Zirconium-coated tungsten target material for spallation neutron source and preparation method of zirconium-coated tungsten target material

Abstract

The invention belongs to the technical field of dissimilar metal welding, and particularly relates to a zirconium-coated tungsten target material for a spallation neutron source and a preparation method of the zirconium-coated tungsten target material for the spallation neutron source, metal zirconium which is good in thermal conductivity, resistant to corrosion and small in after-heat and alloy of the metal zirconium are used as materials for coating tungsten so as to improve the thermal conductivity of the target material and prolong the service life of the target material. The preparation method sequentially comprises the steps of raw material primary processing, assembling, seal welding, hot isostatic pressing and the like. The tungsten target coated with the metal zirconium and the metal zirconium alloy prepared through the method has the advantages of being high in interface bonding strength, free of cracks, good in heat conductivity, small in after-heat, resistant to corrosion and the like, and the problems that a tantalum-coated tungsten target is difficult to cool and dissipate heat, the after-heat is serious, and a target body is damaged or destroyed due to the fact that cooling water is likely to evaporate can be solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of heterogeneous metal welding, and particularly relates to a zirconium-clad tungsten target for a spallation neutron source and a preparation method thereof. Background Art

[0002] In a spallation neutron source, a proton beam from a high-energy particle accelerator is guided onto a target material with a high atomic number, and neutrons are generated from the target material through spallation. Since metallic tungsten has a high melting point, high density, high atomic number, and relatively high thermal conductivity, it has become the preferred solid target material for the China Spallation Neutron Source (CSNS). However, when metallic tungsten is used as a spallation neutron source target, its service environment is extremely harsh. While enduring the impact of instantaneous pulsed thermal stress under the bombardment of pulsed high-energy protons, it is also subjected to irradiation by 1.6 GeV high-energy protons. Irradiation damage to the target material, such as the generation of crystal structure defects by irradiation, the interaction between fission products hydrogen, nitrogen, and defects will accelerate the irradiation brittleness of the material, etc. In addition, all these factors such as the corrosion of the target material by high-pressure cooling water seriously affect the service life of the target body. To improve the service life of the tungsten target in an irradiated and corrosive environment, a corrosion-resistant material with better toughness can be coated on the surface of tungsten. However, since the melting point of metallic tungsten is as high as 3422 °C, generally speaking, the melting point difference between W and dissimilar materials is relatively large, and it is not suitable to use fusion welding methods such as argon arc welding and submerged arc welding. Instead, brazing and diffusion welding are used to achieve the connection between materials. Hot isostatic pressing diffusion welding enables the direct interface bonding of tungsten and dissimilar metals under the simultaneous action of high temperature and high pressure, without introducing low-melting-point brazing filler metal, and can avoid the interface defects of brazing. It is one of the best preparation methods for the interface connection between W and dissimilar metals. Patent CN104470189 A uses metallic Ta as the coating material for W, but the thermal conductivity efficiency of metallic Ta is only one-third of that of tungsten. Therefore, the cooling and heat dissipation of tantalum targets (tantalum-clad tungsten) are much more difficult than those of tungsten, and there are serious post-heat problems. The heat duration is long and it is not easy to dissipate, which easily leads to the evaporation of the cooling water inside the container, causing damage or destruction of the target body.

[0003] In view of this, the present invention is specifically proposed. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a zirconium-clad tungsten target for a spallation neutron source and a preparation method thereof. By using metallic zirconium and its alloys with good thermal conductivity, corrosion resistance, and less post-heat as the materials for coating tungsten, the problems of difficult cooling and heat dissipation, serious post-heat, and easy evaporation of cooling water resulting in damage or destruction of the target body in tantalum-clad tungsten targets are solved. The present invention uses a hot isostatic pressing process to complete the connection of the heterogeneous interface between tungsten and zirconium and its alloys, with high interface bonding strength and no cracks. The metallic zirconium and its alloy-clad tungsten target prepared by this method has the advantages of good interface bonding, good thermal conductivity, small post-heat, and corrosion resistance.

[0005] To achieve the above object, the present invention adopts the following technical solutions: In the first aspect, a zirconium-clad tungsten target for a spallation neutron source, wherein the tungsten is one of pure tungsten or a W-Re alloy, and the zirconium is one of pure zirconium or a nuclear-grade zirconium alloy.

[0006] Further, the composition of the nuclear-grade zirconium alloy includes, by mass percentage: Sn: 0 - 3%; Nb: 0 - 5%; Fe: 0 - 2%; Ni: 0 - 3.5%; Cr: 0 - 1%; Cu: 0 - 1%; Bi: 0 - 1%; Ge: 0 - 1%; Sn, Nb, Fe, Ni, Cr, Cu, Bi, and Ge are not simultaneously 0; and other inevitable impurity elements, with the balance being Zr; And / or, the thickness of the zirconium is 0.1 - 10 mm.

[0007] Further, a metal transition layer is added between the tungsten and the zirconium.

[0008] Furthermore, the material of the metal transition layer is one or more of Ti, Ta, Ni, Nb, Mo, and their alloys, and / or the thickness of the metal transition layer is 0 - 0.1 mm.

