Joint of tungsten and low-activation ferrite steel and method for manufacturing the same

Abstract

To provide a joint of tungsten and low-activation ferrite steel that can be easily formed while suppressing the embrittlement of the low-activation ferrite steel. [Solution] In a tungsten and low-activation ferritic steel joint, a tungsten material (1) and a low-activation ferritic steel material (2) are joined together, with the tungsten material and the low-activation ferritic steel material joined via an intermediate material (3) mainly composed of copper, and this intermediate material has phosphorus dissolved in copper and granular tungsten dispersed in copper.

Description

Technical Field

[0001] The present invention relates to a joined body of tungsten and low-activation ferrite steel in which a tungsten material and a low-activation ferrite steel are joined via an intermediate material, and a method for manufacturing the same.

Background Art

[0002] In a fusion reactor that confines high-temperature plasma, a device called a divertor for removing, for example, surplus gas and impurities is installed as a plasma-facing device. The divertor has a divertor plate with which high-temperature plasma directly contacts. This divertor plate is required to have excellent heat resistance, low-activation characteristics with little activation due to neutron irradiation, and high thermal conductivity. Tungsten, a high-melting-point metal that satisfies these requirements, is used for the divertor plate.

[0003] The divertor plate that contacts high-temperature plasma needs to be cooled strongly, and a heat sink is joined to the side opposite to the surface where the plasma contacts. Low-activation ferrite steel having heat resistance, high thermal conductivity, and low-activation characteristics is promising from the viewpoints of ensuring safety and reducing environmental load for the heat sink. Therefore, a joined body of tungsten and low-activation ferrite steel is required.

[0004] Regarding a joined body of tungsten and low-activation ferrite steel, for example, in Patent Document 1, a gradient functional material for joining a tungsten-based material and a low-activation ferrite steel, which has a layer containing vanadium or chromium and a layer containing iron and aluminum, is described. Further, Patent Document 2 describes a technique in which a film-like body of a titanium alloy is sandwiched between a tungsten-based material and an iron-based metal and heated to 900°C or higher by pulsed energization for joining.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] Patent Document 1 describes forming a bonded structure by joining a tungsten-based material and low-activation ferrite steel via a graded functional material using a directed energy deposition (DED) method, which involves layering (depositing) while varying the composition. The composition is changed by altering the mixing ratio of various material powders supplied. The mixed material powder is then thinly placed, irradiated with laser light to melt it, and a thin metal or alloy layer is deposited by cooling and solidification, a process that is repeated. However, forming a bonded structure of tungsten-based material and low-activation ferrite steel using directed energy deposition requires repeated deposition to the desired thickness, which is not easy from the standpoint of time and manufacturing cost.

[0007] Furthermore, although the melting point of low-activation ferritic steel is around 1500°C, it becomes embrittle when heated to high temperatures, and the embrittlement becomes significant above 800°C. For this reason, heating to 900°C or higher for joining, as described in Patent Document 2, is undesirable, and there has been a need for a tungsten-low-activation ferritic steel joint that can be easily formed while suppressing the embrittlement of the low-activation ferritic steel.

[0008] This invention has been made in view of the above problems, and aims to provide a joint of tungsten and low-activation ferrite steel that can be easily formed while suppressing the embrittlement of low-activation ferrite steel, and a method for manufacturing the same. [Means for solving the problem]

[0009] The joint of tungsten and low-activation ferrite steel according to claim 1 is For use in a diverterIn a tungsten and low-activation ferrite steel joint, the tungsten material and the low-activation ferrite steel material are joined via an intermediate material mainly composed of copper, and the intermediate material is made of copper. The material is an alloy in which phosphorus is in solid solution, and has a layer separated from the tungsten material and the low-activation ferrite steel material, in which granular tungsten is dispersed in the alloy, and the shear strength of the joint between the tungsten material and the low-activation ferrite steel material is 10 MPa or more. It is characterized by the following.

[0010] According to the above configuration, For use in divertors The joint of tungsten and low-activation ferritic steel is made up of tungsten material and low-activation ferritic steel material, Copper is the main component They are joined together via an intermediate material. This is an alloy in which phosphorus is dissolved in copper, and a layer of dispersed granular tungsten is formed at a position separated from the tungsten material and the low-activation ferrite steel material of this alloy. The phosphorus in the intermediate material is used in the joining process. The melting point of the copper in the intermediate material is lowered by phosphorus. It is a product that takes advantage of this fact. It can easily suppress the embrittlement of low-activation ferrite steel at low temperatures. To enable joining and to ensure sufficient strength so that the shear strength of the joint is 10 MPa or more. It can be joined together. Also, intermediate material In the copper, there is a layer in which granular tungsten is dispersed. The inclusion of this material reduces residual stress in the intermediate material after joining, thereby suppressing the occurrence of cracks in the intermediate material and delamination at the joint surface.

