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

Abstract

A ceramic sintered body comprises: a plurality of carbide crystal particles containing a carbide of a first specific element consisting of 5 or 6 elements selected from titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); and a plurality of oxide crystal particles containing at least one oxide of zirconium (Zr) and hafnium (Hf). The carbide crystal particles are a solid solution containing 45 to 55 at% of carbon and in a cross-section of the ceramic sintered body, the ratio of the cross-sectional area of the oxide crystal particles to the cross-sectional area of the ceramic sintered body is from 5% to 60%.

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] Ceramic sintered bodies have been conventionally known (for example, Patent Documents 1 and 2, and Non-Patent Document 1).

[0003] Japanese Patent No. 6929755, Japanese Patent No. 4177493

[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, Volume 75, Issue 10, October 1992, Pages 2671-2678, [searched on March 10, 2025], Internet <https: / / doi.org / 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 still remains room for improvement in the technology for improving both strength and toughness in ceramic sintered bodies.

[0006] An object of the present invention is to provide a technique for improving both strength and toughness 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 plurality of carbide crystal particles containing a carbide of a first specific element consisting of five or six elements selected from titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W), and a plurality of oxide crystal particles containing at least one oxide of zirconium (Zr) and hafnium (Hf), wherein the carbide crystal particles are a solid solution containing 45 at% to 55 at% carbon, and in the cross-section of the ceramic sintered body, the ratio of the cross-sectional area of ​​the oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is 5% to 60%.

[0009] With this configuration, the ceramic sintered body has a structure in which carbide crystal grains and oxide crystal grains are combined, which suppresses grain growth in each crystal grain, resulting in dense and fine crystal grains. Furthermore, since the carbide crystal grains in the ceramic sintered body are a solid solution containing 45 at% to 55 at% carbon, the generation of free carbon at the grain boundaries can be suppressed. In addition, since the oxide crystal grains in the ceramic sintered body contain at least one oxide of zirconium and hafnium, the Young's modulus of the ceramic sintered body becomes smaller. As a result, the strength of the ceramic sintered body can be improved while also improving its toughness.

[0010] (2) In the above-described form of ceramic sintered body, 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.

[0011] (3) In the ceramic sintered body of the above form, at least one of the plurality of oxide crystal grains has a tetragonal crystal phase, and in the diffraction chart obtained by X-ray diffraction, the ratio of the peak intensity of the (-111) plane of the oxide crystal grain having a monoclinic crystal phase to the peak intensity of the (101) plane of the oxide crystal grain having a tetragonal crystal phase may be 5 or less. With this configuration, the ratio of the proportion of monoclinic crystals to the proportion of tetragonal crystals in the oxide crystal grains contained in the ceramic sintered body is relatively small. As a result, stress-induced transformation effects caused by phase transformation from tetragonal to monoclinic crystals are more likely to occur, and thus the toughness of the ceramic sintered body can be further improved while also improving its strength.

[0012] (4) In the ceramic sintered body of the above embodiment, the carbide crystal particles may contain at least one of zirconium and hafnium in an amount of 4 at% to 20 at%. With this configuration, the carbide crystal particles contain at least one of zirconium and hafnium to a certain extent. As a result, the carbide crystal particles and oxide crystal particles are bonded relatively strongly, which improves the toughness while also improving the strength of the ceramic sintered body. Therefore, the thermal shock resistance of the ceramic sintered body can be improved.

[0013] (5) In the above-described form of ceramic sintered body, the ratio of the cross-sectional area of ​​the oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body in the cross-section of the ceramic sintered body may be 5% or more and 40% or less. With this configuration, since the ratio of the cross-sectional area of ​​the oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body in the cross-section of the ceramic sintered body is within a certain range, the strength of the ceramic sintered body can be improved by the oxide crystal particles while the carbide crystal particles provide electrical conductivity.

[0014] (6) 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. According to this configuration, the plasma generating electrode comprises a ceramic sintered body having a structure in which carbide crystal particles and oxide crystal particles are combined. This improves the thermal shock resistance of the plasma generating electrode, and thus extends the life of the plasma generating electrode.

[0015] (7) 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. According to this configuration, the heat-resistant member comprises a ceramic sintered body having a structure in which carbide crystal particles and oxide crystal particles are composited. This improves the thermal shock resistance of the heat-resistant member, and thus extends the life of the heat-resistant member.

