / tU; M5 alloy is relatively sensitive to water environments with high lithium and high dissolved oxygen, and also has insufficient creep resistance; ZIRLO and E635 alloys have relatively balanced performance, but their corrosion resistance still needs improvement under high burnup conditions exceeding 60 GWd / tU. The development of new zirconium alloys for high fuel consumption conditions above 60GWd / tU is time-consuming and costly, and there is a lack of mature materials that are practically usable in engineering in the short term.

[0032] To address the aforementioned problems in the prior art, embodiments of the present invention provide a method for manufacturing a low-creep zirconium alloy guide tube, the method comprising the following steps:

[0033] Step a): Provide zirconium alloy tubing with a wall thickness in the range of 100μm-900μm. Polish the surface of the zirconium alloy tubing to a roughness Ra≤0.1μm, followed by ultrasonic cleaning and argon ion etching with an etching bias of -300V and an etching time of 30min.

[0034] Step b): A Mo transition layer is deposited on the outer surface of the zirconium alloy tube using a DC magnetron sputtering process. Specifically, in a preferred embodiment, the purity of the Mo target used for sputtering is not less than 99.99%, the deposition temperature is 200℃-300℃, the sputtering power is 800W-1200W, the pulse frequency is 200Hz-500Hz, and the argon flow rate is 50sccm-100sccm.

[0035] Step c): A 5μm-30μm Cr coating is deposited on the surface of the Mo transition layer using a high-power magnetron sputtering process. In a preferred embodiment, the purity of the Cr target used for sputtering is not less than 99.99%, and the Cr coating is given a (200) preferred orientation by controlling the bias voltage. Specifically, in some embodiments, the deposition bias voltage is -100V to -200V, the sputtering power is 800W-1200W, the pulse frequency is 200Hz-500Hz, and the deposition temperature is 400℃-500℃.

[0036] Step d): The surface of the Cr coating is subjected to laser remelting to form a fine-grained remelted layer with a thickness of 0.2 μm-0.5 μm on the surface of the Cr coating. In a preferred embodiment, the power of the laser remelting process is 200 W / mm². 2 -400W / mm 2 The scanning speed is 5mm / s-10mm / s, and the repetition frequency is 20Hz. Specifically, in some embodiments, a 1064nm Nd:YAG laser is used for laser remelting.

[0037] In a preferred embodiment, after laser remelting, the process further includes step e): loading the zirconium alloy tube that has undergone coating deposition and laser remelting into a rotary forging device, and performing local necking treatment using an adjustable-angle forging hammer. The forging hammer angle is 5°-30°, the feed rate is 10mm / min-15mm / min, the rotation speed is 500r / min-600r / min, and the contact pressure between the forging hammer and the tube is 50MPa-80MPa. Simultaneously, the surface is polished using a gauge round grinding block with a particle size of 800-1000 mesh to obtain a finished guide tube with an outer diameter error of no more than 0.05mm.

[0038] The partial cross-sectional structure of the finished guide tube is as follows: Figure 1 As shown, the system includes a zirconium substrate 1 and a Mo transition layer 2 deposited on the zirconium substrate 1. A Cr coating 3 is disposed on the Mo transition layer 2. The Cr coating 3 includes a columnar crystal layer 4 and a fine-grained remelted layer 5 on the surface. In a preferred embodiment, the thickness of the Mo transition layer 2 is 0.5 μm-1.5 μm; the total thickness of the Cr coating 3 is 5 μm-30 μm, wherein the average grain size of the fine-grained remelted layer 5 does not exceed 100 nm and the thickness is 0.2 μm-0.5 μm, and the average grain size of the columnar crystal layer 4 is 200 nm-500 nm, which has a preferred orientation of (200).

[0039] The surface of the finished guide tube is coated with a multi-layered composite coating. Among them, the Cr coating 3 has good high-temperature strength. When the guide tube is subjected to creep load, especially the circumferential creep load due to the increase of internal pressure, the high-strength Cr coating 3 can effectively share the load borne by the zirconium substrate 1 and effectively reduce the creep rate of the zirconium substrate 1. Furthermore, the fine-grained remelted layer 5 on the surface can inhibit oxygen diffusion and further improve the oxidation resistance of the guide tube. On the other hand, the nano-fine-grained structure can effectively inhibit dislocation migration in the deformation process dominated by dislocation creep, promote dislocation pile-up at the grain boundary, hinder dislocation rearrangement, maintain the work hardening state, and delay the start of the third stage of creep. At the same time, the columnar crystal layer 4 with (200) preferred orientation can also effectively hinder dislocation migration and reduce the creep rate. If the thickness of the Cr coating 3 is too small, it will not be able to effectively disperse the load of the zirconium substrate 1; while if the thickness is too large, it will increase the thermal resistance of the guide tube, reduce neutron economy, and, since Cr itself is brittle, increase the risk of cracking and failure of the Cr coating 3. The Mo transition layer 2 isolates the Cr coating 3 from the zirconium substrate 1, preventing interdiffusion between the Cr coating 3 and the zirconium substrate 1 under high-temperature conditions to form a brittle phase that would affect the overall strength of the guide tube. The multilayer composite structure alters the diffusion path within the system, making it difficult for dislocations and vacancies to migrate across the interfaces between layers, and hindering long-range vacancy migration, thus further reducing the creep rate. During coating deposition, the zirconium alloy tube is preheated to 400℃-500℃, which can induce recrystallization of the tube structure to a certain extent, optimizing the zirconium alloy tube structure while improving its bonding strength with the coating. The finished guide tube achieves high-precision forming and surface treatment simultaneously through the combination of an adjustable-angle forging hammer and synchronous polishing technology, avoiding coating damage caused by secondary processing.

