Tungsten materials

Abstract

In any surface of the tungsten material, a ratio of 50% or more in which a specific crystal orientation of a first crystal grain and an angle of 2 to 15° formed by the specific crystal orientation of a second crystal grain adjacent to the first crystal grain are formed.

Description

Technical Field

[0001] The present disclosure relates to tungsten materials. This application claims priority based on Japanese Patent Application No. 2021-064811, filed on April 6, 2021. The entire contents of the Japanese Patent Application are incorporated herein by reference. Background Art

[0002] Conventionally, a tungsten material is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-146235 (Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 62-146235 Summary of the Invention

[0006] In any surface of the tungsten material, a ratio of 50% or more in which a specific crystal orientation of a first crystal grain and an angle of 2 to 15° formed by the specific crystal orientation of a second crystal grain adjacent to the first crystal grain are formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] [ Figure 1 ] Figure 1 This is a microstructure diagram of tungsten material with multiple grains. DETAILED DESCRIPTION

[0008] [Problems to be Solved by the Present Disclosure]

[0009] In existing tungsten materials, there is a problem of cracking or deformation when thermal shock is applied within a short period.

[0010] [Description of Embodiments of the Present Disclosure]

[0011] First, embodiments of the present disclosure will be listed and described. (Background Art)

[0013] In Japanese Patent Application Laid-Open No. 62-146235, a tungsten component contains 0.003 to 0.05 mass % of K / Si, and the secondary recrystallized grain size is within the range of 100 mm. 2 Tungsten components have one or fewer grains. They can reduce the grain boundaries that cause intergranular cracking in high-temperature structural materials such as furnace components, and have excellent high-temperature creep strength.

[0014] Tungsten is a high-melting-point material (melting point 3422°C) and can be used in high-temperature heating furnaces even at temperatures exceeding 2000°C. However, it can deform and crack over extended use, making stable furnace operation difficult.

[0015] Furnace components use tungsten materials that have undergone plastic working such as rolling. However, when exposed to temperatures exceeding 1200°C, recrystallization generally occurs, and when the heat load temperature exceeds 1800°C, grain growth occurs, making deformation and cracking more likely to occur.

[0016] Tungsten has a high melting point and is used in high-temperature furnace components. Tungsten used at high temperatures develops high-temperature creep characteristics due to coarsening of its grains over time. On the other hand, it is less susceptible to short-cycle repeated thermal shock.

[0017] To ensure high-temperature deformation resistance, furnace components used in high-temperature atmospheres are constructed from materials such as tungsten. Tungsten, which is less susceptible to deformation at high temperatures, has large grains and a high Young's modulus. Therefore, it is significantly affected by short-term thermal shocks, such as sudden power outages, but is also relatively insensitive to thermal shock.

[0018] Conventionally, the grain size of rolled tungsten material changes to over 200μm due to a temperature load of 2000°C. When used at temperatures exceeding 2000°C, tungsten material with a grain size exceeding 200μm can develop cracks due to thermal shock caused by rapid temperature increases or power outages, potentially making stable furnace operation impossible.

[0019] (the angle between specific crystal orientations of adjacent grains)

[0020] In the present disclosure, novel processing conditions are adopted to form a tungsten material in which the grain boundary characteristics and lattice strain of the rolled material are controlled, thereby improving the thermal shock resistance.

[0021] The tungsten material disclosed herein can improve crack resistance to rapid temperature changes (including repeated temperature changes) by controlling the grain size of recrystallized grains under a temperature load of 2000°C to 200 μm or less, thereby contributing to extending the life of the furnace.

[0022] Based on the above characteristics, the tungsten material disclosed in the present invention can be used in the following components: high-temperature heat-load components such as heaters or reflectors used in high-temperature heating furnaces, components that receive electron beam irradiation such as anode fixed or rotating targets of X-ray generators, and parts facing high-temperature plasma or parts irradiated by neutrons such as divertors or inner wall materials of nuclear fusion furnaces.

[0023] The present disclosure relates to a tungsten material in which, on any surface of the tungsten material, a specific crystal orientation of a first crystal grain and the specific crystal orientation of a second crystal grain adjacent to the first crystal grain form an angle of 2 to 15 degrees (low-angle grain boundary) in a ratio of 50% or more.