[0009] In the second aspect, a method for preparing a zirconium-clad tungsten target for a spallation neutron source, the preparation method sequentially includes the steps of raw material preliminary processing, assembly, seal welding, and hot isostatic pressing; wherein, in the raw material preliminary processing step, the raw materials of tungsten and zirconium are processed into specific shapes and sizes, the raw material of the tungsten is one of pure tungsten or a W-Re alloy; the raw material of the zirconium is one of pure zirconium or a nuclear-grade zirconium alloy. Further, the composition of the nuclear-grade zirconium alloy includes, by mass percentage: Sn: 0 - 3%; Nb: 0 - 5%; Fe: 0 - 2%; Ni: 0 - 3.5%; Cr: 0 - 1%; Cu: 0 - 1%; Bi: 0 - 1%; Ge: 0 - 1%; Sn, Nb, Fe, Ni, Cr, Cu, Bi, and Ge are not simultaneously 0; and other inevitable impurity elements, with the balance being Zr.

[0010] Further, in the raw material preliminary processing step, the raw material of tungsten is processed into a tungsten block; the raw material of zirconium is processed into a zirconium sheet with a thickness of 0.1 - 10 mm, and the zirconium sheet can completely cover the outer surface of the tungsten block after hot pressing; all the surfaces to be welded of the tungsten block and the zirconium sheet are cleaned and set aside.

[0011] Further, in the assembly step, the zirconium sheet is wrapped on the surface of the tungsten block and then put into a metal sheath together.

[0012] Furthermore, a metal transition layer is added between the tungsten block and the zirconium sheet; and / or, the material of the metal cladding is one of steel, tantalum, and titanium; and / or, the material of the metal transition layer is one or more of Ti, Ta, Ni, Nb, Mo, and their alloys; and / or, the thickness of the metal transition layer is 0 - 0.1 mm.

[0013] Further, in the sealing and welding step, the inside of the cladding is first evacuated to a specific vacuum degree, and then the entire cladding is sealed and welded; further, when the vacuum degree is at room temperature, the air pressure inside the cladding does not exceed 1 Pa; and / or, the welding method for the sealing and welding is one or more of electron beam welding, laser welding, and argon arc welding.

[0014] Further, in the hot isostatic pressing step, the sealed and welded cladding is subjected to hot isostatic pressing treatment, with a temperature of 750 - 1450 °C, a pressure of 100 - 200 MPa, and a time of 1 - 8 h.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The solid target material for the spallation neutron source provided by the present invention is a zirconium-clad tungsten target. By using metal zirconium and its alloys with good thermal conductivity, corrosion resistance, and less afterheat as the material for cladding tungsten, the problems of difficult cooling and heat dissipation, serious afterheat, and easy evaporation of cooling water resulting in damage or destruction of the target body in the tantalum-clad tungsten target are solved.

[0016] 2. For the zirconium-clad tungsten target material provided by the present invention, further by using nuclear-grade zirconium alloy to replace pure zirconium for cladding tungsten, the corrosion resistance of pure zirconium as the cladding layer is improved. There are inevitable impurities such as C, N, Al, and Si in zircon. Nuclear-grade zirconium alloy can improve the harmful effects of impurity elements and the corrosion resistance of zircon by adding alloy elements such as Sn, Nb, Fe, and Cr to zircon.

[0017] 3. For the zirconium-clad tungsten target material provided by the present invention, further by using a metal transition layer between zirconium and tungsten, the formation of brittle phases between zirconium and tungsten in a high-temperature environment is avoided, and the problem of easy cracking in interfacial diffusion welding caused by excessive interfacial residual stress is alleviated.

[0018] 4. In the preparation method of the present invention, direct large-area diffusion connection between the zirconium sheet and the tungsten block is achieved through hot isostatic pressing, enabling metallurgical bonding between zirconium and tungsten in the prepared target material. This not only avoids the interfacial defects of brazing but also completes the connection of the heterogeneous interface between tungsten and zirconium and its alloys. The interfacial bonding strength is high, and good thermal conductivity of the spallation neutron source target material is ensured. The used cladding material, the zirconium sheet, is dense, has good thermal conductivity, and less afterheat, enhancing the anti-scouring and corrosion resistance of the target sheet and improving the target sheet life. Description of the Drawings

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 SEM image and EDS result image of the W-Zr bonding interface of the target in Example 1 of the present invention; Figure 2 High-magnification SEM image of the W-Zr bonding interface of the target in Example 1 of the present invention; Figure 3 Metallographic image of the W-Zr bonding interface of the target in Example 1 of the present invention; Figure 4 Schematic diagram of the drawing test adopted in the embodiment of the present invention; Figure 5 SEM image and EDS result image of the W-Zr bonding interface of the target in Example 2 of the present invention; Figure 6 Metallographic image of the W-Zr bonding interface of the target in Example 2 of the present invention; Figure 7 SEM image and EDS result image of the W-Zr bonding interface of the target in Example 3 of the present invention; Figure 8 Metallographic image of the W-Zr bonding interface of the target in Example 3 of the present invention; Figure 9 SEM image and EDS result image of the W-Zr bonding interface of the target in Example 4 of the present invention; Figure 10 Metallographic image of the W-Zr bonding interface of the target in Example 4 of the present invention; Figure 11 SEM image of the target bonding interface containing a transition layer in the embodiment of the present invention. Specific Embodiments

[0021] To make the objectives, technical solutions and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the embodiments of the present invention. Those skilled in the art should understand that the described embodiments are only for helping to understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually according to conventional conditions.