[0016] 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.

[0017] 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 a diagram illustrating the manufacturing conditions for a sample of the ceramic sintered body. This is the first diagram illustrating the characteristics of a sample of the ceramic sintered body. This is the second diagram 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.

[0018] <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.

[0019] The electrode tip 1 is a ceramic sintered body comprising a plurality of carbide crystal particles containing carbides of a first specified element consisting of five or six elements selected from titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W), and a plurality of oxide crystal particles containing at least one oxide of zirconium (Zr) and hafnium (Hf). The carbide crystal particles of the electrode tip 1 are a solid solution containing 45 at% to 55 at% carbon, and in the cross-section of the ceramic sintered body, the ratio of the cross-sectional area of ​​the oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is 5% to 60%.

[0020] Figure 2 is a schematic cross-sectional view of the ceramic sintered body of this embodiment. As shown in Figure 2, the electrode tip 1 of this embodiment comprises a plurality of carbide crystal particles Pcc and a plurality of oxide crystal particles Pco. The carbide crystal particles Pcc have a single-phase structure containing carbides of a first specified element consisting of five or six elements selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten. The carbide crystal particles Pcc of the electrode tip 1 of this embodiment contain titanium, niobium, hafnium, zirconium, and tantalum as the first specified element. The identification and concentration of the first specified element in the carbide crystal particles Pcc are performed using energy-dispersive X-ray spectroscopy (EDS) at a magnification of 500x. Whether or not the carbide crystal particles Pcc have a single-phase structure is determined 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.

[0021] The oxide crystal particles Pco contain at least one oxide of zirconium and hafnium. In this embodiment, the oxide crystal particles Pco contain both zirconium oxide and hafnium oxide. In this embodiment, whether or not the oxide crystal particles Pco contain at least one oxide of zirconium and hafnium is determined by X-ray diffraction.

[0022] The electrode tip 1 of this embodiment has a structure in which carbide crystal particles Pcc and oxide crystal particles Pco are combined, thus suppressing grain growth of the crystal grains. As a result, it is possible to produce a ceramic sintered body with relatively high strength and toughness. Furthermore, since the ceramic sintered body 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 electrostatic sintering method, such as hot pressing, in the manufacturing method of the electrode tip 1 described later.

[0023] In this embodiment, the electrode tip 1 is a solid solution of carbide crystal particles Pcc containing 45 at% to 55 at% carbon. This suppresses the generation of free carbon at the grain boundaries, thereby improving the strength of the ceramic sintered body. In this embodiment, the carbon concentration in the carbide crystal particles Pcc is 48.4 at%. In this embodiment, the carbon concentration in the carbide crystal particles Pcc is determined by energy-dispersive X-ray spectroscopy at a magnification of 500x.

[0024] In the electrode tip 1 of this embodiment, the ratio of the cross-sectional area of ​​oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is 5% or more and 60% or less. This allows the electrode tip 1 to have electrical conductivity as an electrode tip 1 while also having a certain level of strength or higher. In the electrode tip 1 of this embodiment, the ratio of the cross-sectional area of ​​oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is 36.8%. It is more desirable that the ratio of the cross-sectional area of ​​oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body be 5% or more and 40% or less. In this embodiment, the ratio of the cross-sectional area of ​​oxide crystal particles Pco in the cross-section of the ceramic sintered body is calculated by performing binarization processing on the image of the cross-section of the ceramic sintered body captured by a scanning electron microscope (SEM) using the image analysis software WinROOF.

[0025] 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 it is preferable not to include it. Therefore, the amount of iron contained in the electrode tip 1 may be 0 at ppm. The concentration of iron in the electrode tip 1 of this embodiment is 440 at ppm. In this embodiment, the concentration of iron in the ceramic sintered body is determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0026] The electrode tip 1 of this embodiment has few pores because each of the multiple carbide crystal particles Pcc has a single-phase structure, resulting in a so-called dense ceramic sintered body. The density of the electrode tip 1 of this embodiment is calculated by determining the relative density using the specific gravity and open porosity measured according to JIS R1634:1998 "Method for measuring density and open porosity of sintered fine ceramics", and the specific gravity of the mixture of raw material powders used in the manufacture of the electrode tip 1. The specific gravity of the mixture of raw material powders used in the manufacture of the electrode tip 1 is calculated using the specific gravity of each raw material powder weighed during the manufacture of the electrode tip 1 and the mixing ratio. The electrode tip 1 of this embodiment has a relative density of 95.2%.

