Tungsten alloy wire

Abstract

We provide thin, highly elastic tungsten alloy wire. [Solution] The tungsten alloy wire 1 mainly contains an alloy of tungsten and rhenium, has a wire diameter of less than 40 μm, and in a cross section parallel to the wire axis of the tungsten alloy wire 1, the average aspect ratio of the major axis to the minor axis of the crystal grains is 10 or less.

Description

Technical Field

[0001] The present invention relates to a tungsten alloy wire.

Background Art

[0002] Conventionally, a technique for manufacturing a metal mesh using a metal wire made of stainless steel or tungsten has been known (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] To produce a dense metal mesh, not only thinning of the warp or weft wires but also a large elongation is required.

[0005] Therefore, an object of the present invention is to provide a tungsten alloy wire that is thin and has a large elongation.

Means for Solving the Problems

[0006] ]>The tungsten alloy wire according to one aspect of the present invention contains an alloy of tungsten and rhenium as a main component, has a wire diameter of less than 40 μm, and in a cross-section parallel to the wire axis of the tungsten alloy wire, the average value of the aspect ratio of the long diameter to the short diameter of the crystal grains is 10 or less.

Effects of the Invention

[0007] According to the present invention, a tungsten alloy wire that is thin and has a large elongation can be provided.

Brief Description of the Drawings

[0008] [Figure 1] Figure 1 is a perspective view showing a tungsten alloy wire according to an embodiment, and a mesh woven using the tungsten alloy wire. [Figure 2] Figure 2 is a schematic diagram of crystal grains in a cross-section parallel to the wire axis of a tungsten alloy wire according to an embodiment. [Figure 3] Figure 3 is a flowchart showing a method for manufacturing tungsten alloy wire according to an embodiment. [Figure 4] Figure 4 is a diagram illustrating a method for measuring the major and minor axes of crystal grains in a tungsten alloy wire according to an embodiment. [Figure 5A] Figure 5A shows an EBSD image of a cross-section of a tungsten alloy wire according to Example 1. [Figure 5B] Figure 5B shows an EBSD image of a cross-section of a tungsten alloy wire according to Example 2. [Figure 5C] Figure 5C shows an EBSD image of a cross-section of a tungsten alloy wire according to Example 3. [Figure 5D] Figure 5D shows an EBSD image of a cross-section of a tungsten alloy wire according to Example 4. [Figure 5E] Figure 5E shows an EBSD image of a cross-section of a tungsten alloy wire according to Example 5. [Figure 5F] Figure 5F shows an EBSD image of a cross-section of a tungsten alloy wire according to Example 6. [Figure 6A] Figure 6A shows an EBSD image of the cross-section of a tungsten alloy wire relating to Comparative Example 2. [Figure 6B] Figure 6B shows an EBSD image of the cross-section of a pure tungsten wire according to Comparative Example 7. [Figure 6C] Figure 6C shows an EBSD image of a cross-section of a pure tungsten wire related to Comparative Example 8. [Modes for carrying out the invention]

[0009] Hereinafter, the tungsten alloy wire according to the embodiment of the present invention will be described in detail with reference to the drawings. Note that all the embodiments described below show specific examples of the present invention. Therefore, the numerical values, shapes, materials, components, arrangements and connection forms of the components, steps, the order of steps, etc. shown in the following embodiments are merely examples and are not intended to limit the present invention. Thus, among the components in the following embodiments, the components not described in the independent claims are described as optional components.

[0010] Also, each figure is a schematic diagram and is not necessarily drawn precisely. Therefore, for example, the scales in each figure do not necessarily match. Also, in each figure, substantially the same configurations are denoted by the same reference numerals, and overlapping descriptions are omitted or simplified.

[0011] In this specification, terms indicating the relationship between elements such as parallel and perpendicular, terms indicating the shape of elements such as circular, and numerical ranges are not expressions representing only strict meanings, but are expressions meaning ranges that are substantially equivalent, for example, including differences of about several percent.

[0012] In this specification, the "main component" means the component with the highest content rate among all the components constituting the member. For example, a component with a content rate of 50 mass% (mass percent) or more is the main component. The component is a material, an element, a compound, etc. Also, "member A is composed of component B" means that member A substantially contains only component B. However, member A may contain impurities that are inevitably mixed in during manufacturing in addition to component B. The content rate of such inevitable impurities is 1 mass% or less.

