Ceramic sintered body, abrasion resistant member, and method for producing ceramic sintered body

Abstract

In an arbitrarily defined cross-section passing through the center of gravity of a ceramic sintered body according to an embodiment of the present invention, when a portion on the surface side is defined as a surface part and a portion centered at the center of gravity and existing within a radius of 1 mm is defined as a center-of-gravity part, and when an X-Ray Diffractometers (XRD) analysis is performed on the surface part and the center-of-gravity part, detection positions of the top four peaks in a descending order of the intensities of peaks detected within a diffraction angle range of 10-60° are the same between the surface part and the center-of-gravity part within a range of ±0.5°. The surface part is suitably set at a portion 0.5-1.0 mm from the surface.

Description

Ceramic sintered body, wear-resistant member, and method for manufacturing ceramic sintered body

[0001] The embodiments described below relate to a ceramic sintered body, a wear-resistant member, and a method for manufacturing a ceramic sintered body.

[0002] Ceramic sintered bodies are lightweight, have high hardness, excellent wear resistance and corrosion resistance, and have a low coefficient of thermal expansion, and therefore are widely used as components for precision instruments. Examples of ceramic sintered bodies include silicon nitride sintered bodies, aluminum nitride sintered bodies, aluminum oxide sintered bodies, and zirconium oxide sintered bodies. Ceramic sintered bodies are preferably used as wear-resistant components that constitute bearings and the like because of their high hardness and excellent wear resistance. In particular, silicon nitride sintered bodies have high hardness and excellent wear resistance among ceramic sintered bodies, and therefore are preferably used as wear-resistant components that constitute bearings and the like.

[0003] For example, Japanese Patent No. 5732037 (Patent Document 1) discloses a silicon nitride sintered body in which the crystalline compounds in the grain boundary phase are controlled. The silicon nitride sintered body described in Patent Document 1 has reduced variations in Vickers hardness and fracture toughness across parts of a single silicon nitride sintered body.

[0004] Patent No. 5732037

[0005] In Patent Document 1, the wear resistance of bearing balls made of silicon nitride sintered bodies is improved by suppressing variations in the Vickers hardness and fracture toughness of the silicon nitride sintered bodies. However, variations in properties such as Vickers hardness occurred among multiple silicon nitride sintered bodies. Investigation into the cause of this problem revealed that it was due to the cooling process after HIP (hot isostatic pressing). In the production of bearing balls, HIP is performed after the primary sintering process. HIP is a type of sintering method that applies high temperature and high pressure. HIP processes multiple ceramic sintered bodies at once. In some cases, hundreds to thousands of ceramic sintered bodies may be HIP-processed at once. It was found that controlling the cooling rate after HIP, particularly the lower limit of the cooling rate, is the cause of variations in the properties of individual ceramic sintered bodies. The embodiments address this issue.

[0006] In the ceramic sintered body according to the embodiment, in any cross section passing through the center of gravity, the surface side portion is defined as the surface portion, and the portion within a radius of 1 mm from the center of gravity is defined as the center of gravity. When the surface portion and the center of gravity are analyzed with an X-ray diffractometer (XRD), the detection positions of the top four peaks in order of highest peak intensity detected within a diffraction angle range of 10° or more and 60° or less coincide within a range of ±0.5° between the surface portion and the center of gravity.

[0007] Fig. 1 is an external view showing an example of a spherical ceramic sintered body among the ceramic sintered bodies according to the embodiment. Fig. 2 is a view showing an example of a spherical ceramic sintered body among the ceramic sintered bodies according to the embodiment. Fig. 3 is a view showing an example of a rectangular parallelepiped ceramic sintered body among the ceramic sintered bodies according to the embodiment. Fig. 4 is a view showing an example of a bearing using bearing balls made of a spherical ceramic sintered body among the ceramic sintered bodies according to the embodiment. Embodiment

[0008] In the ceramic sintered body according to the embodiment, in any cross section passing through the center of gravity, the surface side portion is defined as the surface portion, and the portion within a radius of 1 mm from the center of gravity is defined as the center of gravity. When the surface portion and the center of gravity are subjected to XRD analysis, the detection positions of the top four peaks in order of highest peak intensity detected within a diffraction angle range of 10° or more and 60° or less coincide within a range of ±0.5° between the surface portion and the center of gravity.

[0009] FIGS. 1, 2, and 3 show an example of a ceramic sintered body according to an embodiment. In the figures, reference numeral 1 denotes a ceramic sintered body, reference numeral 1A denotes a spherical ceramic sintered body within the ceramic sintered body 1, reference numeral 1B denotes a rectangular parallelepiped ceramic sintered body within the ceramic sintered body 1, reference numeral 2 denotes a center of gravity, and reference numeral 3 denotes a surface. FIGS. 1 and 2 show a spherical ceramic sintered body 1A within the ceramic sintered body 1. FIG. 2(A) is an external view of the spherical ceramic sintered body 1A. FIG. 2(B) is a cross-sectional view taken along line IIB-IIB of FIG. 2(A). FIG. 3 shows a rectangular parallelepiped ceramic sintered body 1B within the ceramic sintered body 1. FIG. 3(A) is an external view of the rectangular parallelepiped ceramic sintered body 1B. FIG. 3(B) is a cross-sectional view taken along line IIIB-IIIB of FIG. 3(A). The ceramic sintered body 1 is not limited to this shape and may be cylindrical, square, or the like. The ceramic sintered body 1 may also be in the shape of a part such as a cam roller or a friction stir welding tool. Fig. 4(A) is a front view of a bearing 10 using bearing balls 4. Fig. 4(B) is a cross-sectional view of the bearing 10 using bearing balls 4.

[0010] Here, unless otherwise specified, the ceramic sintered body 1 will be described using the spherical ceramic sintered body 1A in FIG. 2 . The shape of the spherical ceramic sintered body 1A may be a perfect sphere, or may be a solid shape that includes only curved surfaces, and may also include some irregularities on the surface. Furthermore, the ceramic sintered body 1 is not limited to the spherical ceramic sintered body 1A, but may also be a solid shape with height (e.g., a rectangular parallelepiped ceramic sintered body 1B in FIG. 3 ). Even when the ceramic sintered body 1 is a solid shape with height, the composition, structure, and properties are the same as those of the spherical ceramic sintered body 1A, and therefore detailed description thereof will be omitted.

