Tungsten material and plasma-facing material

Abstract

A tungsten material and a plasma-facing material according to the present invention have a plurality of crystal grains. In a plane where the average aspect ratio of the plurality of crystal grains is the minimum, the area ratio occupied by the (100) crystal plane is 2.0-8.0%.

Description

Tungsten Materials and Plasma-Facing Materials

[0001] This disclosure relates to tungsten materials and plasma-facing materials. This application claims priority to Japanese Patent Application No. 2024-047649, filed March 25, 2024. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] Conventionally, tungsten materials have been disclosed in, for example, WO 2022 / 215551 (Patent Document 1), JP 2002-371301 A (Patent Document 2), JP 2004-277810 A (Patent Document 3), JP 2004-279194 A (Patent Document 4), and JP 62-146235 A (Patent Document 5).

[0003] International Publication No. 2022 / 215551 Japanese Patent Application Laid-Open No. 2002-371301 Japanese Patent Application Laid-Open No. 2004-277810 Japanese Patent Application Laid-Open No. 2004-279194 Japanese Patent Application Laid-Open No. 62-146235

[0004] The tungsten material has a plurality of crystal grains, and the area ratio of the (100) crystal plane is 2.0% or more and 8.0% or less on the plane where the average aspect ratio of the plurality of crystal grains is smallest.

[0005] [Problem to be Solved by the Present Disclosure] There has been a demand for a tungsten material that is resistant to recrystallization and exhibits high ductility after recrystallization.

[0006] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0007] Conventionally, tungsten materials that have undergone plastic processing such as rolling recrystallize in high-temperature environments, resulting in a decrease in ductility. Recrystallization occurs more easily when there is a large amount of strain in the material, which is the driving force behind recrystallization.

[0008] If the grain size after recrystallization is coarse, the ductility will be further reduced. The coarse (100) recrystallized grains generated by heating during hot rolling will eat away at the surrounding crystal grains when the material is placed in a high-temperature environment and recrystallizes, resulting in a coarse structure.

[0009] Generally, there is a trade-off between the difficulty of recrystallization and the grain size after recrystallization (ductility). More severe processing increases the amount of strain, making recrystallization easier, but the crystal grains after processing become finer, and the grain size after recrystallization also becomes finer.

[0010] In the present disclosure, by focusing on the proportion of (100) crystal faces, which is strongly related to the grain size and processing degree after recrystallization, and controlling it within an appropriate range, it is possible to achieve both resistance to recrystallization and ductility after recrystallization.

[0011] The tungsten material has a plurality of crystal grains, and the area ratio of the (100) crystal plane is 2.0% or more and 8.0% or less in the plane where the average aspect ratio of the plurality of crystal grains is smallest. When the area ratio of the (100) crystal plane is 2.0% or more and 8.0% or less, a tungsten material that is resistant to recrystallization and exhibits high ductility after recrystallization can be provided.

[0012] More preferably, the area ratio of the (100) crystal plane is 2.0% or more and 6.0% or less, since this range further improves the ductility after recrystallization.

[0013] Preferably, the average crystal grain size is 80 μm or less. A tungsten material having a plurality of crystal grains and having been subjected to recrystallization heat treatment, in which the area ratio of the (100) crystal plane in the plane where the average aspect ratio of the plurality of crystal grains is smallest is 5.0% or more and 30.0% or less, and the average crystal grain size is 100 μm or less.

[0014] Preferably, the recrystallization heat treated tungsten material has a Vickers hardness of 500 HV or less.

[0015] Preferably, the recrystallization heat treated tungsten material has a Vickers hardness of 400 HV or less.

[0016] Preferably, the recrystallization heat treated tungsten material has a Vickers hardness of 380 HV or less.

[0017] Preferably, the tungsten material contains 10 ppm by mass or more and 100 ppm by mass or less of potassium (K).

[0018] Preferably, the tungsten material contains 20% by mass or less in total of at least one element selected from the group consisting of C (carbon), Ti (titanium), Cr (chromium), Zr (zirconium), Mo (molybdenum), Ta (tantalum), Re (rhenium), and La (lanthanum).

[0019] The plasma-facing material is any of the above tungsten materials, and is a material that is exposed to plasma in, for example, a nuclear fusion reactor.

[0020] It has been discovered that the tungsten material of the present disclosure is effective when it has the following characteristic values:

[0021] It has been discovered that by controlling the (100) crystal plane in the plane where the average aspect ratio of the crystal grains of the tungsten material is smallest, it is possible to achieve both high ductility after recrystallization and resistance to recrystallization.