[0027] In this embodiment, the electrode tip 1 has at least one of the plurality of oxide crystal particles Pco having a tetragonal crystal phase. In the ceramic sintered body of this embodiment, the ratio of the peak intensity of the (-111) plane of oxide crystal particles Pco having a monoclinic crystal phase to the peak intensity of the (101) plane of oxide crystal particles Pco having a tetragonal crystal phase (hereinafter simply referred to as "peak ratio m / t") in the diffraction chart obtained by X-ray diffraction is 5 or less. That is, the ratio of the proportion of monoclinic oxide crystal particles to the proportion of tetragonal oxide crystal particles Pco contained in the ceramic sintered body is relatively small. As a result, stress-induced transformation effects due to phase transformation from tetragonal to monoclinic are more likely to occur, improving the toughness of the ceramic sintered body, especially its fracture toughness. Therefore, the strength of the ceramic sintered body can be further improved. In the electrode tip 1 of this embodiment, the peak ratio m / t is 4.7. It is more preferable that the peak ratio m / t is 1 or less. In this embodiment, the peak ratio m / t is calculated by X-ray diffraction. Specifically, for example, when a ceramic sintered body contains zirconium oxide, the presence and intensity of tetragonal (around 30.2°) and monoclinic (around 28.1°) peaks are confirmed in the analysis of the crystal structure of electrode tip 1 by X-ray diffraction using CuKα1 rays. If the presence of both tetragonal and monoclinic peaks is confirmed, the peak intensities of the tetragonal and monoclinic peaks are measured, and the peak ratio m / t is calculated from their ratio.

[0028] The electrode tip 1 of this embodiment contains carbide crystal particles Pcc that contain at least one of zirconium and hafnium in an amount of 4 at% to 20 at%. This allows for relatively strong bonding between the carbide crystal particles and oxide crystal particles, resulting in a relatively strong bond between the carbide crystal particles Pcc and oxide crystal particles Pco. Therefore, while improving the strength of the ceramic sintered body, the toughness can be improved, and thus the thermal shock resistance can be improved. The carbide crystal particles Pcc of the electrode tip 1 of this embodiment contain zirconium and hafnium, and the total concentration of zirconium and hafnium in the carbide crystal particles Pcc is 18.7 at%. In this embodiment, the concentration of zirconium in the carbide crystal particles Pcc is determined by energy-dispersive X-ray spectroscopy at a magnification of 500.

[0029] 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.

[0030] Next, the manufacturing method for electrode tip 1 will be described. As a manufacturing method for electrode tip 1, first, the weighed raw material powder is placed in a ball mill together with acetone solvent and mixed and ground for 20 hours to produce a slurry. The types of raw material powder to be weighed are titanium carbide powder (TiC, average particle size: 1.7 μm), niobium carbide powder (NbC, average particle size: 1.1 μm), hafnium carbide powder (HfC, average particle size: 0.7 μm), and tantalum carbide powder (TaC, average particle size: 1.0 μm) as carbide raw materials, and zirconium oxide partially stabilized with 2 mol% yttria (Y2O3) (hereinafter referred to as "2YSZ", average particle size: 0.6 μm) as an oxide raw material. These raw material powders are weighed so that the slurry to be prepared contains 20 mol% titanium carbide, niobium carbide, and tantalum carbide, 10 mol% hafnium carbide, and 30 mol% 2YSZ. The prepared slurry is dried in a water bath at 60°C and then 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 fired using the hot pressing method (HP) at a pressure of 30 MPa in a vacuum atmosphere at a temperature of 2000°C to complete electrode tip 1.

[0031] 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.

[0032] Figure 3 illustrates the production conditions for the ceramic sintered body samples. In this evaluation test, 21 types of ceramic sintered body samples, Sample 1 to Sample 21, were prepared. Figure 3 shows the production conditions for each of Samples 1 to 21, including the type and molar percentage of the "carbide" as the "main raw material," the type and molar percentage of the "oxide," and the "firing conditions," such as the "firing method," "temperature" (unit: °C), and "pressure" (unit: MPa).