[0011] First, an arbitrary cross section passing through the center C of the spherical ceramic sintered body 1A is prepared. This cross section may also be simply referred to as a cross section. Here, the center C does not mean a strict narrow point within the spherical ceramic sintered body 1A, but may be a wide region such that the diameter of the cut cross section is 80% or more of the diameter of the spherical ceramic sintered body 1A. The center C of the spherical ceramic sintered body 1A is the midpoint of the diameter. The radius from the midpoint is called the central radius. A central radius of 1 mm refers to a region of 1 mm or less radially from the midpoint. The center of gravity 2 is the portion within the central radius of 1 mm in an arbitrary cross section passing through the center C (the portion within the dashed circle in Figure 2(B)).

[0012] The surface portion 3 is the surface side portion in a cross section passing through the center C of the spherical ceramic sintered body 1A. For example, when the diameter of the spherical ceramic sintered body 1A is 10 mm or more, the surface portion 3 is defined as a portion extending from the surface in the thickness direction (perpendicular to the surface) of 0.5 mm to 1.0 mm (the portion between the two dashed-two-dot circles in FIG. 2(B)). On the other hand, when the diameter of the spherical ceramic sintered body 1A is smaller than 10 mm, the surface portion 3 is defined as a portion extending from the surface in the thickness direction of 0.05 × D mm to 0.10 × D mm, where D is the diameter. In other words, regardless of the size of the spherical ceramic sintered body 1A, the center of gravity portion 2 and the surface portion 3 do not overlap.

[0013] 3, when the ceramic sintered body 1 is a rectangular parallelepiped ceramic sintered body 1B, the center of gravity portion 2 is a portion within a radius of 1 mm from the center of gravity C of the rectangular parallelepiped ceramic sintered body 1B in any cross section passing through the center of gravity C and along the height direction H (the portion within the dashed circle in FIG. 3(B)). Also, when the ceramic sintered body 1 is a rectangular parallelepiped ceramic sintered body 1B, the surface portion 3 is a portion from 0.5 mm to 1.0 mm in the thickness direction (direction perpendicular to the surface) from the surface in a cross section passing through the center C (the portion between the two dashed-dot rectangles in FIG. 3(B)).

[0014] When the surface portion 3 and the center of gravity portion 2 of the spherical ceramic sintered body 1A are subjected to XRD analysis (2θ), several peaks (XRD peaks) appear. In the spherical ceramic sintered body 1A, the detection positions of the top four peaks in order of peak intensity detected within a diffraction angle range of 10° to 60° coincide within a range of ±0.5° between the surface portion 3 and the center of gravity portion 2.

[0015] First, the conditions for XRD analysis will be described. The measurement surface for XRD analysis is an arbitrary cross section passing through the center C of the spherical ceramic sintered body 1A. The measurement surface has a surface roughness Ra of 1 μm or less. XRD analysis is performed using a Cu target (Cu-Kα), with a tube voltage of 40 kV, a tube current of 40 mA, a scan speed of 2.0° / min, a slit (RS) of 0.15 mm, and a scan range (2θ) of 10° to 60°. A BRUKER D8_ADVANCE or one with equivalent performance is used for the measurement.

[0016] XRD analysis can be used to perform qualitative or quantitative analysis depending on the crystalline compound. Furthermore, the peaks that appear in XRD analysis are affected by the composition, crystallinity, abundance, orientation, residual stress, etc. of the crystalline compound. Peaks detected within a diffraction angle range of 10° to 60° are used because this is the region where typical peaks of ceramic sintered bodies are detected.

[0017] As the representative peaks, a Powder Diffraction File (PDF) provided by the International Centre for Diffraction Data (ICDD) may be used, i.e., four representative peaks may be selected from the PDF of the ceramic base material.

[0018] For example, silicon nitride sintered bodies have representative peaks (2θ) set at positions around 23.4°, 27.1°, 33.6°, and 36.1°. α-aluminum oxide sintered bodies have representative peaks (2θ) set at positions around 25.6°, 35.2°, 43.4°, and 57.5°. zirconium oxide sintered bodies have representative peaks (2θ) set at positions around 30.0°, 34.5°, 50.0°, and 59.0°. α-aluminum oxide sintered bodies have a trigonal crystal structure. α-aluminum oxide sintered bodies are used in wear-resistant components such as bearing balls.

[0019] The top four peaks detected at diffraction angles (2θ) of 10° to 60° refer to the top four peaks in descending order of peak intensity ratio of the ceramic base material. The top four peaks detected at diffraction angles (2θ) of 10° to 60° are sometimes simply referred to as the top four peaks. The peak detection position is the diffraction angle at which the peak tops. The reason for the 10° to 60° peaks is that this is the range in which peaks of the base material of the ceramic sintered body are detected.

[0020] As described above, in the spherical ceramic sintered body 1A, the detected positions of the top four peaks in the surface portion 3 and the center of gravity portion 2 coincide within a range of ±0.5°. The coincidence of the detected peak positions within a range of ±0.5° is sometimes simply referred to as the coincidence of the detected peak positions.

[0021] The fact that the peak detection positions are the same means that the difference (Dp) between the peak position at the surface portion 3 and the peak position at the center of gravity portion 2 of the spherical ceramic sintered body 1A satisfies the following formula (1): −0.5°≦Dp≦0.5° (1)

[0022] The fact that the detection positions of the top four peaks in the surface portion 3 and the center of gravity portion 2 of the spherical ceramic sintered body 1A are the same indicates that the composition, crystallinity, abundance, orientation, residual stress, etc. of the crystalline compound are the same between the surface portion 3 and the center of gravity portion 2. This makes it possible to suppress variation in the characteristics of the HIP-treated body. The fact that the detection positions of the peaks are shifted by more than ±0.5° indicates that there is a deviation in one or more of the composition, crystallinity, abundance, orientation, and residual stress of the crystalline compound. Note that peaks other than the top four may or may not be the same. What is important is that the top four representative peaks are the same.

[0023] Furthermore, it is preferable that the peak intensities of the top four peaks in the surface portion 3 and the center of gravity portion 2 of the spherical ceramic sintered body 1A, whose peak detection positions are offset from each other by ±0.5°, match within a range of ±10% between the surface portion 3 and the center of gravity portion 2. Matching of peak intensities within a range of ±10% is sometimes simply referred to as "matching peak intensities." This indicates that not only the peak detection positions but also the peak intensities match. Matching of peak detection positions and peak intensities indicates that one or more of the composition, crystallinity, abundance, orientation, and residual stress of the crystalline compounds match.

[0024] Furthermore, the fact that the peak intensities are consistent means that the difference ratio based on the difference (Ds) between the peak intensity at the surface portion 3 and the peak intensity at the center of gravity portion 2 of the spherical ceramic sintered body 1A satisfies the following formula (2): −10%≦(Ds / peak intensity at surface portion 3)×100≦10% (2).

