Ceramic sintered compact and electrode for plasma generation

Abstract

To provide a technique for improving durability to thermal stress in a ceramic sintered compact.SOLUTION: A ceramic sintered body of the present invention comprises: a first specific element selected from five or six elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element selected from one element selected from yttrium (Y) and aluminum (Al); and carbon (C). The total of the first specific element, the second specific element, and the carbon element is 98 at% or more. The ceramic sintered body has multiple types of structures with different compositions, and one of the multiple types of structures has a solid solution containing at least three or more elements from the first specific element.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a ceramic sintered body and an electrode for plasma generation.

Background Art

[0002] Conventionally, a ceramic sintered body used for an electrode for plasma generation has been known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, even with prior art such as Patent Document 1, there is still room for improvement in the technology for improving the durability against thermal stress in the ceramic sintered body.

[0005] An object of the present invention is to provide a technology for improving the durability against thermal stress in a ceramic sintered body.

Means for Solving the Problems

[0006] The present invention has been made to solve at least a part of the above-described problems and can be realized in the following forms.

[0007] (1) According to one embodiment of the present invention, a ceramic sintered body is provided. This ceramic sintered body contains a first specific element composed of 5 or 6 elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W), a second specific element composed of 1 element selected from yttrium (Y) and aluminum (Al), and a carbon element (C). The total of the first specific element, the second specific element, and the carbon element is 98 at% or more. The ceramic sintered body includes a plurality of types of structures with different compositions, and one of the plurality of types of structures has a solid solution containing at least 3 or more elements of the first specific element.

[0008] According to this configuration, the ceramic sintered body contains 98 at% or more of the first specific element, the second specific element, and the carbon element, which are composed of 5 or 6 elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten. One of the plurality of types of structures included in the ceramic sintered body has a solid solution containing at least 3 or more elements of the first specific element. Since the solid solution containing 3 or more elements of the first specific element contains an element with a melting point lower than that of hafnium carbide, for example, a dense ceramic sintered body can be produced by a method such as hot pressing. Therefore, the strength of the ceramic sintered body can be improved, and the durability against thermal stress can be improved.

[0009] (2) In the ceramic sintered body of the above embodiment, another one of the plurality of types of structures may be spinodally decomposed. According to this configuration, another one of the plurality of types of structures is spinodally decomposed. Thereby, the electrical resistance between the structures becomes small, and the heat generation of the ceramic sintered body can be suppressed. Therefore, the consumption of the ceramic sintered body due to heat generation can be suppressed.

[0010] (3) In the ceramic sintered body of the above form, another one of the plurality of types of the structures may have a solid solution containing at least two or more elements among the first specific elements. According to this configuration, another one of the plurality of types of structures has a solid solution containing at least two or more elements among the first specific elements. Thereby, since the ceramic sintered body becomes denser, the strength of the ceramic sintered body can be further improved.

[0011] (4) In the ceramic sintered body of the above form, the second specific element contained in the ceramic sintered body may be 3000 atppm or less. According to this configuration, since the second specific element contained in the ceramic sintered body is 3000 atppm or less, the formation of pores between the structures is suppressed. Thereby, since the ceramic sintered body becomes denser, the strength of the ceramic sintered body can be further improved.

[0012] (5) In the ceramic sintered body of the above form, the carbon element contained in the ceramic sintered body may be 45 at% or more and 55 at% or less. According to this configuration, since the carbon element contained in the ceramic sintered body is 45 at% or more and 55 at% or less, it is possible to suppress the precipitation of the metal phase of the first specific element and the precipitation of free carbon. Thereby, the strength of the ceramic sintered body can be further improved.

[0013] (6) In the ceramic sintered body of the above form, the iron element (Fe) contained in the ceramic sintered body may be 800 atppm or less. According to this configuration, since the concentration of the iron element in the ceramic sintered body is 800 atppm or less, the precipitation of iron-based particles is suppressed. Thereby, since the melting of the ceramic sintered body accompanying the temperature rise is suppressed, the consumption of the ceramic sintered body due to heat generation can be further suppressed.

[0014] (7) According to another aspect of the present invention, an electrode for plasma generation is provided. This electrode for plasma generation includes the ceramic sintered body of the above aspect. According to this configuration, the electrode for plasma generation includes a ceramic sintered body having a first structure that is a solid solution containing at least three or more elements among the first specific elements. Thereby, since the durability of the electrode for plasma generation against thermal stress can be improved, the life of the electrode for plasma generation can be extended.

[0015] Note that the present invention can be realized in various aspects. For example, it can be realized in the form of a method for manufacturing a ceramic sintered body, an apparatus including the ceramic sintered body, a control method for an apparatus including the ceramic sintered body, and the like.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0017] <First Embodiment> FIG. 1 is a cross-sectional view of a plasma generating electrode 10 including an electrode chip 1 (ceramic sintered body) according to the present embodiment. The plasma generating electrode 10 according to the present embodiment is used, for example, to generate oxygen plasma in a cutting machine, a surface treatment apparatus, a thermal spraying apparatus, etc. that use plasma. The plasma generating electrode 10 includes an electrode chip 1 as a plasma generating cathode and a chip support portion 2 that supports the electrode chip 1.

