JP4426904B2 - Tungsten wire and method for manufacturing the same - Google Patents

Description

  The present invention relates to a tungsten wire material used for a lamp, a discharge lamp or the like.

  The linear material in the present invention means a linear material having a diameter of about 0.01 mm to 20 mm, including metal linear and rod-shaped discharge lamp electrodes such as filaments.

  Since tungsten materials have a high melting point, they have been widely used as electrodes for filaments, lamps and discharge lamps.

  Pure tungsten substantially free of additive elements undergoes recrystallization when used at a high temperature, resulting in a so-called stone wall-like crystal state of fine crystals shown in FIG.

  Tungsten having a stone wall-like structure has low toughness and impact resistance, and has a drawback that it is easily broken during transportation or mounting. In addition, there is a disadvantage that the grain boundary slip is likely to occur at a high temperature, and as a result, deformation (sag) is likely to occur during use. Hereinafter, the property in which this “sag” hardly occurs is referred to as “sag resistance”.

  As described in Patent Document 1 and Patent Document 2, it is known that improvement in sag resistance can be realized by adding a dopant typified by potassium to tungsten.

  That is, by adding the dopant, stone wall-like crystals are not generated, and as a result, long crystals that are long in the length direction of the linear material as shown in FIG. 4 are generated. Compared to fine stone-walled crystals, this long crystal has a small grain boundary with respect to the entire volume, and therefore it is less likely to slip in the longitudinal cross-sectional direction and has high sag resistance.

  However, tungsten to which sag resistance is increased by adding a dopant, for example, W to which K is added, is not sufficient in toughness and impact resistance except when Re is added. The problem of destruction cannot be solved.

However, W alloy added with Re, which is most resistant to destruction during manufacturing and transportation, is very expensive, and the price of the linear material is lower than that of ordinary W linear material. The price is more than 100 times.
JP 2000-106131 A Japanese Patent Laid-Open No. 05-290802

  In order to increase the impact resistance of the tungsten wire material as the electrode for the discharge lamp and the filament, it is necessary to improve the sag resistance and enlarge the crystal grains so that the grain boundaries between the grains are difficult to slip.

  From this point of view, a linear material made of a single crystal is most preferable. However, a linear material made of a single crystal cannot be manufactured industrially due to the characteristics of W, and after recrystallization, as shown in FIG. An unfavorable stone wall-like structure is formed.

  Also preferred according to the single crystal is a long crystal grain grown in the length direction as shown in FIG. 4 which is produced when the aforementioned dopant is added. However, in order to obtain such long crystal grains, there is a problem that the recrystallization heat treatment requires a huge time such as several hours to several hundred hours at a temperature of 1273K.

  An object of the present invention is to provide a W-wire material excellent in sag resistance, mechanical properties such as toughness and impact resistance, and suitable for discharge lamp electrodes and filaments, in particular, long-sized crystal grains grown in the length direction at low cost. There is to get in.

  In the present invention, the formation of a coating layer made of an element other than W on the surface of the W linear material suppresses the movement of the W element to the grain boundary due to the presence of the coating element during the heat treatment. This is based on the knowledge that the growth of secondary recrystallized grains in the interior is promoted and grains having a large aspect ratio are formed inside the W material while suppressing the grain growth in the surface portion.

  Thus, the recrystallized structure obtained by heat-treating the W linear material formed with a coating layer composed of an element other than W has crystal growth noticeable only inside, thereby causing coarse particles to extend in the longitudinal direction. Impact resistance and sag resistance equivalent to the grown crystal state can be obtained. This crystal structure is made of tungsten with enhanced sag resistance by adding a dopant to make a tough alloy with the applied components. Compared with conventional doping materials other than Re, for example, tungsten doped with K Thus, a material with much higher toughness can be obtained.

  As the W linear material used in the present invention, pure tungsten, an alkali metal typified by K, a doped tungsten doped with 10-100 PPM of an alkaline earth metal, or tungsten with C, Re, Ta, Mo, B, Sc Tungsten-based material added with several hundred ppm of at least one additive element composed of high melting point elements such as Ti, Cr, Fe, Co, Ni, Ru, Rh, Hf, Gd, Dy, La, Y, and Th. A tungsten wire material having a diameter of 0.03 mm to 25 mm can be used which is sintered by means such as kneading and then subjected to forging such as swaging and drawing to obtain a desired cross-sectional shape.

  As component elements for forming a coating layer on the surface of the W linear material, C, Re, Ta, Mo, B, Sc, Ti, Cr, Fe, Co, Ni, Ru, Rh, Hf, Gd, Dy, It is appropriate to use component elements belonging to the element group of La, Y, and Th. In particular, a higher melting point is desirable because it does not evaporate during use. These elements alloy with W and have a function of suppressing W diffusion. Further, at the time of recrystallization, depending on the heat treatment temperature and conditions, these elements are finally present by forming an alloy with W grain boundaries and W on the surface of the W linear material.

  As a means for forming the coating layer, any means such as coating, plating, and dusting of powder can be applied.