[0025] Furthermore, even in any cross section that does not pass through the center C of the spherical ceramic sintered body 1A, it is preferable that the detection positions of the top four peaks in order of peak intensity detected within a diffraction angle range of 10° to 60° in the center of gravity portion 2 and the surface portion 3 coincide within a range of ±0.5°.

[0026] The state of the crystalline compounds in the surface portion 3 and center of gravity portion 2 of the spherical ceramic sintered body 1A is homogenized. HIP treatment is a type of sintering method that applies high temperature and high pressure. Because high temperature and high pressure are transmitted from the surface side to the center side of the spherical ceramic sintered body 1A, it was difficult to homogenize the state of the crystalline compounds in the surface portion 3 and center of gravity portion 2. However, as described below, homogenization was made possible by controlling the cooling rate after HIP treatment.

[0027] Furthermore, even in any cross section that does not pass through the center C of the spherical ceramic sintered body 1A, it is preferable that the peak intensities of the top four peaks in the surface portion 3 and the center of gravity portion 2, in order of highest peak intensity, coincide within a range of ±10% between peaks whose peak detection positions are ±0.5° apart.

[0028] Furthermore, with regard to the XRD peaks due to the grain boundary phase, it is preferable that the peak intensities of the peaks whose positions are at an angle of ±0.5° from the highest peak in the surface portion 3 and the center of gravity portion 2 of the spherical ceramic sintered body 1A coincide within a range of ±10%.

[0029] Furthermore, observation areas of 50 μm × 50 μm are set on the surface portion 3 and the center of gravity portion 2 of the spherical ceramic sintered body 1A, and these areas are photographed with a scanning electron microscope (SEM). Based on the SEM image obtained, it is preferable that the top 50 ceramic crystal grains with the largest major axis have an average major axis within the range of 0.5 μm to 20 μm.

[0030] First, we will explain the method for measuring ceramic crystal particles using an SEM. The SEM used is a JEOL Schottky field emission scanning electron microscope JSM-7200F, or an equivalent or better model. The measurement area is selected from the surface 3 and center of gravity 2 of the spherical ceramic sintered body 1A. An SEM image of an observation area (measurement area) of 50 μm x 50 μm is obtained at 5000x magnification.

[0031] The longest diagonal line of a ceramic crystal particle in an SEM image is taken as the major axis. The top 50 particles with the largest major axis in an SEM image are selected, and the average of their major axes is taken as the average major axis. If 50 particles cannot be collected in an observation area of ​​50 μm × 50 μm, another observation area of ​​50 μm × 50 μm is used. Although ceramic crystal particles may appear overlapping in an SEM image, the top 50 largest particles that appear in the SEM image are selected.

[0032] When the average major axis of the ceramic crystal grains in the spherical ceramic sintered body 1A is within the range of 0.5 μm to 20 μm, it is possible to achieve both homogeneity and improved strength in the surface region 3 and the center of gravity region 2. If the average major axis is less than 0.5 μm, the ceramic crystal grains are too small, and slight segregation of the grain boundary phase may impair the homogeneity of the surface region 3 and the center of gravity region 2. Furthermore, if the average major axis is greater than 20 μm, there is a possibility that the size of the gaps between the ceramic crystal grains may vary. For this reason, the average major axis of the ceramic crystal grains is preferably within the range of 0.5 μm to 20 μm, and more preferably 1 μm to 10 μm. Furthermore, homogeneity can be improved by controlling the top 50 largest ceramic crystal grains.

[0033] The spherical ceramic sintered body 1A preferably contains a grain boundary phase in an amount of 1 mass % to 20 mass %. The grain boundary phase preferably contains one or more elements selected from the group consisting of rare earth elements, Al, Ti, Zr, Hf, Mo, W, Co, Fe, and C. The rare earth elements are one or more elements selected from the group consisting of yttrium and lanthanoid elements.

[0034] The grain boundary phase of the spherical ceramic sintered body 1A is primarily composed of a sintering aid. The grain boundary phase fills the gaps between the ceramic crystal grains that form the base material. The sintering aid improves sinterability and densifies the spherical ceramic sintered body 1A. Densification leads to improved strength of the spherical ceramic sintered body 1A. If the grain boundary phase is less than 1 mass%, the effect may be insufficient. Furthermore, if the grain boundary phase is more than 20 mass%, the advantages of the ceramic crystal grains that form the base material may not be fully utilized. For this reason, the grain boundary phase is preferably in the range of 1 mass% to 20 mass%, and even more preferably 5 mass% to 17 mass%. A simple method for measuring the mass percentage of the grain boundary phase may be to subtract the mass percentage of the ceramic crystal grains that form the base material from 100 mass%. This method may be used for ceramic sintered bodies with a relative density of 98% or higher. Naturally, the mass percentage of the grain boundary phase may also be measured directly.

[0035] The grain boundary phase of the spherical ceramic sintered body 1A may be either an amorphous compound or a crystalline compound. Furthermore, the elements present in the grain boundary phase, selected from rare earth elements, Al, Ti, Zr, Hf, Mo, W, Co, Fe, and C, are preferably present as one or more elements selected from the group consisting of simple substances, oxides, nitrides, silicides, carbides, and sulfides. Oxides, nitrides, silicides, carbides, and sulfides each include composite compounds. Examples of composite compounds include oxynitrides.

[0036] The spherical ceramic sintered body 1A can achieve homogeneity between the surface portion 3 and the center of gravity portion 2 even if amorphous compounds, crystalline compounds, or both are present in the grain boundary phase. In other words, it is possible to obtain homogeneity in the detection position and peak intensity of the top peak detected in order of XRD peak intensity within a diffraction angle range of 10° to 60° in the surface portion 3 and the center of gravity portion 2. By obtaining homogeneity in the XRD peak due to the grain boundary phase, it is possible to further improve the characteristics.

[0037] Furthermore, it is preferable that the spherical ceramic sintered body 1A is a silicon nitride sintered body. Examples of the spherical ceramic sintered body 1A include silicon nitride sintered bodies, aluminum nitride sintered bodies, aluminum oxide sintered bodies, and zirconium oxide sintered bodies, in addition to silicon nitride sintered bodies. The ceramic crystal grains serving as the base material for silicon nitride sintered bodies are silicon nitride crystal grains. Silicon nitride sintered bodies also include sialon sintered bodies. Furthermore, the ceramic crystal grains serving as the base material for aluminum nitride sintered bodies are aluminum nitride crystal grains. The ceramic crystal grains serving as the base material for aluminum oxide sintered bodies are aluminum oxide crystal grains. The ceramic crystal grains serving as the base material for zirconium oxide sintered bodies are zirconium oxide crystal grains. Furthermore, the base material refers to the crystal grains that are most numerous in the ceramic sintered body. In other words, the spherical ceramic sintered body 1A is a polycrystalline body.