[0024] When the ratio is less than 50%, deformation and cracks are likely to occur due to the heat load of 2000°C, resulting in the growth of particles exceeding 200μm. The ratio is more preferably 55% or more. In this specification, "small-angle grain boundary" means that the angle between the specific crystal orientation of the first grain and the specific crystal orientation of the second grain adjacent to the first grain is 2 to 15°. The small-angle grain boundary is more preferably 80% or less. A ratio exceeding 80% is difficult and is not suitable for mass production due to the occurrence of cracks during processing and the need for precise condition control.

[0025] Figure 1 This is a diagram of the organization of tungsten material with multiple grains. Figure 1 As shown, the tungsten material 1 has a plurality of crystal grains 11, 12, and 13. The boundaries of the plurality of crystal grains 11, 12, and 13 are grain boundaries 21 and 22. The specific crystal orientation (e.g. <100> ) is indicated by arrow 32. The crystal orientation in grain 13 is indicated by arrow 33, which is the same as the crystal orientation of arrow 32. The proportion of low-angle grain boundaries where the angle θ formed by arrows 32 and 33 is 2 to 15° is 50% or more.

[0026] Furthermore, when the tungsten material is heat treated at 1500° C. for 1 hour, the ratio of low-angle grain boundaries is more preferably 25% or less, and more preferably 10% or less.

[0027] The method for measuring the low-angle grain boundary is as follows.

[0028] The measurement surface was selected from any surface of the tungsten material. After mechanical grinding, the surface was cross-sectioned using a cross-section polisher at an acceleration voltage of 6 kV and an irradiation current of 130 μA, and then the measurement was performed. The measurement field of the measurement surface was 200 μm × 600 μm, as shown in the following example. Figure 1 That contains grains. Grain 12 is in contact with grains 11 and 13. Measure the angle θA formed by the specific crystal orientations of grains 11 and 12. Set the angle formed by the specific orientations of grains 12 and 13 to θB. Use the above method to measure the angle between adjacent grains centered on grain 12 contained in the field of view. The measurement is performed with grain 12 as the center. Until the number of angle measurements reaches 200, as needed, move the field of view range of 200μm×600μm while measuring 200 angles formed between adjacent different grains, and use the above 200 measurement results to calculate the proportion of small-angle grain boundaries of 2 to 15° or less.

[0029] The grain boundary characteristics within the measurement field were measured using EBSD with an SEM (ZEISS Gemini 450). The SEM conditions were an accelerating voltage of 30 kV and an irradiation current of 25 nA, and the EBSD conditions were a WD of 13 mm and a step size of 0.5 μm.

[0030] The measured data were analyzed using Symmetry manufactured by Oxford.

[0031] (Lattice strain)

[0032] The average value of the (100) lattice strain in any 10 fields of view of the tungsten material is preferably 0.25% or less. It has been found that even when the value exceeds 0.25%, cracking does not occur due to thermal shock at high temperatures, while when the value is 0.25% or less, deformation at high temperatures does not occur, demonstrating its superiority in applications such as furnace components. A more preferred value is 0.20% or less.

[0033] The method for measuring the lattice strain is as follows.

[0034] The measurement surface was mechanically polished and then electropolished using a 10V DC electrolytic solution at a temperature of 22°C and a 1N KOH electrolyte. The surface after mechanical polishing removed 20 μm of the hardened layer.

[0035] Select any 10 fields of view on the measurement surface. Use an X-ray diffraction device (Empyrean, DY 1204 manufactured by Malvern Panalytical) to measure the lattice strain. As the measurement conditions, the bulb is Cu, the voltage is 45kV, the current is 40mA, a 10mm slit is used, the scanning speed is set to 0.11° / s, and the measurement is performed at 2θ: 35-135°. The measured data is analyzed using High score plus, and the lattice strain of (100) is calculated based on the Rietveld method. The average value of the lattice strain of the 10 fields of view is calculated.

[0036] (Purity of tungsten material)

[0037] The purity of the tungsten material is preferably 99.9 mass % or higher.

[0038] If the content is less than 99.9% by mass, the inherent impurities may volatilize, contaminating the furnace, which may shorten the furnace life, especially when used in a vacuum atmosphere. It should be noted that "may" indicates a small but possible occurrence, and does not mean a high probability of occurrence.

