METHOD FOR MANUFACTURING Ta ALLOY MEMBER

Abstract

To provide a method for manufacturing a Ta alloy member, which is suited for space use by using additional manufacturing.SOLUTION: This method for manufacturing a Ta alloy member comprises: a step of preparing alloy powder of a Ta alloy which contains 2.0-4.5 mass% of W and the residual part consisting of Ta and inevitable impurities; an additional manufacturing step of stacking the alloy powder by the additional manufacturing technique to form a molded object; and a stabilization step of heat-treating the molded object at 1400°C-2000°C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing refractory Ta alloy components applicable to space applications by additive manufacturing and heat treatment. [Background technology]

[0002] Because of its excellent corrosion resistance and heat resistance, Ta's pure metal and alloys are used in a variety of applications, including capacitors, chemical plants, medical materials, etc. In addition, due to its high heat resistance, refractory Ta alloys are expected to be used in space applications, particularly in thruster (engine) nozzles.

[0003] In rocket and satellite thrusters, Nb alloy members are used in parts exposed to high temperatures. If these could be replaced with Ta alloy members, the fuel could be burned at a higher temperature, increasing the thrust of the thruster. Non-Patent Document 2 describes an oxidation resistance test of an oxidation-resistant coating of Ta-10W alloy intended for aerospace applications, conducted at 1800°C.

[0004] Practical Nb alloy components are generally formed by cutting ingots or forged rods, but in many cases, more than 90% of the material is removed from the finished product, posing a cost issue. In response to this, active research and development has been conducted into the production of fire-resistant Nb alloy components using additive manufacturing, which can produce complex shapes from powder materials. For example, Patent Document 1 discloses a method for producing fire-resistant Nb alloy components by additive manufacturing and heat treatment. Ta, a scarce resource, is even more expensive than Nb, so there is an even greater demand for additive manufacturing methods, rather than casting or forging, to be used to produce Ta alloy components. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7412867 [Non-patent literature]

[0006] [Non-Patent Document 1] Katsuhiro Nose, "Metal Sketches Series No. 19 Tantalum," Material, Japan Institute of Metals, 2021, Vol. 60, No. 11, p. 685 [Non-patent document 2] Z. Cai et al., "Microstructure and oxidation resistance of a YSZ modified silicide coating for Ta-W alloy at 1800°C," Corrosion Science, Elsevier BV, 2018, vol. 143, pp. 116-128 Summary of the Invention [Problem to be solved by the invention]

[0007] Because additive manufacturing uses powdered raw materials and involves rapid heating and cooling, the properties of objects made by additive manufacturing are different from those of cast or forged materials, even if they are the same alloy, and the composition of a Ta alloy suitable for manufacturing space components by additive manufacturing was unknown.In addition, since it is not easy to conduct tests to measure mechanical strength at high temperatures, no heat treatment method was known to make Ta alloys suitable for space applications.

[0008] The present invention has been made in consideration of the above, and aims to provide a method for producing a Ta alloy member applicable to space applications using additive manufacturing. [Means for solving the problem]

[0009] The method for producing a Ta alloy member of the present invention includes the steps of: preparing an alloy powder of a Ta alloy containing 2.0 to 4.5 mass% W and the remainder being Ta and unavoidable impurities; an additive manufacturing step of layering the alloy powder by an additive manufacturing technique to form a shaped object; and a stabilization step of heat treating the shaped object at a temperature of 1400°C or higher and 2000°C or lower.

[0010] Another method for producing a Ta alloy member of the present invention includes the steps of preparing a Ta alloy powder containing 2.0 to 4.5 mass% W, 0.5 to 1.2 mass% Re, 0.5 to 1.0 mass% Hf, 0.005 to 0.045 mass% C, with the remainder being Ta and unavoidable impurities, an additive manufacturing step of layering the alloy powder by an additive manufacturing technique to form a shaped object, and a stabilization step of heat-treating the shaped object at a temperature of 1400° C. to 2000° C. Preferably, oxides of Hf and carbides of Ta are precipitated in the stabilization step.