[0011] The joint of tungsten and low-activation ferrite steel according to claim 2 is, in the invention of claim 1, the intermediate material is On the tungsten material side of the layer in which granular tungsten is dispersed in the copper, Contains titanium Having layers It is characterized by the following. According to the above configuration, intermediate material Titanium-containing layer Titanium that 、 This promotes the reaction between the intermediate material and the tungsten material, thereby strengthening the bond.

[0012] The tungsten and low-activation ferritic steel joint of the invention of claim 3 is characterized in that, in the invention of claim 1, a refrigerant passage for circulating a refrigerant is formed in the low-activation ferritic steel material. According to the above configuration, tungsten material can be cooled by cooling low-activation ferrite steel material with a refrigerant, and can be used, for example, in plasma-facing equipment in a nuclear fusion reactor.

[0013] The method for manufacturing a joint of tungsten and low-activation ferrite steel according to claim 4 is: For use in a diverterIn a method for manufacturing a tungsten and low-activation ferrite steel joint, in which a tungsten material and a low-activation ferrite steel material are joined together, between the tungsten material and the low-activation ferrite steel material, An intermediate material mainly composed of copper, wherein a mixture of copper powder and tungsten powder is laminated between phosphorus copper foil containing 6% by mass of phosphorus. An intermediate material is sandwiched in the direction of the stacking of the intermediate material, and while the intermediate material is pressurized in the direction of the stacking, by an electric heating method 700℃ The method is characterized by joining the tungsten material and the low-activation ferrite steel material via the intermediate material by heating them to ~800°C.

[0014] According to the above configuration, For use in a diverter Tungsten material and low-activation ferritic steel material are joined via an intermediate material mainly composed of copper. The intermediate material is a mixture of copper powder and tungsten powder. , contains 6% by mass of phosphorus It is constructed in a laminated form by sandwiching it between phosphorus copper foil. This copper-based intermediate material is sandwiched between tungsten material and low-emission ferrite steel material in the direction of the intermediate material's lamination, and then heated by applying electric current while under pressure. 700℃ The materials are heated to a temperature between 0°C and 800°C for joining. Since the melting point of the intermediate copper is lowered by phosphorus, embrittlement of the low-activation ferritic steel can be suppressed. The phosphorus copper foil and copper powder are promoted to melt at a low temperature, and the tungsten material and the low-activation ferritic steel material are easily joined. Furthermore, the shear strength of the joint is sufficient to be 10 MPa or more. It can be joined together. Also, this intermediate material for, The copper contains dispersed granular tungsten that does not dissolve in copper. Because layers are formed, The residual stress in the intermediate material after joining is relieved, which can suppress the occurrence of cracks in the intermediate material and delamination at the joint surface.

[0015] The method for manufacturing a joint of tungsten and low-activation ferritic steel according to claim 5 is characterized in that, in the invention of claim 4, the intermediate material further has titanium foil and phosphor copper foil laminated on the tungsten material side. According to the above configuration, the molten phosphorus copper foil and titanium foil react when heated by electric current, causing titanium to diffuse. The titanium then promotes the reaction between the intermediate material and the tungsten material, resulting in a strong bond.

[0016] The manufacturing method of the joined body of tungsten and low-activation ferrite steel according to the invention of claim 6 is characterized in that, in the invention of claim 5, a pure copper foil is further laminated on the low-activation ferrite steel side of the intermediate material. According to the above configuration, when the pure copper foil melts by reacting with the molten phosphorus copper foil by electric heating and phosphorus diffuses to the low-activation ferrite steel side, the pure copper foil suppresses the arrival of phosphorus to the low-activation ferrite steel material. Therefore, an excessive reaction between phosphorus and the low-activation ferrite steel material can be suppressed, and deterioration of the low-activation ferrite steel material due to joining can be suppressed.

[0017] The manufacturing method of the joined body of tungsten and low-activation ferrite steel according to the invention of claim 7 is characterized in that, in the invention of claim 5, the mixture of the intermediate material is formed by mixing copper powder, tungsten powder, and synthetic resin. According to the above configuration, since the mixture of copper powder and tungsten powder is a molded body formed by mixing and molding synthetic resin, it is easier to handle than in a powder state, and the productivity of the joined body of tungsten and low-activation ferrite steel can be improved.