[0013] In this specification, ordinal numbers such as "first" and "second" do not mean the number or order of components unless otherwise specified, and are used for the purpose of avoiding confusion and distinguishing between the same kind of components.

[0014] (Embodiment) First, the configuration of the tungsten alloy wire according to the embodiment will be described with reference to FIG. 1. FIG. 1 is a perspective view showing a tungsten alloy wire 1 according to the present embodiment and a mesh 10 woven using the tungsten alloy wire 1.

[0015] The tungsten alloy wire 1 is stored in a wound state on a winding frame 2 called a bobbin, spool, reel, or the like. The tungsten alloy wire 1 is unwound from the winding frame 2 and used for various applications.

[0016] For example, the tungsten alloy wire 1 is used as a warp or weft of the mesh 10. Specifically, the mesh 10 can be manufactured by weaving using the tungsten alloy wire 1 as at least one of the warp and weft.

[0017] The mesh 10 is an example of a tungsten product including the tungsten alloy wire 1. The mesh 10 is, for example, a plain weave mesh, but may also be a mesh such as a twill weave, a basket weave, or a twill basket weave. Both the warp and weft of the mesh 10 may be the tungsten alloy wire 1, or one of the warp and weft may be another metal wire such as a stainless steel wire. Alternatively, one of the warp and weft of the mesh 10 may be a resin fiber.

[0018] The mesh 10 is, for example, a screen mesh used for screen printing. Alternatively, the mesh 10 may be used for clothing such as protective clothing and gloves for anti-cutting or radiation shielding, or may be used for a filter for removing foreign substances. Further, the tungsten alloy wire 1 may be used for a twisted wire, a rope, a saw wire, a knitted fabric, a non-woven fabric, or the like, in addition to the mesh 10.

[0019] When attempting to manufacture a dense mesh 10 with narrow spacing between warp threads or weft threads, the tungsten alloy wire 1 bends significantly at the intersections of the warp and weft threads (the radius of curvature decreases). As a result, the tungsten alloy wire 1 may break. Breakage when bent is likely to occur starting from the grain boundaries of the multiple crystal grains that make up the tungsten alloy wire 1. Therefore, it is effective to strengthen the grain boundaries, reduce the number of grain boundaries, or do both. In the tungsten alloy wire 1 according to this embodiment, the elongation can be increased by strengthening the grain boundaries and reducing the number of grain boundaries. Increased elongation suppresses breakage when bent, making it possible to manufacture a dense mesh 10.

[0020] The tungsten alloy wire 1 according to this embodiment mainly contains an alloy of tungsten (W) and rhenium (Re). Specifically, the tungsten alloy wire 1 is composed of an alloy of tungsten and rhenium. The rhenium contained in the tungsten alloy wire 1 can remove impurities such as oxygen that may remain at the grain boundaries during the manufacturing process. This makes it possible to increase the strength of the grain boundaries.

[0021] The tungsten content in the tungsten alloy wire 1 is, for example, 90 mass% or more. However, the tungsten content in the tungsten alloy wire 1 may be 91 mass% or more, 93 mass% or more, 95 mass% or more, 97 mass% or more, 98 mass% or more, 99 mass% or more, 99.5 mass% or more, or 99.9 mass% or more.

[0022] The rhenium content in the tungsten alloy wire 1 is, for example, 10 mass% or less. However, the rhenium content in the tungsten alloy wire 1 may be 9 mass% or less, 7 mass% or less, 5 mass% or less, 3 mass% or less, 2 mass% or less, 1 mass% or less, 0.5 mass% or less, or 0.1 mass% or less.

[0023] The diameter of the tungsten alloy wire 1 is less than 40 μm. The diameter of the tungsten alloy wire 1 may be 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 18 μm or less, 15 μm or less, 12 μm or less, 10 μm or less, 8 μm or less, or 5 μm or less.

[0024] The cross-sectional shape of the tungsten alloy wire 1 perpendicular to its axis is circular, and the wire diameter refers to the diameter of this circle. If the cross-sectional shape is other than circular, the wire diameter can be considered to be the maximum width of the cross-section of the tungsten alloy wire 1. The wire diameter of the tungsten alloy wire 1 is generally uniform.