[0033] First, we will explain the "carbides" used as the "main raw materials." In the preparation of Samples 1 to 16 of Samples 1 to 21, four to five types of materials were used as "carbides" from among titanium carbide (TiC), vanadium carbide (VC), chromium carbide (Cr3C2), zirconium carbide (ZrC), niobium carbide (NbC), molybdenum carbide (Mo2C), hafnium carbide (HfC), tantalum carbide (TaC), and tungsten carbide (WC), as shown in Figure 3. In the preparation of Samples 1 to 16, powders of "carbides" having the average particle size shown below were used. Titanium carbide: 1.7 μm Vanadium carbide: 1.8 μm Chromium carbide: 4.5 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

[0034] Next, we will explain the "oxides" used as the "main raw materials." In the preparation of Samples 1 to 16, as shown in Figure 3, one material was used as the "oxide" from among titanium dioxide (TiO2), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), 2YSZ, and hafnium oxide (HfO2). In the preparation of Samples 1 to 16, the following average particle sizes of the "oxide" powders were used: Titanium dioxide: 1.0 μm Zirconium oxide: 0.5 μm Tantalum oxide: 1.0 μm Niobium oxide: 1.0 μm 2YSZ: 0.6 μm Hafnium oxide: 2.0 μm

[0035] For the preparation of Samples 1 to 16, a slurry was prepared in the same manner as in the manufacturing method for electrode tip 1. In preparing the slurry, the "main raw material" was weighed so that its molar percentage in the slurry matched the value shown in Figure 3, and then placed in a ball mill with acetone solvent for mixing and grinding for 20 hours. Next, the prepared slurry was dried in a water bath at 60°C, and then passed through a sieve with a mesh size of 100 μm to produce granulated powder.

[0036] For the preparation of Samples 1 to 16, firing was performed using the hot press method (HP), as shown in the "Firing Conditions" and "Firing Method" sections of Figure 3. For the preparation of Samples 1 to 16, 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 Figure 3.

[0037] Sample 17 is a sintered body of hafnium carbide, prepared using hafnium carbide powder. Sample 17 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 17, 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 17 is the reference sample for comparison in this evaluation test.

[0038] As shown in Figure 3, Sample 18 was prepared using zirconium carbide, tantalum carbide, niobium carbide, and tungsten carbide as raw materials for the carbides, while not using oxide raw materials. Sample 18 was prepared using the four types of carbides described above, in the same manner as the preparation of Samples 1 to 16. The firing of Sample 18 was performed by a hot press (HP) method, which involved applying pressure of 30 MPa in a vacuum atmosphere at a temperature of 1800°C.

[0039] For Sample 19 and Sample 20, the respective metal oxides were weighed so that the composition ratios of hafnium, titanium, tantalum, and niobium were the same. In addition, carbon was weighed so that the ratio of total metal element content (ME) to carbon (C) in the entire ceramic sintered body was ME:C = 0.6:0.4 for Sample 19 and ME:C = 0.4:0.6 for Sample 20. These metal oxides and carbon were mixed in a ball mill and heat-treated in a vacuum atmosphere at 1600°C for 3 hours. Next, in the preparation of Sample 19 and Sample 20, zirconium carbide and zirconium oxide were added to the heat-treated powder in equal molar amounts, as well as the same molar amounts as the other metal elements, and mixed in a ball mill. Using the mixed raw material powder, Sample 19 and Sample 20 were prepared in the same manner as in the preparation of Samples 1 to 16.

[0040] Sample 21 contains a higher amount of "oxides" than Samples 1 to 16. In preparing Sample 21, titanium carbide, niobium carbide, hafnium carbide, and tantalum carbide were each weighed to a concentration of 10 mol% as "carbides," and zirconium oxide was weighed to a concentration of 60 mol% as an "oxide." Sample 21 was prepared using the weighed raw material powders in the same manner as the preparation of Samples 1 to 16.

[0041] Figure 4 is the first diagram illustrating the characteristics of the ceramic sintered body samples. Figure 5 is the second diagram illustrating the characteristics of the ceramic sintered body samples. Figure 4 shows items related to carbide crystal particles and items related to oxide crystal particles for each of Samples 1 to 21. Figure 5 shows multiple items indicating the characteristics of iron concentration, relative density, and strength for each of Samples 1 to 21. Here, the measurement or calculation methods for each item of the samples shown in Figures 4 and 5 will be explained. In this evaluation test, for the measurement or calculation methods of each item of the samples shown in Figures 4 and 5, each of Samples 1 to 21, prepared by the method described above, was processed to a size of 3 mm × 4 mm × 35 mm. Note that for each item shown in Figures 4 and 5, items that were not measured are marked with "-".