[0011] Preferably, any of the above methods for producing a Ta alloy member further includes, after the additive manufacturing step, a residual stress relief step of heat treating the shaped article at 1100°C or higher and 1300°C or lower. [Effects of the Invention]

[0012] According to the method for producing a Ta alloy part of the present invention, additive manufacturing can be used to obtain a Ta alloy part applicable to space applications such as thruster nozzles. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a process flow diagram of a method for producing a Ta alloy member according to one embodiment. [Figure 2] These are the results of room temperature tensile tests on as-formed materials. [Figure 3] A to C: Results of room temperature tensile tests on as-formed and heat-treated materials. [Figure 4] FIG. 1 is an EBSD diagram showing grain boundaries of a Ta pure metal member. [Figure 5] 3 is an EBSD diagram showing grain boundaries of the Ta alloy members of the comparative example and the example. FIG. [Figure 6] 3 is an EBSD diagram showing grain boundaries of the Ta alloy members of the comparative example and the example. FIG. [Figure 7] 3 is an EBSD diagram showing grain boundaries of the Ta alloy members of the comparative example and the example. FIG. [Figure 8]FIG. 2 is an EBSD diagram showing grain boundaries of a Ta alloy member of a comparative example. [Figure 9] A to D: SEM images showing precipitates in some samples. [Figure 10] A and B are the results of tensile tests on heat-treated materials at 500 to 1000°C. [Figure 11] These are the results of tensile tests on heat-treated materials at 1400 to 1600°C. [Figure 12] Room temperature tensile test results of samples using different additive manufacturing methods. [Figure 13] FIG. 1 is a diagram showing the shape of a test piece for a tensile test at 1400 to 1600°C. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the method for producing a Ta alloy member according to the present invention will be described with reference to the process flow shown in FIG.

[0015] The Ta alloy powder used in this embodiment contains Ta as the main component and a small amount of W. W improves the strength of the Ta alloy by solid solution strengthening.

[0016] An example of such a Ta alloy is an alloy whose representative composition by mass is represented by "Ta-2.5W," containing 2.0 to 3.5 mass% W, with the remainder consisting of Ta and unavoidable impurities. Note that, in this specification, the number preceding the alloying element in the representative composition indicates the content in mass%. R05252, the Universal Numbering System (UNS) for alloys established by the American Society for Testing and Materials (ASTM) and the Society of Automotive Engineers (SAE), specifies an alloy whose representative composition is Ta-2.5W, containing 2.0 to 3.5 mass% W, with the remainder consisting of Ta and unavoidable impurities. The standard specifies the maximum impurity values, by mass, as Nb: 0.50%, Fe: 0.010%, Ti: 0.010%, Mo: 0.020%, Si: 0.005%, Ni: 0.010%, C: 0.010%, O: 0.015%, N: 0.010%, and H: 0.0015%. The Ta alloy powder used in this embodiment contains the elements listed here as typical unavoidable impurities. Due to the large surface area of ​​powder raw materials used in additive manufacturing, the content of non-metallic impurities may exceed the maximum value specified in the standard. In particular, oxygen (O) inevitably exceeds the maximum value specified in the standard in most cases.

[0017] Another example of a Ta alloy has a typical composition by mass of "Ta-4W-1Re-0.7Hf-0.025C," which contains 2.0–4.5% W, 0.5–1.2% Re, 0.5–1.0% Hf, and 0.005–0.045% C by mass, with the remainder consisting of Ta and unavoidable impurities. This alloy was designed based on ASTAR-811C (typical composition: Ta-8W-1Re-0.7Hf-0.025C), developed in the United States in the 1960s for casting, taking into account the effects of residual stresses in additively manufactured materials. Additively manufactured materials have higher residual stresses than cast materials. Experimental results, described below, showed that Ta-13W alloy cracked after prolonged polishing. Therefore, it was deemed necessary to reduce the W content for additive manufacturing. Therefore, the W content of ASTAR-811C was reduced to 4% by mass. As with Ta-2.5W, the powder feedstock used for additive manufacturing contains a higher content of nonmetallic impurities than the cast product. Furthermore, carbon (C) in this alloy is not an impurity but an alloying element added for the purpose of precipitation hardening through carbide formation. The powder used in the examples described below also contained approximately 0.04% C, which was higher than that of ASTAR-811C. Zr may be added to this alloy at 0.05 to 0.15 mass% for precipitation hardening through oxide formation.