[0038] The silicon nitride sintered body as the spherical ceramic sintered body 1A can have a three-point bending strength of 600 MPa or more, or even 900 MPa or more. The aluminum nitride sintered body has a three-point bending strength of approximately 200 to 500 MPa. The aluminum oxide sintered body has a three-point bending strength of approximately 400 to 600 MPa. The zirconium oxide sintered body has a three-point bending strength of approximately 600 to 900 MPa. The silicon nitride sintered body is a ceramic sintered body with high strength. Generally, the silicon nitride crystal grains that form the base material of the silicon nitride sintered body are mostly elongated crystal grains with an aspect ratio of 2 or more. The high strength is achieved by the complex entanglement of the elongated crystal grains. On the other hand, the crystal grains of aluminum nitride sintered bodies, aluminum oxide sintered bodies, and zirconium oxide sintered bodies are less entangled than silicon nitride crystal grains. For this reason, there is a limit to how much strength can be improved. Even if the spherical ceramic sintered body 1A has a structure in which elongated silicon nitride crystal grains are intricately intertwined, as in the case of a silicon nitride sintered body, it is possible to achieve homogenization of the surface portion 3 and the center of gravity portion 2. In other words, the spherical ceramic sintered body 1A is preferably a silicon nitride sintered body.

[0039] The diameter of the spherical ceramic sintered body 1A is preferably 5 mm or more. The diameter refers to the longest diameter of the spherical ceramic sintered body 1A. On the other hand, if the ceramic sintered body 1 is a solid having height, the height (length along the height direction H) is preferably 5 mm or more. Here, the height refers to the length of the longest side of the rectangular parallelepiped ceramic sintered body 1B. Note that when the ceramic sintered body 1 has height, the ceramic sintered body 1 is not limited to a rectangular parallelepiped, but may also be a solid having a polygonal base, a cone, or a cylinder. The ceramic sintered body 1 may also be a polygonal face. Furthermore, the ceramic sintered body 1 may have the shape of a part such as a cam roller or a friction stir welding tool. Furthermore, the ceramic sintered body 1 can achieve homogenization of the surface portion 3 and the center of gravity portion 2 even when the height or diameter is 5 mm or more, or even 9 mm or more.

[0040] Furthermore, the spherical ceramic sintered body 1A can have a difference (Dv) between the Vickers hardness of the surface portion 3 and the Vickers hardness of the center of gravity portion 2 within ±10%. Vickers hardness is measured by a method conforming to Japanese Industrial Standards (JIS R1610). A difference (Dv) between the Vickers hardness of the surface portion 3 of the spherical ceramic sintered body 1A and the Vickers hardness of the center of gravity portion 2 within ±10% means that the following formula (3) is satisfied. JIS R1610 corresponds to ISO 14705. -10%≦(Dv / Vickers hardness of surface portion)×100≦10% (3)

[0041] Furthermore, the spherical ceramic sintered body 1A can have a difference rate based on the difference (Dt) between the fracture toughness value of the surface portion 3 and the fracture toughness value of the center of gravity portion 2 within ±20%. The fracture toughness value is calculated based on the crack length measured using the IF method specified in the Japanese Industrial Standards (JIS_R1607) and the Niihara formula. The indentation load used when measuring the fracture toughness value is 20 kgf. A difference rate based on the difference (Dt) between the fracture toughness value of the surface portion 3 and the fracture toughness value of the center of gravity portion 2 of the spherical ceramic sintered body 1A within ±20% means that the following formula (4) is satisfied. JIS_R1607 corresponds to ISO15732. -20%≦(Dt / fracture toughness value of surface portion)×100≦20% ... (4)

[0042] The silicon nitride sintered body as the spherical ceramic sintered body 1A can have a Vickers hardness HV of 1460 or more. The silicon nitride sintered body also has a fracture toughness of 6.0 MPa m １／２ That is, the silicon nitride sintered body can have a Vickers hardness HV of 1460 or more, and the difference in Vickers hardness between the surface portion 3 and the center of gravity portion 2 can be within ±10%. A Vickers hardness HV of 1460 or more means that both the surface portion 3 and the center of gravity portion 2 are 1460 or more. Furthermore, the silicon nitride sintered body has a fracture toughness value of 6.0 MPa m １／２ In addition, the difference in fracture toughness between the surface portion 3 and the center of gravity portion 2 can be kept within ±20%. １／２ The above means that both the surface portion 3 and the center of gravity portion 2 have a resistance of 6.0 MPa m １／２ Indicates that this is the case.

[0043] Furthermore, when the Vickers hardness HV of any 10 spherical ceramic sintered bodies 1A is measured, the Vickers hardness HV can be such that the maximum value minus the minimum value is ≦50. Furthermore, when the fracture toughness value of any 10 silicon nitride sintered bodies is measured, the maximum value minus the minimum value is ≦0.8 MPa m １／２ It can be the following:

[0044] The spherical ceramic sintered compact 1A can be used as a wear-resistant member. Examples of wear-resistant members include bearing balls, rollers, check balls, wear pads, plungers, rollers, and friction stir welding tool members. These wear-resistant members slide against mating members made of metal or ceramics. To increase the durability of the sliding surface, it is preferable to polish the surface to a surface roughness (Ra) of 0.5 μm or less, preferably 0.1 μm or less, and more preferably 0.05 μm or less.

[0045] The spherical ceramic sintered body 1A has reduced variations in hardness. This reduces variations in polishing efficiency, allowing for a similar polished surface to be obtained with the same polishing time. For example, variations in the hardness and fracture toughness of the ceramic sintered body may result in variations in the way it is polished during the polishing process.

[0046] Another example of a wear-resistant member is a bearing ball. The spherical ceramic sintered body 1A is exemplified by a silicon nitride sintered body. Figure 4 shows an example of a bearing using a bearing ball. In the figure, reference numeral 4 denotes a bearing ball, reference numeral 5 denotes an inner ring, reference numeral 6 denotes an outer ring, and reference numeral 10 denotes a bearing.

[0047] The bearing balls 4 of the bearing 10 are made of silicon nitride sintered body as the spherical ceramic sintered body 1A. The bearing 10 has bearing balls 4 arranged between the inner ring 5 and the outer ring 6. The bearing 10 in FIG. 4 uses 16 bearing balls 4. The bearing 10 is used with a plurality of bearing balls 4 arranged. Motors for use in electric vehicles (EVs) and hybrid electric vehicles (HEVs) are being developed. The maximum rotation speed of passenger car motors is said to reach 10,000 to 15,000 rpm. Since electric vehicles start moving from a stationary state, the motor's rotation speed varies between 0 and 15,000 rpm. Inverter motors have been developed to accommodate changes in rotation speed.