Effect of the Invention

[0018] According to the joined body of tungsten and low-activation ferrite steel and its manufacturing method of the present invention, there is provided a joined body of tungsten and low-activation ferrite steel that can suppress embrittlement of the low-activation ferrite steel material and can be easily formed.

Brief Description of the Drawings

[0019] [Figure 1] It is a diagram showing the inside of a fusion reactor. [Figure 2] It is a perspective view showing an example of a divertor plate formed by the joined body of tungsten and low-activation ferrite steel of the present invention. [Figure 3] It is a perspective view of a cylindrical test body for evaluating the joined body of tungsten and low-activation ferrite steel. [Figure 4] It is a configuration diagram of a pulse electric current pressure sintering apparatus used for manufacturing the test body of FIG. 3. [Figure 5] This table shows the formation conditions and evaluation results for the test specimens of Examples 1-5 and Comparative Example 1. [Figure 6] This is a cross-sectional SEM image of the joint portion of the test specimen in Example 3. [Figure 7] Figure 6 shows a magnified cross-sectional SEM image of the main section and its EDS elemental mapping. [Figure 8] This table shows the formation conditions and evaluation results for the test specimens of Examples 6-11 and Comparative Example 2. [Modes for carrying out the invention]

[0020] As shown in Figure 1, inside the fusion reactor that confines the high-temperature plasma, there is a plasma-facing device, such as a divertor, to remove excess gas and impurities. The divertor has a divertor plate A that comes into contact with the high-temperature plasma.

[0021] For example, as shown in Figure 2, the diverter plate A is formed from a tungsten and low-activation ferrite steel joint, in which a tungsten material 1 and a low-activation ferrite steel material 2 are joined via an intermediate material 3. The tungsten material 1 and the low-activation ferrite steel material 2 each possess excellent heat resistance, low activation characteristics with minimal activation due to neutron irradiation, and high thermal conductivity, respectively. To cool the diverter plate A, a refrigerant passage is formed inside the low-activation ferrite steel material 2 for circulating a refrigerant, for example, flowing in from an inlet pipe B and out from an outlet pipe C.

[0022] Such tungsten and low-activation ferritic steel joints can also be applied to the first wall and protective limiter, which are plasma-facing components in fusion reactors. In the following, the tungsten and low-activation ferritic steel joint may be simply referred to as the "joint," and the low-activation ferritic steel 2 may be referred to as "RAFM steel 2," based on the initials of its English name, Reduced Activation Ferritic / Martensitic.

[0023] The thickness of the tungsten material 1 used in the divertor plate A of a nuclear fusion reactor is, for example, about 1 mm to 30 mm, but is not limited to this and can be determined appropriately depending on the application. Similarly, the thickness of the low-activation ferritic steel material 2 used in the divertor plate A is, for example, about 10 mm to 30 mm, but is not limited to this and can be determined appropriately depending on the application. The shape and size of the joint will be set according to the application.

[0024] Low-activation ferritic steel 2 has a melting point of approximately 1500°C, but even at temperatures lower than this melting point, above 800°C, the deterioration of its properties (embrittlement) becomes significant. Therefore, it is difficult to directly join tungsten material 1, which has a melting point exceeding 3000°C, and low-activation ferritic steel 2 while suppressing embrittlement. Instead, an intermediate material 3 is interposed between tungsten material 1 and low-activation ferritic steel 2 during the joining process.

[0025] For example, in a non-oxidizing atmosphere, the intermediate material 3 is compressed between the tungsten material 1 and the low-activation ferrite steel material 2, and then heated to a temperature of 800°C or lower by an electric heating method, melting at least a portion of the intermediate material 3 to join them. Non-oxidizing atmospheres include vacuum, inert gas atmospheres such as argon gas, and reducing atmospheres such as argon gas with added hydrogen gas. The electric heating method is a method in which an electric current is passed through a conductive object to be heated, and the object is directly heated by the Joule heat generated according to the electrical resistance of the object.

[0026] Next, we will describe the cylindrical test specimen used to evaluate the joint. As shown in Figure 3, the cylindrical test specimen is made by joining tungsten material 1 and low-activation ferritic steel material 2 via an intermediate material 3. Here, a commercially available cylindrical tungsten material 1 with a diameter of 9.4 mm and a length (thickness) of 10 mm was used. For the low-activation ferritic steel material 2, a cylindrical F82H steel (Fe-8Cr-2W-0.2V-0.04Ta-0.1C) with a diameter of 9.4 mm and a length (thickness) of 10 mm was used. Note that the type of low-activation ferritic steel material 2 is not limited to the above; for example, JLF-1 steel (Fe-9Cr-2W-0.2V-0.08Ta-0.1C-0.05N) can also be used.

