Ceramic sintered body, electrode for plasma generation, and heat-resistant member

Abstract

This ceramic sintered body contains: first specific elements comprising four or five elements selected from among titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element comprising one element selected from among yttrium (Y) and aluminum (Al); carbon (C); and chromium (Cr). The total of the first specific elements, the second specific element, elemental carbon, and elemental chromium contained in the ceramic sintered body is 98 at% or more. The second specific element contained in the ceramic sintered body constitutes 3000 atppm or less. The carbon contained in the ceramic sintered body constitutes 45 at% to 55 at% and has a single-phase structure that includes the first specific elements and chromium.

Description

Ceramic sintered body, plasma generation electrode, and heat-resistant member

[0001] The present invention relates to a ceramic sintered body, a plasma generation electrode, and a heat-resistant member.

[0002] Conventionally, ceramic sintered bodies used for plasma generation electrodes have been known (for example, Patent Documents 1 and 2, and Non-Patent Document 1).

[0003] Japanese Patent No. 6929755, Japanese Patent No. 3247095

[0004] Shiro Shimada, Michio Inagaki, Kunihito Matsui, "Oxidation Kinetics of Hafnium Carbide in the Temperature Range of 480° to 600°C", Journal of the American Ceramic Society, Volume75, Issue10, October 1992, Pages 2671-2678, [Retrieved February 9, 2026], Internet <https: / / ceramics.onlinelibrary.wiley.com / doi / abs / 10.1111 / j.1151-2916.1992.tb05487.x>

[0005] However, even with prior arts such as those disclosed in Patent Documents 1 and 2 and Non-Patent Document 1, there is still room for improvement in the technology for improving oxidation resistance in high-temperature environments for ceramic sintered bodies.

[0006] An object of the present invention is to provide a technique for improving oxidation resistance in high-temperature environments in a ceramic sintered body.

[0007] The present invention has been made to solve at least part of the above-described problems, and can be implemented as the following embodiments.

[0008] (1) According to one embodiment of the present invention, a ceramic sintered body is provided. This ceramic sintered body comprises a first specific element consisting of four or five elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element consisting of one element selected from yttrium (Y) and aluminum (Al); carbon (C); and chromium (Cr). The total amount of the first specific element, the second specific element, carbon, and chromium contained in the ceramic sintered body is 98 at% or more; the amount of the second specific element contained in the ceramic sintered body is 3000 at ppm or less; the amount of carbon contained in the ceramic sintered body is 45 at% or more and 55 at% or less; and it has a single-phase structure containing the first specific element and chromium.

[0009] According to this configuration, the ceramic sintered body contains a first specified element consisting of four or five elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten; a second specified element consisting of one element selected from yttrium and aluminum; carbon; and chromium, and has a single-phase structure containing the first specified element and chromium. The single-phase structure containing the first specified element and chromium is resistant to oxidation even in high-temperature environments. This improves the oxidation resistance of the ceramic sintered body in high-temperature environments.

[0010] (2) In the ceramic sintered body of the above form, the amount of iron (Fe) contained in the ceramic sintered body may be 1000 at ppm or less. With this configuration, since the amount of iron contained in the ceramic sintered body is 1000 at ppm or less, the precipitation of iron-based particles with relatively low melting points is suppressed. This makes it possible to suppress the decrease in strength of the ceramic sintered body in a high-temperature environment and to improve its oxidation resistance in a high-temperature environment.

[0011] (3) In the ceramic sintered body of the above form, the amount of chromium contained in the ceramic sintered body may be 5 at% or more and 9 at% or less. With this configuration, since the chromium is contained at a concentration within a certain range, the deposition of chromium-containing alloys or chromium oxides, which have relatively low melting points, at the grain boundaries is suppressed. This makes it possible to suppress the decrease in strength of the ceramic sintered body in a high-temperature environment and to improve its oxidation resistance in a high-temperature environment.

[0012] (4) According to another embodiment of the present invention, a plasma generating electrode is provided. This plasma generating electrode comprises a ceramic sintered body as described above. With this configuration, the plasma generating electrode comprises a ceramic sintered body having a single-phase structure containing a first specific element and chromium, thereby improving the oxidation resistance of the plasma generating electrode in high-temperature environments. This extends the lifespan of the plasma generating electrode.

[0013] (5) According to yet another embodiment of the present invention, a heat-resistant member is provided. This heat-resistant member comprises a ceramic sintered body as described above. With this configuration, the heat-resistant member comprises a ceramic sintered body having a single-phase structure containing a first specific element and chromium, thereby improving the oxidation resistance of the heat-resistant member in high-temperature environments. This extends the lifespan of the heat-resistant member.