[0018] The particle size of the alloy powder is preferably 10 to 100 μm, more preferably 20 to 60 μm, in terms of the volume-based median particle size (d50) measured by laser diffraction / scattering. Furthermore, as a raw material powder for additive manufacturing, it is preferable for it to have a fairly wide particle size distribution so as to increase the packing rate when forming a thin layer. As a guide for the particle size distribution width, (d90 - d10) is preferably 0.5 to 1.5 times d50. Note that d10, d50, and d90 represent the particle sizes at the 10%, 50%, and 90% points, respectively, of the cumulative curve when the total volume is 100%.

[0019] The alloy powder is used to create components using additive manufacturing technology. The preferred additive manufacturing method is selective laser melting (SLM). SLM is a type of powder bed fusion method in which the raw alloy powder is spread on a build stage to form a uniform thin layer, and a laser beam is scanned and irradiated onto specific locations on the thin layer to melt and solidify the alloy powder, thereby stacking the alloy layers and creating the desired shape.

[0020] Due to the manufacturing method, objects manufactured using the SLM method contain many columnar crystals extending in the lamination direction of the alloy. Therefore, mechanical properties such as tensile strength differ between the lamination direction and the direction perpendicular to it. Hereinafter, the lamination direction during manufacturing is referred to as the Z direction, and the direction perpendicular to the lamination direction is referred to as the XY direction. Note that in the SLM method, in order to reduce the influence of bias in the scanning direction of the laser light, the scanning direction is rotated by a predetermined angle for each layer during lamination, so the structure of the object is isotropic in a plane perpendicular to the Z direction. In this specification, the XY direction simply means being perpendicular to the Z direction, and does not refer to a specific direction in a plane perpendicular to the Z direction.

[0021] Next, the object produced by additive manufacturing is heat-treated to remove residual stress. In additive manufacturing of high-melting-point metals such as Ta alloys, the molten powder solidifies rapidly, resulting in particularly large residual stress after manufacturing. Removing the residual stress prevents the object from cracking during heat treatment to stabilize the structure, as described below, or during processing to finish the product.

[0022] Residual stress relief treatment is preferably carried out at a temperature of 1100°C or higher and 1300°C or lower. If the treatment temperature is too low, residual stress will not be sufficiently removed. On the other hand, if the treatment temperature is too high, the molded object may crack while being heated to the treatment temperature. The time for holding the molded object at the treatment temperature is preferably 30 minutes or higher and 5 hours or lower. If the holding time is too short, the internal temperature may not rise to the set temperature depending on the shape of the molded object. On the other hand, longer holding times will not be particularly effective and will result in reduced productivity.

[0023] In order to distinguish between heat treatment for residual stress relief and heat treatment for stabilizing the structure, which will be described below, the former will be referred to as "residual stress relief treatment" and the latter as "stabilization treatment" or simply "heat treatment."

[0024] The molded product from which residual stress has been removed is further heat-treated at a high temperature to stabilize the structure, etc. The purpose of this heat treatment is to impart ductility to the molded product and stabilize the structure. This stabilization treatment reduces dislocation density, thereby improving the ductility of the molded product. The stabilization treatment temperature is 1400°C or higher, preferably 1600°C or higher. This provides sufficient ductility and stabilizes the structure. Furthermore, the higher the temperature, the faster the stabilization of the structure progresses. On the other hand, the stabilization treatment temperature is 2000°C or lower, more preferably 1800°C or lower. Increasing the treatment temperature beyond this level does not provide any particular effect and increases the treatment cost.

[0025] Although the stabilization treatment uniformly dissolves solute atoms, the stabilization treatment in this embodiment differs from the solution treatment used for precipitation-hardened alloys. Precipitation-hardened alloys undergo solution treatment to uniformly dissolve solute atoms, followed by aging treatment to precipitate precipitates. Solution treatment involves water or air cooling, which is somewhat rapid, to maintain the solution structure. In contrast, Ta-2.5W is a solution-strengthened alloy containing W, so solution treatment is not required. It is said that ASTAR-811C also exhibits the effect of precipitation hardening due to carbide precipitation. While aging treatment may be performed on the Ta-4W-1Re-0.7Hf-0.025C alloy, this embodiment does not perform aging treatment after heat treatment. Furthermore, rapid cooling is not required for the stabilization treatment in this embodiment.