[0022] In the ranges disclosed in the present invention, the endpoints and any values of the ranges are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0023] According to the first aspect of the present invention, a zirconium-clad tungsten target for a spallation neutron source, wherein the tungsten is one of pure tungsten or a W-Re alloy, and the zirconium is one of pure zirconium or a nuclear-grade zirconium alloy.

[0024] The solid target for a spallation neutron source provided by the present invention is a zirconium-clad tungsten target. By using metal zirconium and its alloys with good thermal conductivity, corrosion resistance, and low afterheat as the material for cladding tungsten, the problems of difficult cooling and heat dissipation, severe afterheat, and easy evaporation of cooling water resulting in damage or destruction of the target body in a tantalum-clad tungsten target are solved. Further, a W-Re alloy can be selected to replace pure tungsten to be clad, and the W-Re alloy can improve the toughness and corrosion resistance of pure tungsten. The cladding material can be pure zirconium or a nuclear-grade zirconium alloy. There are inevitable impurities such as C, N, Al, Si, etc. in zirconium. By adding alloying elements such as Sn, Nb, Fe, Cr, Ni, etc. to zirconium in a nuclear-grade zirconium alloy, the harmful effects of impurity elements can be improved, and the corrosion resistance of zirconium can be improved. By using a nuclear-grade zirconium alloy to replace pure zirconium for cladding tungsten, the corrosion resistance of pure zirconium as a cladding layer can be improved.

[0025] As an alternative embodiment of the zirconium-clad tungsten target of the present invention, the composition of the nuclear-grade zirconium alloy includes, by mass percentage: Sn: 0-3%; Nb: 0-5%; Fe: 0-2%; Ni: 0-3.5%; Cr: 0-1%; Cu: 0-1%; Bi: 0-1%; Ge: 0-1%; Sn, Nb, Fe, Ni, Cr, Cu, Bi, and Ge are not all 0 at the same time; and other inevitable impurity elements, with the balance being Zr.

[0026] In the above technical solution, the nuclear-grade zirconium alloy may specifically be a Zr-Sn series alloy, a Zr-Nb series alloy, or a Zr-Sn-Nb series alloy. More specifically, the alloy grades of the nuclear-grade zirconium alloy include but are not limited to grade Zr-2 (composition: Zr-1.5% Sn-0.2% Fe-0.1% Cr-0.05% Ni), grade Zr-4 (composition: Zr-1.5% Sn-0.2% Fe-0.1% Cr), grade ZIRLO (composition: Zr-1.0% Sn-1.0% Nb-0.1% Fe), grade Zr-2.5Nb (composition: Zr-2.5% Nb), grade M5 (composition: Zr-1.0% Nb-0.125% O), grade E110 (composition: Zr-1.0% Nb), grade E635 (composition: Zr-1.2% Sn-1% Nb-0.35% Fe), grade NDA (composition: Zr-1.0% Sn-1% Nb-0.4% Fe), grade MDA (composition: Zr-0.8% Sn-0.5% Nb-0.2% Fe-0.1% Cr), grade N18 (composition: Zr-1% Sn-0.3% Nb-0.3% Fe-0.1% Cr), grade N36 (composition: Zr-1% Sn-1% Nb-0.3% Fe), grade HANA3 (composition: Zr-1.5% Nb-0.4% Sn-0.1% Fe-0.1% Cu), grade HANA4 (composition: Zr-1.5% Nb-0.4% Sn-0.2% Fe-0.1% Cr), grade HANA6 (composition: Zr-1.1% Nb-0.05% Cu), grade ELS0.8 (composition: Zr-0.8% Sn-0.3% Fe).

[0027] As an alternative embodiment of the zirconium-coated tungsten target material of the present invention, the thickness of the zirconium is 0.1-10 mm (such as 0.2 mm, 0.5 mm, 0.7 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, etc.).

[0028] In the above technical solution, controlling the thickness of the zirconium to 0.1-10 mm can not only ensure complete tungsten coating after hot pressing but also ensure the neutron yield during application. If the thickness of the zirconium is too small, incomplete coating may occur after hot isostatic pressing, exposing the internal tungsten target. If the thickness is too large, the neutron yield will decrease.

[0029] As an alternative embodiment of the zirconium-coated tungsten target material of the present invention, a metal transition layer is provided between the tungsten and the zirconium.

[0030] In the above technical solution, by further using a metal transition layer between the zirconium and the tungsten, the problem of easy cracking of the interfacial diffusion welding caused by the formation of brittle phases between the zirconium and the tungsten in a high-temperature environment is avoided.

[0031] As an alternative embodiment of the zirconium-coated tungsten target of the present invention, the material of the metal transition layer is one or more of Ti, Ta, Ni, Nb, Mo and their alloys, and / or the thickness of the metal transition layer is 0 - 0.1 mm (such as 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, etc.).

[0032] In the above technical solution, controlling the thickness of the metal transition layer within the scope of the present invention can not only avoid introducing a third metal due to excessive thickness, but also avoid incomplete formation of brittle phases due to too small thickness.