[0027] Intermediate material 3 is a disc-shaped material with a diameter of 9.4 mm, mainly composed of copper, and its basic structure consists of a mixture of copper powder and tungsten powder sandwiched between two circular phosphorus copper foils. Hereafter, the mixture of copper powder and tungsten powder may be referred to as the "Cu·W mixture."

[0028] For the copper powder, electrolytic copper powder with a particle size of 30-40 μm was used. The melting point of copper powder is approximately 1085°C. For the tungsten powder, powder with a particle size of approximately 3-4 μm was used. The melting point of tungsten powder exceeds 3000°C. The Cu·W mixture was prepared by mixing copper powder and tungsten powder in a mass ratio of 85:15, and 0.78 g of the Cu·W mixture was used in the basic configuration described above.

[0029] The phosphorus copper foil is an alloy foil consisting of 94% copper by mass and 6% phosphorus by mass (manufactured by Toyo Yozai Co., Ltd., product number BC-106), with a melting point of 705°C at the solidus and 850°C at the liquidus. Here, a circular piece with a diameter of 9.4 mm was cut from a sheet of phosphorus copper foil with a thickness of 0.1 mm and used.

[0030] For intermediate material 3, in addition to the basic configuration described above, we also used laminated titanium foil and phosphor copper foil, laminated pure copper foil, and variations with different amounts of Cu·W mixture. For the titanium foil, we used commercially available sheets with a thickness of 0.15 mm, cut into circles with a diameter of 9.4 mm. For the pure copper foil, we used commercially available sheets with a thickness of 0.01 mm, cut into circles with a diameter of 9.4 mm. For the Cu·W mixture, in addition to the basic configuration described above, we used a mixture adjusted to 0.39 g and a mixture without Cu·W mixture (0 g). Furthermore, we added a synthetic resin (molding material) equivalent to 1 mass% of the Cu·W mixture and mixed it, then molded it into a disc shape with a mass of 1 g, a thickness of 1.8 mm, and a diameter of 9.4 mm. This disc-shaped molded body was held in a heat treatment furnace at 850°C in a hydrogen atmosphere for 1 hour to remove the resin component and create a robust molded body.

[0031] As an electrical heating method, spark plasma sintering (SPS method) is preferred. In spark plasma sintering, a pulsed current pressurizing sintering apparatus is used to heat the object to be heated by applying a large current pulse to it while pressurizing it. Since heat is generated according to the electrical resistance of the object to be heated, the heating temperature can be controlled by the current value, current application time, current application period, etc.

[0032] Next, the pulse current pressurized sintering apparatus 10 will be described based on Figure 4. The pulse current pressurized sintering apparatus 10 has a cylindrical artificial graphite die 12 with an inner diameter of 10 mm inside a casing 11, and a pair of cylindrical artificial graphite punches 13 and 14 with a diameter of 9.5 mm that are inserted into the die 12 from above and below. A heating object, for example, consisting of low-activation ferrite steel material 2, an intermediate material 3, and tungsten material 1 stacked in that order from bottom to top, is placed between the pair of punches 13 and 14. The heating object is mechanically pressurized (compressed) via the pair of punches 13 and 14. In order to prevent the heating object from sticking to the punches 13 and 14, graphite sheets (not shown) with the same diameter as the punches 13 and 14 and a thickness of 0.2 mm are sandwiched between the heating object and the punches 13 and 14.

[0033] The casing 11 is equipped with a lower jig, which is a spacer 15 made of artificial graphite, whose diameter decreases towards the punch 13 side. Similarly, the upper jig is equipped with a spacer 16 made of artificial graphite, whose diameter decreases towards the punch 14 side.

[0034] The die 12 has an opening in the middle side portion, and the temperature of the object to be heated (heating temperature) is measured by a thermocouple 17 inserted into the opening. The position of this thermocouple 17 corresponds to the position of the intermediate material 3. For insulation, a 5 mm thick carbon felt (not shown) is attached to the outer circumference of the die 12 so as to cover the die 12. The casing 11 airtightly covers these upper and lower fixtures, the die 12, and a pair of punches 13 and 14.

[0035] The pulsed current pressurizing sintering apparatus 10 further includes a pressurizing unit 18, a pulse power supply 19, a cooling mechanism 20, a vacuum unit 21, and a gas supply unit 22. The pressurizing unit 18 pressurizes the object to be heated via an upper jig, a lower jig, and punches 13 and 14. The pulse power supply 19 applies a DC pulse current to the object to be heated via the punches 13 and 14. The cooling mechanism 20 cools at least one pair of punches 13 and 14 by continuously circulating a coolant. The vacuum unit 21 evacuates the inside of the casing 11. The gas supply unit 22 supplies argon gas containing, for example, 3% by mass of hydrogen into the casing 11.