[0026] The Ta alloy component of this embodiment is obtained by the additive manufacturing, residual stress relief, and stabilization treatment described above. The obtained Ta alloy component is then subjected to processes such as cutting, polishing, cleaning, drying, and protective coating to inhibit oxidation as necessary to become a final product. [Example]

[0027] The method for manufacturing the Ta alloy member of this embodiment will be described in further detail based on experimental results.

[0028] Four types of Ta alloy powders and pure Ta powder with different compositions were used, and additive manufacturing was performed using the SLM method. Ta alloy parts and Ta pure metal parts of the examples and comparative examples were produced by varying the presence or absence and conditions of residual stress relief treatment and stabilization treatment.

[0029] Additive manufacturing was performed using a powder deposition modeling system (EOS GmbH, M100) equipped with a Yb fiber laser (200 W power, 40 μm beam diameter). Some alloy compositions were also fabricated using a larger powder deposition modeling system (EOS GmbH, M290, Yb fiber laser, 400 W power, 80 μm beam diameter).

[0030] Residual stress relief treatment was performed by placing the molded object in an electric furnace and heating it at 900-1200°C for 1-4 hours. Stabilization treatment was performed by further increasing the temperature of the electric furnace after the residual stress relief treatment and heating it at 1400-1600°C for 1-4 hours, then cooling it to 1200°C at 200°C / h, then from 1200°C to 400°C at 10°C / min, and then furnace cooling. Note that the residual stress relief treatment and stabilization treatment do not have to be performed consecutively; instead, the object may be cooled after the residual stress relief treatment, and then heated again to perform the stabilization treatment.

[0031] The cross-sections of the components were observed using an optical microscope, a scanning electron microscope (SEM), and energy dispersive X-ray analysis (EDS), and the grain size and crystal orientation were measured using electron backscatter diffraction (EBSD).

[0032] The mechanical properties of the components were evaluated by tensile tests, which measured 0.2% yield strength, tensile strength, and elongation at break. Tensile tests at room temperature in air were conducted in accordance with ASTM E8-21. The test rate was a stress ramp rate of 9 MPa / s up to 0.2% yield strength, and a strain rate of 20% / min thereafter. Tensile tests at 500–1600°C in an Ar atmosphere were conducted using an MTS808 materials testing machine in accordance with ASTM E21-20. The test specimens were heated at a rate of 50°C / min and held at the test temperature for 30 minutes before starting the test. The test rate was a strain rate of 0.5% / min up to 0.2% yield strength, and a strain rate of 5% / min thereafter. Tensile tests at −170°C in air were conducted using an MTS810 materials testing machine in accordance with ASTM E8-21. The test specimen was cooled to -170°C and held at the test temperature for 30 minutes before starting the test. The test rate was a stress increase rate of 9 MPa / s up to 0.2% yield strength, and a strain rate of 20% / min thereafter. In the following, 0.2% yield strength and tensile strength will be collectively referred to as "strength," and fracture elongation will simply be referred to as "elongation."

[0033] For tensile tests at room temperature and between 500 and 1000°C, round test specimens with a straight section diameter of 3 mm and a length of 15 mm were used. Tensile test specimens in the stacking direction (Z direction) were fabricated by additively manufacturing a 6 × 6 × 46 mm rectangular parallelepiped along its long side and then cutting it. Tensile test specimens in the direction perpendicular to the stacking direction (XY direction) were fabricated by additively manufacturing the same rectangular parallelepiped along its short side and then cutting it. Meanwhile, for tensile tests at 1400 and 1600°C, flat test specimens were used, as shown in Figure 13. Tensile test specimens in the Z direction were fabricated by additively manufacturing a 3 mm thick rectangular plate along its long side and then cutting it. Tensile test specimens in the XY direction were fabricated by additively manufacturing a 3 mm thick rectangular plate along its short side and then cutting it. All test specimens were polished with abrasive paper to an arithmetic mean roughness (Ra) of 0.8 μm. In addition, for the tensile tests at 1400°C to 1600°C, a chuck made by additive manufacturing of Ta-3W alloy was used.