[0018] The electrode chip 1 is a ceramic sintered body and contains a first specific element composed of five or six elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W), a second specific element composed of one element selected from yttrium (Y) and aluminum (Al), and a carbon element (C). The total of the first specific element, the second specific element, and the carbon element contained in the ceramic sintered body that is the electrode chip 1 is 98 at% or more. The total of the first specific element, the second specific element, and the carbon element may be 100 at%, and the second specific element may be 0 atppm. The second specific element contained in the electrode chip 1 is 3000 atppm or less, and the carbon element is 45 at% or more and 55 at% or less. The concentration of the first specific element and the concentration of the carbon element in the electrode chip 1 are measured using energy dispersive X-ray analysis (EDS). Identification of the second specific element and measurement of the concentration in the electrode chip 1 are performed using an inductively coupled plasma (ICP) emission spectroscopic analyzer.

[0019] The ceramic sintered body that is the electrode chip 1 includes a plurality of types of structures having different compositions from each other. One of the plurality of types of structures included in the ceramic sintered body that is the electrode chip 1 according to the present embodiment has a solid solution containing at least three or more of the first specific elements, and another one of the plurality of types of structures has a solid solution containing at least two or more of the first specific elements. Another one of the plurality of types of structures included in the ceramic sintered body that is the electrode chip 1 according to the present embodiment is undergoing spinodal decomposition.

[0020] Figure 2 is a cross-sectional SEM image of the ceramic sintered body of the first embodiment. Figure 2 schematically shows an image (cross-sectional SEM image) taken by a scanning electron microscope (SEM) of the cross-section of the electrode chip 1 after the thermal etching process. Multiple types of structures (crystalline grains) are shown in Figure 2. Among the multiple types of structures shown in Figure 2, the first structure C1 is a solid solution containing at least three or more elements among the first specific elements. In the electrode chip 1, the first structure C1 is a crystalline grain of a carbide represented by the composition formula (HfZrTaVW)C, which contains hafnium, zirconium, tantalum, vanadium, and tungsten. In the first structure C1, the entire structure is solid-solved. The second structure C2 is a solid solution containing two elements among the first specific elements. In the electrode chip 1, the second structure C2 is a crystalline grain of a carbide represented by the composition formula (VW)C, which contains vanadium and tungsten. The second structure C2 has undergone spinodal decomposition as shown in Figure 2. In the second structure C2, as shown in Figure 2, the entire structure has undergone spinodal decomposition. In this embodiment, whether the ceramic sintered body of the electrode chip 1 has multiple types of structures, and whether one of the multiple types of structures is a solid solution containing at least two or three or more elements among the first specific elements, is identified by X-ray diffraction method using an X-ray diffractometer. Specifically, in the analysis of the crystal structure of the electrode chip 1 by the X-ray diffraction method using CuKα1 line, when measuring 2θ from 20° to 80°, if there are two or more peaks respectively derived from the <111> direction, <200> direction, <220> direction, <311> direction, <222> direction of the NaCl-type structure, or if there is one or more peak respectively from the peak derived from the NaCl-type structure and the peak derived from the hexagonal crystal structure, it is determined that the electrode chip 1 has multiple types of structures. The composition of the structure included in the ceramic sintered body is identified by a combination of the cross-sectional SEM image and the analysis combining the cross-sectional SEM image and energy dispersive X-ray analysis (EDS). Whether one of the multiple types of structures included in the ceramic sintered body of the electrode chip 1 has undergone spinodal decomposition is determined by small-angle X-ray scattering measurement in addition to the observation of the cross-sectional SEM image as shown in Figure 2.

[0021] The ceramic sintered body included in the electrode chip 1 of the present embodiment contains yttrium as the second specific element. The yttrium contained in the ceramic sintered body of the electrode chip 1 is 145 atppm, which is 3000 atppm or less.

[0022] The ceramic sintered body included in the electrode chip 1 of the present embodiment contains iron element as an inevitable impurity. The iron element (Fe) contained in the ceramic sintered body of the electrode chip 1 is 537 atppm, which is 800 atppm or less. Note that the iron element contained in the ceramic sintered body of the electrode chip 1 may be 0 atppm.

[0023] In the ceramic sintered body included in the electrode chip 1 of the present embodiment, the concentration difference between the first specific elements is 1.33 at%, which is less than 5 at%. Thereby, in the first structure C1, a solid solution is likely to be formed. In the present embodiment, the concentration difference between the first specific elements is obtained from the calculation result of the composition ratio in the crystal grains using energy dispersive X-ray spectroscopy.

[0024] The chip support portion 2 is a bottomed cylindrical member, and is formed, for example, by processing a copper rod-shaped member. A hole 2b into which the electrode chip 1 is fitted is formed in the bottom portion 2a of the chip support portion 2. The plasma generation electrode 10 of the present embodiment is completed by fitting the electrode chip 1 into the hole 2b of the chip support portion 2.