[0040] In Example 1, after polishing, cleaning, and argon ion etching, the zirconium alloy tube was preheated to 300°C and a 1μm thick Mo transition layer was deposited on the outer surface of the zirconium alloy tube by DC magnetron sputtering at a sputtering power of 1000W. With a bias voltage of -150V, a pulse frequency of 300Hz, and a preheating temperature of 400°C, a 20μm thick Cr coating was deposited on the Mo transition layer by high-power magnetron sputtering at a sputtering power of 1000W and a pulse frequency of 300Hz. Using 300W / mm... 2 The surface was laser-remelted using laser pulses at a speed of 8 mm / s; finally, a finished guide tube with an outer diameter error of 0.03 mm was obtained through rotary forging. Long-term creep performance tests were conducted under conditions of 380℃ and an internal pressure load of 16 MPa, and the results are as follows: Figure 2 As shown, the steady-state creep rate is 8 × 10⁻⁶. -6 / h.

[0041] In Example 2, after polishing, cleaning, and argon ion etching, the zirconium alloy tube was preheated to 300°C and a 1μm thick Mo transition layer was deposited on the outer surface of the zirconium alloy tube by DC magnetron sputtering at a sputtering power of 1000W. With a bias voltage of -150V, sputtering power of 1000W, preheating temperature of 400°C, and pulse frequency of 300Hz, a 25μm thick Cr coating was deposited on the Mo transition layer using high-power magnetron sputtering. A 400W / mm² sputtering method was employed. 2 The surface was laser-remelted using laser pulses at a speed of 8 mm / s; finally, a finished guide tube with an outer diameter error of 0.03 mm was obtained by rotary forging. Long-term creep performance tests were conducted under conditions of 380℃ and an internal pressure load of 16 MPa, and the steady-state creep rate was 7 × 10⁻⁶. -6 / h.

[0042] In a comparative example, using the same zirconium alloy tubing as in Examples 1 and 2, without applying a surface coating after surface polishing and cleaning, long-term creep performance was directly tested under conditions of 380°C and 16MPa internal pressure. The results are as follows: Figure 2 As shown, the steady-state creep rate exceeds 1.3 × 10⁻⁶. -5 / h, significantly higher than in Examples 1 and 2.

[0043] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent substitution of the technical features involved, as well as combination of implementation methods in different embodiments without causing structural and principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a low-creep zirconium alloy guide tube, characterized in that, Includes the following steps: Step a): Provide a zirconium alloy tube and perform argon ion etching on the outer surface of the zirconium alloy tube; Step b): A Mo transition layer is deposited on the outer surface of the zirconium alloy tube using a magnetron sputtering process; Step c): A 5μm-30μm Cr coating is deposited on the surface of the Mo transition layer using magnetron sputtering. The Cr coating is made to have a (200) preferred orientation by controlling the deposition bias voltage. The average grain size of the Cr coating is 200nm-500nm. The sputtering target has a purity of not less than 99.99%, the deposition bias voltage is -100V to -200V, the sputtering power is 800W-1200W, the pulse frequency is 200Hz-500Hz, and the deposition temperature is 400℃-500℃. Step d): The Cr coating is subjected to laser remelting to form a fine-grained remelted layer with a thickness of 0.2 μm-0.5 μm on the surface of the Cr coating. The laser remelting power is 200 W / mm. 2 -400W / mm 2 The scanning speed is 5mm / s-10mm / s, the repetition frequency is 20Hz, and the average grain size of the fine-grained remelted layer does not exceed 100nm.

2. The method for manufacturing a low-creep zirconium alloy guide tube according to claim 1, characterized in that, In step b), the sputtering target has a purity of not less than 99.99%, the deposition temperature is 200℃-300℃, the sputtering power is 800W-1200W, and the pulse frequency is 200Hz-500Hz; the thickness of the Mo transition layer is 0.5μm-1.5μm.

3. The method for manufacturing a low-creep zirconium alloy guide tube according to claim 1 or 2, characterized in that, Step d) is followed by step e): the zirconium alloy tube is subjected to rotary forging, wherein the feed rate is 10 mm / min-15 mm / min, the rotation speed is 500 r / min-600 r / min, and the contact pressure between the forging hammer and the zirconium alloy tube is 50-80 MPa.

4. A low-creep zirconium alloy guide tube, characterized in that, The guide tube is manufactured using the manufacturing method of any one of claims 1 to 3. The zirconium alloy guide tube includes a zirconium substrate, and a Mo transition layer and a Cr coating are sequentially disposed on the surface of the zirconium substrate. The Cr coating includes a columnar crystal layer and a fine-grained remelted layer. The thickness of the Cr coating is 5 μm-30 μm, and the thickness of the fine-grained remelted layer is 0.2 μm-0.5 μm.

5. The low-creep zirconium alloy guide tube according to claim 4, characterized in that, The columnar crystal layer has a (200) preferred orientation.

6. The low-creep zirconium alloy guide tube according to claim 4, characterized in that, The zirconium substrate has a thickness of 100μm-900μm, the Mo transition layer has a thickness of 0.5μm-1.5μm, the columnar crystal layer has an average grain size of 200nm-500nm, and the fine-grained remelted layer has an average grain size of no more than 100nm.

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