[0034] Table 1 shows the composition and particle size of the powders used. Table 2 shows the manufacturing conditions for the components. In Tables 1 and 2, "CPTa" is commercially pure Ta. "Ta2.5W" and "Ta3W" are both alloys with the representative composition Ta-2.5W. "Ta4W+" is an alloy with the representative composition Ta-4W-1Re-0.7Hf-0.025C. The Ta4W+ alloy powder was manufactured with a target C content of 0.025% by mass, but analysis revealed that the C content was approximately 0.04% by mass. "Ta13W" is a Ta-13W alloy.

[0035] [Table 1]

[0036] [Table 2]

[0037] When cross sections perpendicular to the stacking direction were examined using an optical microscope, numerous cracks were observed at the grain boundaries of Ta13W in both the as-printed material and the sample that had undergone residual stress relief treatment and stabilization treatment at 1600°C for 1 hour. These cracks are believed to have formed during polishing for cross-sectional observation. This indicates that Ta13W additively manufactured materials have extremely high residual stresses and that recrystallization did not occur even after stabilization treatment at 1600°C. No such cracks were observed in any samples other than Ta13W.

[0038] Table 3 shows the results of the tensile test at room temperature.

[0039] [Table 3]

[0040] Figure 2 shows the results of tensile tests at room temperature for as-printed materials. For Ta2.5W, data is shown for materials printed using the same machine (M100) as the other compositions. The effects of differences in machine are discussed later. From the results in Table 3 and Figure 2, it was confirmed that for samples from CPTa to Ta4W+, strength increased and elongation decreased as the W content increased. Ta4W+ exhibited very high strength, but poor ductility and low elongation. Ta13W had low strength and elongation, likely due to the presence of microcracks in the test specimens.

[0041] Figure 3 shows the results of tensile tests at room temperature for the as-printed material (AS) and heat-treated material. For Ta2.5W, data is shown for material printed using the same equipment (M100) as the other compositions. The results in Table 3 and Figure 3 show that for CPTa, residual stress relief treatment and stabilization treatment resulted in a slight decrease in strength and an increase in elongation. For Ta2.5W and Ta3W, stabilization treatment tended to increase both strength and elongation. For Ta4W+, stabilization treatment resulted in a decrease in strength and an increase in elongation. For Ta13W, sufficient elongation was not achieved even with stabilization treatment. Since the cracks caused by residual stress in Ta13W are not improved by heat treatment, it is thought that ductility was not achieved.

[0042] For space applications, strength at room temperature is not a particular issue, but a certain degree of elongation is required to withstand the vibrations that occur during launch, and an elongation of approximately 5% or more is preferable. In this regard, CPTa, Ta2.5W, and Ta3W exhibited sufficient elongation even in the as-formed state. For Ta4W+, elongation was low in the as-formed state, but heat treatment at 1500°C increased elongation to over 5%, and heat treatment at 1600°C showed similarly good elongation in both the Z and XY directions. This indicates that the heat treatment temperature for Ta4W+ should preferably be 1500°C or higher, with 1600°C or higher being even more preferable.

[0043] The changes in the structure due to heat treatment were investigated using EBSD. Figures 4 to 8 show the grain boundaries obtained by EBSD. The figures show an area of ​​700 x 1750 μm in a cross section parallel to the stacking direction, and the areas where the crystal orientation is off by 15 degrees or more are considered to be grain boundaries. Figures 4 to 8 show that for all compositions, the size of the grains does not appear to change much due to heat treatment.

[0044] Table 4 shows the average and standard deviation of the distance between two parallel lines sandwiching a crystal grain in Figures 4 to 8. In Table 4, H is the value in the horizontal direction in Figures 4 to 8, and V is the value in the vertical direction (stacking direction Z) in Figures 4 to 8. Hereinafter, this distance will be referred to as the "grain size in the cross section." Because the cut surface does not pass through the part of each crystal grain where the grain size is largest, the grain size in the cross section will be smaller than the actual grain size and will vary greatly, but it does provide a quantitative indicator of the size of the crystal grain. From Table 4, it appears that the grain size in the cross section increases slightly due to heat treatment, but this is not a significant change, and since the structure does not recrystallize, it is considered to be within the margin of error.