[0014] Furthermore, the present invention can be realized in various forms, for example, in the form of a method for manufacturing a ceramic sintered body, a method for manufacturing an electrode for plasma generation, a method for manufacturing a heat-resistant member, an apparatus equipped with a ceramic sintered body, a method for controlling such apparatus, and so on.

[0015] This is a cross-sectional view of a plasma generating electrode comprising a ceramic sintered body according to the first embodiment. This is a schematic cross-sectional view of the ceramic sintered body according to the first embodiment. This is the first figure illustrating the production conditions for a sample of the ceramic sintered body. This is the second figure illustrating the production conditions for a sample of the ceramic sintered body. This is the first figure illustrating the characteristics of a sample of the ceramic sintered body. This is the second figure illustrating the characteristics of a sample of the ceramic sintered body. This is a perspective view of a heat-resistant member comprising a ceramic sintered body according to the second embodiment.

[0016] <First Embodiment> Figure 1 is a cross-sectional view of a plasma generating electrode 10 equipped with an electrode tip 1 (ceramic sintered body) according to this embodiment. The plasma generating electrode 10 of this embodiment is used, for example, to generate oxygen plasma in a cutting machine, surface treatment apparatus, thermal spray apparatus, etc. that uses plasma. The plasma generating electrode 10 comprises an electrode tip 1 as a plasma generating cathode and a tip support portion 11 that supports the electrode tip 1.

[0017] The electrode tip 1 is a ceramic sintered body containing a first specified element consisting of four or five elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specified element consisting of one element selected from yttrium (Y) and aluminum (Al); carbon (C); and chromium (Cr). The total amount of the first specified element, the second specified element, carbon, and chromium contained in the electrode tip 1 is 98 at% or more, the amount of the second specified element contained in the electrode tip 1 is 3000 at ppm or less, and the amount of carbon contained in the electrode tip 1 is 45 at% or more and 55 at% or less. The first specified element in the electrode tip 1, and the concentration of the first specified element and the concentration of carbon are measured by energy-dispersive X-ray spectroscopy (EDS). The identification of the second specific element in electrode tip 1 and the measurement of its concentration are performed by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0018] Figure 2 is a schematic cross-sectional view of the ceramic sintered body of this embodiment. The electrode tip 1 of this embodiment has multiple solid-solution single-phase structures C1 containing a first specific element and chromium. In the electrode tip 1 of this embodiment, oxidation is suppressed even in high-temperature oxidizing environments because it has a solid-solution single-phase structure containing a first specific element and chromium, so the electrode tip 1 has relatively high oxidation resistance in high-temperature environments. Furthermore, since the electrode tip 1 of this embodiment contains an element with a lower melting point than hafnium carbide (HfC), a dense sintered body can be produced by sintering methods other than the current-driven sintering method, such as hot pressing, in the manufacturing method of the electrode tip 1 described later. In addition, because the electrode tip 1 of this embodiment contains chromium, which has a smaller ionic radius compared to other elements, crystal lattice distortion is more likely to occur, improving high-temperature oxidation resistance. In this embodiment, whether or not the electrode tip 1 has a solid-solution single-phase structure is identified by X-ray diffraction (XRD) using an X-ray diffractometer. Specifically, in the analysis of the crystal structure of electrode tip 1 by X-ray diffraction using CuKα1 rays, when 2θ is measured from 20° to 80°, if there is only one peak each at 30.0°–37.2°, 34.8°–43.1°, 50.2°–62.3°, 59.7°–74.4°, and 62.7°–78.5°, originating from the <111>, <200>, <220>, <311>, and <222> directions of the NaCl-type structure, then it is determined that electrode tip 1 has a single-phase structure. Furthermore, if two or three peaks are observed within any of the following ranges: 30.0°–37.2°, 34.8°–43.1°, 50.2°–62.3°, 59.7°–74.4°, or 62.7°–78.5°, it is determined that the tissue has a diphasic structure.

[0019] The electrode tip 1 of this embodiment contains four or five elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten as a first specified element. The ceramic sintered body preferably contains four or five elements selected from titanium, vanadium, zirconium, niobium, hafnium, and tantalum as a combination of the first specified elements, and more preferably contains titanium, vanadium, niobium, and tantalum. The electrode tip 1 of this embodiment contains titanium, vanadium, niobium, and tantalum as a first specified element. In the electrode tip 1 of this embodiment, the difference in atomic concentration of titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, and chromium is preferably 5 at% or less. In the electrode tip 1 of this embodiment, the difference in atomic concentration of titanium, vanadium, niobium, tantalum, and chromium is 2.66 at%.