[0039] The purity of tungsten materials is defined as follows. Purity analysis is conducted in accordance with JIS H1402 (2001) and JIS H1403 (2001). The Mo, Fe, Al, Ca, Mg, and Si contents of the plate are determined by chemical analysis. Al, Ca, Mg, and Si are converted to oxides, assuming they are all present as oxides (Al2O3, CaO, MgO, and SiO2). The value obtained by subtracting the Mo, Fe, and Al2O3, CaO, MgO, and SiO2 converted to oxides from 100 is considered the tungsten purity.

[0040] However, when used under a reducing atmosphere such as hydrogen or an inert atmosphere such as argon, a tungsten alloy containing elements other than tungsten may also be used. Even under a temperature load exceeding 2000° C., the tungsten alloy not only has a grain size of less than 200 μm, but also can be expected to achieve high strength due to solid solution / dispersion strengthening of the added elements.

[0041] In addition to tungsten, tungsten alloy also contains at least one element selected from the group consisting of Re (rhenium), Ta (tantalum), Cr (chromium), K (potassium), Mo (molybdenum), Ti (titanium) and Zr (zirconium) totaling less than 20% by mass. Such tungsten alloy can not only suppress the particle growth under the thermal load of 2000 ° C, but also can be expected to be highly strengthened. When the total addition of each element exceeds 20% by mass, processing cracks may occur during rolling, so the total addition is preferably suppressed to less than 20% by mass.

[0042] The additives can be in the form of not only pure metals but also oxides, hydrides, and carbides.

[0043] (Grain size after heat treatment)

[0044] The grain size of the tungsten material after heat treatment at 2000°C for 1 hour is preferably 200 μm or less. If it exceeds 200 μm, cracks or deformation may occur due to thermal shock. More preferably, it is 100 μm or less.

[0045] The crystal grain size was measured by taking a photograph of an arbitrary surface at a magnification of 200 times, measuring the major axes of at least 50 arbitrary particles on the photograph, and taking the average value thereof as the crystal grain size.

[0046] (shape)

[0047] As long as the tungsten material possesses the aforementioned characteristics, the same effects can be achieved regardless of the thickness. There are no restrictions on manufacturing conditions; high-temperature presses (HIP, HP) can also be used for sintering. There are also no restrictions on plastic working methods; forging, rolling, or extrusion are all acceptable.

[0048] Tungsten material is not only a simple shape, but also can obtain the same effect by machining a hole, or implementing bending processing etc. In addition, even if it is implemented and joined with materials other than tungsten such as stainless steel, copper or copper alloy by brazing or pressing, the same effect can be obtained.

[0049] The plate thickness of the tungsten material was measured at arbitrary 10 locations using a micrometer, and the average value was used.

[0050] [Details of the embodiments of the present disclosure]

[0051] The present invention will be described below based on examples.

[0052] (Example 1)

[0053] (1) Manufacturing of tungsten materials

[0054] (1-1) Tungsten sintered body manufacturing process

[0055] W oxide was reduced to obtain pure W powder as a raw material. The FSSS average particle size of the pure W powder using the Fischer method was 2.5 μm. Re powder with an FSSS average particle size of 4.0 μm, Ta and Cr powders with 20 μm, Mo powder with an FSSS average particle size of 4.2 μm, TiH2 powder with 20 μm, and ZrC powder with an FSSS average particle size of 3.0 μm were prepared as needed for the pure W powder, and a certain amount was added to the pure W powder and mixed using a mortar to obtain a mixed powder. K was obtained by spraying a KOH aqueous solution onto the W oxide and reducing it to obtain a W powder containing K. Powders of sample numbers 1 to 24, 31 to 54, and 61 to 80 shown in Tables 1 to 3 were thus obtained. Sample numbers 61 to 80 are pure W powders.

[0056] [Table 1]

[0057]

[0058] [Table 2]

[0059]

[0060] [Table 3]

[0061]

[0062] Composition: pure tungsten

[0063] The powder was pressed through a die using a press machine to produce a pressed compact.

[0064] The pressed compact was sintered in a hydrogen atmosphere at 2200° C. for 30 hours using a sintering furnace to obtain a W sintered body.

[0065] The size of the sintered body at this time is 100 mm × 100 mm × 100 mm thick. The density after sintering is 18.2 g / cm 3 .

