Sintered ceramics

Abstract

The present application discloses a ceramic sintered body that exhibits both toughness and abrasion resistance. A ceramic sintered body according to the present disclosure contains a first compound and a second compound. The first compound is silicon carbide, and the second compound is a diboride of a Group 4 element. The proportion of the second compound in the ceramic sintered body is 50-70 mass%. In a case where a 300 µm x 300 µm area of a polished surface of the ceramic sintered body is divided into 400 15 µm x 15 µm compartments, and the areal ratio of the first compound is specified for each of the compartments, the coefficient of variation CV of the areal ratio of the first compound is more than 0.14 and less than 0.23.

Description

[Technical Field]

[0001] The present application discloses a ceramic sintered body. [Background technology]

[0002] Ceramic sintered bodies are used as various structural materials. High toughness is sometimes required for ceramic sintered bodies. One method for increasing the toughness of ceramic sintered bodies is to mix two phases with different thermal expansion coefficients and generate residual stress, thereby suppressing crack propagation (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-132607 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-035803 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional ceramic sintered bodies have room for improvement in terms of achieving both toughness and wear resistance. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> A ceramic sintered body containing a first compound and a second compound, the first compound is silicon carbide; the second compound is a diboride of a Group 4 element, a ratio of the second compound in the ceramic sintered body is 50% by mass or more and 70% by mass or less, When a 300 μm × 300 μm region of the polished surface of the ceramic sintered body is divided into 400 15 μm × 15 μm sections and an area ratio of the first compound is specified for each of the sections, the coefficient of variation CV of the area ratio of the first compound is greater than 0.14 and less than 0.23. Sintered ceramics. <Aspect 2> The second compound is Ti 1-x Zr x Represented by B2 (0≦x≦0.05), The ceramic sintered body of embodiment 1. <Aspect 3> The coefficient of variation CV is 0.15 or more and 0.20 or less. The ceramic sintered body according to aspect 1 or 2. <Aspect 4> 5.0 mPa m 1 / 2 or more, It has a bending strength of 480 MPa or more. The ceramic sintered body according to any one of aspects 1 to 3. <Aspect 5> 5.5 mPa m 1 / 2 or more, It has a bending strength of 500 MPa or more. The ceramic sintered body according to any one of aspects 1 to 3. <Aspect 6> When an abrasive wear test was conducted on the ceramic sintered body, the amount of wear of the ceramic sintered body per unit amount of particles was 0.5 mm 3 / kg or less, The ceramic sintered body according to any one of aspects 1 to 5. <Aspect 7> A ceramic sintered body containing a first compound and a second compound, the first compound is silicon carbide; The second compound is Ti 1-x Zr x It is a diboride of a Group 4 element represented by B2 (0≦x≦0.05), a ratio of the second compound in the ceramic sintered body is 50% by mass or more and 70% by mass or less, 5.0 mPa m 1 / 2 or more, It has a bending strength of 500 MPa or more, When an abrasive wear test was conducted on the ceramic sintered body, the amount of wear of the ceramic sintered body per unit amount of particles was 0.5 mm 3 / kg or less, Sintered ceramics. [Effects of the Invention]

[0006] The ceramic sintered body of the present disclosure has both high toughness and wear resistance. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a ceramic sintered body. [Figure 2A] FIG. 1 is a schematic diagram for explaining the propagation of a crack in a ceramic sintered body having a small coefficient of variation CV. [Figure 2B] FIG. 1 is a schematic diagram for explaining the propagation of a crack in a ceramic sintered body having a coefficient of variation CV within a predetermined range. [Figure 2C] FIG. 1 is a schematic diagram for explaining the propagation of a crack in a ceramic sintered body having a large coefficient of variation CV. [Figure 3] FIG. 1 is a schematic diagram for explaining an abrasive testing device. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, a ceramic sintered body according to an embodiment will be described with reference to the drawings. However, the ceramic sintered body according to the present disclosure is not limited to the following embodiment.