[0020] The electrode tip 1 of this embodiment contains a second specific element, which is one element selected from yttrium and aluminum. This results in a relatively low voltage for initiating discharge, thus extending the lifespan of the electrode tip 1. The electrode tip 1 of this embodiment contains yttrium. The concentration of yttrium in the electrode tip 1 of this embodiment is 101 at ppm.

[0021] In this embodiment, the electrode tip 1 has a chromium concentration of 5 at% to 9 at%. This suppresses the precipitation of chromium-containing alloys or chromium oxides, which have relatively low melting points, at the grain boundaries, thereby achieving both suppression of strength reduction in high-temperature environments and improvement of oxidation resistance. In this embodiment, the chromium concentration is determined from the calculation results of the composition ratio in the crystal grains by energy-dispersive X-ray spectroscopy. The chromium concentration in the electrode tip 1 of this embodiment is 8.71 at%.

[0022] The electrode tip 1 of this embodiment contains iron (Fe) as an unavoidable impurity. In this embodiment, the amount of iron contained in the electrode tip 1 is 1000 at ppm or less. Since iron has a relatively low melting point, it may reduce the heat resistance of the electrode tip 1, and therefore it is preferable not to include it. Accordingly, the amount of iron in the electrode tip 1 may be 0 at ppm. The concentration of iron in the electrode tip 1 of this embodiment is 966 at ppm.

[0023] As shown in Figure 2, the electrode tip 1 of this embodiment has a solid-solution single-phase structure containing a first specific element and chromium, resulting in fewer pores and a so-called dense ceramic sintered body. The density of a ceramic sintered body is expressed by the theoretical density value calculated from the lattice constant obtained by Rietveld analysis and the relative density calculated using the specific gravity and open porosity measured according to JIS R1634:1998 "Method for measuring density and open porosity of sintered fine ceramics". The electrode tip 1 of this embodiment has a relative density of 99.1%.

[0024] The chip support portion 11 is a bottomed cylindrical member, formed, for example, by processing a copper rod-shaped member. A hole 11b is formed in the bottom portion 11a of the chip support portion 11 into which the electrode tip 1 is fitted. The plasma generating electrode 10 of this embodiment is completed when the electrode tip 1 is fitted into the hole 11b of the chip support portion 11.

[0025] Next, the manufacturing method for electrode tip 1 will be described. As a method for manufacturing electrode tip 1, first, weighed carbide powder is placed in a ball mill with ethanol and mixed and ground for 20 hours to produce a carbide mixture. The types of carbide powder to be weighed are chromium carbide powder (Cr3C2, average particle size: 4.5 μm), titanium carbide powder (TiC, average particle size: 1.7 μm), vanadium carbide powder (VC, average particle size: 1.8 μm), niobium carbide powder (NbC, average particle size: 1.1 μm), and tantalum carbide powder (TaC, average particle size: 1.0 μm). The carbide mixture to be produced is weighed so that chromium carbide is 6 mol%, and titanium carbide, vanadium carbide, niobium carbide, and tantalum carbide are each 23.5 mol%. Next, yttrium oxide powder (Y2O3) is added to the prepared carbide mixture in an amount equivalent to 0.02 wt%, and the mixture is then mixed and ground for 20 hours to produce a slurry. The prepared slurry is placed in a heated vacuum container and dried under reduced pressure while being heated to 60°C. The dried powder produced by drying the slurry is passed through a sieve with a mesh size of 100 μm to produce granulated powder. The prepared granulated powder is placed in a mold for hot pressing, and the electrode tip 1 is completed by firing using the hot pressing method (HP) under a pressure of 30 MPa in a vacuum atmosphere at a temperature of 1700°C.

[0026] Next, we will describe the evaluation tests for ceramic sintered bodies used as electrode tips for plasma generation electrodes. In these evaluation tests, multiple ceramic sintered bodies with different manufacturing conditions were fabricated, and the effect of the manufacturing conditions on the properties of the ceramic sintered bodies was evaluated.

[0027] Figure 3 is the first diagram illustrating the conditions for preparing the ceramic sintered body samples. Figure 4 is the second diagram illustrating the conditions for preparing the ceramic sintered body samples. In this evaluation test, 30 types of ceramic sintered body samples, Sample 1 to Sample 30, were prepared. Figures 3 and 4 show the preparation conditions for each of Sample 1 to Sample 30, including the type and molar percentage of the "main raw material," the type and weight percentage of the "additives," and the "firing conditions," which include the "firing method," "temperature" (unit: °C), and "pressure" (unit: MPa).

