Manufacturing method of ceramic sintered body and ceramic sintered body

Abstract

In the present invention, a dense ceramic sintered body is appropriately produced. A method for producing a ceramic sintered body according to the present invention comprises: a step for heat-treating, under a first condition, a ceramic molded body that is a molded body of ceramic powder; a step for heat-treating, under a second condition in which pressure is higher than the pressure of the first condition, the ceramic molded body that has been heat-treated under the first condition; and a step for producing a ceramic sintered body by heat-treating, under a third condition in which pressure is higher than the pressure of the second condition, the ceramic molded body that has been heat-treated under the second condition.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a ceramic sintered body and a ceramic sintered body. [Background technology]

[0002] When manufacturing sintered ceramics, HIP (Hot Isostatic Pressing) processing is sometimes used. With HIP processing, a compact is heat-treated under a high pressure environment, resulting in a dense sintered body with few defects.

[0003] In order to perform HIP treatment appropriately, it is necessary to increase the density of the green body to a certain extent in a previous process. Patent Documents 1 to 3 describe that the density of the green body is increased by a CIP (Cold Isostatic Pressing) method in which isostatic pressure is applied to the green body in water, and then the HIP treatment is performed.

[0004] [Patent Document 1] Patent No. 4642956 [Patent Document 2] Patent No. 6075811 [Patent Document 3] Patent No. 6400478 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is room for improvement in the appropriate production of dense ceramic sintered bodies.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a ceramic sintered body that can appropriately manufacture a dense ceramic sintered body, and the ceramic sintered body. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the objectives, the method for manufacturing a ceramic sintered body according to the present disclosure includes the steps of heat-treating a ceramic molded body, which is a molded body of ceramic powder, under first conditions, heat-treating the ceramic molded body heat-treated under the first conditions under second conditions that are higher pressure than the first conditions, and heat-treating the ceramic molded body heat-treated under the second conditions under third conditions that are higher pressure than the second conditions, thereby manufacturing a ceramic sintered body.

[0008] In order to solve the above-mentioned problems and achieve the object, the ceramic sintered body according to the present disclosure is a spherical ceramic sintered body of silicon nitride, and when the radius of the ceramic sintered body is r, the fracture toughness value (K IC ) is 6.5 MPa m 1 / 2 or more, and the difference ΔKA between the maximum and minimum fracture toughness values ​​in the region of 1 / 10r from the surface of the ceramic sintered body is 2.0 MPa m 1 / 2 or less, and the difference ΔKB between the maximum and minimum fracture toughness values ​​in the region of 1 / 10r to 2 / 10r of the ceramic sintered body is 1.5 MPa m 1 / 2 The following is the result. [Effects of the Invention]

[0009] According to the present invention, a dense ceramic sintered body can be appropriately produced. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a flowchart illustrating the method for producing a ceramic sintered body according to this embodiment. [Figure 2] FIG. 2 is a flowchart illustrating the details of the ceramic compact production process. [Figure 3] FIG. 3 is a diagram showing an example of the configuration of a heat treatment furnace in this embodiment. [Figure 4] FIG. 4 is a graph showing the fracture toughness values ​​in Example 2. [Figure 5]FIG. 5 is a graph showing the fracture toughness values ​​in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments, and when there are multiple embodiments, the present invention also includes configurations that are made by combining the respective embodiments. Furthermore, numerical values ​​include the range of rounding.

[0012] (ceramic sintered body) In the manufacturing method according to this embodiment, a ceramic powder is molded to produce a ceramic molded body, and the ceramic molded body is fired to produce a ceramic sintered body. In this embodiment, the ceramic sintered body is a sintered body of silicon nitride (Si3N4), and the ceramic powder is silicon nitride powder. The ceramic sintered body may contain silicon nitride as a main component, materials other than silicon nitride, and may contain unavoidable impurities. For example, the ceramic sintered body may have a silicon nitride content of 80% or more, 83% or more, or 85% or more by weight. The ceramic sintered body manufactured by this manufacturing method is used, for example, as balls for ball bearings (e.g., bearing balls), but its use is not limited thereto and may be any application.

[0013] As described above, the manufacturing method according to this embodiment is for manufacturing a silicon nitride sintered body, but it may be used to manufacture a sintered body of any ceramic, not limited to silicon nitride. That is, the ceramic sintered body may be a sintered body made of any ceramic, not limited to silicon nitride, and the ceramic powder may be a powder made of any ceramic, not limited to silicon nitride.

[0014] (Ceramics Molding Production) Fig. 1 is a flowchart illustrating a method for producing a ceramic sintered body according to this embodiment, and Fig. 2 is a flowchart illustrating the details of the ceramic molded body production process. As shown in Fig. 1, this production method first produces a ceramic molded body by molding ceramic powder (step S10). In this embodiment, the ceramic molded body is produced by gel casting.

[0015] FIG. 2 shows details of an example of a process for producing a ceramic green body by gel casting in step S10 of FIG. 1. As shown in FIG. 2, when producing a ceramic green body by gel casting, a ceramic slurry is produced (step S10b). The ceramic slurry is a slurry in which ceramic powder is dispersed in a solvent. The method for producing the ceramic slurry is not particularly limited, and it is sufficient to add a dispersant, sintering aid, resin, and resin hardener to a slurry containing ceramic powder and a solvent, depending on the type of solvent, etc. For example, the ceramic slurry is produced by first mixing ceramic powder, a solvent, a dispersant, and a sintering aid to obtain a slurry (hereinafter also referred to as raw ceramic slurry), and then adding a resin and a resin hardener to the raw ceramic slurry. Ceramic powder is an essential component when performing gel casting, and the ceramic powder may be, for example, silicon nitride, aluminum nitride, titanium nitride, or silicon carbide powder. The solvent is an essential component when performing the gel casting method, and is a liquid used to uniformly mix and mold the ceramic powder, sintering aid, resin, and resin curing agent. Examples of the solvent include water, organic solvents, and alcohols, as long as they do not remain in the ceramic sintered body after sintering. Examples of alcohols that can be used include methyl alcohol and ethyl alcohol. Examples of organic solvents that can be used include benzene, toluene, and xylene. These solvents can be used alone or in combination. The dispersant is an optional additive that aids in dispersing the ceramic powder in the solvent. Examples of dispersants include pH adjusters such as tetramethylammonium hydroxide, polymeric dispersants such as polycarboxylic acid polymers, inorganic dispersants such as phosphates such as sodium hexametaphosphate, and anionic, cationic, and nonionic organic surfactant dispersants. Sintering aids are optional additives that aid in the sintering of ceramic powder. For example, if the ceramic powder is silicon nitride, rare earth oxide powders such as magnesium oxide (MgO), aluminum oxide (Al2O3), spinel (magnesia-alumina spinel; MgO·Al2O3), yttrium oxide (Y2O3), and ytterbium oxide (Yb2O3) can be used as sintering aids. Before producing a slurry (raw ceramic slurry), ceramic powder is prepared in advance and mixed while being pulverized to make the particle size of the ceramic powder nearly uniform. For pulverization and mixing, a ball mill, for example, is used, but any pulverization and mixing method may be used.