[0036] Using a pulse current pressurized sintering apparatus 10, cylindrical test specimens of joints formed by joining tungsten material 1 and low-activation ferrite steel material (RAFM steel material) 2 via an intermediate material 3 were prepared in Examples 1 to 11 and Comparative Examples 1 and 2, each with different formation conditions (composition of intermediate material 3, heating temperature, heating time, or pressure). A pulse current pressurized sintering apparatus (model: SPS-515S, maximum load 50kN, maximum pulse current output 1500A) manufactured by Sumitomo Coal Mining Co., Ltd. was used to prepare the test specimens.

[0037] The common formation conditions for the test specimens of Examples 1-11 and Comparative Examples 1 and 2 are shown. During heating, the atmosphere inside the casing 11 was reduced to a 50 kPa reducing atmosphere by first evacuating it to approximately 4 Pa, and then introducing argon gas with 3% by mass of hydrogen gas added. The heating rate was set to 50°C / min to 100°C / min from room temperature to the heating temperature. After the heating time (the time for maintaining the heating temperature) had elapsed, heating was stopped and the specimen was allowed to cool naturally in a casing 11 with an argon gas atmosphere containing 3% by mass of hydrogen gas. The cooling rate at this time was 30°C / min to 80°C / min. After cooling to below 200°C, the inside of the casing 11 was evacuated, then air was introduced and the test specimen was removed.

[0038] For each specimen, the shear strength was measured by applying stress in shear mode at a crosshead speed of 1 mm / min using an electronic universal testing machine (CATY-2002S, manufactured by Yonekura Seisakusho Co., Ltd.). A higher shear strength indicates a stronger joint. In addition, the joint (fractured) portion of the specimen was analyzed as appropriate using a scanning electron microscope (SEM, JSM-IT200, manufactured by JEOL Ltd.) equipped with an energy-dispersive X-ray spectrometer (EDS).

[0039] Figure 5 shows the formation conditions for Examples 1-5 and Comparative Example 1, and the evaluation results of the obtained test specimens. In Examples 1-5 and Comparative Example 1, an intermediate material 3 was used, in which titanium foil and phosphorus copper foil were laminated on the tungsten material 1 side, to the basic configuration of a Cu·W mixture with a mass of 0.78 g sandwiched between two phosphorus copper foils. Then, under pressure of 40 MPa in the lamination direction, the materials were bonded by heating at different heating temperatures for 10 minutes. The heating temperatures were 800°C for Example 1, 750°C for Example 2, 720°C for Example 3, 700°C for Example 4, 650°C for Example 5, and 600°C for Comparative Example 1.

[0040] Intermediate material 3, which is laminated with titanium foil, phosphorus copper foil, and a Cu·W mixture with voids between particles, has many interfaces (contact surfaces) where electrical resistance tends to be high, and generates more heat than tungsten material 1 and RAFM steel material 2 when energized. Also, because pulse current is applied, the temperature of intermediate material 3 fluctuates repeatedly in short periods of time. Therefore, even if the heating temperature measured by thermocouple 17 is lower than the melting point of phosphorus copper foil, the temperature within intermediate material 3 may reach the melting point of the phosphorus copper foil locally and instantaneously.

[0041] In Examples 1-5 and Comparative Example 1, which differed only in heating temperature, there was a tendency for the shear strength to decrease with decreasing heating temperature. While joining was possible when the heating temperature was 650°C to 800°C, Comparative Example 1, which was joined at a lower temperature of 600°C, fractured before shear strength measurement. In Comparative Example 1, it is thought that the intermediate material 3 did not react sufficiently with the tungsten material 1 due to the low heating temperature, and therefore could not be joined with sufficient strength. Since a shear strength of approximately 10 MPa or higher is practically preferable, a heating temperature of 700°C to 800°C is preferable. Furthermore, since a lower heating temperature is preferable to suppress embrittlement of the RAFM steel material 2, a heating temperature of 700°C to 720°C is preferable.

[0042] Figure 6 shows an SEM image of a cross-section parallel to the lamination direction at the joint of the specimen of Example 3 after shear strength measurement (after fracture). In Figure 6, tungsten material 1 and intermediate material 3 are visible, and the background is visible where RAFM steel material 2 previously existed. The brightest part is tungsten (tungsten material 1, granular tungsten). The slightly darker parts around the granular tungsten of intermediate material 3, and the slightly darker parts in contact with tungsten material 1, are mainly composed of copper, and the dark parts between the copper-dominant parts are titanium. Intermediate material 3 is integrated while largely maintaining the laminated structure.

