Metal member

Abstract

A metal member according to the present disclosure has a base material and a first layer. The base material contains tungsten as a main component. The first layer is positioned on the base material and contains chromium as a main component. The first layer has a first surface that is in contact with the base material, and a second surface that is located further away from the base material than the first surface and serves as the front surface. In cases where the thickness of the first layer is 5 µm or more, or the thickness of the first layer is more than 0 µm and less than 5 µm in the metal member, the base material may have a first region that is away from the surface of the base material by 200 µm or more and a second region that is closer to the surface of the base material than the first region. When the chromium content in the first region is defined as the first chromium content and the chromium content in the second region is defined as the second chromium content, the second chromium content may be higher than the first chromium content.

Description

Metallic materials

[0001] The present disclosure relates to metal members.

[0002] Conventionally, an electrode used for electrically connecting a ceramic heater has been known (see Patent Document 1). This electrode has a metal coating layer provided on the surface of a metal electrode substrate. The electrode described in Patent Document 1 is described as exhibiting excellent durability in a temperature range of 1000°C or less.

[0003] Japanese Unexamined Patent Publication No. 62-243276

[0004] A metal member according to one embodiment of the present disclosure includes a substrate and a first layer. The substrate contains tungsten as a primary component. The first layer is located on the substrate and contains chromium as a primary component. The first layer has a first surface in contact with the substrate and a second surface located further away from the substrate than the first surface and serving as a surface. In other words, the second surface is exposed to the atmosphere. In the metal member, when the thickness of the first layer is 5 μm or more, or when the thickness of the first layer is greater than 0 μm and less than 5 μm, the substrate may have a first region 200 μm or more away from the surface of the substrate and a second region closer to the surface of the substrate than the first region. When the chromium content in the first region is defined as a first chromium content and the chromium content in the second region is defined as a second chromium content, the second chromium content may be greater than the first chromium content.

[0005] FIG. 1 is a schematic side view showing the configuration of a heater. FIG. 2 is a schematic cross-sectional view showing the configuration of a metal member according to an embodiment. FIG. 3 is a schematic cross-sectional view showing another example of a metal member according to an embodiment. FIG. 4 is a table showing the evaluation results of Samples No. 1 and 2. FIG. 5 is a table showing the evaluation results of Samples No. 3 to 7. FIG. 6 is a table showing the evaluation results of Samples No. 8 to 12. FIG. 7 is a SEM photograph of Sample No. 8 before heat treatment. FIG. 8 is a SEM photograph of Sample No. 8 after heat treatment. FIG. 9 is a SEM photograph of Sample No. 11 before heat treatment. FIG. 10 is a SEM photograph of Sample No. 11 after heat treatment.

[0006] Hereinafter, a detailed description will be given of a form for carrying out a metal member according to the present disclosure (hereinafter referred to as an "embodiment") with reference to the drawings. Note that the present disclosure is not limited to the embodiment. Furthermore, each embodiment can be appropriately combined within a range that does not cause contradiction in processing content. Furthermore, the same parts in each of the following embodiments are given the same reference numerals, and duplicated explanations will be omitted.

[0007] Furthermore, in the following embodiments, expressions such as "constant," "orthogonal," "perpendicular," or "parallel" may be used, but these expressions do not necessarily mean "constant," "orthogonal," "perpendicular," or "parallel" in the strict sense. In other words, the above expressions allow for deviations due to, for example, manufacturing precision or installation precision.

[0008] In addition, in the drawings referred to below, for ease of understanding, an orthogonal coordinate system may be shown in which the X-axis direction, Y-axis direction, and Z-axis direction, which are perpendicular to each other, are defined, and the positive Z-axis direction is the vertically upward direction.

[0009] Conventionally, electrodes used for electrically connecting ceramic heaters have been known (see Patent Document 1). Patent Document 1 discloses an electrode having an electrode substrate made of tungsten or the like, a first coating layer made of chromium or the like, and a second coating layer made of an expensive noble metal such as Au, Ag, or Pt.