[0066] Regarding the average particle size of FSSS, if the density of the sintered body is 17.5 g / cm 3 The above sintering method is not limited. Based on various tests, the average FSSS particle size of the W powder is preferably between 1 μm and 10 μm. If the average FSSS particle size exceeds 10 μm, it may not achieve a density that can withstand rolling. If the average FSSS particle size is less than 1 μm, density deviation may occur in the sintered body.

[0067] In addition to hydrogen atmosphere, sintering atmosphere can also be selected from inert atmospheres such as argon and vacuum atmosphere. If the density after sintering is 17.5g / cm 3 As described above, the sintering atmosphere can be combined in multiple ways (for example, hydrogen atmosphere before 1200°C, vacuum atmosphere between 1200°C and 2000°C, etc.), and the sintering temperature and sintering time can also be selected arbitrarily.

[0068] In addition, a sintered body with a high specific gravity can be obtained by performing pressure sintering such as HIP and HP. However, there is also a risk that the tungsten material will come into contact with carbon components during pressure sintering and become embrittled, so sufficient consideration must be given when selecting these processes.

[0069] (1-2) Forging process

[0070] This W sintered body was heated in a heating furnace at 1800°C and then repeatedly forged using a 1-ton air hammer in the first heating cycle until the thickness reached 70 mm. This prepared materials for Samples Nos. 13 to 24, 43 to 54, 67 to 71, and 77 to 80. For Samples Nos. 1 to 12, 31 to 42, 61 to 66, and 72 to 76, this material was further heated to 1800°C and then forged using a 1-ton air hammer in the second heating cycle until the thickness reached 50 mm.

[0071] (1-3) Calendering process

[0072] The material forged to 70 mm or 50 mm was heated in a furnace at 1800°C and rolled to a thickness of approximately 10 mm while repeatedly rolling and heating. Rolling was performed while sampling within the 20 to 10 mm thickness range. Samples 13 to 24, 43 to 54, 67 to 71, and 77 to 80 were produced.

[0073] The heating atmosphere during rolling may be an argon or hydrogen atmosphere in addition to a nitrogen atmosphere.

[0074] The heating temperature during hot rolling is preferably between 1800°C and 2000°C. If it exceeds 2000°C, the life of the heating furnace is shortened, resulting in poor productivity. If it is below 1800°C, it is difficult to control grain boundary properties and lattice strain. The reduction ratio during hot rolling is preferably between 5% and 15%. If it is below 5% or exceeds 15%, it is difficult to control grain boundary properties and lattice strain.

[0075] Next, the material having a thickness of approximately 10 mm produced in the previous rolling step was heated at a heating temperature of 1600° C., and the material was rolled until the thickness became 0.5 mm while sampling while repeating rolling and heating.

[0076] In this manner, samples were produced with sample numbers 1 to 12, 31 to 42, 61 to 66, and 72 to 76. The heating atmosphere during rolling may be an argon or hydrogen atmosphere in addition to a nitrogen atmosphere.

[0077] The heating temperature during rolling is preferably 1600° C. to 1800° C. This is because: if the working progresses, grain growth is likely to occur; if it is lower than 1600° C., it is difficult to control grain boundary characteristics and lattice strain; and if it exceeds 1800° C., grain growth is likely to occur.

[0078] (1-4) Machining

[0079] Each sample after forging and rolling was finished by cutting, grinding, etc. to obtain the respective thickness, width, and length.

[0080] (2) Evaluation results

[0081] (2-1) Determination of composition

[0082] The composition of each sample (sample numbers 1 to 24, 31 to 54, and 61 to 80) was determined using analysis in accordance with JIS H1402 (2001) and JIS H1403 (2001). For example, in sample number 1, the composition "W-0.003K" indicates that it contains 0.003 mass% K, with the remainder being W.

[0083] (2-2) Determination of plate thickness

[0084] The plate thickness (mm) of each sample was measured, and the results are shown in the "plate thickness (mm)" column in the table.

[0085] (2-3) Determination of the proportion (%) of small-angle grain boundaries

[0086] The ratio (%) of low-angle grain boundaries was measured for each sample, and the results are shown in the "Ratio (%) of low-angle grain boundaries" column in the table.