[0016] When producing a ceramic slurry, the amount of ceramic powder added to the solvent is preferably 35% by volume to 65% by volume, more preferably 40% by volume to 60% by volume, and even more preferably 45% by volume to 55% by volume. By using such a blending ratio, a ceramic molded body can be produced appropriately. Furthermore, when producing a ceramic slurry, the amount of dispersant added to the ceramic powder is preferably 0.3% by weight to 3% by weight, more preferably 0.4% by weight to 2% by weight, and even more preferably 0.5% by weight to 1% by weight. By using such a blending ratio, a ceramic molded body can be produced appropriately. Furthermore, when producing a ceramic slurry, the amount of sintering aid added to the ceramic powder is preferably 1% by weight to 15% by weight, more preferably 2% by weight to 12% by weight, and even more preferably 3% by weight to 9% by weight. By using such a blending ratio, a ceramic sintered body can be produced appropriately.

[0017] Next, a resin and a resin curing agent (polymerization initiator) are added to the mixed raw ceramic slurry to generate a ceramic slurry (hereinafter also referred to as a cast ceramic slurry) (step S10b). More specifically, a resin and a resin curing agent (polymerization initiator) are added to the raw ceramic slurry. The resin is a resin that polymerizes and hardens when the resin curing agent is added. In this embodiment, it is preferably a resin that dissolves in the solvent of the ceramic slurry (here, a water-soluble resin). The resin here is, for example, a water-soluble epoxy resin, but is not limited to epoxy resin and may be any resin that polymerizes and hardens when the resin curing agent is added. The resin curing agent is an additive that polymerizes and hardens the resin when added to the resin. The resin curing agent here is, for example, a mixture of triethylenetetramine and dimethylaminomethyl, but is not limited thereto and may be any additive that polymerizes and hardens the resin when added to the resin.

[0018] In this embodiment, a resin-added ceramic slurry (hereinafter also referred to as a first ceramic slurry) is prepared by adding a resin to a raw ceramic slurry, and a curing agent-added ceramic slurry (hereinafter also referred to as a second ceramic slurry) is prepared by adding a resin curing agent to the raw ceramic slurry.The first ceramic slurry and the second ceramic slurry are then mixed to prepare a mixed casting ceramic slurry.

[0019] In this embodiment, the amount of resin added to the ceramic powder in the ceramic slurry is preferably 1% by weight or more and 10% by weight or less, more preferably 1.5% by weight or more and 8% by weight or less, and even more preferably 2% by weight or more and 5% by weight or less. By using such a blending ratio, a ceramic molded body can be appropriately produced. Furthermore, the amount of resin curing agent added to the resin is preferably an amount that is stoichiometrically appropriate for the added resin. By using such a blending ratio, a ceramic molded body can be appropriately produced.

[0020] Next, the cast ceramic slurry is poured into a mold (step S10c). In this embodiment, the resin and the resin curing agent are added separately to the raw ceramic slurry, and then they are mixed together. In other words, the first ceramic slurry and the second ceramic slurry are produced separately and then mixed together. However, this is not limiting. Both the resin and the resin curing agent may be added to the raw ceramic slurry, and the cast ceramic slurry to which both have been added may be poured into a mold.

[0021] In this embodiment, the ceramic slurry is supplied to the mold and held at a predetermined holding temperature for a predetermined holding time. The holding temperature here is preferably 25°C or higher and 100°C or lower, more preferably 30°C or higher and 80°C or lower, and even more preferably 40°C or higher and 60°C or lower. The holding time here is preferably 1 hour or higher and 48 hours or lower, more preferably 2 hours or higher and 24 hours or lower, and even more preferably 3 hours or higher and 12 hours or lower. By setting such a holding temperature and holding time, the resin can be properly hardened. Note that in this embodiment, the mold into which the ceramic slurry has been supplied is not subjected to a press process. In other words, no pressure higher than atmospheric pressure is applied to the mold into which the ceramic slurry has been supplied.

[0022] When the ceramic slurry is supplied to the mold, a pressure higher than atmospheric pressure may be applied to the ceramic slurry.

[0023] After the holding time has elapsed, the hardened ceramic slurry is demolded (removed) from the mold, and the hardened body is appropriately dried and degreased to obtain a ceramic molded body (step S10d). Specifically, the demolded hardened body is dried to obtain a dried molded body, and the dried molded body is degreased to obtain a ceramic molded body. The drying conditions here are arbitrary, but for example, a humidification drying process and a hot air drying process are performed. In the humidification drying process, the hardened body is held in an environment with a humidity of 30% to 98% and a temperature of 25°C to 50°C for 24 to 120 hours. Then, after the humidification drying process is completed, a hot air drying process is performed in an environment with a temperature of 40°C to 100°C, in which the hardened body is exposed to air and held for 3 to 48 hours to obtain a dried molded body. The degreasing method is also optional, but for example, the dried molded body is degreased by holding it in an environment at a temperature of 550° C. to 750° C. for 2 to 12 hours to obtain a ceramic molded body. Here, drying is the process of removing the solvent from the hardened body, and degreasing is the process of removing the resin from the hardened body (dried molded body). Insufficient removal of these processes can cause cracks during the firing process, so these are essential processes in the gel casting method.

[0024] The ceramic molded body formed by this manufacturing method preferably has a relative density of 40% or more, more preferably 45% or more, and even more preferably 50% or more. A higher relative density is preferable, but it may be 65% or less, 60% or less, or 55% or less. Note that the relative density here refers to the value obtained by dividing the molded body density by the material density. The molded body density is the value obtained by dividing the volume calculated from the dimensions of the ceramic molded body by the weight of the ceramic molded body. The material density is calculated from the composition ratio of the ceramic powder and sintering aid and the theoretical density of each material. The density of a material is, for example, that of a ceramic powder (molar mass ag / mol, theoretical density Ag / cm 3 ) and sintering aid (molar mass bg / mol, theoretical density Bg / cm 3 ) are mixed in a composition ratio of X mol % and Y mol %, respectively, the calculation can be performed using the following formula (1).

[0025] (a×X+b×Y) / ((a×X / A)+(b×Y / B))...(1)

[0026] In this embodiment, the ceramic molded body is prepared using the gel casting method as described above. However, the method for producing the ceramic molded body is not limited to the gel casting method and any method may be used. For example, a powder pressing method may be used in which ceramic powder filled in a mold is pressed to form the ceramic molded body.

[0027] (Heat treatment) In this manufacturing method, a ceramic sintered body is manufactured by subjecting a ceramic green body to at least three heat treatments: a heat treatment under first conditions, a heat treatment under second conditions, and a heat treatment under third conditions. The term "heat treatment" refers to a process in which the object is heated to a temperature above the temperature at which at least a portion of the ceramic powder begins to sinter, and does not include room-temperature treatments such as CIP. In the following description, three heat treatments are performed: a heat treatment under first conditions, a heat treatment under second conditions, and a heat treatment under third conditions. However, this is not limited to this, and four or more heat treatments may be performed. Furthermore, the ceramic green body (dried green body) may be subjected to CIP before the heat treatment. CIP allows isotropic pressure to be applied to the ceramic green body, thereby increasing the relative density of the green body.