[0010] However, when the electrode described in Patent Document 1 has an electrode substrate made of tungsten, the electrode substrate may oxidize at high temperatures, resulting in a loss of electrical continuity with the ceramic heater, which may limit the use of the electrode in a high-temperature atmospheric environment.

[0011] Therefore, there is room for further improvement in terms of improving the oxidation resistance of electrodes in a high-temperature air atmosphere, and a technology that can overcome the above-mentioned problems and improve oxidation resistance is desired.

[0012] Below, an example will be described in which the metal member according to the embodiment is applied to a power supply terminal for supplying power to a heater. The metal member according to the embodiment can also be applied to applications other than power supply terminals. For example, the metal member according to the embodiment may be applied to an electrode or filament of a lamp or discharge lamp. Furthermore, the metal member according to the embodiment may also be applied to, for example, an electrode for TIG welding, a power supply terminal for an electrostatic chuck, a power supply terminal for a high-frequency process device, or a power supply terminal for a temperature measurement device.

[0013] First, the configuration of a heater 1 having a metal member 100 as a power supply terminal will be described with reference to Fig. 1. Fig. 1 is a schematic side view showing the configuration of the heater 1. Note that Fig. 1 shows an example having one metal member 100, but the heater 1 may have two or more metal members 100.

[0014] As shown in FIG. 1, a heater 1 may include a base 2, a resistor 3, and a metal member 100 serving as a power supply terminal (hereinafter also referred to as the power supply terminal 100).

[0015] The substrate 2 may be, for example, a flat plate-shaped member. The material of the substrate 2 may be, for example, an insulating ceramic. This makes it possible to provide a heater 1 that is highly reliable during rapid temperature rise. The material of the substrate 2 may be, for example, oxide ceramics, nitride ceramics, or carbide ceramics. Specifically, alumina ceramics, silicon nitride ceramics, aluminum nitride ceramics, yttria ceramics, zirconia ceramics, or silicon carbide ceramics may be used.

[0016] The resistor 3 may be located inside the base 2. The resistor 3 may extend in the longitudinal direction of the base 2, in the X-axis direction here, and one end may be connected to a power supply terminal 100 described later. The resistor 3 may be a member that generates heat when a current flows through it. The resistor 3 may include a high-resistance conductor containing, for example, tungsten, molybdenum, or platinum. The shape of the resistor 3 is not limited to that shown in FIG. 1 and can be changed as appropriate depending on, for example, the heat generation characteristics required of the heater 1.

[0017] The power supply terminal 100 may be located closer to the end than the center in the longitudinal direction of the base 2, in the X-axis direction here. As shown in FIG. 1 , the power supply terminal 100 may have an elongated shape extending in the vertical direction in FIG. 1 . Specifically, the power supply terminal 100 may extend in a direction perpendicular to the extension direction of the resistor 3, in the Z-axis direction here. A first end 100a of the power supply terminal 100 in the extension direction may be electrically connected to one end of the resistor 3. A second end of the power supply terminal 100 may be electrically connected to an external power source via a lead wire (not shown) or the like. Power supplied from an external power source may be supplied to the resistor 3 via the lead wire and the power supply terminal 100.

[0018] 1, at least a portion of the first end 100a of the power supply terminal 100 may be covered with a brazing material 4. Examples of materials that may be used for the brazing material 4 include nickel, gold, platinum, silver, and activated solder. This will be described later.

[0019] Next, the configuration of the metal member 100 according to the embodiment will be described with reference to Fig. 2. Fig. 2 is a schematic cross-sectional view showing the configuration of the metal member 100 according to the embodiment.

[0020] As shown in FIG. 2 , the metal member 100 may have a substrate 10 and a first layer 20. The substrate 10 may contain tungsten as a primary component. Here, the primary component refers to a material that accounts for, for example, 50% by mass or more of the material. The substrate 10 may contain 90% by mass or more of tungsten. Alternatively, the substrate 10 may contain 99% by mass or more of tungsten. Alternatively, the substrate 10 may be made of only tungsten, excluding impurities.