[0025] Next, a method for manufacturing the electrode chip 1 will be described. As a method for manufacturing the electrode chip 1, first, vanadium carbide powder (average particle size: 1.8 μm), zirconium carbide powder (average particle size: 2.4 μm), niobium carbide powder (average particle size: 1.1 μm), hafnium carbide powder (average particle size: 0.7 μm), and tungsten carbide powder (average particle size: 1.1 μm) are each weighed to be 20 mol% in a ceramic sintered body. For each of the weighed metal powders, they are put into a bead mill together with an acetone solvent and pulverized for 10 hours in a circulation method. Each of the five types of slurries obtained by pulverization in the bead mill is put into a ball mill in a predetermined amount and mixed. Next, zirconium partially stabilized with 0.4 wt% yttria (Y2O3) (hereinafter referred to as "3YSZ", average particle size: 1.0 μm) is added to the mixed slurry, and ball mill mixing is performed for 8 hours to prepare a mixed slurry. The prepared mixed slurry is put into a heating vacuum container, and the slurry is dried under reduced pressure while heating to 60 °C to prepare a dried powder. The granulated powder obtained by passing the prepared dried powder through a sieve with an opening of 100 μm is put into a hot press mold in a predetermined amount, and firing is performed in a vacuum atmosphere under the conditions of a firing temperature of 1800 °C and a firing pressure of 60 MPa (HP method). Thereby, the electrode chip 1 is completed.

[0026] Next, an evaluation test regarding the ceramic sintered body used as the electrode chip of the plasma generation electrode will be described. In this evaluation test, a plurality of ceramic sintered bodies with different production conditions were produced, and the influence of the production conditions on the characteristics of the ceramic sintered body was evaluated.

[0027] Figure 3 is the first figure explaining the production conditions of the ceramic sintered body samples. Figure 4 is the second figure explaining the production conditions of the ceramic sintered body samples. In this evaluation test, 24 types of samples, from sample 1 to sample 24, were produced as samples of the ceramic sintered body. Figures 3 and 4 show, as the production conditions for each of samples 1 to 24, the types of "main raw materials" and their respective molar percentages, the types of "additives" and their respective weight percentages, and, as the "firing conditions", the "firing method", the "temperature" (unit: °C), and the "pressure" (unit: MPa).

[0028] First, the "main raw material", which is the first specific element contained in the ceramic sintered body, will be explained. Among samples 1 to 24, in the production of samples 1 to 18, sample 21, and sample 22, as shown in Figures 3 and 4, 5 or 6 types of materials out of titanium carbide, vanadium carbide, zirconium carbide, niobium carbide, molybdenum carbide, hafnium carbide, tantalum carbide, and tungsten carbide were used as the "main raw material". In the production of samples 1 to 18, sample 21, and sample 22, powders of the "main raw material" having the average particle sizes shown below were used. Titanium carbide powder: 1.7 μm Vanadium carbide powder: 1.8 μm Zirconium carbide powder: 2.4 μm Niobium carbide powder: 1.1 μm Molybdenum carbide powder: 1.8 μm Hafnium carbide powder: 0.7 μm Tantalum carbide powder: 1.0 μm Tungsten carbide powder: 1.1 μm

[0029] Next, the "additive" which is the second specific element contained in the ceramic sintered body will be described. In the preparation of Samples 1 to 18, Sample 21, and Sample 22, as shown in FIGS. 3 and 4, either 3YSZ or aluminum oxide (Al2O3) was used as the "additive". In the preparation of Samples 1 to 18, Sample 21, and Sample 22, powders of the "additive" having the average particle sizes shown below were used. 3YSZ: 1.0 μm Al2O3: 0.3 μm

[0030] In the preparation of Samples 1 to 18, Sample 21, and Sample 22, in the same manner as the manufacturing method of the electrode chip 1, first, the molar percentages of the "main raw materials" were weighed so as to be the values shown in FIG. 3 or FIG. 4. For each weighed metal powder, it was put into a bead mill together with an acetone solvent and pulverized for 10 hours in a circulation method. Five or six types of slurries obtained by pulverization in the bead mill were put into a ball mill in a predetermined amount and mixed. After that, the "additive" was added to the mixed slurry so that the weight percentage was the value shown in FIG. 3 or FIG. 4, and ball mill mixing was performed for 8 hours to prepare a mixed slurry. The prepared mixed slurry was put into a heating vacuum container, and while heating to 60°C, the slurry was dried under reduced pressure, and the obtained dried powder was passed through a sieve with an opening of 100 μm to obtain granulated powder. The obtained granulated powder was put into a hot press mold in a predetermined amount, and Samples 1 to 18, Sample 21, and Sample 22 were obtained by performing firing under predetermined conditions (firing temperature: 1800°C, firing pressure: 60 MPa, treatment atmosphere: vacuum).