[0043] Furthermore, Figure 7 shows an enlarged cross-sectional SEM image of the rectangular R portion in Figure 6 and its EDS elemental mapping. According to the SEM image, the portion that was a Cu·W mixture has reacted with the molten phosphorus copper foil, causing the copper powder to melt and solidify, and now contains dispersed tungsten powder (granular tungsten) within the copper. The granular dark areas within the copper are voids, and some of the voids that existed in the Cu·W mixture remain. According to the EDS elemental mapping, the copper containing the tungsten powder also contains phosphorus (P), and segregation of phosphorus and iron (Fe) is observed at the joint surface (fracture surface) between the intermediate material 3 and the RAFM steel material 2.

[0044] Next, Figure 8 shows the formation conditions and evaluation results of the obtained test specimens for Examples 6 to 11 and Comparative Example 2. In Example 6, only the basic configuration of intermediate material 3 described above was used, and the materials were joined by heating at 720°C for 10 minutes under pressure of 40 MPa. The only difference from Example 3 was the configuration of intermediate material 3, resulting in a shear strength of 32 MPa, which was lower than that of Example 3 (68 MPa), but sufficient strength was achieved in the joint. It is thought that the titanium foil reacts with the molten phosphorus copper foil, causing titanium to diffuse, and this titanium promotes the reaction between intermediate material 3 and tungsten material 1, thereby strengthening the joint.

[0045] Examples 7 and 8 used an intermediate material 3 in which titanium foil and phosphorus copper foil were laminated on the tungsten material 1 side, and pure copper foil was laminated on the RAFM steel material 2 side, in addition to the basic configuration described above. Then, under pressure of 40 MPa, Example 7 was heated at 720°C for 10 minutes and Example 8 was heated at 720°C for 30 minutes to bond them. Although the configuration of the intermediate material 3 differs from that of Example 3, and Example 8 was heated for a longer period of 30 minutes than Example 7, the shear strengths were 62 MPa and 57 MPa, respectively, which are about the same as those of Example 3. For the bonding of the test specimens in this case, a heating time of 10 minutes is sufficient. Furthermore, even when pure copper foil is interposed on the RAFM steel material 2 side to suppress the excessive reaction between phosphorus and RAFM steel material 2, which is estimated from the phosphorus and iron segregation in Example 3, a bond with sufficient strength can be achieved.

[0046] In Example 9, a Cu·W mixture was mixed with a synthetic resin equivalent to 1% by mass, molded into a 1g disc, sandwiched between phosphorus copper foil, and then titanium foil and phosphorus copper foil were laminated on the tungsten material 1 side to form an intermediate material 3. The materials were then joined by heating at 720°C for 10 minutes under pressure of 40 MPa. Unlike Example 3, the Cu·W mixture was a molded body and had a larger mass. Although the shear strength was lower than in Example 3 at 25 MPa, sufficient strength was achieved for joining. The molded Cu·W mixture is easier to handle than the powder form, contributing to improved productivity of the joined materials.

[0047] Example 10 used the same intermediate material 3 as in Example 3, and was joined by heating at 720°C for 10 minutes under a lower pressure of 5 MPa. Only the heating pressure was lower than in Example 3 at 5 MPa, resulting in a lower shear strength of 12 MPa compared to Example 3. A higher shear strength is preferable, but joining under a pressure of at least 5 MPa is sufficient.

[0048] In Example 11 and Comparative Example 2, the intermediate material 3 was modified from the basic configuration above by changing the mass of the Cu·W mixture to 0.39g (half amount) and 0g (no Cu·W mixture), respectively, and a titanium foil and phosphorus copper foil were laminated on the tungsten material 1 side. The materials were then joined by heating at 720°C for 10 minutes under pressure of 40 MPa. In Example 11, sufficient joining was possible even with half the amount of Cu·W mixture compared to Example 3, and the shear strength was 49 MPa. On the other hand, in Comparative Example 2, which did not use the Cu·W mixture, the material had already fractured when removed from the pulse current pressurized sintering apparatus 10 and could not be joined.

[0049] In the Cu·W mixture, the copper powder melts upon reaction with the molten phosphorus copper foil, but the tungsten powder remains unmelted and is incorporated into the copper. Since copper has a higher coefficient of thermal expansion than tungsten, it shrinks significantly when cooled, resulting in increased residual stress in the intermediate material 3 after joining, causing fracture as seen in Comparative Example 2. However, it is believed that the dispersion of tungsten powder (granular tungsten) in the molten copper suppresses the shrinkage of the intermediate material 3 upon cooling, thereby easing the residual stress and preventing fracture.