[0021] The first layer 20 may be located on the substrate 10. The first layer 20 may contain chromium as a main component. The chromium content in the first layer may be 90% by mass or more. The chromium content in the first layer may be 95% by mass or more. The first layer 20 may contain oxygen, carbon, or other elements other than chromium. The first layer 20 may have a first surface 21 in contact with the surface of the substrate 10. The first layer 20 may have a second surface 22 located farther from the substrate 10 than the first surface 21. The second surface 22 of the first layer 20 may be a surface. In other words, no other substance may be present on the second surface 22 of the first layer 20, and the second surface 22 may be exposed to the atmosphere. The thickness t1 of the first layer 20 may be 5 μm or more.

[0022] The metal member 100 configured as described above can be produced, for example, by subjecting the tungsten base material 10 to a chrome plating process.

[0023] As described above, the metal component 100 according to the embodiment has a chromium-containing first layer 20 located on the surface of a tungsten-containing substrate 10. The second surface 22 of the first layer 20 is exposed to the atmosphere. With this configuration, when the metal component 100 is exposed to a high-temperature atmosphere, the chromium contained in the first layer 20 undergoes an oxidation reaction, forming a passive film on the second surface 22, which is the surface of the first layer 20. This passive film makes it difficult for the tungsten contained in the substrate 10 to oxidize. Therefore, the metal component 100 according to the embodiment can improve the oxidation resistance of the metal component 100 in a high-temperature atmosphere. In particular, the combination of tungsten and chromium can improve the oxidation resistance of the metal component 100 in a high-temperature atmosphere. It goes without saying that even when the second surface 22 of the first layer 20 has a passive film, the metal component 100 is still a metal component 100 according to the present disclosure.

[0024] 1 , when the metal member 100 according to the embodiment is used as a power supply terminal, at least a portion of one end of the metal member 100 may be covered with the brazing material 4. In this case, the portion of the metal member 100 that is covered with the brazing material 4 does not have to be covered with the first layer 20. In other words, the portion of the metal member 100 that comes into contact with the resistor 3 of the heater 1 does not have to be chrome plated.

[0025] Next, the configuration of another example of the metal member 100 according to the embodiment will be described with reference to Fig. 3. Fig. 3 is a schematic cross-sectional view showing another example of the metal member 100 according to the embodiment.

[0026] As shown in FIG. 3 , the substrate 10 may have a first region 11 that is a region that is 200 μm or more away from the surface 10 a of the substrate 10, and a second region 12 that is a region that is closer to the surface 10 a of the substrate 10 than the first region 11.

[0027] When the thickness t1 of the first layer 20 is greater than 0 μm and not greater than 5 μm, the chromium content in the first region 11 may be defined as the first chromium content, and the chromium content in the second region 12 may be defined as the second chromium content, and the second chromium content may be greater than the first chromium content. In other words, the substrate 10 may have a region on its surface where chromium is diffused.

[0028] The metal member 100 configured as described above can be produced, for example, by chrome plating the tungsten substrate 10 and then heat treating it. The heat treatment is performed to diffuse the chromium contained in the first layer 20, which is a chromium film located on the surface of the substrate 10, from the surface to the interior of the substrate 10. Specifically, by subjecting the chromium-plated substrate 10 to heat treatment, the chromium contained in the first layer 20 diffuses into the tungsten substrate 10. As a result, the chromium content in the region of the substrate 10 near the surface 10a increases as the heat treatment progresses, resulting in the production of the metal member 100 having the second region 12 as described above. The second region 12 may also be referred to as a diffusion region. The heat treatment may involve, for example, maintaining the substrate in an inert atmosphere, such as a nitrogen atmosphere, at a temperature ranging from 1400°C to 1650°C for 30 minutes or more.