[0028] (Heat treatment under the first condition) First, the heat treatment under the first condition will be described. As shown in FIG. 1, once the ceramic molded body is produced, the ceramic molded body is subjected to a heat treatment under the first condition (step S12). Here, under the first condition, the temperature at which the ceramic molded body is heated is defined as the first heating temperature, the pressure applied to the ceramic molded body is defined as the first pressure, and the heating time is defined as the first heating time. The first condition, i.e., the first heating temperature, the first pressure, and the first heating time, may be appropriately set depending on the properties of the ceramic powder, the amount and type of sintering aid added, the relative density, shape, and dimensions of the ceramic molded body, etc. For example, for silicon nitride, the first heating temperature is preferably 1600°C or higher and 1800°C or lower, more preferably 1620°C or higher and 1780°C or lower, and even more preferably 1650°C or higher and 1750°C or lower. By setting the heating temperature within this range, the relative density of the sintered body can be adjusted to an appropriate range. Furthermore, the first pressure is preferably 0.01 MPa or more and 5 MPa or less, more preferably 0.05 MPa or more and 3 MPa or less, and even more preferably 0.1 MPa or more and 1 MPa or less. By setting the first pressure within this range, the relative density of the sintered body can be set within an appropriate range. Furthermore, from the viewpoints of mass productivity and ease of operation, it is most preferable that the heat treatment under the first conditions be performed at normal pressure (atmospheric pressure), i.e., 0.1 MPa. Furthermore, the first heating time is preferably 1 hour or more and 20 hours or less, more preferably 2 hours or more and 18 hours or less, and even more preferably 5 hours or more and 15 hours or less. By setting the first heating time within this range, the relative density of the sintered body can be set within an appropriate range.

[0029] In this embodiment, the heat treatment under the first condition is performed in a nitrogen atmosphere. By performing the heat treatment under the first condition in a nitrogen atmosphere, the ceramic powder, which is silicon nitride, can be appropriately sintered.

[0030] The ceramic compact is subjected to the first sintering, i.e., primary sintering, by undergoing the heat treatment under the first condition in this way. By first performing the low-pressure heat treatment under the first condition, porosity in the sintered compact can be reduced, and the subsequent heat treatments under the second and third conditions can be carried out effectively.

[0031] Here, if the ceramic molded body heat-treated under the first condition is referred to as the first sintered body, the relative density of the first sintered body is preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more. The relative density here is the value obtained by dividing the density of the first sintered body measured according to JIS R 1634 by the material density calculated from the composition ratio of the ceramic powder and sintering aid and the theoretical density of each material. By keeping the relative density within this range, the subsequent heat treatments under the second and third conditions can be carried out effectively.

[0032] (Heat treatment under the second condition) Next, the heat treatment under the second condition will be described. As shown in FIG. 1 , after the heat treatment under the first condition, the ceramic molded body heat-treated under the first condition, i.e., the first sintered body, is subjected to a heat treatment under the second condition (step S14). The heat treatment under the second condition is performed under a higher pressure environment than the heat treatment under the first condition, and can also be called a GPS (Gas Pressure Sintering) treatment. Here, under the second condition, the temperature to which the first sintered body is heated is called the second heating temperature, the pressure applied to the first sintered body is called the second pressure, and the heating time is called the second heating time. The second heating temperature is preferably higher than the first heating temperature under the first condition but may be equal to or lower than the first heating temperature. The second heating temperature is preferably 1650°C to 1900°C, more preferably 1680°C to 1850°C, and even more preferably 1700°C to 1800°C. By setting the second heating temperature within this range, the subsequent heat treatment under the third condition can be performed effectively. The second pressure is higher than the first pressure used in the heat treatment under the first condition. The difference between the second pressure and the first pressure is preferably 0.3 MPa to 20 MPa, more preferably 1 MPa to 18 MPa, and even more preferably 2 MPa to 15 MPa. The second pressure is preferably 0.5 MPa to 20 MPa, more preferably 3 MPa to 18 MPa, and even more preferably 5 MPa to 15 MPa. By setting the second pressure within this range, the subsequent heat treatment under the third condition can be performed effectively. More specifically, by setting the second pressure to 0.5 MPa or higher, the effect of the pressurized heat treatment can be properly maintained, and by setting it to 20 MPa or lower, the penetration of high-pressure gas into the pores of the first sintered body can be suppressed, resulting in an appropriate relative density after sintering. The second heating time is preferably shorter than the first heating time. The second heating time is preferably 0.1 hours to 10 hours, more preferably 0.15 hours to 8 hours, and even more preferably 0.2 hours to 6 hours. By setting the second heating time within this range, the subsequent heat treatment under the third condition can be carried out effectively.

[0033] In this embodiment, the heat treatment under the second conditions is performed in a nitrogen atmosphere. By performing the heat treatment under the second conditions in a nitrogen atmosphere, the ceramic powder, which is silicon nitride, can be appropriately sintered.

[0034] The heat treatment under the second conditions may be carried out after the heat treatment under the first conditions is completed, the first sintered body is removed and cooled, or may be carried out immediately after the heat treatment under the first conditions without cooling the first sintered body.

[0035] The first sintered body is subjected to a second sintering, i.e., secondary sintering, by being subjected to a heat treatment under the second conditions in this way. It is thought that by performing a heat treatment under the second conditions, which is higher in pressure than the first conditions, the fine open pores on the surface of the sintered body are reduced and the surface is made denser. This prevents the high-pressure gas from penetrating into the sintered body in the subsequent heat treatment under the third conditions, making it possible to effectively perform the heat treatment under the third conditions.

[0036] Here, if the ceramic molded body heat-treated under the second conditions, i.e., the first sintered body heat-treated under the second conditions, is referred to as the second sintered body, the relative density of the second sintered body is preferably 95% or more, more preferably 97% or more. The higher the relative density of the second sintered body, the better, but it may be 99% or less. By keeping the relative density within this range, the subsequent heat treatment under the third conditions can be carried out effectively.

[0037] (Heat treatment under the third condition) Next, the heat treatment under the third condition will be described. As shown in FIG. 1 , after the heat treatment under the second condition, the ceramic molded body heat-treated under the second condition, i.e., the second sintered body, is subjected to a heat treatment under the third condition (step S16) to produce a ceramic sintered body. The heat treatment under the third condition is performed under a higher pressure environment than the heat treatment under the second condition, and can also be considered a HIP treatment. Here, under the third condition, the temperature to which the second sintered body is heated is referred to as a third heating temperature, the pressure applied to the second sintered body is referred to as a third pressure, and the heating time is referred to as a third heating time. The third heating temperature is preferably higher than the first heating temperature under the first condition, but may be equal to or lower than the first heating temperature. Furthermore, the third heating temperature may be higher than the second heating temperature under the second condition, or may be equal to or lower than the second heating temperature. The third heating temperature is preferably 1650°C to 1900°C, more preferably 1680°C to 1850°C, and even more preferably 1700°C to 1800°C. By setting the third heating temperature within this range, the relative density of the ceramic sintered body can be adjusted to an appropriate value. Furthermore, the third pressure is higher than the second pressure in the heat treatment under the second condition. The difference between the third pressure and the second pressure is preferably 30 MPa to 180 MPa, more preferably 40 MPa to 160 MPa, and even more preferably 50 MPa to 130 MPa. Furthermore, the third pressure is preferably 50 MPa to 200 MPa, more preferably 60 MPa to 180 MPa, and even more preferably 70 MPa to 150 MPa. By setting the third pressure within this range, the relative density of the ceramic sintered body can be adjusted to an appropriate value. The third heating time is preferably 0.1 hours to 10 hours, more preferably 0.15 hours to 8 hours, and even more preferably 0.2 hours to 6 hours. By setting the third heating time within this range, the relative density of the ceramic sintered body can be adjusted to an appropriate value.