[0045] [Table 4]

[0046] Furthermore, although not shown, EBSD data showed that the crystal orientation of each crystal grain varied in the samples shown in Figures 4 to 8, and no change in this tendency was observed even after heat treatment. As will be described later, in the Ta2.5W fabricated using M290, the crystal orientation was body-centered cubic in the Z direction. <001> Although the direction was consistent, there was no difference between the as-formed material and the heat-treated material.

[0047] From these results, it is thought that the heat treatment hardly changes the size of the crystal grains, but increases ductility by reducing the dislocation density within the crystal grains, and the structure remains stable thereafter. However, Ta13W had internal cracks that did not improve even with heat treatment.

[0048] Furthermore, the effects of oxygen (O) and carbon (C) were investigated using SEM and EDS. Figure 9 shows SEM images of the as-printed and heat-treated Ta4W+ samples, and the heat-treated Ta2.5W sample. The length of the bar at the bottom of Figure 9 is 1 μm. No precipitates were observed in the as-printed Ta4W+ sample (Figure 9A). In contrast, precipitates were observed at the grain boundaries in the Ta4W+ samples heat-treated at 1500°C (Figure 9B) and 1600°C (Figure 9C). There was no significant difference between Figures 9B and 9C. Furthermore, no precipitates were observed in the heat-treated Ta2.5W sample (Figure 9D) that did not contain Re or Hf.

[0049] EDS element distribution (not shown) confirmed that the relatively large precipitates in the heat-treated Ta4W+ material were carbides, and the smaller precipitates were oxides. Furthermore, the oxides were confirmed to be oxides of Hf. The oxides were likely HfO2. The carbides were also confirmed to be carbides of Ta. According to the Ta-C binary phase diagram, the carbides are likely Ta2C. The heat-treated Ta2.5W material (Figure 9D) did not precipitate oxides due to the absence of Hf, and carbides were not precipitated due to the low C content.

[0050] From the above results, it is thought that the rapid cooling after additive manufacturing of Ta4W+ results in poor ductility due to the presence of impurities such as O, as well as C and the metallic elements W, Re, and Hf in a supersaturated solid solution in the Ta matrix phase in the as-formed material, and that ductility is restored by the stabilization treatment, which causes O to precipitate as Hf oxide and C to precipitate as Ta carbide at the grain boundaries. Furthermore, the oxides and carbides that form are stable, and therefore it is presumed that the structure after high-temperature stabilization treatment is stable and does not change with the cooling rate.

[0051] The results of tensile tests at high and low temperatures for the heat-treated materials are shown in Table 5. Figure 10 shows the test results at 500 to 1000°C, and Figure 11 shows the test results at 1400 to 1600°C.

[0052] [Table 5]

[0053] Comparing the results of Table 5 and Figures 10 and 11 with the results of tensile tests at room temperature (Table 3 and Figure 3), the strength of all samples decreased, and the strength gradually decreased as the test temperature increased. In addition, for CPTa, the elongation also clearly decreased as the test temperature increased.

[0054] Table 5 and Figure 11 show that samples of Ta2.5W stabilized at 1500°C or 1600°C exhibited sufficient strength even at 1600°C, which is higher than the heat resistance temperature of Nb alloys. Furthermore, a sample of Ta4W+ heat-treated at 1600°C exhibited an extremely high tensile strength of 208 MPa in the XY directions at 1600°C. Although no tensile test results are available for the Z direction of this sample at 1600°C, room temperature tensile tests (Table 3 and Figure 3) show similar strength and elongation in both the Z and XY directions, suggesting that the strength and elongation in the Z direction at 1600°C will also be similar to those in the XY directions. Ta13W also exhibited small elongation in tensile tests at 1600°C.

[0055] As mentioned in the explanation of the tensile test results at room temperature, the as-printed Ta4W+ material had poor ductility due to the rapid cooling after additive manufacturing, which resulted in the supersaturation of impurities such as O, C, and the metallic elements W, Re, and Hf in the Ta matrix phase, but it is thought that the stabilization treatment restored ductility by precipitating O as oxides and C as carbides at the grain boundaries. Furthermore, the oxides and carbides precipitated at the grain boundaries suppressed recrystallization, stabilizing the structure and contributing to improved tensile strength at high temperatures.