[0029] In the metal component 100 configured in this manner, in addition to the presence of the first layer 20, the second region 12 of the substrate 10 forms a strong surface layer, which makes it difficult for oxidation of the tungsten contained in the substrate 10 to proceed when the metal component 100 is left in a high-temperature air atmosphere. Therefore, according to the metal component 100 according to the embodiment, it is possible to improve the oxidation resistance of the metal component 100 in a high-temperature air atmosphere.

[0030] As described above, the first region 11 may be located at a position 200 μm or more away from the surface 10 a of the substrate 10. In other words, the distance d1 from the surface 10 a of the substrate 10 to the first region 11 may be 200 μm or more.

[0031] The thickness t2 of the second region 12 may be 40 μm or more. In particular, the thickness t2 of the second region 12 may be 50 μm or more.

[0032] Examples of the present disclosure will be specifically described below.

[0033] Example 1 The metal member according to Example 1 was fabricated as follows. First, a cylindrical tungsten (height 40 mm, diameter 2 mm) was prepared as a substrate. Next, a 5 μm-thick Al—Cr—N-based coating film containing 43 mass % chromium was formed on the prepared tungsten by PVD. This sample is Sample No. 1 in FIG. 4. The prepared tungsten was also subjected to a known chromium plating process to form a 5 μm-thick first layer containing 95 mass % or more chromium on the surface of the tungsten. This sample is Sample No. 2 in FIG. 4.

[0034] Next, these two types of samples were subjected to an oxidation resistance test in which they were held in air at 700°C for 100 hours. The surfaces of the samples were then observed to confirm the presence or absence of yellow tungsten oxide. A sample was deemed to have passed if no tungsten oxide was observed, and a sample was deemed to have failed if tungsten oxide was observed. In the table shown in Figure 4, a passing sample is indicated as "OK," and a failing sample is indicated as "NG." Sample No. 1, which was 5 µm or thicker but did not contain chromium as a primary component, failed the test. On the other hand, Sample No. 2, which was 5 µm or thicker and contained chromium as a primary component, passed the test.

[0035] Example 2 A first layer, which was a chromium film containing 95% by mass or more of chromium and had the thickness shown in FIG. 5, was formed on the surface of a cylindrical tungsten steel similar to that of Example 1. FIG. 5 shows Samples 3 to 7, which had different first layer thicknesses. These samples were subjected to the same oxidation resistance test as in Example 1 to check for the presence or absence of tungsten oxides. Note that Sample 2 in FIG. 4 and Sample 5 in FIG. 5 are the same sample. Tungsten oxides were detected in Samples 1 and 2, which had first layer thicknesses of less than 5 μm, and they failed the test. On the other hand, no tungsten oxides were detected in Samples 5 to 7, which had first layer thicknesses of 5 μm or more, and they passed the test.

[0036] Example 3: A first layer, a chromium film containing 95% by mass or more of chromium and having the thickness shown in FIG. 6 , was formed on the surface of a cylindrical tungsten substrate similar to that of Example 1. The substrate was then heat-treated in a nitrogen atmosphere at 1600°C for 30 minutes to diffuse chromium from the surface to the interior of the substrate. Figure 6 shows the thickness of the first layer and the diffusion distance of chromium before and after heat treatment for Samples 8 to 12, which have different first layer thicknesses. The diffusion distance of chromium in Sample 12 is slightly shorter than that of Samples 10 and 11, likely due to the fact that Sample 12 was placed in a slightly lower temperature location in the heat treatment furnace.

[0037] Fig. 7 is a SEM photograph of Sample No. 8 before heat treatment. Fig. 8 is a SEM photograph of Sample No. 8 after heat treatment. Fig. 9 is a SEM photograph of Sample No. 11 before heat treatment. Fig. 10 is a SEM photograph of Sample No. 11 after heat treatment. In Figs. 7 and 9, the light gray areas indicate the substrate containing tungsten, and the dark gray areas located above the light gray areas indicate the first layer containing chromium.