[0033] According to the second aspect of the present invention, a preparation method of a zirconium-coated tungsten target for a spallation neutron source or the zirconium-coated tungsten target described in the first aspect successively includes steps such as raw material preliminary processing, assembly, sealing welding, hot isostatic pressing, etc., wherein: In the raw material preliminary processing step, the raw materials of tungsten and zirconium are processed into specific shapes and sizes, and the surfaces of all materials to be welded are cleaned; the raw material of tungsten is one of pure tungsten or a W-Re alloy; the raw material of zirconium is one of pure zirconium or a nuclear-grade zirconium alloy; further, the raw material of tungsten is processed into a tungsten block; the raw material of zirconium is processed into a zirconium sheet, the length and width of the zirconium sheet are matched with the tungsten block and can completely cover the outer surface of the tungsten block after hot pressing, and the thickness is 0.1 - 10 mm (such as 0.2 mm, 0.5 mm, 0.7 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, etc.).

[0034] In the assembly step, the zirconium sheet is wrapped on the surface of the tungsten block and then put into a metal jacket together. Further, in order to ensure the welding effect, a metal transition layer can be selected to be added between tungsten and zirconium. Furthermore, the material of the metal jacket is one of steel, tantalum, and titanium; and / or the material of the metal transition layer is one or more of Ti, Ta, Ni, Nb, Mo and their alloys; and / or the thickness of the metal transition layer is 0 - 0.1 mm (such as 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, etc.).

[0035] In the said sealing welding step, first evacuate the inside of the jacket to a specific vacuum degree, and then perform sealing welding on the entire jacket. Evacuating the vacuum is mainly to reduce the corrosion of zirconium metal by oxygen. Further, when at room temperature, the air pressure inside the jacket does not exceed 1 Pa (such as 1 Pa, 0.8 Pa, 0.6 Pa, 0.4 Pa, 0.2 Pa, 0.1 Pa, 0.05 Pa, 0.01 Pa, 0.001 Pa, etc.); and / or, the welding method of the said sealing welding is one or more of electron beam welding, laser welding, and argon arc welding.

[0036] In the said hot isostatic pressing step, put the jacket after sealed welding into a hot isostatic pressing furnace for hot isostatic pressing, and obtain a zirconium-coated tungsten target after taking it out. Specifically, the temperature of the said hot isostatic pressing is 750 - 1450 °C (such as 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, 1400 °C, etc.), the pressure is 100 - 200 MPa (such as 110 MPa, 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, etc.), and the time is 1 - 8 h (such as 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, etc.).

[0037] In the above technical solution, in the process of hot press diffusion welding, temperature is the main determining factor. The setting of the temperature is mainly determined by the low melting point metal components in the material. If the temperature is low, the kinetics is insufficient and the diffusion is not sufficient, so welding cannot be achieved; if the temperature is high, generally when it is as high as 1100 °C, it can cause the reaction between tungsten and zirconium elements to produce brittle phases. The higher the temperature, the faster the phase transformation speed, and a large number of generated brittle compounds will lead to an increase in interface hardness and a decrease in plasticity, thus reducing the mechanical properties of the diffusion welding interface. And too high a temperature will cause metal recrystallization and performance degradation. Applying pressure is also beneficial to diffusion, but too high a pressure will damage the equipment.

[0038] To more clearly illustrate the characteristics and advantages of the present invention, the present invention uses the following examples and comparative examples for detailed description.

[0039] Example 1 (1)Initial processing of raw materials: Pure tungsten and pure zirconium are used as target material raw materials. The tungsten blocks and zirconium sheets are processed into specific sizes. The thickness of the zirconium sheet is 1 mm, and its length and width are precisely matched with the tungsten blocks. One zirconium sheet basically covers one side of the tungsten block, or one zirconium sheet completely covers one side of the tungsten block, ensuring that the zirconium sheet can completely cover the outer surface of the tungsten block after hot pressing. To ensure the subsequent welding quality and make the welded tungsten block and zirconium sheet fit more closely, in this embodiment, the surface to be welded is first wiped with a wire drawing cloth, then cleaned with alcohol, then ultrasonically cleaned, and finally dried; (2)Assembly: The zirconium sheet is closely attached to the surface of the tungsten block and they are together placed into a 316L steel jacket; (3)Sealing welding: First, evacuate the inside of the jacket to 0.01 Pa, and then use the argon arc welding method to weld the 316L steel jacket completely.

[0040] (4)Hot isostatic pressing: The sealed and welded jacket is placed into a hot isostatic pressing furnace for hot isostatic pressing. The temperature is 900 °C, the pressure is 140 MPa, and the time is 3 h. After the hot isostatic pressing process is completed, the jacket is removed to obtain the target.

[0041] It can be seen from the SEM image and metallographic image of the tungsten-zirconium interface of the target prepared in this embodiment that the interface of the obtained target has good bonding, and no obvious defects such as pores and cracks are found, as Figures 1-3 . And through Figures 1-2 it can be seen that tungsten and zirconium elements diffuse into each other to form a diffusion layer with a thickness of about 0.2 μm. Metallurgical bonding is formed at the tungsten-zirconium welding joint, and no brittle phase is generated in its composition. Subsequently, a drawing test as shown in Figure 4 was carried out. The GB / T 8642 standard was implemented, and a total of 10 samples were taken at different positions of the target interface. The average drawing strength of the tungsten-zirconium interface of the target obtained in this embodiment is 53.28 MPa. Therefore, by using the preparation method provided in this embodiment, the connection strength between zirconium and tungsten in the obtained target is high, and there is no cracking at the connection interface.