[0009] 1. Sintered ceramics The ceramic sintered body of the present disclosure includes a first compound and a second compound. The first compound is silicon carbide. The second compound is a diboride of a Group 4 element. The proportion of the second compound in the ceramic sintered body is 50 mass% or more and 70 mass% or less. When a 300 μm×300 μm region of a polished surface of the ceramic sintered body is divided into 400 15 μm×15 μm sections and the area ratio of the first compound is determined for each of the sections, the coefficient of variation CV of the area ratio of the first compound is greater than 0.14 and less than 0.23.

[0010] 1.1 First compound The ceramic sintered body of the present disclosure contains silicon carbide as the first compound. The proportion of the first compound in the ceramic sintered body depends on the proportion of the second compound described below. The proportion of the first compound in the ceramic sintered body may be, for example, 30% by mass or more and 50% by mass or less, 32% by mass or more and 48% by mass or less, or 34% by mass or more and 46% by mass or less. These lower and upper limits may be combined arbitrarily.

[0011] In the ceramic sintered body of the present disclosure, the form of the first compound is not particularly limited. For example, as shown in FIG. 1, the ceramic sintered body 10 has a first phase 10a made of the first compound. The size and shape of the first phase 10a are not particularly limited. The first phase 10a may be made of crystal grains of the first compound. When the first phase 10a is made of a single crystal grain, the diameter of the crystal grain (equivalent circle diameter in cross section) may be, for example, 1 μm to 10 μm, or 2 μm to 5 μm. These lower and upper limits may be arbitrarily combined. A "crystal grain" may be made of a single crystallite, or may be made up of multiple crystallites that combine to form a single grain. Note that even when the crystal grains of the first compound or the crystal grains of the second compound described below are made up of multiple crystallites that combine to form a single grain, cracks are considered to propagate between the crystal grains of the first compound and the crystal grains of the second compound.

[0012] In the ceramic sintered body of the present disclosure, the first compound is unevenly distributed to some extent so that the coefficient of variation CV of the area ratio thereof falls within a predetermined range. The coefficient of variation CV will be described in detail later.

[0013] 1.2 Second compound The ceramic sintered body of the present disclosure contains a diboride of a Group 4 element as the second compound. The Group 4 element (titanium group element) is at least one of titanium, zirconium, and hafnium. That is, the second compound may be a diboride of titanium, a diboride of zirconium, a diboride of hafnium, a composite diboride of titanium and zirconium, a composite diboride of titanium and hafnium, a composite diboride of zirconium and hafnium, or a composite diboride of titanium, zirconium, and hafnium. According to the findings of the present inventors, when the second compound is a diboride containing titanium, the ceramic sintered body is likely to have even better toughness and wear resistance. In particular, when the second compound is a diboride containing Ti 1-x Zr x When the alloy is represented by B2 (0≦x≦0.05), a significant improvement in toughness and wear resistance can be expected.

[0014] The proportion of the second compound in the ceramic sintered body is 50% by mass or more and 70% by mass or less. If the proportion of the second compound in the ceramic sintered body is too low, the ceramic sintered body is likely to have poor toughness and wear resistance. On the other hand, if the proportion of the second compound in the ceramic sintered body is too high, the ceramic sintered body is likely to have poor wear resistance. In addition, the proportion of the second compound in the ceramic sintered body also affects other mechanical properties of the ceramic sintered body, such as the bending strength of the ceramic sintered body. According to the findings of the present inventors, when the proportion of the second compound in the ceramic sintered body is 50% by mass or more and 70% by mass or less, the ceramic sintered body is likely to have both high toughness and wear resistance and excellent bending strength, etc. The proportion of the second compound in the ceramic sintered body may be 52% by mass or more and 68% by mass or less, or 54% by mass or more and 66% by mass or less. These lower and upper limits may be combined arbitrarily.

[0015] In the ceramic sintered body of the present disclosure, the form of the second compound is not particularly limited. For example, as shown in FIG. 1, the ceramic sintered body 10 has a second phase 10b made of the second compound. The size and shape of the second phase 10b are not particularly limited. The second phase 10b may be made of crystal grains of the second compound. When the second phase 10b is made of a single crystal grain, the diameter of the crystal grain (equivalent circle diameter in cross section) may be, for example, 1 μm or more and 10 μm or less, or 2 μm or more and 5 μm or less. These lower and upper limits may be arbitrarily combined. The "crystal grain" may be made of a single crystallite, or may be made up of multiple crystallites grouped together to form a single grain.