[0038] In this embodiment, the heat treatment under the third condition is performed in a nitrogen atmosphere. By performing the heat treatment under the third condition in a nitrogen atmosphere, the ceramic powder, which is silicon nitride, can be appropriately sintered.

[0039] The heat treatment under the third conditions may be carried out after the heat treatment under the second conditions is completed, the second sintered body is removed and cooled, or it may be carried out immediately after the heat treatment under the second conditions without cooling the second sintered body.

[0040] The second sintered body is thus subjected to a third sintering, i.e., tertiary sintering, by being subjected to heat treatment under the third conditions. By performing HIP treatment under the third conditions after firing under the first and second conditions, i.e., by performing firing in stages while increasing the pressure, it is possible to properly perform HIP treatment and produce a dense ceramic sintered body without performing, for example, CIP treatment.

[0041] (Characteristics of sintered ceramics) The ceramic sintered body after the heat treatment under the third condition preferably has a relative density of 99% or more. By keeping the relative density in this range, the performance of the ceramic sintered body can be ensured.

[0042] Furthermore, the ceramic sintered body preferably has a three-point bending strength of 900 MPa or more, more preferably 910 MPa or more, and even more preferably 915 MPa or more, at a span of 30 mm, measured by the method specified in JIS R 1669. By having the three-point bending strength within this range, the strength of the ceramic sintered body can be maintained appropriately. Furthermore, the ceramic sintered body preferably has a fracture toughness value of 5.0 MPa m, measured by the method specified in JIS R 1669. 1 / 2 Preferably, it is 5.5 MPa m or more. 1 / 2 More preferably, it is 6.0 MPa m 1 / 2 It is more preferable that the fracture toughness value is in this range or more. When the fracture toughness value is in this range, the strength of the ceramic sintered body can be maintained appropriately. In addition, the ceramic sintered body has a fracture toughness of 1 mm2 The number of pores of 5 μm or more observed using an optical microscope for an area of ​​1 mm or more 2 The number of pores per area is preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. The maximum diameter of the pores in the ceramic sintered body is preferably 25 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. By keeping the number and maximum diameter of the pores within these ranges, the performance of the ceramic sintered body can be ensured.

[0043] (diameter) The ceramic sintered body is preferably a silicon nitride sintered body and is spherical. Here, "spherical" does not necessarily mean a perfect sphere. For example, the sphericity may be within 3%, more preferably within 2.5%, and even more preferably within 2% of the diameter. For example, for a sintered body with a diameter of 50 mm, the sphericity is preferably 1.5 mm or less, more preferably 1.25 mm or less, and even more preferably 1.0 mm or less. For example, for a sintered body with a diameter of 10 mm, the sphericity is preferably 0.3 mm or less, more preferably 0.25 mm or less, and even more preferably 0.2 mm or less. The diameter of the ceramic sintered body is preferably 0.5 mm to 80 mm, more preferably 30 mm to 55 mm, and even more preferably 49 mm to 51 mm. Having a diameter within this range makes it suitable for use as, for example, a bearing ball. Herein, the "diameter" may refer to the average diameter (the arithmetic mean of the maximum and minimum diameters). Hereinafter, the radius of the ceramic sintered body will be referred to as r. The radius r may be set to half the diameter of the ceramic sintered body.

[0044] (Fracture toughness value) The fracture toughness value (K IC ) is 6.5 MPa m 1 / 2 It is preferable that this is equal to or greater than this. The difference ΔKA between the maximum and minimum fracture toughness values ​​in the range from the surface to a depth of r / 10 is 2.0 MPa m 1 / 2It is preferable that the temperature is 1.5 MPa m or less. 1 / 2 More preferably, it is 1.2 MPa m or less. 1 / 2 It is even more preferable that: The difference ΔKB between the maximum and minimum fracture toughness values ​​of the ceramic sintered body in the range from a depth of r / 10 from the surface to a depth of 2r / 10 from the surface is 1.5 MPa m 1 / 2 It is preferable that the temperature is 1.0 MPa m or less. 1 / 2 More preferably, it is 0.7 MPa m or less. 1 / 2 It is even more preferable that: By having the fracture toughness value in the range from the surface to a depth of r / 10 within this range, particle shedding due to microscopic fracture is suppressed, and wear of the ceramic sintered body can be suppressed. Furthermore, by having ΔKA and ΔKB within this range, the variation in fracture toughness value is small, the ceramic sintered body becomes dense, and non-uniformity of particles is suppressed, so that wear of the ceramic sintered body can be more suitably suppressed. In other words, the ceramic sintered body according to this embodiment has a high fracture toughness value, especially near the surface, and there is little variation in the fracture toughness value. Therefore, the ceramic sintered body has improved wear resistance, and it is possible to provide a ceramic sintered body with, for example, excellent sliding properties. The fracture toughness values ​​in the range from the surface to a depth of r / 10 and the fracture toughness values ​​in the range from a depth of r / 10 below the surface to a depth of 2r / 10 below the surface are obtained by cutting a ceramic sintered body into a disk along the diameter, polishing one of the cut surfaces, and measuring the fracture toughness at each position along the radius of the sphere. For example, the fracture toughness value in the range from the surface to a depth of r / 10 refers to the fracture toughness value in the region of the cut surface from the periphery to a position r / 10 away from the periphery toward the center. The fracture toughness value can be measured using a Vickers hardness testing system ARS9000 manufactured by FutureTech Corporation under conditions of a load of 5 kg and an indentation time of 15 seconds. The fracture toughness measurement method may be the same as described below. The range from the surface of the ceramic sintered body to a depth of r / 10 can also be rephrased as the range from the surface to 2.5 mm, for example. Furthermore, the range from a position r / 10 deeper than the surface to a position 2r / 10 deeper than the surface of the ceramic sintered body can also be rephrased as the range from a position 2.5 mm deeper than the surface to a position 5.0 mm deeper than the surface.

[0045] The fracture toughness value of the ceramic sintered body in the range from the surface to a depth of 2r / 10 is 6.5 MPa m 1 / 2 It is preferable that this is equal to or greater than this. By ensuring that the fracture toughness value in the range from the surface to a depth of 2r / 10 falls within this range, particle shedding due to microscopic fracture is suppressed, and wear of the ceramic sintered body can be more suitably suppressed. The range from the surface to a depth of 2r / 10 of the ceramic sintered body can also be rephrased as the range from the surface to a depth of 5.0 mm, for example.