[0031] In the preparation of Sample 19 and Sample 20, raw materials of multiple metal oxides and a carbon raw material were weighed so as to have the same composition ratio as that of Sample 1. Specifically, in Sample 19, the raw materials of multiple metal oxides and the carbon raw material were weighed so that the ratio of the total amount of metal elements (ME) to carbon (C) was ME:C = 0.6:0.4. In Sample 20, the raw materials of multiple metal oxides and the carbon raw material were weighed so that the ratio of the total amount of metal elements (ME) to carbon (C) was ME:C = 0.4:0.6. In the preparation of Sample 19 and Sample 20, the weighed powders of the raw materials of metal oxides and the carbon raw material were heat-treated under predetermined conditions (treatment temperature: 1600 °C, treatment time: 3 hours, treatment atmosphere: vacuum). The powders after heat treatment were charged into a hot press mold in a predetermined amount and fired under predetermined conditions (firing temperature: 1800 °C, firing pressure: 60 MPa, treatment atmosphere: vacuum) to obtain Sample 19 and Sample 20. As raw materials, zirconium oxide (ZrO2), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), vanadium oxide (V2O5), tungsten oxide (WO3) which are metal oxides, and carbon (C) were used. In the preparation of Sample 19 and Sample 20, raw material powders having the average particle sizes shown below were used. Zirconium oxide powder: 1.0 μm Tantalum oxide powder: 3.0 μm Niobium oxide powder: 1.0 μm Vanadium oxide powder: 5.0 μm Tungsten oxide powder: 0.7 μm Carbon powder: 5.0 μm

[0032] Sample 23 was prepared by a spark plasma sintering method (SPS method) for a single-phase sintered body of HfC. Specifically, hafnium carbide powder (average particle size: 0.7 μm) was charged into a square SPS mold having a size of 35 × 35 mm so that the thickness of the ceramic sintered body was 5 mm, and fired under predetermined conditions (firing temperature: 1900 °C, firing pressure: 70 MPa, treatment atmosphere: vacuum) to prepare Sample 23.

[0033] Sample 24 was prepared using zirconium carbide (average particle size: 2.4 μm), hafnium carbide (average particle size: 0.7 μm), and tantalum carbide (average particle size: 1.0 μm) as the "main raw materials". Sample 24 was prepared by the same procedure as that for Samples 1 to 18, Sample 21, and Sample 22. In this evaluation test, Samples 1 to 24 prepared by the above-described method were processed into a size of 3 × 4 × 35 mm and used.

[0034] FIG. 5 is a first diagram for explaining the characteristics of samples of the ceramic sintered body. FIG. 6 is a second diagram for explaining the characteristics of samples of the ceramic sintered body. FIGS. 5 and 6 show the "composition", "particle size", and "ratio" of each of two or three types of structures included in Samples 1 to 24.

[0035] The "composition" shown in FIGS. 5 and 6 is the composition of the structure (crystalline grains) identified by using energy dispersive X-ray analysis for the range of the cross-sectional SEM image taken for the sample after the thermal etching treatment, similar to the ceramic sintered body provided in the electrode chip 1 of the present embodiment. The "particle size" shown in FIGS. 5 and 6 is the average particle size of the structure obtained by the intercept method from the secondary electron image at a magnification of 2000 times, which was taken by a scanning electron microscope after the sample after the strength test described below was mirror-polished with diamond abrasive grains and subjected to thermal etching treatment under predetermined conditions (treatment atmosphere: vacuum, treatment temperature: 1800 ° C., treatment time: 5 minutes). The "spinodal decomposition" of the "second structure" indicates whether the second structure has undergone spinodal decomposition. Whether the second structure has undergone spinodal decomposition was determined by small-angle X-ray scattering measurement in addition to the observation of the cross-sectional SEM image for the second structure provided in each sample, similar to the ceramic sintered body provided in the electrode chip 1 of the present embodiment. The "ratio" shown in FIGS. 5 and 6 is a value obtained by calculating the area ratio of the cross-sectional SEM images of each structure within the range of the SEM image by identifying the "composition" within the range of the taken cross-sectional SEM image.

[0036] FIG. 7 is a third diagram for explaining the characteristics of the samples of the ceramic sintered body. FIG. 8 is a fourth diagram for explaining the characteristics of the samples of the ceramic sintered body. In FIGS. 7 and 8, the respective "Y concentration", "Al concentration", "Fe concentration", "C concentration", "atomic concentration difference of the first specific element", "relative density", "strength", "on-off durability", and "consumption amount" of Samples 1 to 24 are shown.

[0037] Each of the "Y concentration", "Al concentration", "Fe concentration", and "C concentration" shown in FIGS. 7 and 8 indicates the respective concentrations of the yttrium element, aluminum element, iron element, and carbon element contained in the sample. In this evaluation test, for the samples after thermal etching treatment, quantitative analysis in energy dispersive X-ray analysis (EDS) targeting the range of the cross-sectional SEM image taken at a magnification of 500 times was used to measure the "Y concentration", "Al concentration", "Fe concentration", and "C concentration".