[0087] (2-4) Determination of the Ratio (%) of Low-Angle Grain Boundaries after Heat Treatment

[0088] The ratio (%) of low-angle grain boundaries after heat treatment at 1500° C. for 1 hour was measured for each sample. The results are shown in the “Ratio (%) of low-angle grain boundaries after heat treatment” column in the table.

[0089] (2-5) Determination of grain size (μm) after heat treatment

[0090] For each sample, the crystal grain size (μm) after heat treatment at a temperature of 2000° C. for 1 hour was measured. The results are shown in the column “Crystal grain size (μm) after heat treatment” in the table.

[0091] (2-6) Thermal shock crack test

[0092] Each sample was placed in a hydrogen atmosphere furnace, as is, using a band heater (10 mm width x 100 mm length x mm thickness). Power was applied to the radiation thermometer until the temperature reached 2000°C, then immediately turned off. After 10 seconds, the output was turned on again until the temperature reached 2000°C. This cycle was repeated 1000 times.

[0093] Each sample was then inspected for cracks and deformation. Regarding post-test cracks, samples with no cracks observed using a 5x magnifying glass were rated A, while samples with one or two cracks observed, each confined to the surface, were rated B. Samples with three or more cracks observed or cracks extending into the interior were rated C.

[0094] The results are shown in the column "Test results (thermal shock cracking)" in the table.

[0095] (2-7) Thermal deformation test

[0096] After evaluation in (2-6), place the 10 mm x 100 mm surface of each sample (heater after test) on a flat platen and measure the warpage (the gap between each sample and the platen) using a gap gauge. If the gap is 3 mm or less, the evaluation is A. If the gap exceeds 3 mm and reaches 10 mm, the evaluation is B. Materials with a gap of 10 mm or more or cracks are evaluated as C.

[0097] It is understood that when the ratio of the low-angle grain boundaries is 50% or more, an evaluation of A or B is obtained in the thermal shock cracking, and an evaluation of A or B is obtained in the thermal deformation.

[0098] It is found that the ratio of low-angle grain boundaries is reduced to 25% or less by heat treatment at 1500°C for 1 hour. If the grain size after heat treatment at 2000°C for 1 hour is 200 μm or less, the thermal shock cracking rating is A or B.

[0099] (Example 2)

[0100] Using pure W powder, according to "(1) Production of tungsten material" in Example 1 above, sample numbers 81 to 87 in Table 4 were obtained.

[0101] [Table 4]

[0102]

[0103] In sample numbers 81 to 86, the heating conditions during rolling were changed during production.

[0104] Various physical properties were evaluated and lattice strain was measured according to "(2) Evaluation Results" of Example 1. The results are shown in Table 4.

[0105] As can be seen from Table 4, when the lattice strain is 0.25% or less, an A rating is obtained in thermal shock cracking and thermal deformation.

[0106] The embodiments and examples disclosed herein are intended to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all variations within the meaning and scope equivalent to the claims.

[0107] Explanation of symbols

[0108] 1 Tungsten material, 11, 12, 13 grains, 21, 22 grain boundaries, 32, 33 arrows.

Claims

1. A tungsten material, On any surface of the tungsten material, the ratio of the angle between a specific crystal orientation of a first crystal grain and the specific crystal orientation of a second crystal grain adjacent to the first crystal grain being 2 to 15 degrees is 50% or more. The tungsten material is a tungsten material with a thickness of 10 to 20 mm, which is rolled at a temperature of 1800° C. to 2000° C. and a reduction rate of 5% to 15%. in, In any 10 fields of view of the tungsten material, the average value of the (100) lattice strain is less than 0.25%, The tungsten material contains 20 mass % or less of at least one element selected from the group consisting of Re, Ta, Cr, K, Mo, Ti, and Zr in total.

2. The tungsten material according to claim 1, wherein The purity of the tungsten material is 99.9 mass % or higher.

3. The tungsten material according to claim 1, wherein The tungsten material is heat-treated at 2000° C. for 1 hour, so that the grain size is 200 μm or less.

4. The tungsten material according to claim 1, wherein The ratio of the angles of 2 to 15° after the tungsten material is heat-treated at 1500° C. for 1 hour is 25% or less.

5. The tungsten material according to claim 1, wherein The tungsten material is used for the divertor or inner wall material of a nuclear fusion reactor.

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