[0016] 1.3 Other ingredients The ceramic sintered body of the present disclosure may contain other components in addition to the first compound and second compound. Examples of other components include components derived from impurities contained in raw materials, components derived from impurities introduced during the manufacturing process, and components derived from sintering aids and the like that mainly constitute the grain boundary phase (carbides other than the first compound, borides other than the second compound, etc.). Specifically, the other components may include at least one selected from carbides of Group 4 elements and boron carbide. The amount of other components is preferably small. For example, the total proportion of the first compound and second compound in the ceramic sintered body may be 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, or 99% by mass or more and 100% by mass or less. These lower and upper limits may be combined arbitrarily.

[0017] 1.4 Coefficient of variation CV It is believed that a ceramic sintered body with a higher fracture toughness, which indicates the resistance to crack propagation, is more likely to be fractured during wear and have improved wear resistance. Possible methods for increasing the fracture toughness of a ceramic sintered body include (1) developing columnar grains and (2) combining two or more materials to create a stress field that makes crack propagation less likely or to bend the propagation path. Method (1) is used for certain materials that undergo dissolution and reprecipitation during the sintering process, primarily Si3N4-based materials. In the ceramic sintered body disclosed herein, the fracture toughness is increased by method (2). Specifically, the difference in thermal expansion between the two materials is utilized, and the residual stress generated when the temperature returns to room temperature from the high temperature during sintering suppresses crack propagation, thereby achieving high toughness.

[0018] As shown in Patent Document 1, the fracture toughness of a ceramic sintered body can be further improved by increasing the segregation of the mixed dissimilar materials and generating a larger residual stress field. However, according to the inventors' findings, the presence of such large uneven distribution can lead to large defects that can initiate fracture. For example, large residual stress can cause initial cracks between the dissimilar materials. For brittle materials such as ceramics, the smaller the initial defects and the higher the fracture toughness, the stronger the material. However, fracture toughness is merely an indicator of the resistance to crack propagation, and large initial defects can lead to fracture even with relatively small stresses. According to the inventors' findings, if the distribution of two materials in a ceramic sintered body is too large, even if the fracture toughness is high, the defects that can initiate fracture will become large, resulting in poor wear resistance.

[0019] As described above, by unevenly distributing the two components (phases) in a ceramic sintered body, residual stress-induced crack propagation can be suppressed over a relatively large area, resulting in high toughness. If the two components (phases) are not unevenly distributed (i.e., if the two components (phases) are uniformly dispersed), cracks tend to propagate linearly in the ceramic sintered body, resulting in poor toughness (Figure 2A). On the other hand, if the two components (phases) are excessively unevenly distributed, the area that peels off when the ceramic sintered body wears increases, resulting in an increased wear volume and poor wear resistance (Figure 2C). In other words, achieving an appropriate uneven distribution of the two components (phases) in a ceramic sintered body can achieve both high toughness and wear resistance (Figure 2B).

[0020] From the above viewpoints, in the ceramic sintered body of the present disclosure, when a 300 μm × 300 μm region of the polished surface of the ceramic sintered body is divided into 400 15 μm × 15 μm sections and the area ratio of the first compound is determined for each of the sections, the coefficient of variation CV of the area ratio of the first compound is greater than 0.14 and less than 0.23, thereby achieving both high toughness and wear resistance ( FIG. 2B ). If the coefficient of variation CV is too small, cracks tend to propagate linearly ( FIG. 2A ). On the other hand, if the coefficient of variation CV is too large, the wear volume tends to increase ( FIG. 2C ). In particular, when the coefficient of variation CV is 0.15 or more and 0.20 or less, high toughness and wear resistance are further improved.