[0038] The "atomic concentration difference of the first specific element" shown in FIGS. 7 and 8 indicates the concentration difference between the first specific elements contained in the sample. The "atomic concentration difference of the first specific element" was calculated using the concentration of the first specific element measured by quantitative analysis by energy dispersive X-ray analysis.

[0039] The "relative density" shown in FIGS. 7 and 8 represents the denseness of the ceramic sintered body. The "relative density" was calculated using the specific gravity and open porosity measured by the method according to JIS R1634 for the sample, and the specific gravity of the carbide powder mixture at the time of sample preparation. The specific gravity of the carbide powder mixture at the time of sample preparation was calculated using the respective specific gravities of the carbide powders weighed at the time of sample preparation and the mixing ratio in the sample. The "strength" indicates the value measured in the three-point bending strength test according to JIS R1601 for the sample.

[0040] The "on-off durability" shown in FIGS. 7 and 8 indicates the resistance to breakage when the energization and de-energization of the sample are repeated, and represents the durability against thermal stress. In this evaluation test, first, the sample was processed to be φ1mm×L10mm, and the evaluation electrode was fabricated. With the fabricated evaluation electrode as the cathode, the anode grounded, and connected to a DC pulse power supply, a plasma test (electric power: 200W, on-off cycle: 1 minute of discharge and 10 seconds of discharge stop) was carried out in a mixed gas of nitrogen and oxygen. In this plasma test, the length of the cumulative time until the sample was damaged was classified into "A", "B", "C", and "D" as follows. The state of damage to the sample was visually confirmed after the plasma test was carried out for a certain period of time. A: Did not break even when the cumulative time reached 5 hours or more B: Broke when the cumulative time was more than 3 hours and less than 5 hours C: Broke when the cumulative time was more than 30 minutes and less than 3 hours D: Broke when the cumulative time was less than 30 minutes

[0041] The "consumption amount" shown in FIGS. 7 and 8 indicates the degree of consumption when a sample of the ceramic sintered body is used as the plasma generation electrode, and represents the wear resistance. The "consumption amount" is a value calculated using the value obtained by measuring the weight loss of the evaluation electrode after the test in the above-mentioned plasma test. The "consumption amount" indicates the relative value when the "consumption amount" of sample 24 is set to 100. That is, the smaller the numerical value, the less the consumption amount.

[0042] As shown in FIGS. 3 and 4, Samples 1 to 22 each contain a first specific element composed of 5 or 6 elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten, a second specific element composed of 1 element selected from yttrium and aluminum, and a carbon element. Further, in Samples 1 to 22, the total of the first specific element, the second specific element, and the carbon element is 98 at% or more, and as shown in FIGS. 5 and 6, they have a first structure and a second structure with different compositions from each other. Furthermore, the first structure included in Samples 1 to 22 is a solid solution containing at least 3 or more elements among the first specific elements.

[0043] Samples 1 to 22 were confirmed to have a value in "relative density" that is equal to or greater than that of Sample 23, which is a single-phase sintered body of HfC. Also, Samples 1 to 22 were confirmed to have greater "strength" and higher "on-off durability" than Sample 23. Furthermore, Samples 1 to 22 were confirmed to have a smaller "consumption amount" than Sample 24 in which the first structure is a solid solution containing two elements. From these facts, it was confirmed that Samples 1 to 22 become a ceramic sintered body as dense as or more dense than Sample 23, thereby improving strength, improving durability against thermal stress more than Sample 23, and being less likely to be consumed than Sample 24.

[0044] Also, Sample 23 contains hafnium carbide and is produced by the spark plasma sintering method (SPS method). On the other hand, since Samples 1 to 22 contain elements with a melting point lower than that of hafnium carbide, it was confirmed that a dense ceramic sintered body can also be produced by the hot pressing method (HP method).

[0045] Samples 1 to 22 and Sample 24 are selected with a first specific element that forms two or more types of tissues between a first tissue and a second tissue as the main raw material. As a result, in each of the two or more types of tissues, grain growth of crystal grains is suppressed, so that a ceramic sintered body having a relatively high strength can be produced.

[0046] In Samples 1 to 22, the "first tissue" has a solid solution containing at least three or more elements among the first specific elements. As a result, a ceramic sintered body that is difficult to be consumed even when heated by energization can be produced. Note that the more types of components contained in the crystal grains, the smaller the consumption amount due to plasma generation in the high temperature region.

[0047] Regarding the "consumption amount" in Samples 1 to 16, Samples 2, 8, 11, 15, and 16 showed relatively small values, and it was confirmed that all of them were less than 20. Samples 2, 8, 11, 15, and 16 have a "second tissue" with spinodal decomposition. Since the "second tissue" has spinodal decomposition, the electrical resistance between tissues (grain boundaries) becomes small, so that heat generation due to energization is suppressed. As a result, consumption due to heat generation can be suppressed.