  For example, in the case of coating, particles obtained by pulverizing to 0.1 μm to several tens of μm of the component forming the coating layer are mixed with water or an alcohol binder with an organic substance or the like, and applied in a slurry or spray. To do. In the case of plating, known methods such as electroplating, vacuum plating, and hot dipping can be employed.

  The thickness of this coating layer is 1 μm although it cannot be generally stated in the form of the coating, considering the thermal energy applied through the surface layer during heat treatment and the function of the coating layer that promotes crystal growth of the internal crystal grains. Even if it is less than the above, it is effective.

  The heat treatment after forming the coating layer on the surface of the W linear material is performed in a non-oxidizing atmosphere such as vacuum, hydrogen gas, nitrogen gas, or rare gas. In this case, the heat treatment temperature is suitably 1500 to 3000K. At 1500K or less, recrystallization does not occur, so coarse crystals are not formed, and at 3000K or more, no change in structure is observed.

  Moreover, the temperature increase rate of heat processing is 100-10000 K / s, especially 1000-8000 K / s is suitable. The heat treatment temperature is a factor that affects the particle diameter of the finally obtained discharge lamp electrode, and also has an influence of gas generation when used in a lamp. In industrial terms, this speed is preferably as high as possible. By performing processing such as cutting and surface treatment after the heat treatment to obtain a desired shape, a tungsten linear material, a discharge lamp electrode, and a filament can be obtained.

  According to the present invention, a filament having a long crystal particle that promotes crystal growth and an electrode for a discharge lamp can be obtained.

  FIG. 1 shows a schematic cross-sectional view of the crystal grain structure obtained by the method of the present invention. As shown in the figure, the tungsten wire material of the present invention has a different average crystal grain size when the surface portion A and the inside B of the wire material are compared, the surface portion is small, the inside is large and the ratio is large. Is 2 or more.

  The electrode for a discharge lamp which has almost the same performance in terms of impact resistance and sag resistance due to the large inside, which is preferable according to the single crystal, and in which the coarse particles as shown in FIG. 4 grow in the longitudinal direction. Can be obtained. Further, L / W2 obtained by dividing the average particle diameter in the major axis direction of the internal particles by the average particle diameter in the minor axis direction needs to be 2 or more in order to improve impact resistance and improve sag resistance. In addition, as shown in FIG. 5, the measurement of the minor axis and the major axis is to extract the outer shape of the crystal from the structure photograph of the cross section of the linear material, the length of the longest portion of the length in the long direction of the linear material, the major axis, The length of the longest portion in the radial direction of the linear material was defined as the short diameter.

  The W linear material of the present invention is excellent in sag resistance, has a sufficiently high toughness, and does not break during transportation or assembly. In the production, the crystal grain size can be easily controlled by controlling the temperature during the heat treatment. The heat treatment time in production is short and can be used industrially. Compared with Re-W alloy etc., it can manufacture at low cost.

  Embodiments of the present invention will be described below with reference to examples.

  An example in which the tungsten wire material is a rod-shaped electrode for a discharge lamp shown in FIG.

  A tungsten rod having a W purity of 99.999 atomic%, a diameter of 2.0 mm, and a length of 10 mm was prepared.

  A slurry in which Re powder having an average particle size of 0.5 μm was dispersed in methanol was applied to the rod, and then methanol was dried to attach Re particles to the surface by 30 μm. The adhered Re particles were put into a heat treatment furnace without being peeled, and heat treatment was performed in a hydrogen gas atmosphere at a heating rate of 985 K / s and a heat treatment temperature of 2973 K. Re particles adhering to the surface after cooling were removed, and the cross-sectional structure was observed. As for the cross-sectional structure, the average particle size was about 10 μm at the portion close to the surface, the average particle size of the major axis was about 80 μm, and the minor axis was about 30 μm. A schematic diagram of this structure is shown in FIG. Further, Re component was detected around the rod surface.

  Moreover, when the same experiment was conducted by changing the heat treatment temperature, it was found that the heat treatment temperature is suitably 1500K to 3000K. At 1500K or lower, recrystallization did not occur and coarse crystals were not formed, and at 3000K or higher, no change in structure was observed.

  Next, the tungsten wire material was ground into a discharge lamp electrode shape shown in FIG. When the obtained electrode was mounted on a discharge lamp and used, the electrode of the present invention was not damaged even when a large impact was applied to the electrode and the device. In addition, the manufacturing cost is only an increase in the cost for coating and heat treatment compared to the tungsten wire, and the cost can be kept low compared with Re-W or the like.

  As with Re, experiments were conducted on each element of C, Ta, Mo, B, Sc, Ti, Cr, Fe, Co, Ni, Ru, Rh, Hf, Gd, Dy, La, Y, and Th. Was able to obtain the same effect as Re. The same was true when two or more elements were used.

Comparative Example 1
A discharge lamp electrode having the same shape as in Example 1 was made of tungsten having a purity of 99.999 atomic% and substantially no added dopant, but this discharge lamp electrode is brittle and is resistant to impact and stress. It was not suitable for practical use because it was easily destroyed. Further, when the discharge lamp electrode was thin and long, sag occurred and it could not be used.