[0042] Of the items listed under "Carbide Crystal Particles" in Figure 4, "Composition," "Crystal Phase" indicating whether the carbide crystal particles are single-phase or not, "C Concentration (at%)" indicating the concentration of carbon, and "Zr Concentration (at%)" indicating the sum of the zirconium and hafnium concentrations were measured or calculated using the same method as the measurement or calculation method for electrode tip 1 in this embodiment. The "Particle Size (μm)" of the "Carbide Crystal Particles" was calculated using the intercept method with a secondary electron image (magnification: 2000x) of the cross-section of the ceramic sintered body imaged by a scanning electron microscope. The "Composition" of the "Carbide Crystal Particles" was measured on a sample that had been mirror-polished with diamond abrasive grains after the strength test described later, and then thermally etched for 5 minutes in a vacuum atmosphere at a temperature of 1650°C.

[0043] Among the items of "oxide crystal particles" shown in FIG. 4, each of "composition", "ratio (%)" indicating the ratio of the cross-sectional area of oxide crystal particles to the cross-sectional area of the ceramic sintered body as a sample, and "m / t (-)" indicating the peak ratio m / t was measured or calculated using the same method as the measurement method or calculation method for the electrode tip 1 of the present embodiment. "Particle diameter (μm)" in the items of "oxide crystal particles" was calculated using the same method as "particle diameter (μm)" of the above-mentioned "carbide crystal particles". The measurement of "composition" of "oxide crystal particles" was performed on a sample after a strength test described later that was mirror-polished with diamond abrasive grains and then subjected to thermal etching for 5 minutes in a vacuum atmosphere at a temperature of 1650° C.

[0044] "Fe concentration (appm)" indicating the iron concentration in a sample and "relative density (%)" shown in FIG. 5 were measured or calculated using the same method as the measurement method or calculation method for the electrode tip 1 of the present embodiment. Since Sample 17 has a single composition, "relative density (%)" was calculated using the specific gravity and open porosity measured in accordance with JIS R 1634:1998 "Methods for measuring density and open porosity of fine ceramic sintered bodies".

[0045] "Strength (MPa)" shown in FIG. 5 was measured by a three-point bending strength test in accordance with JIS R 1601:2008 "Testing method for room temperature bending strength of fine ceramics". "Fracture toughness (MPa·m 0.5 )" was measured by the indentation method using a Vickers indenter in accordance with JIS R 1607:2015 "Testing method for fracture toughness of fine ceramics at room temperature", using a mirror-polished sample that was used for the three-point bending test with diamond abrasive grains. The test conditions were an indentation load of 98 N and a holding time of 15 seconds. "Young's modulus (GPa)" was measured by the ultrasonic pulse method in accordance with JIS R 1602:1995 "Testing method for elastic modulus of fine ceramics" on the sample used for the three-point bending test.

[0046] The "high-temperature oxidation resistance" shown in Fig. 5 indicates the resistance to oxidation in high-temperature environments. "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, thereby measuring the amount of wear of the sample. In the measurement of the wear amount of the sample using the 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 change in weight of Sample 17 is set to 100, the ratio of the rate of change in weight of each sample is defined as "high-temperature oxidation resistance", which is shown in Fig. 5. That is, for the "high-temperature oxidation resistance" shown in Fig. 5, the smaller the value, the better the oxidation resistance in high-temperature environments.

[0047] The "repeated discharge" shown in Fig. 5 indicates whether a defect occurs and the degree of the defect when repeated discharge is performed using a sample as a plasma generating electrode. "Wear resistance" indicates the degree of wear when a sample is used as a plasma generating electrode. "Repeated discharge" and "wear resistance" were calculated by a test assuming use as a plasma generating electrode. 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 discharge with a power of 400 W was performed in an atmosphere containing a mixed gas of nitrogen and oxygen, with one cycle consisting of 1 minute of discharge and 10 seconds of stop. In the evaluation of "repeated discharge", the presence of defects in the sample after the test was visually checked, and the cumulative discharge time until a defect occurred was used to obtain the following evaluation indicators: S: No defect occurred for 2 hours or more A: A defect occurred within 1 hour or more and less than 2 hours B: A defect occurred within 30 minutes or more and less than 1 hour C: A defect occurred within less than 30 minutes

[0048] In determining "wear resistance," the weight loss of the sample was measured after discharge, and the amount of sample consumed was calculated. In this evaluation test, the ratio of the weight loss of each sample to the weight loss of sample 18 (set as 100) was defined as "wear resistance," and is shown in Figure 5. In other words, the smaller the "wear resistance" value shown in Figure 5, the less likely the sample is to wear down.