[0050] As described above, in the joints of Examples 1 to 11, a tungsten material 1 and a low-activation ferritic steel material 2 are joined via an intermediate material 3 mainly composed of copper, which consists of a mixture of copper powder and tungsten powder sandwiched between phosphorus copper foil. The intermediate material 3 contains phosphorus derived from the phosphorus copper foil dissolved in the copper, and multiple granular tungsten dispersed in the copper. The phosphorus lowers the melting point of the copper in the intermediate material 3, enabling joining at a temperature that suppresses the embrittlement of the low-activation ferritic steel material 2. In addition, the inclusion of granular tungsten in the intermediate material 3 relieves the residual stress of the intermediate material 3 after joining, suppressing the occurrence of cracks and delamination of the intermediate material 3 that could lead to fracture of the joint.

[0051] Furthermore, the titanium foil, which is laminated on the tungsten material 1 side sandwiched between phosphorus copper foil, reacts with the molten phosphorus copper foil, causing titanium to diffuse. This titanium is thought to promote the reaction between the tungsten material 1 and the intermediate material 3, thereby strengthening the bond. On the other hand, the pure copper foil, which is layered on the low-activation ferritic steel material 2 side, reacts with the molten phosphorus copper foil and melts. When it reacts with the low-activation ferritic steel material 2, it functions as a buffer to suppress the reaction between phosphorus and the low-activation ferritic steel. This allows for bonding while suppressing the alteration of the low-activation ferritic steel material 2. In addition, the Cu·W mixture can be made into a molded body by mixing it with a synthetic resin, making it easier to handle and facilitating the formation of the bonded body.

[0052] The operation and effects of the present invention will be explained. For use in divertorsThe joint between tungsten and low-activation ferritic steel is formed by joining the tungsten material 1 and the low-activation ferritic steel material 2 via an intermediate material 3 mainly composed of copper. The copper contains phosphorus in solid solution. Furthermore, the intermediate material 3 has a layer in which granular tungsten is dispersed in copper, which is formed so as not to come into contact with the tungsten material and the low-activation ferritic steel material. The phosphorus in the intermediate material 3 is present during joining. The melting point of copper is lowered by phosphorus. It is a product that takes advantage of this fact. The embrittlement of the low-activation ferrite steel 2 can be easily suppressed at a temperature that allows for this process. To enable joining and to ensure sufficient strength so that the shear strength of the joint is 10 MPa or more. It can be joined together. Also, the intermediate material 3 to, Granular tungsten is dispersed in copper. The layer that The inclusion of this material relieves residual stress in the intermediate material 3 after joining, thereby suppressing the occurrence of cracks in the intermediate material 3 and delamination at the joint surface. On the tungsten side of the layer where granular tungsten is dispersed in copper, Furthermore, it contains titanium. Having layers In that case, This layer Titanium promotes the reaction between the intermediate material 3 and the tungsten material 1, enabling a strong bond.

[0053] The low-activation ferrite steel 2 has refrigerant passages formed in it for circulating a refrigerant, and the tungsten material 1 can be cooled by cooling the low-activation ferrite steel 2 with the refrigerant. Therefore, the joint of tungsten and low-activation ferrite steel can be used, for example, as a plasma-facing device that comes into contact with the high-temperature plasma of a nuclear fusion reactor.

[0054] For use in a divertor, The tungsten material 1 and the low-activation ferritic steel material 2 are intermediate materials 3 mainly composed of copper, and a mixture of copper powder and tungsten powder (Cu·W mixture) , contains 6% by mass of phosphorus The materials are joined via an intermediate material 3, which is constructed in a laminated manner by sandwiching it between phosphorus copper foil. At this time, the intermediate material 3 is sandwiched between a tungsten material 1 and a low-activation ferrite steel material 2 in the direction of the laminate of the intermediate material 3, and while under pressure, it is heated by applying electric current to suppress the embrittlement of the low-activation ferrite steel. 700℃ The materials are heated to a temperature of 800°C to join them. The melting point of the copper in the intermediate material 3 is lowered by the phosphorus in the phosphorus copper foil, which can suppress the embrittlement of the low-activation ferritic steel. This promotes the melting of the phosphorus copper foil and copper powder at a low temperature, and easily joins the tungsten material 1 and the low-activation ferritic steel material 2. Furthermore, the shear strength of the joint is sufficient to be 10 MPa or more. It can be joined together. Also, this intermediate material 3 is copper It contains dispersed granular tungsten that does not melt. Because a layer is formed This reduces the residual stress in the intermediate material 3 after joining, thereby suppressing the occurrence of cracks in the intermediate material 3 and delamination at the joint surface.