[0046] The average fracture toughness value of the ceramic sintered body in the range from the surface to a depth of 4r / 10 is 7.0 MPa m 1 / 2 It is preferable that this is equal to or greater than this. By having the average fracture toughness value within this range from the surface to a depth of 4r / 10, particle shedding due to microscopic fracture is suppressed, and wear of the ceramic sintered body can be more effectively suppressed. The range from the surface to a depth of 4r / 10 of the ceramic sintered body can also be rephrased as the range from the surface to 10.0 mm, for example.

[0047] The ceramic sintered body preferably has a standard deviation of fracture toughness values ​​in the range from the surface to a depth of r / 10 of 0.70 or less, more preferably 0.60 or less, and even more preferably 0.40 or less. When the standard deviation of the fracture toughness values ​​in the range from the surface to a depth of r / 10 falls within this range, the variation in the fracture toughness values ​​is small, the ceramic sintered body becomes dense, and the unevenness of the particles is suppressed, thereby more effectively suppressing wear of the ceramic sintered body.

[0048] The ceramic sintered body preferably has a standard deviation of fracture toughness values ​​in the range from the surface to a depth of 4r / 10 of 0.55 or less, more preferably 0.50 or less, and even more preferably 0.48 or less. By setting the standard deviation of the fracture toughness values ​​within this range from the surface to a depth of 4r / 10, the variation in the fracture toughness values ​​is small, the ceramic sintered body becomes dense, and particle non-uniformity is suppressed, thereby more effectively suppressing wear of the ceramic sintered body.

[0049] (hardness) The ceramic sintered body preferably has a Vickers hardness of 10 HV or more in the range from the surface to a depth of 2r / 10, more preferably 12 HV or more, and even more preferably 14 HV or more. By ensuring that the Vickers hardness in the range from the surface to a depth of 2r / 10 falls within this range, particle shedding due to microscopic fracture is suppressed, and wear of the ceramic sintered body can be more suitably suppressed. The Vickers hardness in the range from the surface to a depth of 2r / 10 can be obtained by cutting a ceramic sintered body into a disk along the diameter, polishing one of the cut surfaces, and measuring the Vickers hardness at each position along the radius of the sphere. For example, the fracture toughness value in the range from the surface to a depth of 2r / 10 refers to the Vickers hardness in the region of the cut surface from the periphery to a position 2r / 10 away from the periphery toward the center. Vickers hardness can be measured using a Vickers Hardness Testing System ARS9000 manufactured by FutureTech Corporation under conditions of a load of 5 kg and an indentation time of 15 seconds.

[0050] The ceramic sintered body according to this embodiment is manufactured by the manufacturing method described in this embodiment, but any manufacturing method may be used as long as it has the properties described above.

[0051] FIG. 3 is a diagram showing an example of the configuration of a heat treatment furnace in this embodiment. In this embodiment, the heat treatment furnace 10 shown in FIG. 3 may be used to perform heat treatment under the third condition, i.e., HIP treatment. The heat treatment furnace 10 is a furnace capable of HIP treatment. As shown in FIG. 3, the heat treatment furnace 10 includes a container 12, a base 14, a heating unit 16, and an insulating unit 18. The base 14 is a base on which a second sintered body A, which is an object to be heat treated, is placed. The heating unit 16 is a heater disposed around the space on the base 14 in which the second sintered body A is placed, and heats the second sintered body A on the base 14. The insulating unit 18 is a member that covers the heating unit 16 and the space on the base 14 in which the second sintered body A is placed. The insulating unit 18 is made of a highly insulating material and insulates the internal space from the external space. The container 12 houses the base 14, the heating unit 16, and the insulating unit 18. The container 12 is formed with a gas inlet 12a. When performing heat treatment under the third condition, the second sintered body A is placed on the base 14, and nitrogen is supplied from the gas inlet 12a to pressurize the inside of the container 12 to a third pressure in a nitrogen atmosphere. An isotropic pressure at the third pressure is applied to the second sintered body A. Then, the second sintered body A is heated to a third heating temperature by the heating unit 16 and held for a third heating time, whereby the second sintered body A is subjected to heat treatment, i.e., HIP treatment, to produce a ceramic sintered body.

[0052] The heat treatment furnace 10 may be used for the heat treatment under the first condition and may also be used for the heat treatment under the second condition. By using the same heat treatment furnace 10, the heat treatment under the first condition, the heat treatment under the second condition, and the heat treatment under the third condition can be performed consecutively. However, the configuration of the heat treatment furnace 10 is only an example, and in this manufacturing method, the heat treatment under the first condition, the heat treatment under the second condition, and the heat treatment under the third condition may be performed using any equipment.

[0053] As described above, the method for manufacturing a ceramic sintered body according to this embodiment includes the steps of heat-treating a ceramic molded body, which is a molded body of ceramic powder, under first conditions, heat-treating the ceramic molded body (first sintered body) heat-treated under the first conditions under second conditions that are higher pressure than the first conditions, and heat-treating the ceramic molded body (second sintered body) heat-treated under the second conditions under third conditions that are higher pressure than the second conditions, thereby manufacturing a ceramic sintered body.

[0054] In this manufacturing method, the heat treatment is performed stepwise while increasing the pressure under the first, second, and third conditions, so that a dense ceramic sintered body can be properly manufactured, with sufficient pores removed and high strength. In particular, when performing heat treatment at high pressure, if the pores are not removed to a certain extent, the high-pressure gas may penetrate the pores, preventing proper sintering. In contrast, in this manufacturing method, the heat treatment is performed by increasing the pressure stepwise, so that the bubbles can be properly removed and the high-pressure heat treatment can be properly performed.

[0055] Furthermore, this manufacturing method eliminates the need for CIP treatment before high-pressure heat treatment. CIP treatment requires sealing the molded body with a rubber mold or other device to prevent water penetration, which can increase the workload and make it difficult to process complex shapes. On the other hand, if CIP treatment is not performed, HIP treatment cannot be performed properly, which can result in the failure to produce a dense sintered body. In contrast, this manufacturing method performs heat treatment stepwise under the first, second, and third conditions while increasing the pressure. This allows high-pressure HIP treatment to be performed properly without CIP treatment, thereby reducing the workload and producing dense ceramic sintered bodies with complex shapes.

[0056] In this manufacturing method, it is preferable that the difference between the second pressure applied to the ceramic compact in the step of heat treating under the second conditions and the first pressure applied to the ceramic compact in the step of heat treating under the first conditions be 0.3 MPa or more and 20 MPa or less, and the difference between the third pressure applied to the ceramic compact in the step of heat treating under the third conditions and the second pressure be 30 MPa or more and 180 MPa or less. By keeping the difference between the respective pressures within this range, it is possible to appropriately carry out stepwise heat treatment while increasing the pressure, and appropriately manufacture a dense ceramic sintered body.