[0048] An inverter motor is a mechanism that controls the rotational speed of an AC (alternating current) motor by controlling the frequency of the power supplied to the motor. Changes in rotational speed lead to changes in torque. In mechanics, torque is the moment of force acting around a fixed axis of rotation. An environment in which the rotation speed changes is an environment in which the torque (and therefore the stress) acting on the bearing balls changes.

[0049] The silicon nitride sintered body used as the spherical ceramic sintered body 1A has reduced variation in fracture toughness. Fracture toughness is an index showing the resistance to fracture when a mechanical load is applied to a material with cracks or crack-like defects. It is a specific index of toughness, which refers to the material's resilience to fracture. For example, when the torque changes with a change in the rotational speed of the bearing 10, the stress applied to the bearing balls 4 changes. The stress changes as the rotational speed changes and the balls slide. In particular, eccentricity occurs as the rotational speed increases. Eccentricity causes a slight change in the alignment between the bearing balls and the inner and outer rings, increasing their aggressiveness.

[0050] This can lead to a decrease in wear resistance and electrolytic corrosion. Even in such an environment, the variation in fracture toughness value is suppressed, so the bearing balls 4 manufactured from the spherical ceramic sintered compact 1A are resistant to attacking the inner ring 5 and outer ring 6. This improves the durability of the bearing 10. This improves the durability of not only the bearing balls but also the bearing itself. In other words, this is suitable for bearing balls used in inverter motor bearings.

[0051] Furthermore, it is preferable that the detection positions of the top four peaks of the spherical ceramic sintered body 1A coincide within a range of ±0.5° even after polishing. For example, the bearing ball 4 is manufactured by polishing the spherical ceramic sintered body 1A as described above. A ceramic sintered body for a bearing ball before polishing is sometimes called a raw ball. Furthermore, a bearing ball made of a ceramic sintered body after polishing is sometimes called a finished ball. Whether it is a raw ball or a finished ball, it is preferable that it has the above configuration. In other words, the ceramic sintered body according to the embodiment also includes one after polishing.

[0052] Next, a method for manufacturing the ceramic sintered body 1 will be described using the spherical ceramic sintered body 1A. The manufacturing method for the spherical ceramic sintered body 1A is not limited as long as it has the above-mentioned configuration, but the method for obtaining it with a good yield is as follows. Furthermore, even if the ceramic sintered body 1 is a solid body with height, the manufacturing method is the same as that for the spherical ceramic sintered body 1A.

[0053] First, ceramic powder is prepared as the base material. The base material can be one selected from silicon nitride, aluminum nitride, aluminum oxide, and zirconium oxide. For example, silicon nitride powder can be produced by the direct nitridation method or the imide decomposition method. Silicon nitride powder produced by the direct nitridation method contains a lot of impurities such as Fe, but is relatively inexpensive. Silicon nitride powder produced by the imide decomposition method contains few impurities such as Fe, but is relatively expensive. Either type of silicon nitride powder can be used.

[0054] Next, a sintering aid powder is prepared. Examples of the sintering aid powder include one or more compounds selected from rare earth elements, Al, Ti, Zr, Hf, Mo, W, Co, Fe, and C. Examples of the compounds include oxides, nitrides, silicides, carbides, sulfides, and composite compounds thereof. Examples of composite compounds include oxynitrides. Silicon carbide (SiC) may also be added as a sintering aid. When the total of the ceramic powder and the sintering aid is 100% by mass, the proportion of the sintering aid is preferably in the range of 1% by mass to 20% by mass. The mixture of the ceramic powder and the sintering aid powder is called a raw material mixed powder.

[0055] Next, a binder and a solvent are added to the mixed raw material powder as required, and a crushing step using a ball mill or the like may be carried out.

[0056] Next, a molding step is carried out. Examples of the molding step include mold molding, CIP (cold isostatic pressing), injection molding, and a doctor blade method. The molded body obtained by mold molding may also be subjected to CIP. By carrying out the molding step, a molded body can be obtained.

[0057] Next, the compact is subjected to a degreasing process. The degreasing process is preferably carried out at a temperature in the range of 400°C or higher and 600°C or lower. The degreasing process is also preferably carried out in the air or nitrogen gas. The degreasing process can remove binders and solvents from the compact. A degreasing process can be carried out to obtain a degreased compact.

[0058] Next, the degreased body is subjected to a sintering process. The sintering process is preferably carried out within a range of 1500°C to 2000°C. Either atmospheric sintering or pressure sintering may be used. The sintering atmosphere may be a non-oxidizing atmosphere, air, or vacuum. The non-oxidizing atmosphere is preferably a nitrogen gas atmosphere or a reducing atmosphere containing nitrogen gas. The pressure inside the sintering furnace may be a pressurized atmosphere. The sintering time is preferably within a range of 3 hours to 12 hours. For example, in the case of a silicon nitride sintered body, if the sintering temperature exceeds 2000°C, the silicon nitride will decompose into Si and N. ２ It may decompose into

[0059] Furthermore, after the sintering step, a high-temperature, high-pressure treatment step is performed, in which the ceramic sintered body is treated at a high temperature and pressure. The high-temperature, high-pressure treatment step refers to a step in which a temperature of 1500°C or higher and a pressure of 10 MPa or higher are applied. Examples of high-temperature, high-pressure treatments include HIP (hot isostatic pressing) treatment and GPS (gas pressure sintering) treatment. By performing the high-temperature, high-pressure treatment step, the spherical ceramic sintered body 1A can be densified. The relative density of the spherical ceramic sintered body 1A can be increased to 99% or higher. This improves the three-point bending strength, fracture toughness, and Vickers hardness. In terms of the variation in the properties of individual ceramic sintered bodies, the high-temperature, high-pressure treatment step preferably involves a cooling rate from the heating temperature to 200°C of 20°C / min or more and 150°C / min or less.

[0060] The heating temperature is set to 1500°C or higher. The heating temperature is the highest temperature reached at temperatures above 1500°C that are maintained for 10 minutes or more. There is no particular upper limit to the heating temperature, but it is preferably 2000°C or lower. It is also preferably lower than the temperature in the sintering process described above. By lowering the heating temperature in the process of processing under high temperature and high pressure below the temperature in the sintering process, it is possible to suppress the grain growth of the ceramic crystal particles that are the base material.

[0061] The pressure in the high-temperature, high-pressure treatment step is 10 MPa or more. There is no particular upper limit to the pressure, but it is preferably 200 MPa or less. If the pressure exceeds 200 MPa, there is a possibility that the production cost will increase. Therefore, the pressure in the high-temperature, high-pressure treatment step is preferably in the range of 10 MPa or more and 200 MPa or less, and more preferably 80 MPa or more and 170 MPa or less.