[0025] The tungsten alloy wire 1 is composed of multiple crystal grains. Many of the crystal grains have an elongated shape along the wire axis of the tungsten alloy wire 1.

[0026] In this embodiment, the average aspect ratio (= major axis ÷ minor axis) of the crystal grains in a cross-section parallel to the wire axis of the tungsten alloy wire 1 is 10 or less. The average aspect ratio may be 7.5 or less, 7 or less, 6.5 or less, 6 or less, 5.5 or less, 5 or less, or 4.5 or less.

[0027] The major and minor axes of the crystal grains are defined as follows. Figure 2 is a schematic diagram of the crystal grains in a cross-section parallel to the line axis of the tungsten alloy wire 1 according to this embodiment. As shown in Figure 2, the minor and major axes of the crystal grains are considered to be the lengths of the minor axis and major axis of the approximate ellipse of the crystal grain, respectively. The approximate ellipse is determined, for example, by elliptic approximation using the least squares method for the crystal grain, but is not limited to this. The measurement of the minor and major axes of the crystal grains, and the calculation of the aspect ratio, are performed by image processing. The specific measurement and calculation methods will be described later.

[0028] Furthermore, in a cross-section parallel to the wire axis of the tungsten alloy wire 1, the average value of the minor axis of the crystal grains is 200 nm or more. The average value of the minor axis of the crystal grains may also be 250 nm or more, 300 nm or more, 350 nm or more, 370 nm or more, 400 nm or more, 420 nm or more, or 440 nm or more.

[0029] In this way, the crystal grains contained in the tungsten alloy wire 1 can be made thicker and shorter, thus reducing the number of crystal grain boundaries. In this way, the strength of the crystal grain boundaries can be increased and the number of crystal grain boundaries can be reduced, which increases the elongation of the tungsten alloy wire 1.

[0030] [Manufacturing method] Next, the method for manufacturing the tungsten alloy wire 1 according to this embodiment will be explained with reference to Figure 3. Figure 3 is a flowchart showing the method for manufacturing the tungsten alloy wire 1 according to this embodiment.

[0031] First, rhenium is mixed with tungsten powder (S10). For example, tungsten powder is mixed with an aqueous solution of APR (ammonium perrhenate), and the water is evaporated by heating. After the water has evaporated, the powder is placed in a container and heated in a hydrogen atmosphere furnace at 800°C for a predetermined time (for example, about 20 minutes) to mix the tungsten and rhenium. By adjusting the mixing ratio, the respective content of tungsten and rhenium in the tungsten alloy wire 1 after manufacturing can be adjusted. The average particle size of the tungsten powder is, for example, in the range of 1 μm to 4 μm, but is not limited to this. Furthermore, there are no particular limitations on the method of mixing tungsten powder and rhenium.

[0032] Next, the mixture is sintered (S11). For example, the mixture is pressed to form a compressed powder compact of a predetermined shape, and the formed powder compact is heated to a temperature below its melting point to densify it. This forms an ingot (sintered body) mainly composed of an alloy of tungsten and rhenium. The ingot is, for example, a rod-shaped body with a cross-sectional diameter of approximately 17 mm. The cross-sectional diameter of the ingot may be, for example, between 15 mm and 20 mm, but is not limited to this.

[0033] Next, the ingot is subjected to a swaging process (S12). Specifically, the ingot is compressed and stretched from all sides by forging, thereby forming it into a thin wire. Rolling may be performed instead of swaging. The swaging process may be repeated multiple times while annealing is carried out. The annealing temperature is, for example, 1800°C. The swaging process is carried out until a tungsten alloy wire with a diameter of, for example, 3 mm is obtained.

[0034] After swaging, the tungsten alloy wire is wound onto a winding device, then unwound via an unwinding device, and the subsequent processes are carried out. In other words, the subsequent processes are performed sequentially in-line as the tungsten alloy wire is fed along the wire axis. Alternatively, the processes may be carried out in-line from the swaging stage.

[0035] Next, intermediate annealing is performed (S13). The term "intermediate" is used to distinguish it from the "final" annealing (S16), which will be described later. Intermediate annealing is an annealing process performed before the line drawing process or in the middle of repeated line drawing processes.