[0021] The coefficient of variation CV for the area ratio of the first compound can be determined by obtaining the element distribution on the polished surface of the ceramic sintered body using SEM-EDS, EPMA, or the like. For example, a mapping image of the element distribution on the polished surface can be measured using SEM-EDS, and the area fraction can be measured using image analysis software. A 300 μm × 300 μm region of the obtained observation image is divided into 400 15 μm × 15 μm sections (20 × 20 sections), and the area fraction of silicon carbide, the first compound, is determined for each of the sections. Based on the area fraction determined for each section, the standard deviation and average value (arithmetic mean value) of the area fraction are determined, and the coefficient of variation CV can be determined by dividing the standard deviation by the average value. Note that when the area of ​​the polished surface of the sintered body is 10 mm 2 If the coefficient of variation is less than 0.14, it is sufficient to determine the coefficient of variation CV for one region on the polished surface, and it is confirmed whether the coefficient of variation CV for that one region is greater than 0.14 and less than 0.23. 2 If the above area can be ensured, calculate the coefficient of variation CV for each of 10 regions such that the distance between the center points of each region is 1 mm or more, and check whether the coefficient of variation CV for each region is greater than 0.14 and less than 0.23. In the ceramic sintered body of the present disclosure, the coefficient of variation CV for all of the 10 regions is greater than 0.14 and less than 0.23.

[0022] 1.5 Other As described above, the ceramic sintered body of the present disclosure contains the first compound and a predetermined amount of the second compound, and satisfies the coefficient of variation CV, thereby achieving both high toughness and wear resistance. The ceramic sintered body of the present disclosure may have, for example, the following mechanical properties.

[0023] 1.5.1 Fracture toughness value (KIC) The ceramic sintered body of the present disclosure has a viscosity of, for example, 5.0 mPa m 1 / 2 The fracture toughness value may be 5.5 mPa·m or more. 1 / 2 The upper limit of the fracture toughness value is not particularly limited, and the higher the value, the better. The ceramic sintered body of the present disclosure has a fracture toughness value of, for example, 6.0 mPa m 1 / 2 The material may have the following fracture toughness values: The fracture toughness values ​​are measured by the SEPB method in accordance with JIS-R1607.

[0024] 1.5.2 Bending strength The ceramic sintered body of the present disclosure may have a bending strength of, for example, 480 MPa or more. Preferably, it has a bending strength of 500 MPa or more. There is no particular upper limit to the bending strength, and the higher the bending strength, the better. The ceramic sintered body of the present disclosure may have a bending strength of, for example, 550 MPa or less. The bending strength is measured by a three-point bending test in accordance with JIS-R1601.

[0025] The ceramic sintered body according to one embodiment has a resistivity of, for example, 5.0 mPa·m 1 / 2 or more, and a bending strength of 480 MPa or more, and 1 / 2 or more, and may have a bending strength of 500 MPa or more, and 1 / 2 6.0mPa m or more 1 / 2 and a bending strength of 480 MPa or more and 550 MPa or less, and 5.5 mPa·m 1 / 26.0mPa m or more 1 / 2 The alloy may have a fracture toughness value of 500 MPa or more and a bending strength of 500 MPa or more and 550 MPa or less.

[0026] 1.5.3 Abrasion resistance For example, when an abrasive wear test is performed on the ceramic sintered body of the present disclosure, the wear amount of the ceramic sintered body per unit amount of particles input is 0.5 mm 3 / kg or less. The "abrasive wear test" referred to in this application refers to a test performed using the apparatus shown in Figure 3. Specifically, a 55mm x 20mm x 20mm test piece 1 is cut from a ceramic sintered body, and the entire 55mm x 20mm test surface is ground using a #2000 diamond grinding wheel on a grinding machine before use. Using the apparatus shown in Figure 3, a foil 3 with a diameter of 224mm and a width of 12mm and a nitrile rubber bonded to its surface is used. The foil 3 is rotated at 200 rpm, and the pressure load on the test piece 1 is 130N. Silica sand No. 6 as abrasive particles 4 is fed from a projection nozzle 2 between the test piece 1 and the foil 3 at a rate of 350g / min. The test is continued until the total amount of abrasive particles 4 reaches 21kg. The weight of the test piece 1 was measured before and after the test, and the wear volume was calculated from the change in weight and the density obtained by Archimedes' method. This was then divided by the total weight of the wear particles 4 introduced, to obtain the "wear volume (mm) of the ceramic sintered body per unit of input particle (1 kg of input particle)." 3 / kg) is calculated. Just before the weight measurement, the test piece 1 is subjected to ultrasonic cleaning in acetone to remove any particles or dust remaining on the surface of the test piece 1 before the weight measurement. Conditions other than those mentioned above shall be in accordance with ASTM G65.