[0028] First, we will explain the chromium contained in the ceramic sintered body and the "main raw materials" which are the first specified elements. Of the samples 1 to 30, samples 1 to 21 were prepared using 5 to 6 types of materials as "main raw materials" from among chromium carbide (Cr3C2), titanium carbide (TiC), vanadium carbide (VC), zirconium carbide (ZrC), niobium carbide (NbC), molybdenum carbide (Mo2C), hafnium carbide (HfC), tantalum carbide (TaC), and tungsten carbide (WC), as shown in Figures 3 and 4. In the preparation of samples 1 to 21, powders of the "main raw materials" having the average particle size shown below were used. Chromium carbide: 4.5 μm Titanium carbide: 1.7 μm Vanadium carbide: 1.8 μm Zirconium carbide: 2.4 μm Niobium carbide: 1.1 μm Molybdenum carbide: 1.8 μm Hafnium carbide: 0.7 μm Tantalum carbide: 1.0 μm Tungsten carbide: 1.1 μm

[0029] Next, we will explain the "additives" that constitute the second specified element in the ceramic sintered body. In the preparation of Samples 1 to 21, as shown in Figures 3 and 4, either yttrium oxide (Y2O3) or aluminum oxide (Al2O3) was used as the "additive." In the preparation of Samples 1 to 21, the following average particle sizes of the "additive" powders were used: Y2O3: 0.3 μm, Al2O3: 0.3 μm

[0030] In the preparation of Samples 1 to 21, carbide mixtures were prepared in the same manner as in the manufacturing method for electrode tip 1. In preparing the carbide mixtures, the molar percentage of the "main raw material" in the carbide mixture was weighed to the value shown in Figure 3 or Figure 4, and then placed in a ball mill with ethanol and mixed and ground for 20 hours. Next, an amount of "additive" corresponding to the value shown in Figure 3 or Figure 4 was added to the weight of the prepared carbide mixture, and the mixture was mixed and ground for another 20 hours to prepare a slurry. Next, the prepared slurry was placed in a heated vacuum container, and the slurry was dried under reduced pressure while being heated to 60°C to produce a dried powder, which was then passed through a sieve with a mesh size of 100 μm to produce granulated powder.

[0031] For the preparation of Samples 1 to 21, firing was performed using the hot press method (HP), as shown in the "Firing Conditions" and "Firing Method" sections of Figures 3 and 4. For the preparation of Samples 1 to 21, the obtained granulated powder was placed in a rectangular hot press mold measuring 35 mm x 35 mm so that the sample thickness would be 5 mm. Firing was then performed in a vacuum atmosphere under the "Temperature" and "Pressure" conditions specified in the "Firing Conditions" section of Figures 3 and 4.

[0032] Sample 22 is a single-phase sintered body of chromium carbide, prepared using chromium carbide powder. Sample 22 was prepared by sintering in a vacuum atmosphere at a temperature of 1650°C under a pressure of 30 MPa using a hot press (HP). Similar to the preparation of Samples 1 to 21, chromium carbide powder was placed in a rectangular hot press mold measuring 35 mm x 35 mm so that the sample thickness would be 5 mm. Sample 22 is the reference sample for comparison in this evaluation test.

[0033] Sample 23 is a single-phase sintered body of hafnium carbide, prepared using hafnium carbide powder. Sample 23 was prepared by discharge plasma sintering (SPS) under a vacuum atmosphere at a temperature of 1900°C and a pressure of 70 MPa. To prepare Sample 23, hafnium carbide powder was placed in a rectangular discharge plasma sintering mold measuring 35 mm x 35 mm so that the sample thickness would be 5 mm. Sample 23 is the reference sample for comparison in this evaluation test.

[0034] For the preparation of Samples 24 and 25, the following raw materials were used: metal oxides chromium oxide (Cr2O3), titanium oxide (TiO2), tantalum oxide (Ta2O5), and niobium oxide (Nb2O5), and metal carbides vanadium carbide and carbon. For the preparation of Samples 24 and 25, the following average particle sizes were used for the raw material powders: chromium oxide: 1.5 μm, titanium oxide: 1.0 μm, tantalum oxide: 3.0 μm, niobium oxide: 1.0 μm, vanadium carbide: 1.8 μm, carbon: 5.0 μm.

[0035] In the preparation of sample 24, the composition was (TiTaNbVCr) 0.6 C 0.4 The above raw materials were weighed to achieve the following result. In the preparation of sample 25, the composition was (TiTaNbVCr) 0.4 C 0.6 The raw materials described above were weighed accordingly. For the preparation of Sample 24 and Sample 25, the weighed raw materials were mixed in a ball mill, and the mixed powder was heat-treated for 3 hours in a vacuum atmosphere at a temperature of 1600°C. After that, calcination was performed in the same procedure as for the preparation of Samples 1 to 21 to prepare Sample 24 and Sample 25.