[0036] Next, wire drawing is performed (S14). Wire drawing is performed using one or more wire drawing dies. The reduction in cross-sectional area of ​​the tungsten alloy wire due to one wire drawing process using one wire drawing die is, for example, 10% to 40%.

[0037] Intermediate annealing (S13) and wire drawing (S14) are repeated until the desired wire diameter is obtained (No. in S15). In the repeated wire drawing, a wire drawing die with a smaller bore diameter is used than the wire drawing die used in the previous drawing. The wire drawing may also be performed while heating (i.e., heated wire drawing). In heated wire drawing, a lubricant in which graphite is dispersed in water may be used.

[0038] Intermediate annealing (S13) is performed to recrystallize the tungsten alloy wire in a primary manner, preventing the crystals from becoming too fine. If the crystals become too fine during repeated wire drawing, it becomes difficult to achieve the desired thickness (aspect ratio) of crystals in the final annealing (S16) described later. For example, the heating time becomes longer or the heating temperature becomes higher, making it impossible to achieve high elongation. By performing intermediate annealing, the crystal grains that are refined by wire drawing can be made thicker and shorter, contributing to the achievement of high elongation in the final annealing. The annealing temperature for intermediate annealing is, for example, between 1200°C and 1500°C.

[0039] The desired wire diameter depends on the wire diameter of the tungsten alloy wire 1 as the final product. Therefore, the desired wire diameter is, for example, less than 40 μm, but may be greater than 40 μm considering the reduction in wire diameter due to electrolytic polishing (S17). Note that the reduction in wire diameter due to electrolytic polishing is limited to a maximum reduction in cross-sectional area of ​​about 40%.

[0040] If the desired wire diameter is obtained (Yes in S15), the final annealing is performed (S16). The final annealing is performed to cause primary recrystallization of the tungsten alloy wire. This makes the crystal grains of the tungsten alloy wire thicker. The annealing temperature for the final annealing is higher than the annealing temperature for the intermediate annealing. For example, the annealing temperature for the final annealing is between 1500°C and 1750°C. However, the annealing temperature for the final annealing may be 1550°C or higher, or 1600°C or higher. Also, the annealing temperature for the final annealing may be 1700°C or lower, or 1650°C or lower.

[0041] The final annealing is performed, for example, during the period when the tungsten alloy wire, after wire drawing, passes through the heat treatment furnace at a predetermined speed (wire velocity). For example, for a heat treatment furnace with a length of 45 cm (furnace length), the wire velocity can be set to 5 m / min or more and 50 m / min or less, but is not limited to this. The annealing time can be adjusted by adjusting the wire velocity or furnace length.

[0042] The wire speed of the tungsten alloy wire can be controlled by an unwinding device and a winding device. In this case, the tension applied when unwinding (feeding out) the tungsten alloy wire by the unwinding device is smaller than the tension applied when winding the tungsten alloy wire by the winding device. For example, the unwinding tension is 1 cN, while the winding tension is 3 cN. In the final annealing process, the strength of the heated tungsten alloy wire decreases, so if the unwinding tension is too high, the tungsten alloy wire may stretch during the final annealing process. In this case, the elongation of the tungsten alloy wire 1 as the final product decreases. Therefore, by suppressing the unwinding tension, elongation in the final annealing process can be suppressed, and the decrease in the elongation of the tungsten alloy wire 1 can be suppressed.

[0043] The final annealing is carried out in a reducing atmosphere. This suppresses the oxidation of the tungsten alloy wire. Specifically, the final annealing is performed in a mixed gas atmosphere of nitrogen (N2) and hydrogen (H2) gas. The mixing ratio of N2 gas to H2 gas is, for example, N2:H2=3:1. The flow rate of the mixed gas is, for example, 8 L / min.

[0044] After the final annealing, the tungsten alloy wire is subjected to electropolishing (S17). Electropolishing is performed by applying a voltage while the tungsten alloy wire and the counter electrode are immersed in an electrolyte solution, such as an aqueous sodium hydroxide solution. This removes the surface layer of the tungsten alloy wire, allowing for fine adjustment of the wire diameter. Note that electropolishing is optional. Also, electropolishing may be performed before the final annealing.