[0042] The target obtained in this embodiment was also subjected to an autoclave corrosion test. The experimental conditions were: corrosion in deionized water at 360 °C and 18.6 MPa for 100 d. Compared with the mass of the original material, the weight gain per unit area of the target under this experimental condition is 78.64 mg / dm 2 .

[0043] Example 2 The difference between this embodiment and Example 1 is only that nuclear-grade zirconium alloy Zr-4 (with a composition of Zr-1.5%Sn-0.2%Fe-0.1%Cr) is used to replace pure zirconium as the cladding material. The rest of the settings are the same as those in Example 1.

[0044] The target obtained in this embodiment was also subjected to an autoclave corrosion test. The test conditions were as follows: corrosion in deionized water at 360 °C and 18.6 MPa for 100 days. Compared with the mass of the original material, the weight gain per unit area of the target under these test conditions was 31.47 mg / dm 2 , and the use of nuclear-grade zirconium alloy significantly improved the corrosion resistance of the target compared with pure zirconium as the cladding material.

[0045] In addition, from the SEM images and metallographic images of the W-Zr interface of the prepared target ( Figure 5 , 6 ), it can be seen that the interface of the obtained target is well bonded, and no obvious defects such as pores and cracks are found. Moreover, the width of the interdiffusion zone, i.e., the diffusion layer thickness, at the W-Zr interface of the target prepared in this embodiment is about 0.3 μm, and no brittle phase is generated in its composition. Subsequently, a drawing test as shown in Figure 4 was also carried out. According to the GB / T 8642 standard, 10 samples were taken at different positions of the target interface. The average drawing strength of the W-Zr interface of the target obtained in this embodiment was 58.34 MPa. Therefore, by using the preparation method provided in this embodiment, the connection strength between zirconium and tungsten in the obtained target is high, and there is no cracking at the connection interface.

[0046] Example 3 The difference between this embodiment and Example 2 lies only in the hot isostatic pressing process: (4) Hot isostatic pressing: The sealed and welded jacket was placed in a hot isostatic pressing furnace for hot isostatic pressing at a temperature of 1000 °C, a pressure of 140 MPa, and a time of 3 h. After the hot isostatic pressing process was completed, the jacket was removed to obtain the target.

[0047] All other settings were the same as those in Example 2.

[0048] From the SEM images and metallographic images of the W-Zr interface of the prepared target ( Figure 7 , 8 ), it can be seen that the interface of the obtained target is well bonded, and no obvious defects such as pores and cracks are found. Moreover, the width of the interdiffusion zone at the W-Zr interface of the target prepared in this embodiment is about 0.6 μm and no brittle phase is generated in its composition. Subsequently, a drawing test as shown in Figure 4 was carried out. According to the GB / T8642 standard, 10 samples were taken at different positions of the target interface. The average drawing strength of the W-Zr interface of the target obtained in this embodiment was 79.68 MPa. Therefore, by using the preparation method provided in this embodiment, the connection strength between zirconium and tungsten in the obtained target is relatively high, and there is no cracking at the connection interface.

[0049] The target obtained in this example was also subjected to an autoclave corrosion test. The experimental conditions were: corrosion in deionized water at 360 °C and 18.6 MPa for 100 d. Compared with the mass of the original material, the weight gain per unit area of the target under these experimental conditions was 29.56 mg / dm 2 .

[0050] Example 4 The difference between this example and Example 2 lies only in the hot isostatic pressing process: (4) Hot isostatic pressing: The sealed and welded cladding was placed in a hot isostatic pressing furnace for hot isostatic pressing at a temperature of 1100 °C, a pressure of 140 MPa, and a time of 3 h. After the hot isostatic pressing process was completed, the cladding was removed to obtain the target.

[0051] All other settings were the same as in Example 2.

[0052] From the SEM images and metallographic images of the tungsten-zirconium interface of the obtained target, it can be seen that the interface of the obtained target has good bonding, and no obvious defects such as pores and cracks were found, as Figure 9 、 10 . And from Figure 9 、 10 it can be seen that the tungsten and zirconium elements diffuse into each other at the W-Zr interface of the target, forming a diffusion layer with a thickness of about 2.0 μm. Metallurgical bonding is formed at the tungsten-zirconium weld, but the composition of the diffusion layer contains a W 2 Zr brittle phase ( Figure 9 a platform appears at the intersection of the W line and the Zr line in the EDS result diagram of 2 indicating the generation of the W

[0053] Subsequent drawing tests were carried out as shown in Figure 4 . According to the GB / T 8642 standard, a total of 10 samples were taken at different positions of the target interface. The average drawing strength of the tungsten-zirconium interface of the target obtained in this example was 53.62 MPa. Using the preparation method provided in this example, there was no cracking at the zirconium-tungsten connection interface of the obtained target. However, due to the formation of the brittle phase W 2 Zr in the diffusion zone, the connection strength decreased even at a relatively high hot isostatic pressing temperature.

[0054] The target obtained in this example was also subjected to an autoclave corrosion test. The experimental conditions were: corrosion in deionized water at 360 °C and 18.6 MPa for 100 d. Compared with the mass of the original material, the weight gain per unit area of the target under these experimental conditions was 33.27 mg / dm 2 .