[0022] The material disclosed herein can be used, for example, in reactor wall components used in high-temperature environments, electrode materials for resistance welding, and plasma-facing materials for the divertor and first wall of a fusion reactor. In these applications, tungsten materials are exposed to high-temperature environments, causing them to recrystallize. Recrystallization significantly reduces the ductility of the material, making it more susceptible to cracking. Achieving both high ductility after recrystallization and resistance to recrystallization will extend the life of tungsten components in these applications.

[0023] The material disclosed herein is manufactured, for example, by hot-rolling a sintered body produced by powder metallurgy. In this process, after the hot-rolling pass, which results in a total processing rate of 40 to 60%, a heat treatment at 1000°C for 30 hours is performed to remove the strain that drives recrystallization. As a result, the recrystallization of the material is delayed and the number of (100) recrystallized grains (recrystallized grains with a (100) crystal plane) that occur during the rolling process can be reduced.

[0024] These (100) recrystallized grains are coarse compared to the surrounding grains, and when the entire material recrystallizes at high temperatures, they grow by encroaching on the surrounding grains, resulting in a larger average grain size after complete recrystallization. If the average grain size after complete recrystallization is large, the density of grain boundaries, which serve as annihilation sites for deformation dislocations, decreases, significantly reducing ductility at high temperatures.

[0025] By controlling the (100) crystal plane in the plane where the average aspect ratio of the crystal grains of the tungsten material is smallest within a certain range, it is possible to achieve both high ductility after recrystallization and difficulty in recrystallization, which are normally trade-offs. <Area ratio of (100) crystal plane> The area ratio of the (100) crystal plane in the plane where the average aspect ratio of the crystal grains is smallest is 2.0% or more and 8.0% or less, more preferably 2.0% or more and 6.0% or less.

[0026] Within this range, the material is both resistant to recrystallization and maintains high ductility after recrystallization. If the content is less than 2%, recrystallization occurs easily, and if it exceeds 8%, the ductility after recrystallization decreases.

[0027] To identify the face with the smallest average aspect ratio, 10 arbitrary faces are selected, and the average aspect ratio is measured for each of the 10 faces to identify the face with the smallest average aspect ratio. The (100) occupied area ratio is measured for the face with the smallest average aspect ratio. <Average crystal grain size> The average crystal grain size is preferably 80 μm or less, and more preferably 60 μm or less.

[0028] Within this range, the ductility after recrystallization is high. If it exceeds 80 μm, the ductility after recrystallization may be reduced. "May" means that there is a slight possibility that this will occur, but does not mean that there is a high probability that this will occur. <Average crystal grain size after recrystallization> The average crystal grain size after recrystallization heat treatment is preferably 100 μm or less, and more preferably 80 μm or less.

[0029] In this range, the ductility after recrystallization is high, whereas if it exceeds 100 μm, the ductility after recrystallization is low.

[0030] The area ratio of the (100) crystal plane after recrystallization is preferably 5.0% to 30.0%. Preferably, it is 5% to 25%. <Potassium Content> The potassium content is preferably 10 ppm by mass to 100 ppm by mass. Within this range, recrystallization is more difficult and ductility after recrystallization is higher. A content exceeding 100 wtppm is difficult to achieve due to potassium volatilization during sintering. <Added Impurity Amount> The total content of at least one element selected from the group consisting of C, Ti, Cr, Zr, Mo, Ta, Re, and La is preferably 20% by mass or less. Within this range, recrystallization is more difficult and ductility after recrystallization is higher. <Manufacturing Method> Tungsten material can be manufactured according to the following method. (1) Raw Materials: Pure W powder with an FSSS average particle size of 1 to 10 μm is used as the raw material. A particle size less than 1 μm increases the risk of ignition, while a particle size exceeding 10 μm makes sintering difficult. When K is added, W oxide powder is sprayed with an 85% KOH solution and reduced to produce K-added W powder. Other impurity elements are added using C powder, TiH ２ powder, TiC powder, Cr powder, ZrH ２ powder, ZrC powder, Ta powder, Re powder, La ２ O ３ The powders can be used in combination. The additive powder and W powder are mixed in a mortar to obtain the impurity-added W powder. (2) Molding process The raw material powder is filled into a rubber container and molded under pressure using an isostatic press to obtain a molded body. The pressure is 1 to 3 x 1000 x 9.8 N / cm. ２ 1×1000×9.8 N / cm is preferable. ２ Below this, the pressed body is insufficient in strength and cracks are likely to occur during sintering. ２ Higher pressures are not practical industrially. A die press can also be used for molding. (3) Sintering process: The compact is heated in a hydrogen atmosphere at 1600 to 2300°C for 1 to 40 hours (preferably 2300°C for 1 hour) to obtain a sintered body. At this time, the density is 17.5 to 18.9 g / cm. ３ 17.5 g / cm ３Below this temperature, cracks will occur during rolling. The heating atmosphere can be nitrogen, argon, or vacuum. Hot pressing, hot isostatic pressing, and spark plasma sintering can also be used for molding and sintering. (4) Rolling process The obtained sintered body is heated to 1200-1800°C in a hydrogen atmosphere, removed from the furnace, and rolled. By repeating heating and rolling, it is rolled to the specified thickness. The heating atmosphere can be nitrogen or argon. <Effects> The difficulty of recrystallization is evaluated by the recrystallization rate after heat treatment at 1200°C for 50 hours. A recrystallization rate of 50% or less is effective, and more preferably 25% or less.