[0045] Generally, in wire drawing processes aimed at reducing wire diameter, the crystal grains tend to become thin and elongated in a fibrous manner along the wire axis, resulting in limited elongation. In contrast, this embodiment involves performing a final annealing (S16) after wire drawing. This allows the crystal grains to become thicker and shorter, thereby reducing the number of grain boundaries. Consequently, even tungsten alloy wires with small diameters can achieve increased elongation.

[0046] [Examples] Next, a specific example of the tungsten alloy wire 1 according to this embodiment will be described.

[0047] The metal wires in each of the following examples and comparative examples are manufactured using the manufacturing method described in Figure 3, with various conditions (specifically, wire diameter, rhenium content, final annealing temperature, and linear velocity) appropriately varied. The explanation of common conditions for each example and comparative example will be omitted or simplified, and the explanation will focus on the differing conditions.

[0048] Table 1 shows the main conditions in Examples 1-6 and Comparative Examples 1-8.

[0049] [Table 1]

[0050] Examples 1-4 each have different wire diameters. Examples 5 and 6 have the same wire diameter as Example 2. Tungsten alloy wires according to Examples 1-6 were manufactured by varying the bore diameter of the wire drawing die used in the final wire drawing step during the repeated wire drawing process (S14). The temperature and wire speed during the final annealing (S16) are as shown in Table 1.

[0051] Furthermore, the rhenium content in Examples 5 and 6 differs from that in Examples 1 to 4. The desired rhenium content can be achieved by varying the mixing ratio in the rhenium mixture (S10) with tungsten powder.

[0052] Comparative Examples 1-6 have the same wire diameter and rhenium content as Examples 1-6. Although not shown in Table 1, the tungsten content of Comparative Examples 1-4 and Examples 1-4 is 93 mass%. The tungsten content of Comparative Example 5 and Example 5 is 95 mass%. The tungsten content of Comparative Example 6 and Example 6 is 97 mass%. In other words, Comparative Examples 1-6 have the same composition as Examples 1-6. The only difference between Comparative Examples 1-6 and Examples 1-6 is that they did not undergo final annealing (S16).

[0053] Comparative Examples 7 and 8 both have a rhenium content of 0 mass%. That is, Comparative Examples 7 and 8 are not tungsten alloy wires, but pure tungsten wires with a tungsten content of substantially 100 mass%. Comparative Example 7 did not undergo final annealing (S16). Comparative Example 8 underwent final annealing (S16), and the temperature and linear velocity for the final annealing were the same as in Example 1.

[0054] As shown in Table 1, in Examples 1 to 6, tungsten alloy wires with elongation in the range of 9% to 12% were obtained, and in Examples 1 to 4, tungsten alloy wires with elongation in the range of 10% to 12% were obtained. On the other hand, Comparative Examples 1 to 4, despite having the same wire diameter and composition as Examples 1 to 4, had elongation in the range of 1.39% to 2.24%. Furthermore, Comparative Examples 5 and 6, despite having the same wire diameter and composition as Examples 5 and 6, had elongation of 1.70% and 1.84%, respectively. From this, it can be seen that even if the wire diameter and composition are the same, the elongation differs greatly depending on whether or not final annealing is performed. Specifically, it can be seen that Examples 1 to 6, which underwent final annealing, achieved more than five times the elongation compared to Comparative Examples 1 to 6, which did not undergo final annealing.

[0055] The elongation was measured according to the Japanese Industrial Standards (JIS) tensile testing method for metallic materials (JIS Z 2241). A gauge length (line length) of 100 mm was used.

[0056] Furthermore, in Comparative Example 8, despite performing the final annealing as in each of the examples, only an elongation of 1.91% was obtained. In other words, it can be seen that a large elongation cannot be obtained by simply performing the final annealing. In contrast, it can be seen that the rhenium-containing tungsten alloy wires in each example achieved more than five times the elongation of the pure tungsten wire without rhenium.

[0057] Furthermore, when comparing Example 5 and Example 6, the wire diameter and final annealing conditions were the same, with only the rhenium content differing. Specifically, the rhenium content in Example 5 was higher than that in Example 6. In this case, both the tensile strength and elongation of Example 5 were greater than those of Example 6. From this, it can be seen that, given the same final annealing conditions, increasing the rhenium content can increase both the tensile strength and elongation.