[0055] Example 5 (1)Initial processing of raw materials: Pure tungsten and nuclear-grade zirconium alloy with grade Zr-2 (composition: Zr-1.5%Sn-0.2%Fe-0.1%Cr-0.05%Ni) are used as the target material raw materials. The tungsten block and zirconium sheet are processed into specific dimensions. The thickness of the zirconium sheet is 0.1 mm, and the length and width are precisely matched with the tungsten block. To ensure the subsequent welding quality and make the welded tungsten block and zirconium sheet fit more closely, in this embodiment, the surface to be welded is first wiped with a wire drawing cloth, then washed with weak acid and distilled water, and then ultrasonically cleaned and dried; (2)Assembly: The zirconium sheet is closely attached to the surface of the tungsten block, and they are placed together in a sheath. To improve the welding quality, in this embodiment, a Ti metal sheet with a thickness of 0.05 mm is added between the zirconium sheet and the tungsten block as a transition layer; (3)Hermetic welding: First, evacuate the sheath to 1 Pa. Subsequently, the Ta sheath is welded completely by electron beam welding.

[0056] (4)Hot isostatic pressing: The sealed and welded sheath is placed in a hot isostatic pressing furnace for hot isostatic pressing. The temperature is 800 °C, the pressure is 130 MPa, and the time is 4 h. After the hot isostatic pressing process is completed, the sheath is removed to obtain the target material.

[0057] It can be seen from the SEM image of the tungsten-zirconium interface of the target material obtained in this embodiment that the interface of the obtained target material has good bonding, and no obvious defects such as pores and cracks are found, as Figure 11 . Subsequently, a drawing test as shown in Figure 4 is carried out. The GB / T8642 standard is implemented. A total of 10 samples are taken at different positions of the target material interface. The average drawing strength of the tungsten-zirconium interface of the target material obtained in this embodiment is 80.90 MPa. In this embodiment, a metal Ti with a lower melting point is used as the transition layer. Therefore, even when the hot isostatic pressing temperature is relatively low, the connection strength between zirconium and tungsten in the obtained target sheet is still relatively high, and there is no cracking at the connection interface.

[0058] The target material obtained in this embodiment is also subjected to an autoclave corrosion test. The experimental conditions are: corrosion in deionized water at 360 °C and 18.6 MPa for 100 d. Compared with the mass of the original material, the weight gain per unit area of the target material under this experimental condition is 27.51 mg / dm 2 .

[0059] Example 6 (1)Initial processing of raw materials: Pure tungsten and nuclear-grade zirconium alloy with grade Zr-2.5Nb (composition: Zr-2.5%Nb) are used as the target material raw materials. The tungsten block and zirconium sheet are processed into specific dimensions. The thickness of the zirconium sheet is 10 mm, and the length and width are precisely matched with the tungsten block. To ensure the subsequent welding quality and make the welded tungsten block and zirconium sheet fit more closely, in this embodiment, the surface to be welded is first wiped with a wire drawing cloth, then washed with acetone and distilled water, and then ultrasonically cleaned and dried; (2) Assembly: Press the zirconium sheet tightly against the surface of the tungsten block and place them together in a jacket. In this embodiment, a Ta metal sheet with a thickness of 0.1 mm is added between the zirconium sheet and the tungsten block as a transition layer; (3) Hermetic welding: First, evacuate the inside of the jacket to 0.001 Pa. Subsequently, weld the Ti - material jacket completely by argon - arc welding.

[0060] (4) Hot isostatic pressing: Place the hermetically - welded jacket into a hot isostatic pressing furnace for hot isostatic pressing. The temperature is 1450 °C, the pressure is 200 MPa, and the time is 1 h. After the hot isostatic pressing process is completed, remove the jacket to obtain the target.

[0061] The interface of the target prepared in this embodiment has good bonding, and no obvious defects such as holes and cracks are found. The SEM image of the interface is similar to Figure 11 . Subsequent tensile - pull tests as shown in Figure 4 were carried out. Implementing the GB / T 8642 standard, a total of 10 samples were taken at different positions of the target interface. The average tensile - pull strength of the tungsten - zirconium interface of the target obtained in this embodiment is 68.45 MPa. In this embodiment, refractory metal Ta is used as the transition layer, so a relatively high hot isostatic pressing temperature is adopted. The connection strength between zirconium and tungsten in the obtained target is high, and there is no cracking at the connection interface.

[0062] The target obtained in this embodiment was also subjected to an autoclave corrosion test. The test conditions are: Corrode in de - ionized water at 360 °C and 18.6 MPa for 100 d. Compared with the mass of the original material, the weight gain per unit area of the target under this test condition is 34.65 mg / dm 2 .

[0063] Example 7 (1) Initial processing of raw materials: Use pure tungsten and nuclear - grade zirconium alloy grade M5 (composition: Zr - 1.0% Nb - 0.125% O) as the target. Process the tungsten block and zirconium sheet into specific sizes. The thickness of the zirconium sheet is 6 mm, and the length and width are precisely matched with the tungsten block. To ensure the subsequent welding quality and make the welded tungsten block and zirconium sheet fit better, in this embodiment, first wipe the surface to be welded with a wire - drawing cloth, then clean it with alcohol, and then ultrasonic clean and dry; (2) Assembly: Press the zirconium sheet tightly against the surface of the tungsten block and place them together in a jacket. In this embodiment, a Ni metal sheet with a thickness of 0.05 mm is added between the zirconium sheet and the tungsten block as a transition layer; (3) Hermetic welding: First, evacuate the inside of the jacket to 0.1 Pa. Subsequently, weld the 316L - steel - material jacket completely by laser welding.