[0031] The ductility after recrystallization is evaluated by the tensile elongation at break after heat treatment at 2000° C. for 1 hour. An elongation of 10% or more is considered good, and more preferably 20% or more.

[0032] When both the recrystallization resistance and the recrystallization ductility were good, the effect was judged to be good. [Details of the embodiment of the present disclosure] (Example 1) (A) Comparison of pure tungsten The average crystal grain size, the average crystal grain size after recrystallization heat treatment, the tensile breaking elongation at 200°C, and the recrystallization rate after 1200°C for 50 hours of tungsten plates (tungsten materials) produced under different conditions in the rolling process were evaluated. (1) Regarding production (1-1) Raw material Pure tungsten powder with an FSSS average grain size of 2.0 μm was used as the raw material. (1-2) Molding process The raw material powder was filled into a rubber container and pressure-molded using an isostatic press to obtain a molded body. The isostatic press pressure was 2.0 x 1000 x 9.8 N / cm ３ (1-3) Sintering step The compact was sintered in a hydrogen atmosphere at 2200°C for 1 hour. The size of the sintered body was 100mm x 100mm x 75mm. (1-4) Rolling step The sintered body was rolled according to Table 1.

[0033]

[0034] The sintered bodies of sample numbers 1 to 20 were rolled. For all sample numbers 1 to 20, the temperature during the first rolling pass was 1800°C. The temperature during subsequent rolling passes was 1600°C. The finished plate thickness was 30 mm, 10 mm, or 5 mm. The reduction rate per rolling pass was 10%, 20%, 30%, 40%, or 50%. Some samples were heat-treated at 1000°C for 30 hours after the pass with a total reduction rate of 40 to 60%, while others were not heat-treated.

[0035] The reduction ratio of the final rolling pass was adjusted according to the finished plate thickness. Here, the reduction ratio was defined as [(plate thickness before the pass) - (plate thickness after the pass)] / (plate thickness before the pass), and the total processing ratio was defined as [(sintered body plate thickness) - (plate thickness after the pass)] / (sintered body plate thickness). (2) Regarding Evaluation (2-1) Recrystallization Heat Treatment To compare the properties of the recrystallized material, the rolled material was cut out using wire electric discharge machining (WEDM) to dimensions of 10 x 10 mm (thickness remains the plate thickness at the time of rolling). Heat treatment was performed in a hydrogen atmosphere at 2000°C for 1 hour. The above temperature was selected because heat treatment at 1200°C or higher generally recrystallizes the material. (2-2) Evaluation of the Area Percentage of the (100) Crystal Plane A sample for observation was cut out using WEDM to dimensions of 10 mm x 10 mm (thickness remains the plate thickness at the time of rolling).

[0036] Ten random faces were cut out from the sample for observation, and each face was polished with SiC polishing paper (#180, #600) to achieve a smooth surface. Then, the face was polished with a diamond suspension of 9 μm, 3 μm, and 1 μm, followed by a colloidal silica suspension (Struers OP-S), in that order. Metallographic photographs of the polished faces were taken using an optical microscope. The magnification was set so that 50 or more crystal grains were included within the field of view. The maximum diameter of each crystal grain was defined as the major axis, and the diameter perpendicular to the major axis and passing through the midpoint of the major axis was defined as the minor axis. The average aspect ratio (major axis length / minor axis length) of 50 random crystal grains on each of the 10 faces was calculated. The face with the smallest average value was designated as the face with the smallest average aspect ratio of the multiple crystal grains (the face with the smallest aspect ratio).