[0058] Thus, neither adding rhenium nor performing a final annealing process alone is sufficient to increase elongation. It is evident that a tungsten alloy wire with high elongation can be achieved by manufacturing a tungsten alloy wire primarily composed of a tungsten-rhenium alloy using a manufacturing method that includes a final annealing process.

[0059] In Examples 1-6, the tungsten alloy wire has a tensile strength of 1600 MPa to 2000 MPa. In Examples 1-4, the tungsten alloy wire has a tensile strength of 1800 MPa to 2000 MPa. The tensile strength of the tungsten alloy wire in Examples 1-6 is higher than that achieved by stainless steel wire having the same elongation as Examples 1-6. In other words, tungsten alloy wire can achieve both high elongation and high tensile strength compared to stainless steel wire. To weave mesh 10 using tungsten alloy wire as warp or weft threads, a certain level of tensile strength is required for the tungsten alloy wire. If the tensile strength is too low, there is a risk of breakage due to the tension applied during weaving or use. In each example, the tungsten alloy wire can achieve a tensile strength high enough to prevent breakage. The tensile strength was measured, for example, based on the tensile test of the Japanese Industrial Standards (JIS H 4460 8).

[0060] Next, the dimensions of the crystal grains of the tungsten alloy wire in each embodiment will be described. First, the method for measuring and calculating the dimensions such as the aspect ratio and minor axis of the crystal grains will be explained using Figure 4. Figure 4 is a diagram illustrating the method for measuring the major axis and minor axis of the crystal grains of the tungsten alloy wire according to this embodiment.

[0061] First, a tungsten alloy wire of a predetermined length is prepared. The prepared tungsten alloy wire is cut in a cross-section parallel to the wire axis, and the cross-section is observed by electron backscatter diffraction (EBSD). The cross-section is, for example, a cross-section containing the wire axis of the tungsten alloy wire. After cutting the tungsten alloy wire, the cross-section was polished with a cross-section polisher (CP). An EBSD analyzer manufactured by EDAX, Inc., Velocity was used. The interval between measurement points was 0.03-0.04 μm.

[0062] EBSD yields an image (EBSD image) like the one shown in Figure 4(a). Figure 4(a) is an EBSD image of a cross-section of a tungsten alloy wire according to the above-described example 4.

[0063] Next, the obtained EBSD image is cropped to a predetermined observation area. Figure 4(b) shows the result of cropping to the rectangular area indicated by the dashed line in (a). Here, the size of the observation area was, for example, a rectangular area of ​​7.35 μm × 65.65 μm. However, the size of the observation area is not particularly limited.

[0064] In Figures 4(a) and 4(b), closed regions painted with the same intensity (or color) represent a single crystal grain. If the difference in crystal orientation between the first measurement point and the second measurement point adjacent to the first measurement point is 5° or more, the crystal grain to which the first measurement point belongs is considered to be different from the crystal grain to which the second measurement point belongs.

[0065] Next, image processing is performed on the image shown in Figure 4(b) to separate grain boundaries and exclude edges within the observation area. Grain boundary separation is the process of separating each crystal grain individually, clarifying the grain boundaries between adjacent crystal grains. Edge exclusion is the process of excluding crystal grains that are in contact with the edges (outer frame) of the observation area. In other words, crystal grains that do not entirely fall within the observation area are excluded from the next dimension calculation.

[0066] Next, the average aspect ratio and average minor axis are calculated by measuring the minor and major axes of all crystal grains within the observation range using image processing. Figure 4(c) shows an image obtained by performing grain boundary separation and edge exclusion processing on the EBSD image shown in Figure 4(b). In Figure 4(c), the number of closed regions colored white represents the number of crystal grains for which dimension calculation is performed. Note that the software used for image processing is called MIPAR (v4.5.0.7, manufactured by MIPAR Software LLC), but it is not limited to this software.

[0067] Image processing is used to measure the major and minor axes, and calculate the aspect ratio, for all crystal grains within the observation range that are subject to dimensional calculation. By dividing the sum of the measured minor axes and the sum of the calculated aspect ratios by the number of crystal grains included in the calculation, the average minor axis and average aspect ratio can be calculated.