[0049] Samples 1 to 16 shown in Figure 5 each comprise multiple carbide crystal particles containing carbides of a first specified element consisting of five or six elements selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, and multiple oxide crystal particles containing at least one oxide of zirconium and hafnium. For example, in Samples 1, 10, and 11, as shown in Figure 3, titanium oxide is used as the "oxide" of the "main raw material," but as shown in Figure 4, X-ray diffraction confirmed that hafnium oxide and zirconium oxide (zirconia), which are more stable than titanium oxide, are produced as "oxide crystal particles." Hafnium oxide and zirconium oxide are more susceptible to stress-induced transformation effects due to phase transformation from tetragonal to monoclinic, thereby improving the toughness, particularly fracture toughness, of the ceramic sintered body. Furthermore, because the "oxide crystal grains" contain at least one oxide from zirconium and hafnium, the Young's modulus of the ceramic sintered body is reduced. In addition, it was confirmed that samples 1 to 16 are solid solutions containing 45 at% to 55 at% carbon in the carbide crystal grains, and that the ratio of the cross-sectional area of ​​the oxide crystal grains to the cross-sectional area of ​​the sample is between 5% and 60%. Since all of these samples 1 to 16 have fracture toughness above a certain value and relatively small Young's modulus, it was confirmed that they exhibit relatively excellent resistance to high-temperature oxidation and abrasion.

[0050] As shown in Figure 4, Sample 18 contains four types of carbides of the first specified element contained in the carbide crystal particles: zirconium carbide, tantalum carbide, niobium carbide, and tungsten carbide. Furthermore, as shown in Figure 4, it was confirmed that Sample 18 does not contain oxide crystal particles. Therefore, in Sample 18, a composite structure of carbide crystal particles and oxide crystal particles is not formed, making it easier for grain growth of carbide crystal particles to progress (see "Particle size (μm)" for "Carbide crystal particles" in Figure 4). As a result, compared to Samples 1 to 16, Sample 18 has higher values ​​for both "High-temperature oxidation resistance" and "Wear resistance," confirming that oxidation progresses easily and wears down easily in high-temperature environments.

[0051] As shown in Figure 4, samples 19 and 20 have carbon concentrations in their carbide crystal particles that are either less than 45 at% or greater than 55 at%. In ceramic sintered bodies, when the carbon concentration is between 45 at% and 55 at%, the carbide crystal particles form a single-phase structure containing the first specified element. However, when the carbon concentration is less than 45 at%, the metallic phase of the first specified element tends to precipitate. Since this metallic phase has a lower melting point than the carbide, for example, when used as a plasma generating electrode, it may melt due to rising temperatures, which tends to shorten the lifespan of the plasma generating electrode. Furthermore, when the carbon concentration is greater than 55 at%, free carbon tends to precipitate. When free carbon precipitates, when used as a plasma generating electrode, the voltage required to initiate discharge increases, which can easily lead to high temperatures and melting. For this reason, the lifespan of the plasma generating electrode also tends to be shortened. Samples 19 and 20, which had carbon concentrations lower than 45 at% or higher than 55 at%, showed higher "wear resistance" values ​​compared to samples 1 to 16, confirming that they were more easily worn out.

[0052] As shown in Figure 4, in sample 21, the "percentage (%)" representing the ratio of the cross-sectional area of ​​oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body sample is greater than 60%. When the ratio of the cross-sectional area of ​​oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is greater than 60%, there are more oxide crystal particles, which have relatively lower electrical conductivity than carbide crystal particles, making it difficult for electricity to flow. As a result, it becomes more prone to overheating and breakage, and the lifespan as a plasma generation electrode tends to be shortened. It was confirmed that sample 21, with a "percentage (%)" greater than 60%, is prone to breakage due to repeated discharge when used as a plasma generation electrode. Furthermore, when the ratio of the cross-sectional area of ​​oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is less than 5%, grain growth of carbide crystal particles progresses more easily, reducing the strength of the ceramic sintered body.