[0037] [Correction based on Rule 91, 10.09.2025] The minimum aspect ratio surface was observed using a field emission scanning electron microscope (FE-SEM, JEOL JSM-70001FTTLS) and crystal orientation analysis was performed using electron backscatter diffraction (EBSD). The magnification was 700 μm, the field of view was 120 μm x 120 μm, and the step spacing was 1 μm. The analysis software OIM Analyis (Amatek EDAX) was used to calculate the area fraction of the (100) crystal plane. (2-3) Evaluation of Average Grain Size: As-rolled material (material that was not processed or heat-treated after rolling) cut into 10 x 10 mm pieces (thickness was the same as when rolled) and recrystallized heat-treated material were resin-filled and polished in the same manner as in "(2-2) Evaluation of the Area Fraction of the (100) Crystal Plane."

[0038] The polished surface was corroded with Murakami's reagent (10% by mass potassium ferricyanide / 10% by mass sodium hydroxide aqueous solution). Metallographic photographs were taken using an optical microscope. The magnification was set so that approximately 30 to 200 crystal grains were included in the field of view. The average crystal grain size was calculated from the obtained photographs using the planimetric method of ASTM E112.

[0039] However, when more than 200 crystal grains were found even at a magnification of 2000x, the average crystal grain size (corresponding to the area-average grain size in EBSD analysis) was calculated by performing crystal orientation analysis on a polished sample that had not been corroded using the same method as in "(2-2) Evaluation of the area ratio of the (100) crystal plane." The results are shown in Table 2.

[0040]

[0041] In Table 2, "as rolled" indicates that no processing or heat treatment was performed after rolling. In the "(100) crystal face ratio" column of "as rolled", 2.0% or more and 6.0% or less was rated "A". More than 6.0% and 8% or less was rated "B". Less than 2.0% or more than 8% was rated "C". In the "as rolled" column, "average crystal grain size" was rated "A" if it was 60 μm or less. More than 60 μm and 80 μm or less was rated "B". More than 80 μm was rated "C".

[0042] [Correction based on Rule 91 10.09.2025] In the "After heat treatment at 2000°C for 1 hour", "(100) crystal face ratio" was rated as "A" if it was 5.0% or more and 15.0% or less. "B" if it was more than 15.0% and 30.0% or less. "C" if it was more than 30.0%. In the "After heat treatment at 2000°C for 1 hour", "A" if it was 80 μm or less. "B" if it was more than 80 μm and 100 μm or less. "C" if it was more than 100 μm. (2-4) Evaluation of tensile elongation at break Tensile test specimens were prepared by cutting out the rolled material using WEDM. The prepared test specimens were heat treated at 2000°C for 1 hour and subjected to tensile tests at a test temperature of 200°C and a strain rate of 6.6×10 using an Instron 5867 manufactured by Instron. －４ s －１ The elongation at break was evaluated by the following formula. (2-5) Evaluation of Recrystallization Rate A 10 x 10 mm (thickness was the same as the plate thickness at the time of rolling) material was heat-treated in a hydrogen atmosphere at 1200°C for 50 hours. A 10 x 10 mm (thickness was the same as the plate thickness at the time of rolling) material was heat-treated in a hydrogen atmosphere at 2000°C for 1 hour. The as-rolled material and materials heat-treated at 1200°C for 50 hours or 2000°C for 1 hour were polished in the same manner as in "(2-2) Evaluation of the area ratio of (100) crystal planes," and Vickers hardness was measured in accordance with JIS Z2244:2009. A hardness tester, AVK manufactured by Meisei Hard Machinery Co., Ltd., was used. The test load was 30 kg x 9.8 N. The recrystallization rate X was calculated using the obtained hardness according to formula (1).

[0043] X = [HV(0) - HV(50)] / [HV(0) - HV(Rec)] (1) Here, HV(0) is the hardness as rolled, HV(50) is the hardness after heat treatment at 1200°C for 50 hours, and HV(Rec) is the hardness after heat treatment at 2000°C for 1 hour.

[0044] The results are shown in Table 3.

[0045] [Amendment under Rule 91 10.09.2025]

[0046] [Correction based on Rule 91 10.09.2025] In Table 3, "Tensile elongation at break at 200°C after heat treatment at 2000°C for 1 hour" was rated as "C" for less than 10% and "B" for 10% or more. "Recrystallization rate after heat treatment at 1200°C for 50 hours" was rated as "A" for 25% or less, "B" for over 25% and up to 50%, and "C" for over 50%.

[0047] It was found that if the area ratio of the (100) crystal plane is 2.0 to 8.0%, the tensile breaking elongation at 200°C after heat treatment at 2000°C for 1 hour is 10% or more, and the recrystallization rate after heat treatment at 1200°C for 50 hours is 50% or less, showing good results.