Comparative Example 2
The same raw material as in Example 1 was processed into an electrode shape, and then heat treatment was performed at 2273 K for particle growth by recrystallization. In order for the inside to have the same particle size as the sample of the example, a heat treatment time of about 500 hours was required. Moreover, although the obtained electrode had the same characteristics as the sample of the example, it took too much time for the heat treatment, so that it could not be implemented industrially.

Comparative Example 3
A wire material similar to that in Example 1 was processed into a rod shape using an alloy of W-3 wt% Re. This rod exhibited the same performance as the rod of the present invention in terms of impact resistance, toughness, and sag, but was about 150 times that of the product of the present invention due to the high manufacturing cost Re.

  A filament material which is a single wire wound coil having a wire diameter of φ0.2 and made of doped tungsten in which W is doped with 40 PPM of K was prepared. A slurry in which Ta powder having an average particle size of 0.5 μm was dispersed in methanol was applied to the filament material, and then the methanol was dried to adhere Ta to the surface. The adhered Ta particles were put into a heat treatment furnace without peeling off, and heat treatment was performed in a hydrogen gas atmosphere at a heating rate of 985 K / s and a heat treatment temperature of 2973 K. When the cross-sectional structure was observed after cooling, the cross-sectional structure was found to have an average particle size of about 10 μm at the portion close to the surface and an average particle size of about 50 μm inside. Further, Ta was detected most in the vicinity of the outer periphery, and decreased toward the center of the filament.

  Moreover, when the same experiment was conducted by changing the heat treatment temperature, it was found that the heat treatment temperature is suitably 1500K to 3000K. At 1500K or lower, recrystallization did not occur and coarse crystals were not formed, and at 3000K or higher, no change in structure was observed.

  When the obtained filament was mounted on a lamp and used, the filament of the present invention did not break the electrode even when a large impact was applied to the electrode and the device. Since the toughness is sufficiently high and the impact resistance is sufficient, the environment during transportation and use is not limited. For this reason, it was also suitable for automobile lights.

  As with Ta, experiments were performed on C, Re, Mo, B, Sc, Ti, Cr, Fe, Co, Ni, Ru, Rh, Hf, Gd, Dy, La, Y, and Th shown in element group 1 However, in all cases, the same effect as Ta could be obtained. The same was true when two or more elements were used.

  A filament material which is a single-winding coil having a wire diameter of 0.2 and the same material as in Example 1 (W purity: 99.999%) was prepared. This filament material was plated with Re by vacuum plating. The thickness of the plating layer was about 3 μm.

  Without peeling off the plating layer, it was then placed in a heat treatment furnace, and heat treatment was performed in a hydrogen gas atmosphere at a heating rate of 200 K / s and a heat treatment temperature of 1550 K. The cross-sectional structure was observed after cooling. As for the cross-sectional structure, the portion close to the surface had an average particle size of about 10 μm and the inside had an average particle size of about 50 μm.

  When the obtained filament was mounted on a lamp and used, the filament of the present invention did not break the electrode even when a large impact was applied to the electrode and the device.

  The present invention has been described by taking a tungsten linear material as an example exclusively as a refractory metal, but is not limited to W, and can be applied to other refractory metal linear materials such as Mo, Ta, Rh, and Re. In the case of a tungsten wire, it can be used for filaments and discharge lamp electrodes, such as lamp filaments, halogen lamp electrodes, cold cathodes for cold cathode tubes, lamps for automobiles and other transportation equipment.

The cross-sectional schematic diagram of the crystal structure of the tungsten wire material of this invention is shown. The schematic diagram of the electrode for processed discharge lamps of the present invention is shown. A cross-sectional schematic diagram of a stone wall-shaped crystal structure composed of fine crystals is shown. A cross-sectional schematic diagram of a crystal doped with K and having coarse particles grown in the longitudinal direction is shown. Indicates the measurement points of the short diameter and long diameter

Explanation of symbols

A Surface part of wire material B Inside wire material

Claims (3)

The average particle size of the crystal grains in the surface portion where Re or Ta is present in tungsten is different from the average particle size of the tungsten crystal particles inside the surface portion ,
The average particle size of the internal crystal particles is larger than the average particle size of the surface portion,
When the average grain size in the minor axis direction of the crystal grains on the surface is W1, and the average grain size in the minor axis direction of the inner crystal grains is W2, the ratio of W2 to W1 is 2 or more and A tungsten linear material in which the ratio of L to W2 is 2 or more, where L is the average grain size in the major axis direction of the crystal grains. The tungsten wire material according to claim 1, wherein the tungsten wire material is used as an electrode rod or filament for a discharge lamp. On the surface of the tungsten wire-like material, coated with Re or Ta, After the temperature was raised to 1500~3000K under heating rate of 100~10000K / s, holding, subsequent tungsten wire shaped material cooling and processing Production method.

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