[0027] 1.5.4 Vickers hardness The ceramic sintered body of the present disclosure may have, for example, a Vickers hardness of not less than 2000 and not more than 2500. The Vickers hardness is measured using a mirror-polished ceramic sintered body in accordance with JIS-R1610 at an indentation load of 98 N.

[0028] 1.5.5 Density The ceramic sintered body of the present disclosure has a density of, for example, 3.5 g / cm 3 More than 5.0g / cm 3 The ceramic sintered body may have a density below 97%. However, the density of the ceramic sintered body may vary depending on the type of the second compound, etc. Furthermore, the ceramic sintered body of the present disclosure may have a relative density of, for example, 97% or more. The density is measured by Archimedes' method.

[0029] 2. Manufacturing method of sintered ceramics The ceramic sintered body of the present disclosure can be produced, for example, by the method described below. That is, a method for producing a ceramic sintered body according to one embodiment includes kneading a powder of a first compound, a powder of a second compound, optionally a sintering aid (auxiliary raw material), and optionally other raw materials to obtain granules, and then molding the granules, degreasing them, and firing them.

[0030] 2.1 Powder of the first compound and powder of the second compound The powder of the first compound and the powder of the second compound may each be produced by a known method. Their particle sizes are not particularly limited and may be appropriately selected depending on the desired performance. The average particle size of the powder of the first compound may be, for example, 10 nm to 5 μm. The average particle size of the powder of the second compound may be, for example, 500 nm to 5 μm. The powder of the first compound and the powder of the second compound may each be used alone or in combination of two or more. The average particle size refers to the particle size at 50% of the cumulative value in the volume-based particle size distribution measured by a laser diffraction / scattering method (D50, median size). The average particle size was measured using a laser diffraction particle size distribution analyzer LA-960 manufactured by Horiba, Ltd. The results were obtained by adding sodium hexametaphosphate as a dispersant to a pure water solvent.

[0031] 2.2 Auxiliary raw materials The above powders may be difficult to sinter. Therefore, in a manufacturing method according to one embodiment, a sintering aid may be mixed with the above powder as an auxiliary material. The type of sintering aid as an auxiliary material is not particularly limited. For example, it may be at least one of carbon, such as carbon black, and carbides, such as boron carbide.

[0032] 2.3 Other ingredients In one embodiment of the manufacturing method, other raw materials that can become the first compound or the second compound after firing may be mixed with the powder. For example, by adding a carbide of a Group 4 element (e.g., a carbide of a Group 4 element different from the Group 4 element that constitutes the second compound) to the powder, the powder of the second compound can react with the carbide of the Group 4 element during firing. This can result in, for example, a composite diboride containing multiple Group 4 elements as the second compound.

[0033] 2.4 Powder mixing and granulation Granules are obtained by kneading the above powders and the like. The mixing ratio of the above powders, auxiliary materials, and other raw materials may be appropriately determined depending on the performance of the desired ceramic sintered body. That is, they are mixed at a ratio such that the content of the second compound in the finally obtained ceramic sintered body is 50% by mass or more and 70% by mass or less. The method for kneading and granulating the above powders, auxiliary materials, and other raw materials is not particularly limited. For example, the above powders, auxiliary materials, and other raw materials are mechanically mixed with a binder, a dispersant, and a solvent to obtain a slurry, and the slurry is then dried by spray drying or the like to obtain the desired granules. In this case, the types of binder, dispersant, and solvent are not particularly limited. The size of the granules is also not particularly limited.

[0034] Here, if the amount of dispersant added is small, the raw material powders of the same type will aggregate, resulting in a high coefficient of variation CV. On the other hand, if the amount of dispersant added is large, the raw material powders will be uniformly dispersed, resulting in a low coefficient of variation CV. The type and amount of dispersant used should be determined so that the desired coefficient of variation CV and other parameters are ultimately obtained. Furthermore, if the mixing time when mechanically mixing (kneading) the raw material powders and auxiliary materials is extended, the raw material powders will be disintegrated and the aggregation will be released, resulting in a low coefficient of variation CV. If the mixing time is shortened, the raw material powders will not be disintegrated, resulting in a state where the raw material powders of the same type aggregate, resulting in a high coefficient of variation CV. The mixing means and mixing time should be determined so that the desired coefficient of variation CV and other parameters are ultimately obtained. As described above, the coefficient of variation CV can be controlled within a desired range by controlling the uneven distribution of the raw material powder by adjusting the type and amount of dispersant added, the mixing conditions, and other factors.