[0053] Samples 19 and 21 have a combined zirconium and hafnium concentration in the carbide crystal grains that is less than 4 at% or greater than 20 at%. In ceramic sintered bodies, when the combined zirconium and hafnium concentration is less than 4 at%, the bonding between the carbide crystal grains and oxide crystal grains by zirconium or hafnium is insufficient, resulting in reduced fracture toughness. Also, when the combined zirconium and hafnium concentration is greater than 20 at%, zirconium or hafnium is more likely to segregate at the grain boundaries between the carbide crystal grains and oxide crystal grains, resulting in reduced strength.

[0054] As described above, the electrode tip 1 of this embodiment is a ceramic sintered body and has a structure in which carbide crystal particles Pcc containing carbides of a first specific element selected from five or six elements chosen from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, and oxide crystal particles Pco containing an oxide of at least one of zirconium and hafnium are composited. As a result, grain growth of each crystal particle is easily suppressed, resulting in dense and fine crystal particles. Furthermore, since the carbide crystal particles Pcc in the ceramic sintered body are a solid solution containing 45 at% to 55 at% carbon, the generation of free carbon at the grain boundaries can be suppressed. Moreover, since the oxide crystal particles Pco in the ceramic sintered body contain an oxide of at least one of zirconium and hafnium, the Young's modulus of the ceramic sintered body is reduced. As a result, the toughness of the electrode tip 1 can be improved while increasing its strength.

[0055] 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.

[0056] Furthermore, in this embodiment, the electrode tip 1 has a relatively small ratio of monoclinic oxide crystal particles to tetragonal oxide crystal particles in the oxide crystal Pco contained in the ceramic sintered body. This makes it easier for stress-induced transformation effects caused by phase transformation from tetragonal to monoclinic to occur, thereby further improving the strength and toughness of the electrode tip 1.

[0057] Furthermore, in this embodiment, the electrode tip 1 contains a certain amount of zirconium and hafnium in the carbide crystal particles Pcc, which allows the carbide crystal particles Pcc and oxide crystal particles Pco to bond relatively strongly. This improves the strength of the ceramic sintered body while also improving its toughness, thereby improving the thermal shock resistance of the electrode tip 1.

[0058] Furthermore, in the electrode tip 1 of this embodiment, the ratio of the cross-sectional area of ​​oxide crystal particles Pco to the cross-sectional area of ​​the ceramic sintered body is 36.8%, and within the range of 5% to 40%. As a result, the electrode tip 1 can have a certain degree of electrical conductivity due to the carbide crystal particles Pcc while improving strength due to the oxide crystal particles Pco.

[0059] Furthermore, the plasma generating electrode 10 of this embodiment comprises a ceramic sintered body having a structure in which carbide crystal particles Pcc and oxide crystal particles Pco are composited. This improves the thermal shock resistance of the plasma generating electrode 10, thereby extending the lifespan of the plasma generating electrode 10.

[0060] 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.

[0061] <Second Embodiment> Figure 6 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.

[0062] The heat-resistant member 2 of this embodiment is a ceramic sintered body comprising a plurality of carbide crystal particles containing carbides of a first specific element consisting of five or six elements selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, and a plurality of oxide crystal particles containing an oxide of at least one of zirconium and hafnium. The carbide crystal particles of the heat-resistant member 2 are a solid solution containing 45 at% to 55 at% carbon, and in the cross-section of the ceramic sintered body, the ratio of the cross-sectional area of ​​the oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is 5% to 60%. 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 6 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.

[0063] As described above, the heat-resistant member 2 of this embodiment is a ceramic sintered body comprising a plurality of carbide crystal particles containing carbides of a first specific element consisting of five or six elements selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, and a plurality of oxide crystal particles containing an oxide of at least one of zirconium and hafnium. This makes it possible to improve the toughness while increasing the strength of the heat-resistant member 2.

[0064] Furthermore, the heat-resistant member 2 of this embodiment comprises a ceramic sintered body having a structure in which carbide crystal particles Pcc and oxide crystal particles Pco are composited. This improves the thermal shock resistance of the heat-resistant member 2, thereby extending its lifespan.

[0065] 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.

[0066] <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.