[0056] In space applications, both strength and elongation at high temperatures are important. In this regard, Ta2.5W and Ta4W+ exhibited sufficient strength and elongation in tensile tests at 1600°C, demonstrating their suitability for space applications.

[0057] Table 5 confirms that the sample in which residual stress was removed from Ta3W at 1200°C and stabilized at 1500°C did not exhibit low-temperature brittleness even in a tensile test at -170°C.

[0058] Next, we will discuss the impact of differences in equipment. The M100, which was primarily used in additive manufacturing in this example, is a small equipment used for research and development and the production of small parts, while the M290 is a large equipment used to produce larger components.

[0059] Table 6 and Figure 12 show the results of tensile tests on samples of Ta2.5W printed using M100 and M290. Table 6 and Figure 12 show that in tensile tests at room temperature, the sample printed using M100 had a higher tensile strength. This is thought to be because, as shown in Table 4, the crystal grains of the M100 printing material were smaller than those of M290, resulting in higher strength. It is known that the crystal grain size depends on the laser beam diameter and output. On the other hand, there is no significant difference between the two in terms of elongation. Measurement of crystal orientation using EBSD showed that the crystal orientation was irregular in the material printed using M100, while the material printed using M290 had a body-centered cubic orientation in the Z direction. <001> The crystal orientation was consistent. This difference in crystal orientation is thought to be due to differences in the characteristics of the additive manufacturing equipment, possibly due to differences in the direction of heat flow during solidification. Thus, although there are some differences in the structure and properties of the parts manufactured with M100 and M290, the strength and elongation in tensile tests were comparable, and it is believed that the findings obtained with M100 will also hold true when using M290.

[0060] [Table 6]

[0061] Previously, Ta alloys with a high W content, such as Ta-10W and ASTAR-811C, were often considered for space applications. However, the comparative example Ta13W did not achieve sufficient elongation even after heat treatment. This indicates that Ta alloys with a relatively low W content are suitable for the production of space components using additive manufacturing.

[0062] The results of the tensile test at 1600°C showed that Ta2.5W and Ta4W+ could achieve sufficient strength and elongation by stabilization at 1500°C or higher. The additively manufactured stabilized Ta2.5W material was confirmed to be applicable to space applications, not to mention other applications such as chemical plants. Furthermore, the stabilized Ta4W+ material exhibited extremely high strength at 1600°C, making it the most suitable alloy for space applications among the present examples. Since there was almost no difference in the tensile test results at room temperature between Ta2.5W and Ta3W, it is believed that similar results would be obtained if the W content of Ta4W+ was within the range of 4.0±0.5 mass%.

[0063] The present invention is not limited to the above-described embodiments and examples, and various modifications are possible within the scope of the technical concept thereof.

Claims

1. preparing an alloy powder of a Ta alloy containing 2.0 to 4.5 mass% W, with the remainder being Ta and unavoidable impurities; an additive manufacturing step of depositing the alloy powder by additive manufacturing techniques to form a shaped object; a stabilization step of heat treating the shaped object at a temperature of 1400°C or higher and 2000°C or lower; A method for manufacturing a Ta alloy member having the above structure.

2. preparing an alloy powder of Ta alloy containing 2.0 to 4.5 mass% W, 0.5 to 1.2 mass% Re, 0.5 to 1.0 mass% Hf, 0.005 to 0.045 mass% C, with the remainder being Ta and unavoidable impurities; an additive manufacturing step of depositing the alloy powder by additive manufacturing techniques to form a shaped object; a stabilization step of heat treating the shaped object at a temperature of 1400°C or higher and 2000°C or lower; A method for manufacturing a Ta alloy member having the above structure.

3. The stabilization step causes oxides of Hf and carbides of Ta to precipitate. The method for producing a Ta alloy member according to claim 2.

4. The method further includes a residual stress relief step of heat treating the shaped object at 1100°C or more and 1300°C or less after the additive manufacturing step. The method for producing a Ta alloy member according to any one of claims 1 to 3.

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