[0036] Sample 26 was prepared in the same manner as Samples 1 to 21, except that the slurry was prepared without the addition of either yttrium oxide or aluminum oxide. Sample 27 was prepared by weighing the powder so that its composition was (TiTaNbV)C, which does not contain chromium, and by the same manner as Samples 1 to 21. Sample 28 was prepared by weighing the powder so that its composition was (TiTaNbVWMoCr)C, and by the same manner as Samples 1 to 21. Sample 28 contains six elements as the first specified element and has a higher amount of chromium carbide than Samples 1 to 21.

[0037] Sample 29 was prepared using the same method as Samples 1 to 21, except that the amount of yttrium added was adjusted to 4000 ppm. Sample 30 was prepared by weighing powder to have a composition of (TiTaNbVCr)C and then firing it under pressure of 5 MPa in a vacuum atmosphere at a temperature of 1600°C.

[0038] Figure 5 is the first diagram illustrating the characteristics of the ceramic sintered body samples. Figure 6 is the second diagram illustrating the characteristics of the ceramic sintered body samples. Figure 5 shows the composition, whether or not it is single-phase, relative density, atomic concentration, and characteristics for each of samples 1 to 15. Figure 6 shows the composition, whether or not it is single-phase, relative density, atomic concentration, and characteristics for each of samples 16 to 30. Here, the measurement or calculation methods for each item of the samples shown in Figures 5 and 6 will be explained. In this evaluation test, mirror-polished samples were used for the measurement or calculation methods of each item of the samples shown in Figures 5 and 6. Note that for each item shown in Figures 5 and 6, items that were not measured are marked with "-".

[0039] The term "crystalline phase" indicates whether or not the sample has a single-phase structure containing the first specified element and chromium. The determination of the "crystalline phase" was performed by identifying the crystalline phase of the sample using X-ray diffraction with an X-ray diffractometer. Specifically, similar to the determination method for electrode tip 1, in the analysis of the crystal structure of the sample by X-ray diffraction using CuKα1 rays, if there was only one peak each at 30.0°–37.2°, 34.8°–43.1°, 50.2°–62.3°, 59.7°–74.4°, and 62.7°–78.5°, originating from the <111>, <200>, <220>, <311>, and <222> directions of the NaCl-type structure, the sample was determined to be single-phase. For samples determined to be single-phase, the "relative density (%)" was calculated using the theoretical density value derived from the lattice constant obtained by Rietveld analysis, and the specific gravity and open porosity measured according to JIS R1634:1998 "Method for measuring density and open porosity of sintered fine ceramics". Since samples 22 and 23 have a single composition, their "relative density" was calculated using the specific gravity and open porosity measured according to JIS R1634:1998 "Method for measuring density and open porosity of sintered fine ceramics".

[0040] "Atomic concentration difference (at%)" indicates the concentration difference of the first specified element and chromium contained in the sample. "C concentration (at%)" indicates the concentration of the element carbon contained in the sample. "Atomic concentration difference (at%)" and "C concentration (at%)" were calculated from the results of calculating the composition ratio in the crystal grains by energy-dispersive X-ray spectroscopy.

[0041] The "Cr concentration (at%)", "Y concentration (at ppm)", "Al concentration (at ppm)", and "Fe concentration (at ppm)" respectively represent the concentrations of chromium, yttrium, aluminum, and iron elements contained in the sample. In this evaluation test, the presence or absence of yttrium or aluminum elements in the sample was confirmed using inductively coupled plasma atomic emission spectrometry, and the concentrations of chromium, yttrium, aluminum, and iron elements in the sample were measured.

[0042] "High-temperature oxidation resistance" indicates the difficulty of oxidation in a high-temperature environment. "High-temperature oxidation resistance" was calculated using an arc heating tester. Specifically, first, the weight of the sample to be evaluated was measured. Next, the sample was irradiated with arc plasma generated using a mixed gas of nitrogen and oxygen in a reduced-pressure atmosphere with a pressure of 10 Pa or less, to measure the amount of wear of the sample. In the measurement of the wear amount of the sample using an arc heating tester, the temperature of the sample was adjusted to 1800° C., and the irradiation time was set to 3 minutes. Finally, the weight of the sample was measured, and the rate of change in weight before and after irradiation with arc plasma was calculated. In this evaluation test, when the rate of weight change of Sample 22 is taken as 100, the ratio of the rate of weight change of each sample is defined as "high-temperature oxidation resistance", which is shown in FIG. 5 and FIG. 6. That is, for the "high-temperature oxidation resistance" shown in FIG. 5 and FIG. 6, the smaller the value, the more excellent the oxidation resistance in a high-temperature environment.