[0035] 2.5 Granule molding and firing The granules are molded before firing. The granules may be molded by a known molding method. The molding method may be selected appropriately depending on the shape of the desired ceramic sintered body. For example, the granules may be filled into a mold and press-molded, or may be press-molded by CIP or the like, or a combination of these methods may be used.

[0036] As described above, the coefficient of variation CV for the content of the second compound and the area ratio of the first compound, which are requirements for the ceramic sintered body of the present disclosure, can be achieved by controlling the mixing conditions of the raw material powders, etc. In other words, the requirements for the ceramic sintered body of the present disclosure are met regardless of the firing conditions. In this regard, the firing conditions need only be conditions that allow the raw material powders and auxiliary materials to be properly sintered. The temperature rise rate, maximum temperature, holding time at the maximum temperature, cooling rate, etc. during firing can be optimally selected depending on the type of powder, auxiliary materials, and other raw materials, and can be optimally selected depending on the mechanical properties of the ceramic sintered body to be finally obtained. Firing may be performed multiple times, and HIP may also be performed.

[0037] 3.Applications As described above, the ceramic sintered body of the present disclosure contains a predetermined amount of the second compound together with the first compound, and the coefficient of variation CV for the first compound is within a predetermined range, thereby achieving both high toughness and wear resistance. For example, when the ceramic sintered body of the present disclosure is used as a component exposed to sliding wear, such as a positioning guide roll for passing a steel sheet through the body or a chute liner in a blast furnace top hopper, the wear rate can be suppressed, and the repair cycle of the component can be extended.

[0038] 4. Supplementary Information The ceramic sintered body of the present disclosure may have the following configuration. In this case, high toughness and wear resistance are also achieved. That is, the ceramic sintered body according to one embodiment includes a first compound and a second compound, the first compound being silicon carbide, and the second compound being Ti 1-x Zr x B2 (0≦x≦0.05), the proportion of the second compound in the ceramic sintered body is 50 mass% or more and 70 mass% or less, and the viscosity is 5.0 mPa m 1 / 2 and a bending strength of 500 MPa or more, and when an abrasive wear test is conducted on the ceramic sintered body, the wear amount of the ceramic sintered body per unit amount of particles input is 0.5 mm 3 / kg or less. Details of each component are as described above. [Example]

[0039] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows various conditions to be adopted as long as the object is achieved without departing from the gist of the present invention.

[0040] 1. Preparation of ceramic sintered compacts for evaluation 1.1 Examples 1 to 8, Comparative Examples 1 and 2 SiC powder (α type, average particle size 0.7 μm), TiB powder (average particle size 2 μm), ZrB powder (average particle size 2 μm), and ZrC powder (average particle size 2 μm) were mixed in a tumbling ball mill for 10 hours together with a sintering aid, distilled water, a dispersant, and a binder to obtain a slurry having the composition shown in Table 1. The obtained slurry was spray dried using an air flow method to obtain granules.

[0041] Here, a polyacrylic acid-based dispersant was used, and the amount of dispersant added was 1 mass% based on the total mass of the raw material powder. The amount of distilled water added was 80 mass% based on the total mass of the raw material powder. Furthermore, 1 mass% of carbon powder (carbon black, average particle size 0.05 μm) and boron carbide powder (average particle size 0.8 μm) were added as sintering aids based on the total mass of the raw material powder.

[0042] The resulting granules were molded under uniaxial pressure of 10 MPa, then placed in a rubber container and subjected to CIP molding at 140 MPa to obtain a green body. The resulting green body was degreased in an Ar atmosphere, then held at 2150°C for 8 hours in an Ar atmosphere and sintered at atmospheric pressure to obtain an intermediate sintered body. The intermediate sintered body was then subjected to HIP treatment at 2000°C for 3 hours under Ar gas pressure of 198 MPa to obtain a ceramic sintered body for evaluation.