[0057] In addition, in this manufacturing method, it is preferable that the first pressure applied to the ceramic compact in the step of heat treating under the first conditions is 0.01 MPa or more and 5 MPa or less, the pressure applied to the ceramic compact (first sintered compact) in the step of heat treating under the second conditions is 0.5 MPa or more and 20 MPa or less, and the pressure applied to the ceramic compact (second sintered compact) in the step of heat treating under the third conditions is 50 MPa or more and 200 MPa or less. By setting each pressure within this range, stepwise heat treatment can be appropriately performed while increasing the pressure, and a dense ceramic sintered compact can be appropriately manufactured.

[0058] In addition, in this manufacturing method, it is preferable that the temperature of the heat treatment under the first condition (first heating temperature) is 1600° C. or higher and 1800° C. or lower, the temperature of the heat treatment under the second condition (second heating temperature) is 1700° C. or higher and 1900° C. or lower, and the temperature of the heat treatment under the third condition (third heating temperature) is 1700° C. or higher and 1900° C. By setting each heating temperature within this range, stepwise heat treatment can be appropriately performed while increasing the pressure, and a dense ceramic sintered body can be appropriately manufactured.

[0059] In addition, the present manufacturing method preferably further includes a step of forming a ceramic molded body by a gel casting method using ceramic powder. By using the gel casting method, a ceramic molded body can be appropriately formed. Furthermore, by using the gel casting method, even ceramic molded bodies with complex shapes can be easily manufactured.

[0060] The ceramic sintered body is preferably a silicon nitride sintered body. According to the present production method, a dense silicon nitride sintered body can be appropriately produced.

[0061] In addition, it is preferable to heat treat the ceramic compact in a nitrogen atmosphere in the steps of heat treating under the first, second, and third conditions. By performing the heat treatment in a nitrogen atmosphere, a dense silicon nitride sintered body can be appropriately produced.

[0062] Furthermore, the ceramic sintered body produced by heat treatment under the third condition has a three-point bending strength of 900 MPa or more at a span of 30 mm measured by the method specified in JIS R 1669, and a fracture toughness of 5.0 MPa m 1 / 2 or more, and 1 mm 2 The number of pores of 5 μm or more observed using an optical microscope for an area of ​​1 mm or more 2 It is preferable that the number of pores per unit area is 10 or less and the maximum pore diameter is 10 μm or less. By using this production method to produce a ceramic sintered body with such characteristics, a high-performance ceramic sintered body can be provided.

[0063] Example 1 Next, a description will be given of Example 1. Table 1 shows the manufacturing conditions for the ceramic sintered bodies according to each example, and the evaluation results of the manufactured ceramic sintered bodies.

[0064] [Table 1]

[0065] (Example 1) In Example 1, silicon nitride powder (SN-9FWS manufactured by Denka) as the ceramic powder, spinel powder as the sintering aid, ion-exchanged water as the solvent, and tetramethylammonium hydroxide as the dispersant were mixed and pulverized in a bead mill for 1.5 hours to produce silicon nitride slurry as the raw ceramic slurry. The amount of Sp, i.e., the ratio of the amount of added spinel powder to the amount of ceramic powder, was 2.8 mol%. Then, a water-soluble epoxy resin (EX614B, EX512 manufactured by Nagase ChemteX) was added to a portion of the silicon nitride slurry and mixed to produce a first ceramic slurry, and a resin hardener made from a mixture of triethylenetetramine and dimethylaminomethyl in a mass ratio of 2:1 was added to another portion of the silicon nitride slurry and mixed to produce a second ceramic slurry. The first ceramic slurry and the second ceramic slurry were then depressurized in separate tanks and degassed. While stirring in the tanks, they were simultaneously sent to a mixing mixer and mixed to form a casting ceramic slurry, which was then supplied to a mold connected to the mixer outlet. The mold filled with the ceramic slurry (a mixture of the first ceramic slurry and the second ceramic slurry) was then held at 50°C for 5 hours to harden the ceramic slurry and obtain a hardened body. The hardened body was then demolded from the mold, humidified and dried at 30°C for 4 days, and then hot-air dried at 50°C to obtain a dried molded body. The dried molded body was then heated at 600°C for 3 hours to degrease it, obtaining a ceramic molded body. The green density and relative density of the obtained ceramic green body were measured. Here, the green density was determined by dividing the volume calculated from the dimensions of the ceramic green body by the weight of the ceramic green body, and the material density was calculated from the composition ratio of the ceramic powder and the sintering aid and the theoretical density of each material. The relative density was determined by dividing the green density by the material density. For example, when silicon nitride (theoretical density 3.18 g / cm) was used as the ceramic powder, 3 ) and magnesia-alumina spinel (theoretical density 3.6 g / cm) as a sintering aid.3 ) are mixed at a composition ratio of 95 mol% and 5 mol%, respectively, the volume of 100 g is 31.26 cm 3 and the material density is 3.20 g / cm 3 This becomes: In Example 1, the ceramic molded body was not subjected to CIP treatment. Then, as a heat treatment under the first conditions, the ceramic molded body was heat treated at 1600°C for 10 hours in a nitrogen atmosphere at a pressure of 0.1 MPa to obtain a first sintered body. The sintered body density and relative density of the obtained first sintered body were measured. The sintered body density was measured in accordance with JIS R 1634. The relative density was calculated from the material density calculated from the composition ratio of the ceramic powder and sintering aid and the theoretical density of each material, and the sintered body density divided by the material density was used as the relative density. The first sintered body was then subjected to a heat treatment under the second conditions, that is, a heat treatment at 1700° C. for 1.5 hours in a nitrogen atmosphere under a pressure of 10 MPa, to obtain a second sintered body. The sintered density and relative density of the obtained second sintered body were measured. The second sintered body was then subjected to heat treatment under the third condition, that is, heat treatment at 1750° C. for 2 hours in a nitrogen atmosphere under a pressure of 100 MPa, to obtain a ceramic sintered body. The density, average strength, pore frequency, average pore diameter, and maximum pore diameter of the obtained ceramic sintered body were measured. The average strength was measured using an Autocom type universal testing machine (AC-100KN-C manufactured by TSE Corporation). The pore frequency was measured by measuring the pore size per 1 mm on the polished cross section of the ceramic sintered body. 2 Pores of 5 μm or larger observed using an optical microscope over an area of ​​1 mm or larger 2 The average pore diameter was measured using an industrial microscope (Nikon LV100). The maximum pore diameter was measured using an industrial microscope (Nikon LV100).

[0066] (Example 2) In Example 2, a ceramic sintered body was produced in the same manner as in Example 1, except that the amount of Sp was set to 4 mol % and the heat treatment under the first condition was carried out at 1700° C. for 5 hours.

[0067] (Example 3) In Example 3, a ceramic sintered body was produced in the same manner as in Example 2.

[0068] (Example 4) In Example 4, a ceramic sintered body was produced in the same manner as in Example 1, except that the amount of Sp was set to 4 mol %.