[0067] [Modification 1] In the above embodiment, the ceramic sintered body comprises a plurality of carbide crystal particles containing carbides of titanium, zirconium, niobium, hafnium, and tungsten, and a plurality of oxide crystal particles containing oxides of zirconium and hafnium. The carbide crystal particles may contain carbides of a first specific element consisting of five or six elements selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten. The oxide crystal particles may contain only oxides of zirconium, or only oxides of hafnium.

[0068] [Modification 2] 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 iron concentration may be below the detection limit when measured by inductively coupled plasma atomic emission spectrometry.

[0069] [Modification 3] In the above embodiment, the peak ratio m / t of oxide crystal grains in the ceramic sintered body was 5 or less. The peak ratio m / t of oxide crystal grains may be greater than 5. When the peak ratio m / t of oxide crystal grains is 5 or less, stress-induced transformation effects due to phase transformation from tetragonal to monoclinic are more likely to occur, thereby improving the toughness while increasing the strength of the ceramic sintered body.

[0070] [Modification 4] In the above embodiment, the carbide crystal particles Pcc in the ceramic sintered body had a total concentration of zirconium and hafnium of 18.7 at%, which is between 4 at% and 20 at%. The range of the total concentration of zirconium and hafnium in the carbide crystal particles is not limited to this.

[0071] [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.

[0072] 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.

[0073] <Application Example 1> A ceramic sintered body comprising: a plurality of carbide crystal particles containing a carbide of a first specific element consisting of five or six elements selected from titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); and a plurality of oxide crystal particles containing at least one oxide of zirconium (Zr) and hafnium (Hf), wherein the carbide crystal particles are a solid solution containing 45 at% to 55 at% carbon, and in the cross-section of the ceramic sintered body, the ratio of the cross-sectional area of ​​the oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is 5% to 60%. <Application Example 2> The ceramic sintered body according to Application Example 1, wherein the iron (Fe) contained in the ceramic sintered body is 1000 at ppm or less. <Application Example 3> A ceramic sintered body according to Application Example 1 or Application Example 2, wherein at least one of the plurality of oxide crystal particles has a tetragonal crystal phase, and in the diffraction chart obtained by X-ray diffraction, the ratio of the peak intensity of the (-111) plane of the oxide crystal particle having a monoclinic crystal phase to the peak intensity of the oxide crystal particle having a tetragonal crystal phase is 5 or less. <Application Example 4> A ceramic sintered body according to any one of Application Examples 1 to 3, wherein the carbide crystal particles contain at least one of zirconium and hafnium in an amount of 4 at% to 20 at%. <Application Example 5> A ceramic sintered body according to any one of Application Examples 1 to 4, wherein in the cross-section of the ceramic sintered body, the ratio of the cross-sectional area of ​​the oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is 5% to 40%. <Application Example 6> A plasma generating electrode comprising a ceramic sintered body described in any one of Application Examples 1 to 5.<Application Example 7> A heat-resistant member comprising a ceramic sintered body described in any one of Application Examples 1 to 5.

[0074] 1... Electrode tip 2... Heat-resistant material 10... Electrode for plasma generation Pcc... Carbide crystal particles Pco... Oxide crystal particles

Claims

1. A ceramic sintered body comprising: a plurality of carbide crystal particles containing a carbide of a first specific element consisting of five or six elements selected from titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); and a plurality of oxide crystal particles containing at least one oxide of zirconium (Zr) and hafnium (Hf), wherein the carbide crystal particles are a solid solution containing 45 at% to 55 at% carbon, and in the cross-section of the ceramic sintered body, the ratio of the cross-sectional area of ​​the oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is 5% to 60%.

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, wherein at least one of the plurality of oxide crystal particles has a tetragonal crystal phase, and in a diffraction chart obtained by X-ray diffraction, the ratio of the peak intensity of the (-111) plane of the oxide crystal particle having a monoclinic crystal phase to the peak intensity of the (101) plane of the oxide crystal particle having a tetragonal crystal phase is 5 or less.

4. A ceramic sintered body according to claim 1 or claim 2, characterized in that the carbide crystal particles contain at least one of zirconium and hafnium in an amount of 4 at% to 20 at%.

5. A ceramic sintered body according to claim 1 or claim 2, characterized in that, in the cross-section of the ceramic sintered body, the ratio of the cross-sectional area of ​​the oxide crystal particles to the cross-sectional area of ​​the ceramic sintered body is 5% or more and 40% or less.

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

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

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