[0043] "Wear resistance" indicates the degree of wear when a sample is used as an electrode for plasma generation. "Wear resistance" was calculated by a test assuming use as an electrode for plasma generation. Specifically, an evaluation electrode produced by processing a sample to have a diameter of 1 mm and a length of 10 mm was used as a cathode, the anode was grounded and connected to a DC pulse power supply, and plasma with an electric power of 400 W was discharged for 1 hour in an atmosphere containing a mixed gas of nitrogen and oxygen. After discharge, the amount of weight reduction of the evaluation electrode was measured, and the wear amount of the evaluation electrode was calculated. In this evaluation test, when the amount of weight reduction of Sample 23 is taken as 100, the ratio of the amount of weight reduction of each sample is defined as "wear resistance", which is shown in FIG. 5 and FIG. 6. That is, for the "wear resistance" shown in FIG. 5 and FIG. 6, the smaller the value, the less likely the sample is to be worn.

[0044] Samples 1 to 21, shown in Figures 5 and 6, all contained four or five first specified elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, a second specified element selected from yttrium and aluminum, carbon, and chromium, and were confirmed to be single-phase. In other words, it is expected that samples 1 to 21 have a single-phase structure containing the first specified element and chromium. Furthermore, it was confirmed that the concentration of the second specified element in all samples 1 to 21 was 3000 at ppm or less, and the concentration of carbon was 45 at% to 55 at%. It was confirmed that all of these samples 1 to 21 were superior to samples 22 to 30 in terms of "high-temperature oxidation resistance" and "wear resistance," respectively.

[0045] In Sample 28, as shown in Figure 4, six elements were selected as the first specified elements: titanium, tantalum, niobium, vanadium, tungsten, and molybdenum. As shown in Figure 6, it was confirmed that Sample 28 was not single-phase. Compared with Samples 1 to 21, Sample 28 showed relatively high values ​​for both "high-temperature oxidation resistance" and "wear resistance," confirming that oxidation progresses easily in high-temperature environments and that it is prone to wear.

[0046] As shown in FIG. 6, Sample 24, Sample 25, and Samples 27 to 29 have a "C concentration (at%)" smaller than 45 at% or larger than 55 at%. In the ceramic sintered body, when the carbon concentration is 45 at% or more and 55 at% or less, a solid-dissolved single-phase structure containing the first specific element and chromium is formed. However, when the carbon concentration is lower than 45 at%, the metal phase of the first specific element and chromium tends to precipitate. Since such a metal phase has a lower melting point than carbide, when used as, for example, an electrode for plasma generation, it may be melted due to a temperature rise, which tends to shorten the service life as an electrode for plasma generation. In addition, when the carbon concentration is higher than 55 at%, free carbon tends to precipitate. When free carbon precipitates, when used as an electrode for plasma generation, the voltage for starting discharge increases, so the temperature is likely to rise, and there is a risk of melting. For this reason, the service life as an electrode for plasma generation tends to be shortened. As shown in FIG. 6, Sample 24, Sample 25, and Samples 27 to 29, whose "C concentration (at%)" is smaller than 45 at% or larger than 55 at%, each of "high-temperature oxidation resistance" and "consumption resistance" have relatively large values compared with Samples 1 to 21, and it was confirmed that oxidation in a high-temperature environment is likely to proceed and the samples are easily consumed.

[0047] As shown in FIG. 6, Sample 27 has a "Cr concentration (at%)" of 0 at% and does not contain chromium. As described above, the ceramic sintered body contains chromium, which has a smaller ionic radius than other elements, so that distortion of the crystal lattice is likely to occur. Compared with Samples 1 to 21, Sample 27 that does not contain chromium has a particularly large value of "high-temperature oxidation resistance", and it was confirmed that oxidation in a high-temperature environment is likely to proceed.

[0048] As shown in Figure 6, sample 29 has a "Y concentration (at ppm)" greater than 3000 at ppm. When a ceramic sintered body contains more than 3000 at ppm of yttrium or aluminum, yttrium or aluminum precipitates at the grain boundaries of the ceramic sintered body, and unevenness in the concentration of elements in the single-phase structure tends to occur. For this reason, ceramic sintered bodies containing more than 3000 at ppm of yttrium or aluminum are more susceptible to oxidation in an oxygen plasma. Compared to samples 1 to 21, sample 29, which contains more than 3000 at ppm of yttrium, has relatively high values ​​for both "high-temperature oxidation resistance" and "wear resistance," confirming that oxidation progresses easily in high-temperature environments and that it is prone to wear.

[0049] As shown in Figure 6, Sample 26 contains neither yttrium nor aluminum. However, Sample 26 exhibits relatively low values ​​for both "high-temperature oxidation resistance" and "wear resistance," although slightly higher than Samples 1 to 21. In other words, the ceramic sintered body of this embodiment can possess a certain degree of "high-temperature oxidation resistance" and "wear resistance" even without containing either yttrium or aluminum.