[0069] (Example 5) In Example 5, the Sp content was 4 mol%, and the heat treatment under the first condition was performed at 1600°C for 5 hours to obtain a first sintered body.The first sintered body was then heat treated under the second condition, at 1800°C for 5 hours in a nitrogen atmosphere at a pressure of 0.8 MPa, to obtain a second sintered body.The second sintered body was then heat treated under the third condition, at 1750°C for 2 hours in a nitrogen atmosphere at a pressure of 100 MPa, to obtain a ceramic sintered body.

[0070] (Example 6) In Example 6, a ceramic sintered body was produced in the same manner as in Example 1, except that the amount of Sp was set to 4 mol % and the ceramic compact was subjected to CIP treatment.

[0071] (Example 7) In Example 7, a ceramic sintered body was produced in the same manner as in Example 1, except that the ceramic compact was subjected to CIP treatment and the heat treatment under the second condition was carried out at 1800° C. for 0.25 hours.

[0072] (Example 8) In Example 8, a ceramic sintered body was produced in the same manner as in Example 1, except that the amount of Sp was 4 mol %, the ceramic compact was subjected to CIP treatment, and the heat treatment under the second condition was not carried out.

[0073] (Example 9) In Example 9, a ceramic sintered body was produced in the same manner as in Example 8.

[0074] (Example 10) In Example 10, a ceramic sintered body was produced in the same manner as in Example 1, except that the ceramic molded body was subjected to CIP treatment, the heat treatment under the first condition was performed at 1730°C for 3 hours, and the heat treatment under the second condition was not performed.

[0075] (Example 11) In Example 11, a ceramic sintered body was produced in the same manner as in Example 1, except that the amount of Sp was set to 4 mol % and the heat treatment under the second condition was not carried out.

[0076] (Example 12) In Example 12, a ceramic sintered body was produced in the same manner as in Example 1, except that the Sp content was 4 mol%, the heat treatment under the first condition was performed at 1700°C for 5 hours, and the heat treatment under the second condition was not performed.

[0077] (Example 13) In Example 13, a ceramic sintered body was produced in the same manner as in Example 12.

[0078] (Example 14) In Example 14, a ceramic sintered body was produced in the same manner as in Example 1, except that the Sp content was 4 mol%, the heat treatment under the first condition was performed at 1700°C for 5 hours, the heat treatment under the second condition was not performed, and the heat treatment under the third condition was performed at 1750°C for 5 hours.

[0079] (Example 15) In Example 15, a ceramic sintered body was produced in the same manner as in Example 14.

[0080] (Example 16) In Example 16, a ceramic sintered body was produced in the same manner as in Example 1, except that the Sp content was 4 mol%, the heat treatment under the first condition was performed at 1700°C for 5 hours, the heat treatment under the second condition was not performed, and the heat treatment under the third condition was performed at 1800°C for 2 hours.

[0081] (Example 17) In Example 17, a ceramic sintered body was produced in the same manner as in Example 1, except that the heat treatment under the first condition was performed at 1700°C for 15 hours, the heat treatment under the second condition was performed at 1700°C for 1 hour, and the heat treatment under the third condition was not performed.

[0082] (Example 18) In Example 18, a ceramic sintered body was produced in the same manner as in Example 17.

[0083] (Example 19) In Example 19, a ceramic sintered body was produced in the same manner as in Example 1, except that the Sp content was 4 mol%, the heat treatment under the first condition was at 1700°C for 15 hours, the heat treatment time under the second condition was 2 hours, and the heat treatment time under the third condition was 5 hours.

[0084] (Example 20) In Example 20, a ceramic sintered body was produced in the same manner as in Example 1, except that the Sp content was 4 mol%, the heat treatment under the first condition was at 1700°C for 5 hours, the heat treatment time under the second condition was 2 hours, and the heat treatment time under the third condition was 5 hours.

[0085] (Evaluation results) The density of the sintered ceramic is 3.15 g / cm 3 Above is considered to be a pass, and 3.15g / cm 3 Those with an average pore diameter of 6.4 μm or less were rated as passing, and those with an average pore diameter of more than 6.4 μm were rated as failing. Those with a maximum pore diameter of 10 μm or less were rated as passing, and those with an average pore diameter of more than 6.4 μm were rated as failing. Those with a maximum pore diameter of 10 μm or less were rated as passing, and those with an average pore diameter of more than 10 μm were rated as failing. Those with a maximum pore diameter of 10 μm or less were rated as passing, and those with an average pore diameter of more than 10 μm were rated as failing.

[0086] Examples 8 to 10 are reference examples, and it is clear that by performing CIP treatment, a dense, high-strength ceramic sintered body can be produced even with two-stage heat treatment. On the other hand, Examples 11 to 18 are comparative examples, and it is clear that if two-stage heat treatment is performed without CIP treatment, a dense, high-strength ceramic sintered body cannot be produced. Examples 1 to 5, 19, and 20 are working examples, and it is clear that by performing three-stage heat treatment without CIP treatment, a dense, high-strength ceramic sintered body can be produced. Examples 6 and 7 are also working examples, and it is clear that by performing CIP treatment followed by three-stage heat treatment, a dense, high-strength ceramic sintered body can be produced, and further, it is clear that the number and size of pores are smaller than when CIP treatment is not performed.

[0087] Example 2 Next, Example 2, in which the fracture toughness values ​​of ceramic sintered bodies were evaluated, will be described. Examples 21, 22, and 24 are working examples, and Examples 23 and 25 are comparative examples. Table 2 lists the manufacturing conditions for the ceramic sintered bodies of each example. Table 3 shows the evaluation results of the ceramic sintered bodies of each example. Also, FIGS. 4 and 5 are graphs showing the fracture toughness values ​​in Example 2. FIG. 4 shows the fracture toughness values ​​for each distance from the surface relative to the radius r, and FIG. 5 shows the fracture toughness values ​​for each distance from the surface (absolute value).

[0088] [Table 2]

[0089] [Table 3]

[0090] (Example 21) In Example 21, a spherical silicon nitride ceramic sintered body was produced, with a diameter of 51 mm. In Example 21, a spherical mold (diameter 64 mm) was used as the mold, and a spherical silicon nitride sintered body was obtained as the ceramic sintered body. The conditions different from Example 1 were as follows: the amount of Sp was 4 mol %, and the heat treatment under the first condition was performed at 1400°C for 5 hours to obtain a first sintered body. The first sintered body was heat-treated under the second condition at 1800°C for 5 hours in a nitrogen atmosphere under a pressure of 0.8 MPa to obtain a second sintered body. The second sintered body was heat-treated under the third condition at 1750°C for 5 hours to obtain a ceramic sintered body (silicon nitride sintered body). Aside from the above, the ceramic sintered body (silicon nitride sintered body) was produced using the same method as in Example 1. The fracture toughness value (K IC ) and Vickers hardness were measured. IC The ceramic sintered body was cut into a 10 mm thick disk along the diameter of the sintered body, and one side of the cut surface was polished. IC Table 3 shows the K in the region from the surface to a depth of r / 10. IC and the minimum value of K in the range from the surface to a depth of r / 10 IC The difference ΔKA between the maximum and minimum values ​​of K and the K in the range from the position at a depth of r / 10 below the surface to the position at a depth of 2r / 10 below the surface. IC The difference ΔKB between the maximum and minimum values ​​of K and the K in the range from the surface to a depth of 2r / 10 IC and the minimum value of K in the range from the surface to a depth of 4r / 10 IC and the average value of K in the range from the surface to a depth of r / 10 IC and the standard deviation of K from the surface to a depth of 4r / 10 IC and the minimum value of Vickers hardness in the range from the surface to a depth of 2r / 10, where r is the radius of the ceramic sintered body. The measurement was carried out using a Vickers hardness testing system ARS9000 manufactured by Future Tech Co., Ltd., under the conditions of a load of 5 kg and an indentation time of 15 seconds.