[0068] Table 2 below shows the average aspect ratio and average minor axis of the crystal grains for the tungsten alloy wires of Examples 1 to 6 described above, the tungsten alloy wire of Comparative Example 2, and the pure tungsten wires of Comparative Examples 7 and 8. Table 2 also indicates the presence or absence of rhenium and whether or not final annealing was performed.

[0069] [Table 2]

[0070] Figures 5A to 5F show the EBSD images of the tungsten alloy wires according to Examples 1 to 6, respectively. Figures 6A to 6C show the EBSD images of the tungsten alloy wire according to Comparative Example 2, and the pure tungsten wires according to Comparative Examples 7 and 8, respectively. Each figure shows an image cropped to a predetermined observation range, as in Figure 4(b). Figure 4(b) is the same as Figure 5D.

[0071] As can be seen by comparing Figures 5A to 5F with Figures 6A and 6B, in Comparative Examples 2 and 7, which did not undergo final annealing, the crystal grains are clearly elongated in the direction of the wire axis. As shown in Table 2, the average aspect ratio is greater than 10 for both the tungsten alloy wire in Comparative Example 2 and the pure tungsten wire in Comparative Example 7. Furthermore, the average minor axis of each of the tungsten alloy wire in Comparative Example 2 and the pure tungsten wire in Comparative Example 7 is less than 200 nm. For this reason, it is presumed that Comparative Examples 2 and 7 were unable to reduce the number of crystal grain boundaries and therefore could not achieve the large elongation shown in Table 1. Comparative Example 2 contains rhenium, similar to the other examples, but it was not subjected to final annealing, and therefore the number of crystal grain boundaries could not be reduced.

[0072] In the tungsten alloy wires of Examples 1 to 6, as shown in Table 2, the average aspect ratio of the crystal grains is 10 or less. Specifically, the average aspect ratio of the crystal grains is within the range of 4.5 to 7.5. In addition, the average minor diameter of the crystal grains is 200 nm or more. Specifically, the average minor diameter of the crystal grains is within the range of 250 nm to 450 nm. Thus, in the tungsten alloy wires of Examples 1 to 6, the crystal grains can be made thicker and shorter, and the number of crystal grain boundaries can be reduced.

[0073] Furthermore, comparing Figures 5A to 5D with Figure 6C, the average aspect ratio and average minor axis of the crystal grains do not differ significantly between Examples 1 to 4 and Comparative Example 8. This is also shown in Table 2. However, Comparative Example 8, which does not contain rhenium, did not achieve significant elongation, as shown in Table 1. As mentioned above, rhenium can remove impurities such as oxygen that may be present at the grain boundaries, thereby increasing the strength of the grain boundaries. For this reason, even if the same final annealing as in the examples was performed in Comparative Example 8, which does not contain rhenium, the effect of rhenium in increasing the strength of the grain boundaries was insufficient, and significant elongation was not achieved.

[0074] As described above, the tungsten alloy wire according to this embodiment can reduce the number of grain boundaries and increase the strength of the grain boundaries, thereby increasing the elongation.

[0075] Furthermore, in order to confirm that the tungsten alloy wire used in weaving according to this embodiment would not break even when subjected to large bending and loads, a plain weave mesh was actually manufactured. The number of meshes in the manufactured mesh was 200. The weft was the tungsten alloy wire according to Example 4, with a wire diameter of 14 μm, an elongation of 10.4%, a tensile strength of 1973 MPa, and a breaking strength of 0.39 N. For the warp, a metal wire with a sufficiently larger wire diameter and breaking strength than the weft was used. Specifically, the warp had a wire diameter of 50 μm, a tensile strength of 747 MPa, and a breaking strength of 1.87 N. Since the warp had a sufficiently larger wire diameter and breaking strength than the weft, there was almost no deformation of the warp after weaving, and only the weft bent significantly along the surface of the warp. Therefore, the radius of curvature Ri on the inside of the bend in the weft (tungsten alloy wire) can be considered to be the radius of the warp (=25 μm). Thus, the radius of curvature Rc of the weft became 32 μm (=25 + 14 ÷ 2).