[0062] Furthermore, from the viewpoint of variation in the properties of individual ceramic sintered bodies, it is preferable that the cooling rate from the heating temperature to 200°C in the high-temperature, high-pressure treatment step be within the range of 20°C / min to 100°C / min. This refers to the control of the cooling rate in the cooling step in the high-temperature, high-pressure treatment step. For example, the cooling rate in conventional HIP treatment is slow, at 5°C / min or less. A cooling rate within the range of 20°C / min to 100°C / min is a rapid cooling step. In ceramic sintered bodies containing the aforementioned sintering aid, a grain boundary phase is formed based on the sintering aid. The temperature of 1000°C to 1200°C is the temperature at which the grain boundary phase solidifies. Setting the cooling rate from the heating temperature to 200°C within the range of 20°C / min to 100°C / min indicates that the temperature range at which the grain boundary phase solidifies is rapidly cooled. Rapid cooling can improve the homogeneity of the surface portion 3 and the center of gravity portion 2.

[0063] The process of treating under high temperature and high pressure is a process for densifying the ceramic sintered body. The pores are collapsed and filled with the grain boundary phase. Rapid cooling in the temperature range where the grain boundary phase solidifies can maintain the collapsed and filled state with the grain boundary phase. The cooling rate may be constant or may be varied along the way. The cooling rate is calculated by dividing the temperature difference from the heating temperature to 200°C by the time (minutes) required. If the cooling rate is less than 20°C / min, the cooling effect may be insufficient, resulting in increased variation in the properties of individual ceramic sintered bodies. On the other hand, if the cooling rate is faster than 100°C / min, the load on the cooling equipment may increase. For this reason, the cooling rate is preferably within the range of 20°C / min to 100°C / min, and more preferably 30°C / min to 80°C / min.

[0064] Furthermore, the cooling rate in the temperature range below 200°C is arbitrary. This is because the grain boundary phase solidifies at the 200°C stage, making it ineffective to control the cooling rate. Furthermore, the process of treating under high temperature and pressure is preferably HIP treatment. HIP treatment allows for control of temperature and pressure. Furthermore, by using a water-cooled HIP furnace, the cooling rate can also be controlled.

[0065] The spherical ceramic sintered body 1A can be manufactured through the above steps. If necessary, the spherical ceramic sintered body 1A can be polished in a polishing process to manufacture the bearing ball 4. For example, the surface roughness Ra of the finishing process for the bearing ball 4 is 0.1 μm or less. ASTM F2094 also specifies the surface roughness Ra according to the grade of the bearing ball. The maximum Ra is 0.013 μm. To turn the spherical ceramic sintered body 1A into the bearing ball 4, polishing to an Ra of 0.013 μm or less is required. This type of polishing is called finishing.

[0066] (Examples) (Examples 1 to 9, Comparative Examples 1 and 2) Raw material mixed powders were prepared by mixing the ceramic powders and sintering aid powders shown in Table 1. Examples 1 to 4, 6, and 9 and Comparative Example 1 were used to produce silicon nitride sintered bodies, Example 5 and Comparative Example 2 were used to produce α-aluminum oxide sintered bodies, Example 7 was used to produce zirconium oxide sintered bodies, and Example 8 was used to produce an aluminum nitride sintered body. The mixing amounts are based on the total of the ceramic powder and sintering aid powder being 100% by mass.

[0067]

[0068] A binder and a solvent were added to the raw material mixed powder shown in the examples, and the crushing process, molding process, degreasing process, sintering process, and high-temperature, high-pressure treatment process were carried out in this order under the conditions described above. Specifically, a binder and a solvent were added to the raw material mixed powder, and the crushing process was carried out using a ball mill. Then, a binder and other additives were added, and the molding process was carried out. The molding was carried out by die pressing, followed by CIP treatment. The compacts were used to obtain bearing balls.

[0069] Next, the compact was subjected to a debinding process. The resulting debinding body was then subjected to a sintering process. The resulting sintered body was subjected to a high-temperature, high-pressure treatment process (e.g., HIP treatment) to obtain a spherical ceramic sintered body 1A. During this process, the cooling rate was controlled using a cooling mechanism provided in the HIP apparatus. The detailed conditions for the sintering process and HIP treatment in the examples are as shown in Table 2. The HIP treatment temperature [°C] is the heating and holding temperature. Furthermore, the "cooling rate" in Table 2 is the cooling rate from the heating and holding temperature to 200°C. Note that, for the comparative example, the conditions for the crushing process, molding process, debinding process, and polishing process are the same as those for Examples 1 to 8, while the conditions for the sintering process and high-temperature, high-pressure treatment process are shown in Table 2.

[0070]

[0071] A spherical ceramic sintered body 1A was obtained by HIP treatment. The spherical ceramic sintered body 1A was polished to a surface roughness Ra of 0.013 μm. A bearing ball 4 made of a ceramic sintered body was obtained by polishing. The bearing ball was spherical. The ceramic sintered body for bearing balls before polishing is a raw ball, and the bearing ball made of the ceramic sintered body after polishing is a finished ball. Note that when producing Example 9, the cooling rate was excessively high, so although the variation in the properties of the individual spherical ceramic sintered bodies 1A was sufficiently small, the load on the HIP apparatus increased, requiring inspection of the insulation and heater.

[0072] Next, in the examples, cross sections passing through the center C of the spherical ceramic sintered body 1A and the bearing ball (finished ball) 4 were prepared, and XRD analysis was performed on the surface region 3 and the center of gravity region 2. Because the spherical ceramic sintered body 1A and the bearing ball 4 in Examples 1, 5, and 6 had diameters less than 10 mm, the surface region 3 was defined as being within a range of 0.05 × D to 0.1 × D. Furthermore, because the surface region 3 in Examples 2 to 4 had a diameter of 10 mm or greater, it was defined as being within a range of 0.5 mm to 1.0 mm from the surface along the thickness direction (perpendicular to the surface). Furthermore, in Examples 1 to 8, the center of gravity region was defined as being within a range of 1 mm in center radius. The conditions for the XRD analysis were as described above. The top four peaks detected by XRD analysis in a diffraction angle (2θ) range of 10° to 60° were examined in descending order of peak intensity. The results are shown in Tables 3 and 4.

[0073] Similarly, XRD analysis was performed on the surface portion corresponding to surface portion 3 and the center of gravity corresponding to center of gravity portion 2 for the spherical ceramic sintered body of the comparative example. The center of gravity corresponding to center of gravity portion 2 of the spherical ceramic sintered body of the comparative example is the central portion with a radius of 1 mm or less from the center of gravity, similar to center of gravity portion 2. Note that because the spherical ceramic sintered body of the comparative example and the bearing ball based thereon have a diameter of less than 10 mm, the surface portion is in the range of 0.05 × D or more and 0.1 × D or less.