[0091] (Example 22) In Example 22, a ceramic sintered body was produced in the same manner as in Example 21, except that the size of the molding die was 63 mm in diameter and the heat treatment under the first condition was carried out at 1600°C for 5 hours. The diameter of the obtained ceramic sintered body was 50 mm.

[0092] (Example 23) In Example 23, a ceramic sintered body was produced in the same manner as in Example 21, except that the heat treatment under the first condition was not carried out. The diameter was 51 mm.

[0093] (Example 24) In Example 24, a ceramic sintered body was produced in the same manner as in Example 21, except that the size of the spherical molding die was 15 mm in diameter and the heat treatment under the first condition was carried out at 1600°C for 3.5 hours. The diameter of the obtained ceramic sintered body was 12 mm.

[0094] (Example 25) In Example 25, a ceramic sintered body was produced in the same manner as in Example 17, except that the CIP-treated green body was processed to have a diameter of 60.8 mm. The diameter was 50 mm.

[0095] To evaluate abrasion resistance, each ceramic sintered body was rubbed with water-resistant abrasive paper (US#500, manufactured by Struers) to evaluate its susceptibility to scratches. Evaluation samples were prepared in the same manner as samples for measuring fracture toughness. The evaluation samples were rubbed in the radial direction from the surface, and the length of scratches in the radial direction from the surface was measured using an optical microscope. A scratch length of 400 μm or less from the surface in the radial direction was evaluated as pass (◯), and a scratch length of more than 400 μm was evaluated as fail (×). As shown in Table 3, in Examples 21, 22, and 24, which are working examples, K in the region from the surface to a depth of r / 10 IC , ΔKA, and ΔKB are 6.5 or more, 2.0 or less, and 1.5 or less, respectively, which indicates that the material becomes dense and the wear resistance is improved. On the other hand, in Examples 23 and 25, which are comparative examples, the K in the region from the surface to a depth of r / 10 is IC , ΔKA, and ΔKB are outside the above ranges, and it is clear that the wear resistance cannot be improved.

[0096] Although the embodiments and examples of the present invention have been described above, the embodiments are not limited to the contents of these embodiments and examples. Furthermore, the above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments. [Explanation of symbols]

[0097] 10 Heat treatment furnace

Claims

1. A step of heat treating a ceramic compact that is a compact of ceramic powder under first conditions; a step of heat-treating the ceramic formed body heat-treated under the first condition under a second condition that is higher in pressure than the first condition; a step of heat-treating the ceramic compact heat-treated under the second conditions under third conditions that are higher in pressure than the second conditions, thereby producing a ceramic sintered body; Including, The temperature of the heat treatment under the first condition is set to 1600°C or more and 1800°C or less, The temperature of the heat treatment under the second condition is set to 1700°C or more and 1900°C or less, The temperature of the heat treatment under the third condition is set to 1700°C or more and 1900°C or less, The method for producing a ceramic sintered body, wherein the ceramic sintered body has a diameter of 10 mm or more and 80 mm or less and is a sintered body of silicon nitride.

2. A step of heat treating a ceramic compact that is a compact of ceramic powder under first conditions; a step of heat-treating the ceramic formed body heat-treated under the first condition under a second condition that is higher in pressure than the first condition; a step of heat-treating the ceramic compact heat-treated under the second conditions under third conditions that are higher in pressure than the second conditions, thereby producing a ceramic sintered body; Including, The method further includes forming the ceramic powder by a gel casting method to produce the ceramic compact; The method for producing a ceramic sintered body, wherein the ceramic sintered body has a diameter of 10 mm or more and 80 mm or less and is a sintered body of silicon nitride.

3. a difference between a pressure applied to the ceramic formed body in the step of heat treating under the second conditions and a pressure applied to the ceramic formed body in the step of heat treating under the first conditions being 0.3 MPa or more and 20 MPa or less; 3. The method for producing a ceramic sintered body according to claim 1, wherein a difference between a pressure applied to the ceramic molded body in the step of heat treating under the third conditions and a pressure applied to the ceramic molded body in the step of heat treating under the second conditions is 30 MPa or more and 180 MPa or less.

4. The method for producing a ceramic sintered body according to any one of claims 1 to 3, wherein the ceramic sintered body is a silicon nitride sintered body.

5. 5. The method for producing a ceramic sintered body according to claim 4, wherein the ceramic compact is heat-treated in a nitrogen atmosphere in the steps of heat-treating under the first condition, the second condition, and the third condition.

6. The ceramic sintered body produced by heat treatment under the third condition is The three-point bending strength at a span of 30 mm measured by the method specified in JIS R 1669 is 900 MPa or more, The fracture toughness measured by the method specified in JIS R 1669 is 6.0 MPa m １／２ That's all, 1 mm on the polished surface of any cross section ２ The number of pores of 5 μm or more observed using an optical microscope for an area of ​​1 mm or more ２ 10 or less per area, The maximum diameter of the pores is 10 μm or less. The method for producing a ceramic sintered body according to claim 4 or 5.

7. It is a spherical silicon nitride ceramic sintered body, The diameter is 10 mm or more and 80 mm or less, When the radius of the ceramic sintered body is r, the fracture toughness value (K ＩＣ ) is 6.5 MPa m １／２ That's all, The difference ΔKA between the maximum and minimum fracture toughness values ​​in the region of r / 10 from the surface of the ceramic sintered body is 2.0 MPa m １／２ is as follows: The difference ΔKB between the maximum and minimum fracture toughness values ​​in the range of r / 10 to 2r / 10 of the ceramic sintered body is 1.5 MPa m １／２ The following is a ceramic sintered body.

8. The fracture toughness value of the region 2r / 10 from the surface of the ceramic sintered body is 6.5 MPa m １／２ The ceramic sintered body according to claim 7 .

9. The average fracture toughness value in the region of 4r / 10 from the surface of the ceramic sintered body is 7.0 MPa m １／２ The ceramic sintered body according to claim 7 or 8, wherein

10. 10. The ceramic sintered body according to claim 7, wherein the standard deviation of the fracture toughness values ​​in a region r / 10 from the surface of the ceramic sintered body is 0.70 or less.

11. The ceramic sintered body according to claim 10, wherein the standard deviation of the fracture toughness values ​​in a region 4r / 10 from the surface of the ceramic sintered body is 0.55 or less.

12. 12. The ceramic sintered body according to claim 7, wherein a Vickers hardness of a region 2r / 10 from the surface of the ceramic sintered body is 10 Hv or more.

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