[0048] It was found that the lower the area ratio occupied by the (100) crystal plane, the higher the fracture elongation at 200°C after heat treatment at 2000°C for 1 hour and the higher the recrystallization rate after heat treatment at 1200°C for 50 hours.

[0049] (Example 2) (B) Comparison of Potassium Content Similar evaluations were performed on tungsten materials with different potassium contents. Specifically, tungsten powders with different potassium contents were prepared in the "(1-1) Raw Material" step of Example 1, and these were then molded, sintered, and rolled according to the method of Example 1 to produce the tungsten materials shown in the table below.

[0050]

[0051]

[0052] [Amendment under Rule 91 10.09.2025]

[0053] As shown in sample numbers 21 to 34 in Tables 4 to 6, the potassium amounts were compared at less than 3 mass ppm (pure W), 10 mass ppm, 30 mass ppm, 50 mass ppm, 70 mass ppm, 90 mass ppm, and 100 mass ppm.

[0054] The amount of potassium in the rolled material was evaluated by atomic absorption spectrometry (contAA300 manufactured by Analytiquena).

[0055] In the rolling process, the reduction rate per pass was 10% or 50%. After the pass, which resulted in a total reduction rate of 40 to 60%, a heat treatment at 1000°C for 30 hours was performed on all samples. The rest of the evaluation was the same as in Example 1.

[0056] When the amount of potassium was 10 to 100 ppm by mass, the tensile breaking elongation at 200°C after heat treatment at 2000°C for 1 hour was 20% or more, and the recrystallization rate after heat treatment at 1200°C for 50 hours was 50% or less, showing good results. It was found that the recrystallization rate of the potassium-added material was in a more preferable range in all cases except for the 10 ppm by mass material after heat treatment at 1200°C for 50 hours.

[0057] (Example 3) (C) Comparison of Other Additives The same evaluation as in Example 2 was carried out on tungsten materials to which various additives had been added.

[0058]

[0059]

[0060] [Amendment under Rule 91 10.09.2025]

[0061] [Correction based on Rule 91 21.10.2025] As shown in Sample Nos. 35 to 52 in Tables 7 to 9, the amounts of Ti, Cr, Mo, Ta, and Re added to the raw material composition were 1 mass % or 20 mass %. ２ O ３ The amounts of TiC and ZrC added were 0.05% by mass or 20% by mass. Addition of two or more elements was 1% by mass Ta + 1% by mass Re, or 0.001% by mass K + 1% by mass Ta.

[0062] [Correction based on Rule 91 10.09.2025] The amount of potassium in the rolled material was evaluated by atomic absorption spectrometry (ContAA300 manufactured by Analytiquena), and the composition of other elements was evaluated by ICP emission spectroscopy (ICPS-8100CL manufactured by Shimadzu Corporation).

[0063] Samples 35 to 52 showed good results, with a tensile fracture elongation at 200°C of 20% or more after heat treatment at 2000°C for 1 hour, and a recrystallization rate of 50% or less after heat treatment at 1200°C for 50 hours. It was found that the properties of the tungsten material were within a desirable range, except for some low concentration ranges, depending on the additive.

[0064] The embodiments and examples disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

Claims

1. A tungsten material having a plurality of crystal grains, wherein the area ratio of the (100) crystal plane is 2.0% or more and 8.0% or less on the plane where the average aspect ratio of the plurality of crystal grains is smallest.

2. The tungsten material according to claim 1, wherein the average grain size is 80 μm or less.

3. A tungsten material having a plurality of crystal grains after recrystallization, wherein the area ratio of the (100) crystal plane in the plane where the average aspect ratio of the plurality of crystal grains is smallest is 5.0% or more and 30.0% or less, and the average crystal grain size is 100 μm or less.

4. The tungsten material according to claim 3, wherein the Vickers hardness of the recrystallized tungsten material is 500 HV or less.

5. The tungsten material according to claim 3, wherein the Vickers hardness of the recrystallized tungsten material is 400 HV or less.

6. The tungsten material according to claim 3, wherein the Vickers hardness of the recrystallized tungsten material is 380 HV or less.

7. The tungsten material according to claim 1 or 3, containing 10 ppm by mass or more and 100 ppm by mass or less of K.

8. The tungsten material according to claim 1 or 3, containing at least one element selected from the group consisting of C, Ti, Cr, Zr, Mo, Ta, Re, and La in a total amount of 20 mass% or less.

9. A plasma-facing material using the tungsten material according to claim 1 or 3.

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