[0074]

[0075]

[0076] In Tables 3 and 4, 3 / 8 inch is a diameter of 9.525 mm. 1-3 / 16 inch is a diameter of 30.1625 mm. 1-7 / 8 inch is a diameter of 47.625 mm. For both the spherical ceramic sintered body 1A and the bearing ball 4 according to the example, the detection positions of the top four peaks in order of peak intensity detected within a diffraction angle (2θ) range of 10° to 60° in the surface region 3 and the center of gravity 2 coincided within a range of ±0.5°. Furthermore, for both the spherical ceramic sintered body 1A and the bearing ball 4 according to the example, the peak intensity difference rates between the peaks detected within a range of ±0.5° in the surface region 3 and the center of gravity 2 coincided within a range of ±10%.

[0077] The top four peaks in order of peak intensity for the silicon nitride sintered bodies according to Examples 1, 2, 3, 4, and 6 were detected near 23.4°, 27.1°, 33.6°, and 36.1°. For the α-aluminum oxide sintered body according to Example 5, peaks were detected near 25.6°, 35.2°, 43.4°, and 57.5°. For the zirconium oxide sintered body according to Example 7, peaks were detected near 30°, 34.5°, 60°, and 59°. For the aluminum nitride sintered body according to Example 8, peaks were detected near 33.5°, 36.1°, 38.0°, and 49.9°.

[0078] Furthermore, in the spherical ceramic sintered body 1A of Example 9 and the bearing ball 4 based thereon, the detection positions of the top four peaks in order of peak intensity detected within the diffraction angle (2θ) range between the surface portion and the center of gravity of 10° or more and 60° or less were consistent.

[0079] In contrast, in the comparative example of the spherical ceramic sintered body and the bearing ball based thereon, one or two peak detection positions were not aligned. The peaks with misaligned detection positions had peak intensities outside the range of ±10%.

[0080] Furthermore, in both the spherical ceramic sintered body 1A according to the example and the bearing ball 4, the peak intensities of the peaks at the top of the grain boundary phase, which are offset from each other by ±0.5° from the peaks at the surface 3 and the center of gravity 2, matched within a range of ±10%. On the other hand, in the ceramic sintered body according to the comparative example, the peak intensities of the XRD peaks at the top of the grain boundary phase were sometimes offset from each other.

[0081] Next, the surface portion 3 and the center of gravity portion 2 of the spherical ceramic sintered body 1A according to the example were observed using an SEM in an observation area of ​​50 μm × 50 μm. The top 50 ceramic crystal particles with the longest major diameters were extracted from each sample, and the average major diameter was determined. The relative density was also determined. The relative density was calculated by multiplying the density measured by the Archimedes method by the theoretical density by 100. The results are shown in Table 5. The surface portion and the center of gravity of the spherical ceramic sintered body according to the comparative example were also observed using an SEM in an observation area of ​​50 μm × 50 μm, and the average major diameter and relative density were determined using the same method.

[0082]

[0083] As can be seen from Table 5, the relative density of both the Examples and Comparative Examples was in the range of 99% or more and 100% or less. Furthermore, in the Examples, there was no significant difference in the average major axis of the ceramic crystal particles between the center of gravity 2 and the surface region 3 of the spherical ceramic sintered body 1A. On the other hand, in the Comparative Examples, there was a slight difference in the average major axis of the ceramic crystal particles between the center of gravity and the surface region of the spherical ceramic sintered body. This shows that the Examples have greater homogeneity between the surface region 3 and the center of gravity 2. Furthermore, the same tendency as that of the spherical ceramic sintered body 1A was observed for the bearing balls 4.

[0084] Next, for each of the ten ceramic sintered bodies 1 according to Example 1, the Vickers hardness and fracture toughness values ​​of the surface portion 3 were measured, and the Vickers hardness and fracture toughness values ​​of the center of gravity portion 2 were also measured. Based on the measurement results of the ten ceramic sintered bodies according to Example 1, the minimum and maximum Vickers hardness values ​​of the ten surface portions 3 were determined, and the minimum and maximum Vickers hardness values ​​of the ten center of gravity portion 2 were determined, as shown in Table 6. Similarly, for the fracture toughness values, the minimum and maximum values ​​of the surface portion 3 and the center of gravity portion 2 were determined, as shown in Table 7. Note that for Examples 2 to 9 and the Comparative Example, the minimum and maximum Vickers hardness values ​​of the surface portion (shown in Table 6), the minimum and maximum Vickers hardness values ​​of the center of gravity portion (shown in Table 6), the minimum and maximum fracture toughness values ​​of the surface portion (shown in Table 7), and the minimum and maximum fracture toughness values ​​of the center of gravity portion (shown in Table 7) were also determined.

[0085] Furthermore, the Vickers hardness difference rate and the fracture toughness difference rate were determined based on the measurement results of the 10 ceramic sintered bodies according to Example 1. The difference rates in Table 6 correspond to the above-mentioned formula (3). Table 6 lists the difference rate with the largest absolute value among the 10 difference rates for each of the 10 ceramic sintered bodies according to Example 1. On the other hand, the difference rates in Table 7 correspond to the above-mentioned formula (4). Table 6 lists the difference rate with the largest absolute value among the 10 difference rates for each of the 10 ceramic sintered bodies according to Example 1. Note that the Vickers hardness difference rate with the largest absolute value (shown in Table 6) and the fracture toughness difference rate with the largest absolute value (shown in Table 7) were also determined for each of Examples 2 to 9 and the Comparative Example.

[0086]

[0087]

[0088] As can be seen from Table 6, for the spherical ceramic sintered body (i.e., bare sphere) 1A according to the example, the difference in Vickers hardness between the surface portions was at most 50 HV (Example 4), which is an improved variation compared to the range of 120 to 200 HV for the difference in Vickers hardness between the surface portions of the spherical ceramic sintered body according to the comparative example. For the spherical ceramic sintered body 1A according to the example, the difference in Vickers hardness between the center portions of gravity was at most 40 HV (Example 4), which is an improved variation compared to the range of 130 to 180 HV for the difference in Vickers hardness between the center portions of gravity of the spherical ceramic sintered body according to the comparative example.