[0043] 1.2 Comparative Examples 3 to 6 The same raw material powders as those used in Examples 1 to 8 and Comparative Examples 1 and 2 were mixed in a tumbling ball mill for 10 hours together with a sintering aid, distilled water, a dispersant, and a binder to obtain a slurry having the composition shown in Table 1. The obtained slurry was spray dried using an air flow dryer to obtain granules.

[0044] Here, a polyacrylic acid-based dispersant was used, and the amount of dispersant added was 0.5 mass% for Comparative Examples 3 and 4, and 0.2 mass% for Comparative Examples 5 and 6, based on the total mass of the raw material powder. The amount of distilled water added and the type and amount of sintering aid added were the same as those described above. If the amount of dispersant was small, the same type of raw material powder would aggregate, resulting in greater uneven distribution of each phase in the ceramic sintered body. In other words, the smaller the amount of dispersant, the greater the coefficient of variation CV (described below).

[0045] The obtained granules were subjected to molding, degreasing, firing and HIP treatment in the same manner as in Examples 1 to 8 and Comparative Examples 1 and 2 to obtain ceramic sintered bodies for evaluation.

[0046] 1.3 Example 9, Comparative Example 7 200 g of raw material powders having the composition shown in Table 1 below were mixed with 300 ml of an organic solvent in a planetary ball mill, and then dried in a draft to evaporate the organic solvent, yielding a mixed powder. The resulting mixed powder was molded, fired, and HIP-treated in the same manner as in Examples 1 to 8 and Comparative Examples 1 and 2, yielding a ceramic sintered body for evaluation. In Example 9 and Comparative Example 7, 1% by mass of carbon powder (carbon black, average particle size 0.05 μm) and boron carbide powder (average particle size 0.8 μm) were added as sintering aids relative to the total mass of the raw material powders during mixing in the planetary ball mill.

[0047] The mixing time using the planetary ball mill was 6 hours for Example 9 and 12 hours for Comparative Example 7. When the mixing time was long, the raw material powder was crushed more, resulting in a sintered body in which each phase was uniformly dispersed. In other words, the longer the mixing time, the smaller the coefficient of variation CV (described below).

[0048] 2. Evaluation of sintered ceramics The density and relative density, bending strength, fracture toughness (KIC), and Vickers strength of the ceramic sintered body were measured. Furthermore, an abrasive test was conducted on the ceramic sintered body to measure the wear volume of the ceramic sintered body per unit input particle amount (1 kg). A 300 μm × 300 μm area of ​​the polished surface of the ceramic sintered body was divided into 400 15 μm × 15 μm sections, and the area ratio of silicon carbide in each section was determined using SEM-EDS, and the coefficient of variation CV of the area ratio of silicon carbide was measured. Details of each measurement method are as explained in the embodiments. Table 1 below shows the measurement results.

[0049] [Table 1]

[0050] The results shown in Table 1 reveal the following:

[0051] The ceramic sintered body according to Comparative Example 1 had a low content of the second compound (diboride of a Group 4 element), which resulted in insufficient toughness and wear resistance.

[0052] The ceramic sintered body according to Comparative Example 2 has a high content of the second compound (diboride of a Group 4 element). Therefore, although toughness was ensured, when the ceramic sintered body was worn, the area that peeled off became large, resulting in insufficient wear resistance.

[0053] The ceramic sintered bodies according to Comparative Examples 3 to 6 had a large coefficient of variation CV for the area ratio of the first compound (silicon carbide), and the first compound was excessively unevenly distributed. Therefore, although the residual stress caused by the uneven distribution of the two materials suppressed crack propagation and ensured toughness, when the ceramic sintered bodies were worn, the area that peeled off became large, resulting in insufficient wear resistance (see FIG. 2C).

[0054] The ceramic sintered body according to Comparative Example 7 had a small coefficient of variation CV for the area ratio of the first compound (silicon carbide), and the first compound was uniformly dispersed. As a result, the effect of suppressing crack propagation due to residual stress was not obtained, and both the toughness and the wear resistance were insufficient (see FIG. 2A).

[0055] In contrast, the ceramic sintered bodies according to Examples 1 to 9 have a content of the second compound (diboride of a Group 4 element) within a predetermined range and a coefficient of variation CV for the area ratio of the first compound (silicon carbide) within a predetermined range. Therefore, they have high toughness due to the crack propagation suppression effect caused by residual stress, and when the ceramic sintered body is worn, the area that peels off is small, resulting in excellent wear resistance (see FIG. 2B).