[0076] Here, when the warp and weft threads are both made of the same tungsten alloy wire, and the radius of curvature Rc of the tungsten alloy wire is converted to a plain weave mesh of 32 μm, the opening ratio is 42% and the mesh count is 640. This is a high density for a plain weave mesh using ultrafine wires. In particular, it has been shown that the tungsten alloy wire according to this embodiment can be used as a metal wire for manufacturing screen printing meshes for applications requiring thin and uniform printed shapes, such as electrodes for multilayer ceramic capacitors.

[0077] [Effects, etc.] As described above, the tungsten alloy wire according to the first aspect of the present invention is, for example, the tungsten alloy wire 1 described above, which mainly contains an alloy of tungsten and rhenium, has a wire diameter of less than 40 μm, and in a cross section parallel to the wire axis of the tungsten alloy wire, the average value of the aspect ratio between the major axis and minor axis of the crystal grains is 10 or less.

[0078] This allows rhenium to remove impurities such as oxygen that may remain at the grain boundaries during manufacturing, thereby increasing the strength of the grain boundaries. Furthermore, since the grains can be made thicker and shorter, the number of grain boundaries can be reduced. In this way, by adjusting both the strength and number of grain boundaries, the elongation can be dramatically increased. Therefore, according to this embodiment, a thin tungsten alloy wire with high elongation can be realized.

[0079] A tungsten alloy wire according to a second aspect of the present invention is a tungsten alloy wire according to a first aspect, wherein the average value of the minor axis of the crystal grains in a cross section parallel to the wire axis of the tungsten alloy wire is 200 nm or more.

[0080] This allows the crystal grains to be made even thicker, thus reducing the number of grain boundaries. Consequently, the elongation of the tungsten alloy wire can be further increased.

[0081] A tungsten alloy wire according to a third aspect of the present invention is a tungsten alloy wire according to the first or second aspect of the present invention, which is used as a warp or weft thread of mesh 10.

[0082] This makes it possible to manufacture a fine, dense mesh 10 using tungsten alloy wire. For example, if mesh 10 is used as a screen mesh for screen printing, it is possible to achieve high-resolution printing.

[0083] The tungsten alloy wire according to the fourth aspect of the present invention is a tungsten alloy wire according to any one of the first to third aspects, wherein the rhenium content in the tungsten alloy wire is 10 mass% or less.

[0084] This improves the processability of tungsten alloy wire, making it easier to thin it. Therefore, it becomes possible to create tungsten alloy wire that is thin and has high elongation.

[0085] (others) Although the tungsten alloy wire according to the present invention has been described above based on the above embodiments, the present invention is not limited to the above embodiments.

[0086] For example, the tungsten alloy wire 1 may further contain one or more metallic elements other than tungsten and rhenium. That is, the tungsten alloy wire 1 may be an alloy wire of tungsten, rhenium, and one or more metallic elements different from both tungsten and rhenium.

[0087] Furthermore, for example, the present invention may be realized as a tungsten product comprising tungsten alloy wire 1. The tungsten product is, for example, a mesh comprising tungsten alloy wire 1 as at least one of the warp and weft threads. Alternatively, the tungsten product may be a twisted wire, rope, saw wire, knitted fabric or nonwoven fabric comprising tungsten alloy wire 1.

[0088] Furthermore, the present invention also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art could conceive, as well as forms realized by arbitrarily combining the components and functions of each embodiment without departing from the spirit of the present invention. [Explanation of symbols]

[0089] 1 Tungsten alloy wire 10 mesh

Claims

1. It is a tungsten alloy wire, It mainly contains an alloy of tungsten and rhenium, The wire diameter is less than 40 μm. In a cross-section parallel to the wire axis of the tungsten alloy wire, the average aspect ratio between the major and minor axes of the crystal grains is 10 or less. Tungsten alloy wire.

2. In a cross-section parallel to the wire axis of the tungsten alloy wire, the average value of the minor axis of the crystal grains is 200 nm or more. The tungsten alloy wire according to claim 1.

3. The tungsten alloy wire is used as the warp or weft thread of the mesh. The tungsten alloy wire according to claim 1 or 2.

4. The rhenium content in the tungsten alloy wire is 10 mass% or less. The tungsten alloy wire according to claim 1 or 2.

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