[0050] In sample 27, as shown in Figure 6, the "Fe concentration (at ppm)" is greater than 1000 at ppm. In ceramic sintered bodies, iron is an unavoidable impurity and therefore will never be 0 at ppm. However, when ceramic sintered bodies contain more than 1000 at ppm of iron, coarse iron-based particles tend to precipitate. These precipitated iron-based particles have a low melting point and may melt at the temperature at which the ceramic sintered body is used as a plasma generation electrode, potentially shortening its lifespan as a plasma generation electrode.

[0051] As shown in Figure 4, sample 30 was fired at a lower temperature of 1600°C during manufacturing compared to the other samples. Therefore, as shown in Figure 6, sample 30 is not single-phase, and when used as a plasma generation electrode to generate oxygen plasma, oxidation is more likely to occur. Consequently, sample 30 may have a shorter lifespan as a plasma generation electrode.

[0052] As described above, the electrode tip 1 of this embodiment is a ceramic sintered body containing a first specific element consisting of four or five elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, a second specific element consisting of one element selected from yttrium and aluminum, carbon, and chromium, and has a single-phase structure containing the first specific element and chromium. The single-phase structure containing the first specific element and chromium of the electrode tip 1 is resistant to oxidation even in high-temperature environments. This improves the oxidation resistance of the electrode tip 1 in high-temperature environments.

[0053] Furthermore, since the electrode tip 1 of this embodiment has an iron concentration of 1000 at ppm or less, the precipitation of iron-based particles with relatively low melting points is suppressed. This makes it possible to suppress the decrease in strength of the electrode tip 1 in high-temperature environments and to improve oxidation resistance in high-temperature environments.

[0054] Furthermore, since the electrode tip 1 of this embodiment has a chromium concentration of 5 at% to 9 at%, the deposition of chromium-containing alloys or chromium oxides, which have relatively low melting points, at the grain boundaries is suppressed. This makes it possible to suppress the decrease in strength of the electrode tip 1 in high-temperature environments and to improve oxidation resistance in high-temperature environments.

[0055] Furthermore, the plasma generation electrode 10 of this embodiment is equipped with a ceramic sintered body that has relatively good oxidation resistance in high-temperature environments. This improves the oxidation resistance of the plasma generation electrode 10 in high-temperature environments, thereby extending the lifespan of the plasma generation electrode 10.

[0056] Furthermore, the electrode tip 1 of this embodiment is manufactured by hot pressing. As a result, the electrode tip 1 can have a complex shape while reducing equipment and manufacturing costs compared to plasma generation electrodes made of hafnium or hafnium carbide manufactured by electro-sintering. Therefore, it is possible to manufacture at a low cost and improve the degree of freedom in shape.

[0057] <Second Embodiment> Figure 7 is a perspective view of the heat-resistant member of the second embodiment. Compared to the electrode tip of the first embodiment (Figure 1), the heat-resistant member of the second embodiment is applied to a different field of ceramic sintered body.

[0058] The heat-resistant member 2 of this embodiment is a ceramic sintered body containing a first specific element consisting of four or five elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten; a second specific element consisting of one element selected from yttrium and aluminum; carbon; and chromium. The total amount of the first specific element, the second specific element, carbon, and chromium contained in the heat-resistant member 2 is 98 at% or more, the amount of the second specific element contained in the heat-resistant member 2 is 3000 at ppm or less, and the amount of carbon contained in the heat-resistant member 2 is 45 at% or more and 55 at% or less. The heat-resistant member 2 of this embodiment is used, for example, in an oxidizing atmosphere in a high-temperature environment. Although the heat-resistant member 2 shown in Figure 7 has a flat plate shape, the shape of the heat-resistant member 2 is not limited to this. The shape can be selected depending on the situation in which the heat-resistant member 2 is applied.

[0059] As described above, the heat-resistant member 2 of this embodiment is a ceramic sintered body containing a first specific element consisting of four or five elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, a second specific element consisting of one element selected from yttrium and aluminum, carbon, and chromium, and has a single-phase structure containing the first specific element and chromium. The single-phase structure containing the first specific element and chromium of the heat-resistant member 2 is resistant to oxidation even in high-temperature environments. This improves the oxidation resistance of the heat-resistant member 2 in high-temperature environments. Therefore, the lifespan of the heat-resistant member 2 can be extended.

[0060] Furthermore, the heat-resistant member 2 of this embodiment is manufactured by hot pressing. As a result, the heat-resistant member 2 can have a complex shape while reducing equipment costs and manufacturing costs compared to heat-resistant members made of hafnium or hafnium carbide manufactured by electro-sintering. Therefore, it is possible to manufacture at a low cost and improve the degree of freedom in shape.