[0038] By subjecting each of Samples 8 to 12 to heat treatment, chromium diffuses into the tungsten substrate. As a result, the chromium plating thickness decreases as the heat treatment progresses (see FIG. 6), and the chromium content increases in the region near the surface of the substrate, i.e., in the second region 12 in FIG. 3.

[0039] As shown in Figures 7 and 8, in Sample No. 8, which had a chromium plating thickness of 1 μm before heat treatment, all of the chromium diffused into the tungsten after heat treatment. This is evident from the fact that the chromium plating thickness after heat treatment was 0 μm. On the other hand, as shown in Figures 9 and 10, in Sample No. 11, which had a chromium plating thickness of 10 μm before heat treatment, chromium diffused into the tungsten after heat treatment, but chromium remained on the tungsten surface after heat treatment. This is also evident from the fact that the chromium plating thickness after heat treatment was 5 μm.

[0040] After the heat treatment, the same oxidation resistance test as in Examples 1 and 2 was conducted to check for the presence or absence of tungsten oxide. Tungsten oxide was confirmed in Samples Nos. 8 and 9, and they failed the test. On the other hand, no tungsten oxide was confirmed in Samples Nos. 10 to 12, and they passed the test.

[0041] In Examples 1 to 3, the surface resistance was also measured after the oxidation resistance test. All samples that passed the test showed a resistance of 0.25 mΩ or less. On the other hand, samples that failed the test showed a resistance of 1 mΩ or more.

[0042] The present technology may also be configured as follows. (1) A metal member (for example, a metal member 100) has a substrate (for example, a substrate 10) and a first layer (for example, a first layer 20). The substrate contains tungsten as a main component. The first layer is located on the substrate and contains chromium as a main component. The first layer has a first surface (for example, a first surface 21) that contacts the substrate and a second surface (for example, a second surface 22) that is located farther from the substrate than the first surface and serves as a surface. In the metal member, when the thickness of the first layer is 5 μm or more, or when the thickness of the first layer is greater than 0 μm and less than 5 μm, the substrate may have a first region (for example, a first region 11) that is 200 μm or more away from the surface of the substrate and a second region (for example, a second region 12) that is closer to the surface of the substrate than the first region. When the chromium content in the first region is defined as a first chromium content and the chromium content in the second region is defined as a second chromium content, the second chromium content may be greater than the first chromium content. (2) In the metal member described in (1) above, the thickness of the second region may be 50 μm or more. (3) The metal member described in (1) or (2) above may be used as a power supply terminal for supplying power to a heater (for example, heater 1). (4) In the metal member described in (3) above, at least a part of a first end portion (for example, first end portion 100a) of the metal member that is close to the heater may be covered with a brazing material.

[0043] The disclosed embodiments should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in various forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0044] REFERENCE SIGNS LIST 1 heater 2 base 3 resistor 4 brazing material 10 substrate 10a surface 11 first region 12 second region 20 first layer 21 first surface 22 second surface 100 metal member 100a first end

Claims

1. A metal member comprising: a substrate containing tungsten as a primary component; and a first layer located on the substrate and containing chromium as a primary component, wherein the first layer has a first surface in contact with the substrate and a second surface located further away from the substrate than the first surface and serving as a surface; wherein the thickness of the first layer, which is the distance between the first surface and the second surface, is 5 μm or more; or, wherein the thickness of the first layer is greater than 0 μm and less than 5 μm, a region of the substrate that is 200 μm or more away from the surface of the substrate is defined as a first region, and the chromium content in the first region is defined as a first chromium content; and a region of the substrate that is closer to the surface of the substrate than the first region is defined as a second region, and the chromium content in the second region is defined as a second chromium content, wherein the second chromium content is greater than the first chromium content.

2. The metal component according to claim 1, wherein the thickness of the second region is 50 μm or more.

3. The metal member according to claim 1 or 2, which is used as a power supply terminal for supplying power to a heater.

4. The metal member according to claim 3, wherein at least a portion of a first end of the metal member that is closer to the heater is covered with a brazing material.

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