[0064] (4) Hot isostatic pressing: The sealed and welded cladding is placed into a hot isostatic pressing furnace for hot isostatic pressing at a temperature of 750 °C, a pressure of 100 MPa, and a time of 8 h. After the hot isostatic pressing process is completed, the cladding is removed to obtain the target.

[0065] The target obtained in this embodiment has good interfacial bonding, and no obvious defects such as holes and cracks are found. The SEM image of the interface is similar to Figure 11 . Subsequent Figure 4 The drawing test as shown in was carried out, and the GB / T 8642 standard was executed. A total of 10 samples were taken at different positions of the target interface. The average drawing strength of the tungsten-zirconium interface of the target obtained in this embodiment is 63.26 MPa. In this embodiment, the metal Ni with a lower melting point is used as the transition layer. Therefore, even when the hot isostatic pressing temperature is relatively low, the connection strength between zirconium and tungsten in the obtained target is relatively high, and there is no cracking at the connection interface.

[0066] The target obtained in this embodiment was also subjected to an autoclave corrosion test. The test conditions were: corrosion in deionized water at 360 °C and 18.6 MPa for 100 d. Compared with the mass of the original material, the weight gain per unit area of the target under this test condition was 28.42 mg / dm 2 .

[0067] Example 8 (1) Initial processing of raw materials: Pure tungsten and nuclear-grade zirconium alloy grade E110 (composition: Zr-1.0% Nb) are used as the target. The tungsten block and zirconium sheet are processed into specific sizes. The thickness of the zirconium sheet is 7 mm, and the length and width are precisely matched with the tungsten block. In order to ensure the subsequent welding quality and make the welded tungsten block and zirconium sheet fit better, in this embodiment, the surface to be welded is first wiped with a wire drawing cloth, then cleaned with alcohol, and then ultrasonically treated and dried; (2) Assembly: The zirconium sheet is closely attached to the surface of the tungsten block and they are placed together into the cladding; (3) Sealing and welding: First, the inside of the cladding is evacuated to 0.01 Pa. Subsequently, the cladding made of 316L steel is welded completely by laser welding. In this embodiment, a Nb metal sheet with a thickness of 0.04 mm is added between the zirconium sheet and the tungsten block as the transition layer.

[0068] (4) Hot isostatic pressing: The sealed and welded cladding is placed into a hot isostatic pressing furnace for hot isostatic pressing at a temperature of 1200 °C, a pressure of 150 MPa, and a time of 3 h. After the hot isostatic pressing process is completed, the cladding is removed to obtain the target.

[0069] The target obtained in this embodiment has good interfacial bonding, and no obvious defects such as holes and cracks are found. The SEM image of the interface is similar to Figure 11 . Subsequent Figure 4For the pull-out test shown in , the GB / T 8642 standard was executed. A total of 10 samples were taken at different positions of the target material interface. In this embodiment, the average pull-out strength of the tungsten-zirconium interface of the target material was 73.74 MPa. Therefore, with the preparation method provided in this embodiment, the connection strength between zirconium and tungsten in the obtained target slice is relatively high, and there is no cracking at the connection interface.

[0070] The target material obtained in this embodiment was also subjected to an autoclave corrosion test. The experimental conditions were: corrosion in deionized water at 360 °C and 18.6 MPa for 100 d. Compared with the mass of the original material, the weight gain per unit area of the target material under this experimental condition was 34.19 mg / dm 2 .

[0071] Example 9 (1) Initial processing of raw materials: Pure tungsten and nuclear-grade zirconium alloy grade E635 (composition: Zr-1.2%Sn-1%Nb-0.35%Fe) were used as the target material. The tungsten block and zirconium sheet were processed into specific dimensions. The thickness of the zirconium sheet was 5 mm, and the length and width were precisely matched with the tungsten block. To ensure the subsequent welding quality and make the welded tungsten block and zirconium sheet fit better, in this embodiment, the surface to be welded was first wiped with a wire drawing cloth, then cleaned with alcohol, and then ultrasonically treated and dried; (2) Assembly: The zirconium sheet was closely attached to the surface of the tungsten block and placed together in a jacket; (3) Hermetic welding: First, the inside of the jacket was evacuated to 0.01 Pa. Subsequently, the jacket made of 316L steel was welded completely by argon arc welding, and a Mo metal sheet with a thickness of 0.03 mm was added as a transition layer between the zirconium sheet and the tungsten block.

[0072] (4) Hot isostatic pressing: The hermetically welded jacket was placed in a hot isostatic pressing furnace for hot isostatic pressing. The temperature was 1000 °C, the pressure was 130 MPa, and the time was 2 h. After the hot isostatic pressing process was completed, the jacket was removed to obtain the target material.