[0061] <Modifications of this Embodiment> The present invention is not limited to the above-described embodiments, and can be implemented in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0062] [Modification 1] In the above embodiment, the ceramic sintered body was assumed to contain four elements as the first specified element: titanium, tantalum, niobium, and vanadium. It is sufficient to contain four or five elements from among titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten.

[0063] [Modification 2] In the above embodiment, the ceramic sintered body was assumed to contain a combination of titanium, zirconium, hafnium, and tantalum as the first specified element. However, the preferred combination of the first specified element is not limited to this. A combination of zirconium, hafnium, and tantalum is also preferred, and even with a combination of hafnium and tantalum, the oxidation resistance of the electrode tip 1 can be further improved.

[0064] [Modification 3] In the above embodiment, the ceramic sintered body had an iron concentration of 1000 at ppm or less. The iron concentration in the ceramic sintered body is not limited to this. However, when the iron concentration is 1000 at ppm or less, the precipitation of iron-based particles with relatively low melting points is suppressed, and thus the decrease in strength in high-temperature environments can be suppressed. Therefore, a lower iron concentration is desirable. The concentration of iron element may be below the detection limit when measured by an inductively coupled plasma atomic emission spectrometer.

[0065] [Modification 4] In the above embodiment, the ceramic sintered body had a chromium concentration of 5 at% to 9 at%. However, the chromium concentration in the ceramic sintered body is not limited to this range. However, when the chromium concentration is 5 at% to 9 at%, the deposition of chromium-containing alloys or chromium oxides, which have relatively low melting points, at the grain boundaries is suppressed, thereby suppressing the decrease in strength of the ceramic sintered body in high-temperature environments.

[0066] [Modification 5] In the above embodiment, the ceramic sintered body is provided by the plasma generating electrode 10 or the heat-resistant member 2. The technical field to which the ceramic sintered body is applied is not limited to this. It may be used in technical fields where high-temperature oxidation resistance and wear resistance are required.

[0067] The embodiments of this specification have been described above based on the embodiments and modifications described above. The embodiments described above are for the purpose of facilitating understanding of this specification and do not limit it. This specification may be modified and improved without departing from its spirit and the scope of the claims, and equivalents thereof are included in this specification. Furthermore, any technical features that are not described as essential in this specification may be deleted as appropriate.

[0068] <Application Example 1> A ceramic sintered body comprising: a first specific element consisting of four or five elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element consisting of one element selected from yttrium (Y) and aluminum (Al); carbon (C); and chromium (Cr); wherein the total amount of the first specific element, the second specific element, carbon, and chromium contained in the ceramic sintered body is 98 at% or more; the amount of the second specific element contained in the ceramic sintered body is 3000 at ppm or less; the amount of carbon contained in the ceramic sintered body is 45 at% or more and 55 at% or less; and the ceramic sintered body has a single-phase structure containing the first specific element and chromium. <Application Example 2> A ceramic sintered body as described in Application Example 1, characterized in that the amount of iron (Fe) contained in the ceramic sintered body is 1000 at ppm or less. <Application Example 3> A ceramic sintered body as described in Application Example 1 or Application Example 2, characterized in that the amount of chromium contained in the ceramic sintered body is 5 at% or more and 9 at% or less. <Application Example 4> A plasma generating electrode comprising a ceramic sintered body as described in any one of Application Examples 1 to 3. <Application Example 5> A heat-resistant member comprising a ceramic sintered body as described in any one of Application Examples 1 to 4.

[0069] 1... Electrode tip 2... Heat-resistant material 10... Electrode for plasma generation C1... Single-phase structure

Claims

1. A ceramic sintered body comprising: a first specific element consisting of four or five elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element consisting of one element selected from yttrium (Y) and aluminum (Al); carbon (C); and chromium (Cr), wherein the total amount of the first specific element, the second specific element, carbon, and chromium contained in the ceramic sintered body is 98 at% or more; the amount of the second specific element contained in the ceramic sintered body is 3000 at ppm or less; the amount of carbon contained in the ceramic sintered body is 45 at% or more and 55 at% or less; and the ceramic sintered body has a single-phase structure containing the first specific element and chromium.

2. A ceramic sintered body according to claim 1, characterized in that the amount of iron (Fe) contained in the ceramic sintered body is 1000 at ppm or less.

3. A ceramic sintered body according to claim 1 or claim 2, characterized in that the chromium contained in the ceramic sintered body is 5 at% or more and 9 at% or less.

4. A plasma generating electrode comprising a ceramic sintered body according to claim 1 or claim 2.

5. A heat-resistant member comprising a ceramic sintered body according to claim 1 or claim 2.

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