[0055] Intermediate material 3 has titanium foil and phosphorus copper foil laminated on the tungsten material 1 side. The titanium foil reacts with the phosphorus copper foil, which is melted by electric heating, and titanium diffuses. This titanium promotes the reaction between the tungsten material 1 and intermediate material 3, making the bond stronger. Alternatively, pure copper foil may be laminated on the low-activation ferritic steel material 2 side of intermediate material 3. The pure copper foil reacts with the phosphorus copper foil, which is melted by electric heating, and melts, suppressing the arrival of phosphorus from the phosphorus copper foil to the low-activation ferritic steel material 2 as it diffuses to the low-activation ferritic steel material 2. Therefore, excessive reaction between phosphorus and the low-activation ferritic steel material 2 can be suppressed, and the alteration of the low-activation ferritic steel material 2 due to bonding can be suppressed.

[0056] When a mixture of copper powder and tungsten powder is molded into a product by mixing it with a synthetic resin, the handling of this mixture becomes easier than when it is in powder form. Therefore, the productivity of tungsten and low-activation ferritic steel joints can be improved. The thickness of phosphorus copper foil, titanium foil, and pure copper foil, and the amount of the mixture of copper powder and tungsten powder are not limited to those mentioned above, and can be set to ensure sufficient bonding strength while considering that the thermal conductivity between the tungsten material 1 and the low-activation ferritic steel material 2 decreases as the thickness of the intermediate layer 3a increases.

[0057] When manufacturing a joint of tungsten and low-activation ferrite steel used in diverter plates A, etc., the tungsten material 1 and the low-activation ferrite steel material 2 should be joined using materials, jigs, and a pulse current pressure sintering apparatus that are sized to match the joint. The heating time should be set according to the size of the object to be heated, but from the viewpoint of productivity, it is preferable to be 60 minutes or less. Furthermore, those skilled in the art can implement the invention in various forms with modifications to the above embodiments without departing from the spirit of the present invention, and the present invention encompasses such modifications. [Explanation of Symbols]

[0058] 1: Tungsten material 2: Low-emission ferritic steel 3: Intermediate material 10: Pulse current pressurized sintering apparatus 11: Casing 12: Dice 13,14: Punch 15,16: Spacer 17: Thermocouple 18: Pressurized Unit 19: Pulse power supply 20: Cooling mechanism 21: Vacuum Unit 22: Gas supply unit

Claims

1. A tungsten and low-activation ferrite steel joint, in which a tungsten material and a low-activation ferrite steel material are joined for use in a diverter, The tungsten material and the low-activation ferrite steel material are joined together via an intermediate material mainly composed of copper. The aforementioned intermediate material is an alloy in which phosphorus is solid-solved in copper, and is a layer separated from the tungsten material and the low-activation ferrite steel material, having a layer in which granular tungsten is dispersed in the alloy. A joint of tungsten and low-activation ferrite steel, characterized in that the shear strength of the joint between the tungsten material and the low-activation ferrite steel material is 10 MPa or more.

2. The tungsten and low-activation ferritic steel joint according to claim 1, characterized in that the intermediate material has a titanium-containing layer on the tungsten material side of the layer in which granular tungsten is dispersed in the alloy.

3. The tungsten and low-activation ferritic steel joint according to claim 1 or 2, characterized in that a refrigerant passage for circulating a refrigerant is formed in the low-activation ferritic steel material.

4. A method for manufacturing a tungsten and low-activation ferrite steel joint, which is obtained by joining a tungsten material and a low-activation ferrite steel material for use in a diverter, Between the tungsten material and the low-activation ferrite steel material, an intermediate material mainly composed of copper is laminated in the direction of lamination of the intermediate material, with a mixture of copper powder and tungsten powder sandwiched between phosphorus copper foil containing 6% by mass of phosphorus. A method for manufacturing a tungsten and low-activation ferrite steel joint, characterized by joining the tungsten material and the low-activation ferrite steel material via the intermediate material by heating the intermediate material to 700°C to 800°C by an electric heating method while the intermediate material is pressurized in the stacking direction.

5. The method for manufacturing a tungsten and low-activation ferrite steel joint according to claim 4, characterized in that the intermediate material further laminates titanium foil and phosphor copper foil on the tungsten material side.

6. The method for manufacturing a tungsten and low-activation ferrite steel joint according to claim 5, characterized in that the intermediate material further laminates pure copper foil on the low-activation ferrite steel side.

7. The method for manufacturing a tungsten and low-activation ferrite steel joint according to claim 5, characterized in that the intermediate material mixture is formed by mixing copper powder, tungsten powder, and synthetic resin.

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