[0073] The interface of the target material prepared in this embodiment is very good, and no obvious defects such as holes and cracks are found. The SEM image is similar to Figure 11 . Subsequently, the same pull-out test as shown in Figure 4 was also carried out. The GB / T 8642 standard was executed. A total of 10 samples were taken at different positions of the target material interface. In this embodiment, the average pull-out strength of the tungsten-zirconium interface of the target material was 74.47 MPa. Therefore, with the preparation method provided in this embodiment, the connection strength between zirconium and tungsten in the obtained target slice is relatively high, and there is no cracking at the connection interface.

[0074] The target material obtained in this embodiment was also subjected to an autoclave corrosion test. The experimental conditions were: corrosion in deionized water at 360 °C and 18.6 MPa for 100 d. Compared with the mass of the original material, the weight gain per unit area of the target material under this experimental condition was 30.63 mg / dm2 。

[0075] Example 10 The difference between this example and Example 3 is only that a W-Re alloy is used to replace pure tungsten as the material to be coated, and the other settings are the same as those in Example 3.

[0076] The target obtained in this example has good interfacial bonding, and no obvious defects such as holes and cracks are found. The SEM image of the tungsten-zirconium interface of the target is similar to Figure 7 。The tungsten and zirconium elements diffuse into each other at the target interface, forming a diffusion layer with a thickness of about 0.3 μm, and a metallurgical bond is formed at the tungsten-zirconium welding joint. Subsequently, a drawing test as shown in Figure 4 was carried out. The GB / T 8642 standard was executed, and 10 samples were taken at different positions of the target interface. The average drawing strength of the tungsten-zirconium interface of the target obtained in this example was 67.96 MPa. Using the preparation method provided in this example, the connection strength between zirconium and tungsten in the obtained target is relatively high, and there is no cracking at the connection interface.

[0077] The target obtained in this example was also subjected to an autoclave corrosion test. The experimental conditions were: corrosion in deionized water at 360 °C and 18.6 MPa for 100 d. Compared with the mass of the original material, the weight gain per unit area of the target under these experimental conditions was 29.83 mg / dm 2 。

Claims

1. A zirconium-coated tungsten target for a spallation neutron source, characterized in that: The tungsten is pure tungsten or a W—Re alloy, and the zirconium is pure zirconium or a nuclear-grade zirconium alloy.

2. The zirconium-coated tungsten target according to claim 1, characterized in that: The nuclear-grade zirconium alloy composition includes Sn: 0-3% by mass percentage; Nb ：0-5%； Fe: 0-2%; Ni: 0-3.5%; Cr: 0-1%; Cu: 0-1%; Bi: 0-1%; Ge: 0-1%; Sn, Nb, Fe, Ni, Cr, Cu, Bi and Ge are not all 0 at the same time; and other unavoidable impurity elements, the rest is Zr; And / or, the thickness of the zirconium is 0.1-10 mm.

3. The zirconium-coated tungsten target according to claim 1, characterized in that: A metal transition layer is added between the tungsten and the zirconium.

4. The zirconium-coated tungsten target according to claim 3, characterized in that: The material of the metal transition layer is one or more of Ti, Ta, Ni, Nb, Mo and alloys thereof, and / or the thickness of the metal transition layer is 0-0.1 mm.

5. A method for preparing a zirconium-coated tungsten target for a spallation neutron source, characterized in that: The preparation method comprises the steps of raw material preliminary processing, assembly, sealing welding, and hot isostatic pressing in sequence; wherein, in the raw material preliminary processing step, the raw materials of tungsten and zirconium are processed into specific shapes and sizes, and the raw material material of tungsten is pure tungsten or one of W-Re alloys; the raw material material of zirconium is pure zirconium or one of nuclear-grade zirconium alloys.

6. The preparation method according to claim 5, characterized in that: The nuclear-grade zirconium alloy composition includes Sn: 0-3%; Nb: 0-5% by mass percentage; Fe: 0-2%; Ni: 0-3.5%; Cr: 0-1%; Cu: 0-1%; Bi: 0-1%; Ge: 0-1%; Sn, Nb, Fe, Ni, Cr, Cu, Bi and Ge are not all 0 at the same time; and other unavoidable impurity elements, the rest is Zr; And / or, in the raw material initial processing step, the tungsten raw material is processed into a tungsten block; the zirconium raw material is processed into a zirconium sheet with a thickness of 0.1-10 mm, and the zirconium sheet can completely cover the outer surface of the tungsten block after hot pressing; all surfaces of the tungsten block and the zirconium sheet to be welded are cleaned and set aside.

7. The preparation method according to claim 5, characterized in that: In the assembling step, the zirconium sheet is coated on the surface of the tungsten block and then placed into the metal sheath together.

8. The preparation method according to claim 7, characterized in that: A metal transition layer is added between the tungsten block and the zirconium sheet; and / or the material of the metal sheath is one of steel, tantalum, and titanium; and / or the material of the metal transition layer is one or more of Ti, Ta, Ni, Nb, Mo and their alloys; and / or the thickness of the metal transition layer is 0-0.1 mm.

9. The preparation method according to claim 5, characterized in that: In the sealing step, the inside of the package is first evacuated to a specific vacuum degree, and then the entire package is sealed; and / or the sealing is performed by one or more of electron beam welding, laser welding, and argon arc welding.

10. The preparation method according to claim 5, characterized in that: In the hot isostatic pressing step, the sealed and welded package is subjected to hot isostatic pressing at a temperature of 750-1450° C., a pressure of 100-200 MPa, and a time of 1-8 hours.

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