[0048] Regarding the "strength" of Samples 1 to 16, Samples 1 to 4 and Samples 7 to 16, in which the "second structure" has a solid solution containing two or more elements among the first specific elements, and Samples 5 and 6, in which the "second structure" has a solid solution containing one element among the first specific elements, were confirmed to show larger values. Samples 1 to 4 and Samples 7 to 16 have a solid solution in which the "second structure" contains at least two or more elements among the first specific elements. Since the grain growth of the "first structure" is suppressed by having the "second structure" have a solid solution containing at least two or more elements among the first specific elements, a ceramic sintered body with high strength can be produced. In addition, the more types of components contained in the crystal grains in the "second structure", the more the growth of the crystal grains in the "first structure" can be suppressed, so the strength can be further increased.

[0049] Regarding the "strength" of Samples 1 to 18, Sample 21, and Sample 22, Samples 1 to 18 in which the "Y concentration" or "Al concentration" is 3000 ppm or less were confirmed to be superior to Sample 21 or Sample 22 in which the "Y concentration" or "Al concentration" is greater than 3000 ppm. In Samples 21 and 22, since the "Y concentration" or "Al concentration" is greater than 3000 ppm, the densification of the ceramic sintered body is inhibited, and pores are likely to occur between the structures. For this reason, Samples 21 and 22 have low strength and are easily damaged. On the other hand, Samples 1 to 18 in which the "Y concentration" or "Al concentration" is 3000 ppm or less are less likely to have pores between the structures, so they can have a certain level of strength.

[0050] Regarding the "strength" in Samples 1 to 20, Samples 1 to 18 with a carbon element content of 45 at% or more and 55 at% or less showed higher values than Sample 19 with a carbon element content greater than 55 at% and Sample 20 with a carbon element content less than 45 at%. When the concentration of the carbon element in the ceramic sintered body is greater than 55 at%, free carbon precipitates, and the free carbon appears as a brittle phase between the structures, resulting in a decrease in the strength of the ceramic sintered body. When the concentration of the carbon element in the ceramic sintered body is less than 45 at%, the metal contained in the second structure precipitates as a metal phase. Since the melting point of the precipitated metal phase is lower than that of the carbide, the durability of the ceramic sintered body at high temperatures decreases. On the other hand, when the concentration of the carbon element in the ceramic sintered body is 45 at% or more and 55 at% or less, both the generation of free carbon and the precipitation of the metal phase can be suppressed.

[0051] Regarding the "consumption amount" in Samples 1 to 16, Samples 1 to 8 and Samples 11 to 16 with an iron element content of 800 atppm or less showed lower values than Samples 9 and 10 with an iron element content greater than 800 atppm, and all were confirmed to have values less than 40. The ceramic sintered body contains iron element as an impurity, but when the concentration of the iron element becomes greater than 800 atppm, relatively large iron-based particles precipitate. Since the melting point of the iron-based particles is low, the durability of the ceramic sintered body at high temperatures decreases. On the other hand, when the concentration of the iron element in the ceramic sintered body is 800 atppm or less, the precipitation of the iron-based particles can be suppressed.

[0052] In a cutting machine or a surface treatment apparatus using plasma, a high melting point metal material such as hafnium carbide may be used as an electrode for plasma generation. However, since hafnium carbide is difficult to sinter, it is difficult to obtain a dense ceramic sintered body. For this reason, a ceramic sintered body formed of hafnium carbide can be produced only by a spark plasma sintering method. The spark plasma sintering method is, for example, a method of sintering a ceramic compact by attaching electrodes to both ends of a columnar ceramic compact and applying a high voltage to conduct electricity. However, for example, in order to produce a relatively large ceramic sintered body, it is necessary to apply a relatively large voltage, which increases the equipment cost and the manufacturing cost. Also, in the spark plasma sintering method, it is difficult to sinter a thick ceramic compact uniformly, and the degree of freedom in shape is low. Furthermore, even if a relatively dense ceramic sintered body can be produced using hafnium carbide, since minute pores are present in the crystal grain boundaries, the strength of the ceramic sintered body is relatively low. When a ceramic sintered body with low strength is used for the electrode tip of the plasma generation electrode, if an operation such as repeating the generation and stop of plasma is performed, the ceramic sintered body formed of hafnium carbide will be damaged due to thermal stress caused by the repeated on and off.

[0053] According to the ceramic sintered body included in the electrode tip 1 of the present embodiment described above, it contains 98 at% or more of a first specific element, a second specific element, and a carbon element, which are composed of 5 or 6 elements selected from titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten. Among the plurality of types of structures included in the ceramic sintered body, the first structure C1 has a solid solution containing at least 3 or more elements among the first specific elements. Since the solid solution containing 3 or more first specific elements contains elements with a lower melting point than hafnium carbide, for example, a dense ceramic sintered body can be produced by a method such as hot pressing. Therefore, the strength of the ceramic sintered body can be improved, and the durability against thermal stress can be improved.