[0089] As can be seen from Table 7, in the spherical ceramic sintered body 1A according to the example, the difference in fracture toughness between the surface portions was at most 0.8 MPa m １／２ (Example 2), and the difference in fracture toughness between the surface portions of the spherical ceramic sintered bodies according to the comparative example was in the range of 1.0 to 1.2 MPa m １／２ In the spherical ceramic sintered bodies 1A according to the examples, except for Example 4, the difference in fracture toughness between the centers of gravity was at most 0.8 MPa m １／２ (Example 3), and the difference in fracture toughness between the centers of gravity of the spherical ceramic sintered bodies according to the comparative example was in the range of 1.0 to 1.2 MPa m １／２The variability is improved compared to

[0090] In the examples, the difference ratio based on the difference (Dv) between the Vickers hardness of the surface portion 3 and the Vickers hardness of the center of gravity portion 2 also satisfies the above-mentioned formula (3) for each of the spherical ceramic sintered bodies 1A. In the examples, the difference ratio based on the difference (Dt) between the fracture toughness value of the surface portion 3 and the fracture toughness value of the center of gravity portion 2 also satisfies the above-mentioned formula (4). The same tendency as that of the spherical ceramic sintered body 1A was also observed for the bearing ball 4.

[0091] In contrast, the comparative examples showed small minimum values ​​in the fracture toughness values ​​at both the surface and center of gravity. Also, the comparative examples showed large variations in both Vickers hardness and fracture toughness values.

[0092] The appearance of the spherical ceramic sintered body 1A of the example and the spherical ceramic sintered body of the comparative example after polishing was evaluated. The evaluation involved using a ball polishing machine to fix the polishing conditions for each spherical ceramic sintered body, and examining the surface for defects such as processing defects and voids inherent in the sintered body. The processing conditions were as follows: no pressure was applied to the upper platen, the lower platen was rotated, and an abrasive containing diamond and glycerin as a lubricant was supplied for 24 hours. Note that for ceramic balls of the same size, the gap distance with the upper platen, the rotation speed of the lower platen, the amount of ceramic ball material added, and the amount of abrasive supplied were all the same. After processing, 10,000 balls were sampled and visually and image-inspected for appearance. Those without abnormalities such as voids or processing-related scratches were considered good products and the percentage of good products was calculated. The results are shown in Table 8.

[0093]

[0094] As can be seen from Table 8, the bearing balls 4 of the example were able to suppress surface defects after finish processing. This is due to the effect of suppressing variations in the surface portion 3 and the center of gravity portion 2 of the bearing balls 4, thereby suppressing variations in processing. In contrast, poor appearance was occasionally observed in the bearing balls of the comparative example.

[0095] According to at least one of the embodiments described above, it is possible to provide a ceramic sintered body and a wear-resistant member in which the variation in Vickers hardness, which is a characteristic of each ceramic sintered body, is suppressed. Furthermore, according to this embodiment, it is possible to provide a ceramic sintered body and a wear-resistant member in which the variation in fracture toughness, which is a characteristic of each ceramic sintered body, is suppressed, except for relatively large sizes (1 7 / 8 inches in Example 4).

[0096] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

Claims

1. A ceramic sintered body, characterized in that, in any cross section passing through the center of gravity, the surface side portion is defined as the surface portion, and the portion within a radius of 1 mm from the center of gravity is defined as the center of gravity, and when the surface portion and the center of gravity are analyzed with an XRD (X-Ray Diffractometer), the detection positions of the top four peaks in order of peak intensity detected within a diffraction angle range of 10° to 60° coincide within a range of ±0.5° between the surface portion and the center of gravity.

2. The ceramic sintered body according to claim 1, characterized in that the surface portion is a portion extending from the surface along the thickness direction by 0.5 mm to 1.0 mm.

3. A ceramic sintered body as described in any one of claims 1 and 2, characterized in that the peak intensities of the peaks whose detection positions of the top four peaks in order of peak intensity are ±0.5° apart coincide within a range of ±10% between the surface portion and the center of gravity portion.

4. A ceramic sintered body according to any one of claims 1 to 3, characterized in that, based on SEM images obtained by photographing observation areas of 50 μm × 50 μm set on the surface portion and the center of gravity portion, respectively, with a SEM (Scanning Electron Microscope), the top 50 ceramic crystal grains with the largest major axis have an average major axis within the range of 0.5 μm or more and 20 μm or less.

5. A ceramic sintered body according to any one of claims 1 to 3, characterized in that it contains 1 mass % or more and 20 mass % or less of a grain boundary phase.

6. The ceramic sintered body according to claim 5, characterized in that the grain boundary phase contains one or more elements selected from the group consisting of rare earth elements, Al, Ti, Zr, Hf, Mo, W, Co, Fe and C.

7. The ceramic sintered body according to any one of claims 1 to 3, which is a silicon nitride sintered body.

8. The ceramic sintered body according to claim 6, which is a silicon nitride sintered body.

9. The ceramic sintered body according to claim 7, which is a solid having a height of 5 mm or more, or a sphere having a diameter of 5 mm or more.

10. The ceramic sintered body according to claim 8, which is a solid having a height of 5 mm or more, or a sphere having a diameter of 5 mm or more.

11. A ceramic sintered body according to any one of claims 1 to 3, characterized in that the difference in Vickers hardness between the surface portion and the center of gravity is within ±10%.

12. A ceramic sintered body according to any one of claims 1 to 3, characterized in that the difference rate based on the difference in fracture toughness value between the surface portion and the center of gravity portion is within ±20%.

13. A wear-resistant member comprising a ceramic sintered body according to any one of claims 1 to 3.

14. The wear-resistant member according to claim 13, characterized in that the wear-resistant member is a sintered silicon nitride body.

15. A method for producing a ceramic sintered body as described in claim 1, characterized in that in the process of treating under high temperature and high pressure, the cooling rate from the heating and holding temperature to 200°C is within the range of 20°C / min to 150°C / min.

16. A method for producing a ceramic sintered body as described in claim 15, characterized in that in the process of treating under high temperature and pressure, the cooling rate from the heating and holding temperature to 200°C is within the range of 20°C / min or more and 100°C / min or less.

17. The method for producing a ceramic sintered body according to claim 16, wherein the step of treating under high temperature and pressure is HIP (hot isostatic pressing) treatment.

18. The method for producing a ceramic sintered body according to claim 17, characterized in that the heating and holding temperature is within the range of 1500°C or higher and 2000°C or lower.

19. A method for producing a ceramic sintered body as described in claim 7, characterized in that in the process of treating under high temperature and pressure, the cooling rate from the heating and holding temperature to 200°C is within the range of 20°C / min to 100°C / min.

20. The method for producing a ceramic sintered body according to claim 19, characterized in that the step of treating under high temperature and pressure is HIP treatment.

21. The method for producing a ceramic sintered body according to claim 20, characterized in that the heating and holding temperature is within the range of 1500°C or higher and 2000°C or lower.

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