[0056] As shown in Examples 1 to 9, the same effect is achieved whether the second compound is TiB2 or ZrB2. It is believed that the same effect is also achieved with diboride of Hf (hafnium), which belongs to the same group as Ti and Zr in the periodic table. In other words, it can be said that the desired effect is achieved when the second compound is a diboride of a Group 4 element.

[0057] In addition, ZrC as another component in Table 1 is Ti as a second compound in the ceramic sintered body. 1-x Zr x That is, from the results shown in Examples 1 to 9, it is considered that Ti 1-x Zr x It can be said that excellent effects are achieved when B2 (0≦x≦0.05) is used.

[0058] As described above, a ceramic sintered body containing the first compound and the second compound and satisfying the following requirements A to D can be said to have both high toughness and wear resistance. Requirement A: The first compound is silicon carbide. Requirement B: The second compound is a diboride of a Group 4 element. Requirement C: The proportion of the second compound in the ceramic sintered body is 50% by mass or more and 70% by mass or less. Requirement D: When a 300 μm × 300 μm area of ​​the polished surface of the ceramic sintered body is divided into 400 15 μm × 15 μm sections, and the area ratio of the first compound is determined for each of the sections, the coefficient of variation CV of the area ratio of the first compound is greater than 0.14 and less than 0.23.

[0059] Furthermore, from the above results, it is clear that the first compound is silicon carbide and the second compound is Ti 1-x Zr x B2 (0≦x≦0.05), and the ratio of the second compound in the ceramic sintered body is 50 mass% or more and 70 mass% or less, the CV value is set to 0.15 or more and 0.20 or less, and the CV value is 5.0 mPa m 1 / 2 The sintered body has a fracture toughness value of 500 MPa or more and a bending strength of 500 MPa or more. When an abrasive wear test is conducted, the wear amount of the ceramic sintered body per unit amount of particles input is 0.5 mm 3 / kg or less. [Explanation of symbols]

[0060] 1 test piece 2 Projection nozzle 3 foil 4. Wear particles 10. Sintered ceramics 10a 1st phase (silicon carbide) 10b Phase 2 (Diborides of Group 4 Elements)

Claims

1. A ceramic sintered body containing a first compound and a second compound, the first compound is silicon carbide; the second compound is a diboride of a Group 4 element; a ratio of the second compound in the ceramic sintered body is 50% by mass or more and 70% by mass or less, When a 300 μm × 300 μm region of the polished surface of the ceramic sintered body is divided into 400 15 μm × 15 μm sections and an area ratio of the first compound is specified for each of the sections, the coefficient of variation CV of the area ratio of the first compound is greater than 0.14 and less than 0.

23. Sintered ceramics.

2. The second compound is Ti １－ｘ Zr ｘ B ２ (0≦x≦0.05), The ceramic sintered body according to claim 1.

3. The coefficient of variation CV is 0.15 or more and 0.20 or less. The ceramic sintered body according to claim 1.

4. 5.0 mPa·m １／２ or more, Having a bending strength of 480 MPa or more, The ceramic sintered body according to any one of claims 1 to 3.

5. 5.5 mPa·m １／２ or more, Having a bending strength of 500 MPa or more, The ceramic sintered body according to any one of claims 1 to 3.

6. When an abrasive wear test was performed on the ceramic sintered body, the amount of wear of the ceramic sintered body per unit amount of particles was 0.5 mm ３ / kg or less, The ceramic sintered body according to any one of claims 1 to 3.

7. A ceramic sintered body containing a first compound and a second compound, the first compound is silicon carbide; The second compound is Ti １－ｘ Zr ｘ B ２ (0≦x≦0.05), a ratio of the second compound in the ceramic sintered body is 50% by mass or more and 70% by mass or less, 5.0 mPa·m １／２ or more, It has a bending strength of 500 MPa or more, When an abrasive wear test was performed on the ceramic sintered body, the amount of wear of the ceramic sintered body per unit amount of particles was 0.5 mm ３ / kg or less, Sintered ceramics.

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