[0054] Further, according to the ceramic sintered body included in the electrode chip 1 of the present embodiment, the first structure C1 has a solid solution containing at least three or more elements among the first specific elements. Thereby, it is possible to suppress the consumption of the ceramic sintered body itself due to heat generation caused by energization.

[0055] Further, according to the ceramic sintered body included in the electrode chip 1 of the present embodiment, the second structure C2 is spinodal decomposed. Thereby, the electrical resistance between the structures becomes small, and heat generation of the ceramic sintered body can be suppressed. Therefore, it is possible to suppress the consumption of the ceramic sintered body due to heat generation.

[0056] Further, according to the ceramic sintered body included in the electrode chip 1 of the present embodiment, the second structure C2 has a solid solution containing at least two or more elements among the first specific elements. Thereby, since the ceramic sintered body becomes denser, the strength of the ceramic sintered body can be further improved.

[0057] Further, according to the ceramic sintered body included in the electrode chip 1 of the present embodiment, the first specific element is selected so that the composition of the first structure C1 and the composition of the second structure C2 are different from each other. Thereby, the growth of the crystal grains of each of the first structure C1 and the second structure C2 is suppressed, and a higher-strength ceramic sintered body can be obtained.

[0058] Further, according to the ceramic sintered body included in the electrode chip 1 of the present embodiment, since the second specific element contained in the ceramic sintered body is 3000 atppm or less, the formation of pores between the structures is suppressed. Thereby, since the ceramic sintered body becomes denser, the strength of the ceramic sintered body can be further improved.

[0059] Moreover, according to the ceramic sintered body included in the electrode chip 1 of the present embodiment, since the carbon element contained in the ceramic sintered body is 45 at% or more and 55 at% or less, it is possible to suppress the precipitation of the metal phase of the first specific element while suppressing the precipitation of free carbon. Thereby, the strength of the ceramic sintered body can be further improved.

[0060] Moreover, according to the ceramic sintered body included in the electrode chip 1 of the present embodiment, since the concentration of iron element in the ceramic sintered body is 800 atppm or less, the precipitation of iron-based particles is suppressed. As a result, melting accompanying the temperature rise of the ceramic sintered body is suppressed, so that the consumption of the ceramic sintered body due to heat generation can be further suppressed.

[0061] Moreover, according to the plasma generation electrode 10 of the present embodiment, the plasma generation electrode includes a ceramic sintered body having a first structure C1 that is a solid solution containing at least three or more elements among the first specific elements. Thereby, since the durability of the plasma generation electrode against thermal stress can be improved, the life of the plasma generation electrode can be extended.

[0062] <Modification Example of the Present Embodiment> The present invention is not limited to the above-described embodiment, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

[0063] [Modification Example 1] In the above-described embodiment, it is assumed that the ceramic sintered body included in the electrode chip 1 contains five elements of hafnium, zirconium, tantalum, vanadium, and tungsten as the first specific elements. It may contain five or six elements among titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten.

[0064] [Modification Example 2] In the above-described embodiment, it was assumed that the second structure C2 included in the ceramic sintered body was undergoing spinodal decomposition throughout the entire structure. The plurality of types of structures included in the ceramic sintered body may not be undergoing spinodal decomposition, but when the structure undergoes spinodal decomposition, the electrical resistance between the structures decreases, and heat generation of the ceramic sintered body can be suppressed.

[0065] [Modification Example 3] In the above-described embodiment, the second structure C2 is composed of crystal grains represented by the composition formula (VW)C containing vanadium and tungsten, and it was assumed that it was a solid solution containing at least two or more elements among the first specific elements. The plurality of types of structures included in the ceramic sintered body may not be a solid solution containing at least two or more elements among the first specific elements. When the structure is a solid solution containing at least two or more elements among the first specific elements, the ceramic sintered body becomes dense, so the strength of the ceramic sintered body can be improved.

[0066] [Modification Example 4] In the above-described embodiment, it was assumed that the yttrium contained in the ceramic sintered body of the electrode chip 1 was 145 atppm. The concentration of yttrium contained in the ceramic sintered body is not limited to this, but is preferably 3000 atppm or less. When the concentration of yttrium becomes 3000 atppm or less, the formation of pores between the structures is suppressed. As a result, the ceramic sintered body becomes dense, so the strength of the ceramic sintered body can be improved. Further, the second specific element contained in the ceramic sintered body may be aluminum. In this case, it is desirable that the aluminum contained in the ceramic sintered body is 3000 atppm or less.

[0067] [Modification Example 5] In the above-described embodiment, it was assumed that the carbon element contained in the ceramic sintered body of the electrode chip 1 is 45 at% or more and 55 at% or less. The concentration of the carbon element contained in the ceramic sintered body is not limited to this, but it is preferably in the range of 45 at% or more and 55 at% or less. When the concentration of the carbon element in the ceramic sintered body is greater than 55 at%, free carbon precipitates, and the free carbon appears as a brittle phase between the structures, so the strength of the ceramic sintered body decreases. When the concentration of the carbon element in the ceramic sintered body is less than 45 at%, the metal contained in the second structure precipitates as a metal phase. Since the melting point of the precipitated metal phase is lower than that of the carbide, the durability of the ceramic sintered body at high temperatures decreases. Therefore, by setting the concentration of the carbon element in the ceramic sintered body to 45 at% or more and 55 at% or less, it is possible to suppress both the generation of free carbon and the precipitation of the metal phase.

[0068] [Modification Example 6] In the above-described embodiment, it was assumed that the iron element (Fe) contained in the ceramic sintered body provided in the electrode chip 1 is 800 atppm or less. The iron element may be greater than 800 atppm, but since the life becomes shorter when the concentration of the iron element increases due to the melting of the precipitated iron-based particles, it is desirable that the concentration of the iron element be low. The concentration of the iron element may be below the detection limit in quantitative analysis by energy dispersive X-ray analysis (EDS).

[0069] [Modification Example 7] The ceramic sintered body of the above-described embodiment was assumed to be provided in the electrode chip 1. The technical field to which the ceramic sintered body is applied is not limited to this. It may be used in a technical field where durability against thermal stress and wear resistance are required.

[0070] Based on the above embodiments and variations, the present aspect has been described. However, the embodiments of the above-described aspects are for facilitating the understanding of the present aspect and do not limit the present aspect. The present aspect can be changed and improved without departing from its spirit and the scope of the claims, and equivalents thereof are included in the present aspect. Also, if its technical features are not described as essential in this specification, they can be deleted as appropriate.

[0071] <Application Example 1> A ceramic sintered body, a first specific element composed of 5 or 6 elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W), a second specific element composed of 1 element selected from yttrium (Y) and aluminum (Al), and a carbon element (C), wherein the total of the first specific element, the second specific element, and the carbon element is 98 at% or more, the ceramic sintered body has a plurality of types of structures with different compositions from each other, and one of the plurality of types of structures has a solid solution containing at least 3 or more elements of the first specific element. A ceramic sintered body characterized by the above. <Application Example 2> The ceramic sintered body according to Application Example 1, wherein another one of the plurality of types of structures is undergoing spinodal decomposition. A ceramic sintered body characterized by the above. <Application Example 3> The ceramic sintered body according to Application Example 1 or Application Example 2, wherein another one of the plurality of types of structures has a solid solution containing at least 2 or more elements of the first specific element. A ceramic sintered body characterized by the above. <Application Example 4> A ceramic sintered body according to any one of Application Examples 1 to 3, wherein the second specific element contained in the ceramic sintered body is 3000 atppm or less, characterized by the ceramic sintered body. <Application Example 5> A ceramic sintered body according to any one of Application Examples 1 to 4, wherein the carbon element contained in the ceramic sintered body is 45 at% or more and 55 at% or less, characterized by the ceramic sintered body. <Application Example 6> A ceramic sintered body according to any one of Application Examples 1 to 5, wherein the iron element (Fe) contained in the ceramic sintered body is 800 atppm or less, characterized by the ceramic sintered body. <Application Example 7> An electrode for plasma generation, comprising a ceramic sintered body according to any one of Application Examples 1 to 6, An electrode for plasma generation.

Explanation of Signs

[0072] 1... Electrode chip (ceramic sintered body) 10... Electrode for plasma generation

Claims

1. A ceramic sintered body comprising: a first specific element composed of five or six elements selected from titanium (Ti), vanadium (V), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W); a second specific element composed of one element selected from yttrium (Y) and aluminum (Al); a carbon element (C); wherein the total of the first specific element, the second specific element, and the carbon element is 98 at% or more; the ceramic sintered body includes a plurality of types of structures having different compositions from each other; one of the plurality of types of structures has a solid solution containing at least three or more elements of the first specific element; A ceramic sintered body characterized by the above.

2. The ceramic sintered body according to Claim 1, wherein another one of the plurality of types of structures is undergoing spinodal decomposition. A ceramic sintered body characterized by the above.

3. The ceramic sintered body according to Claim 1 or Claim 2, wherein another one of the plurality of types of structures has a solid solution containing at least two or more elements of the first specific element. A ceramic sintered body characterized by the above.

4. The ceramic sintered body according to Claim 1 or Claim 2, wherein the second specific element contained in the ceramic sintered body is 3000 atppm or less. A ceramic sintered body characterized by the above.

5. The ceramic sintered body according to Claim 1 or Claim 2, wherein the carbon element contained in the ceramic sintered body is 45 at% or more and 55 at% or less. A ceramic sintered body characterized by the above.

6. The ceramic sintered body according to Claim 1 or Claim 2, wherein the iron element (Fe) contained in the ceramic sintered body is 800 atppm or less. A ceramic sintered body characterized by the above.

7. An electrode for plasma generation, comprising the ceramic sintered body according to Claim 1 or Claim 2. An electrode for plasma generation.

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