Silicon nitride sintered body, rolling element for bearing, silicon nitride solid ball, and bearing

Abstract

Provided is a silicon nitride-based sintered compact in which a total content of at least one metal M selected from the group consisting of Mg, Ca, and Y is 0.2 to 8.0 mass%, a content of Al is 4.0 to 12.0 mass%, a content of O is 4.0 to 12.0 mass%, and a fracture toughness value is 5.0 to 10.0 MPa·m1 / 2.

Description

[Technical Field]

[0001] The present invention relates to a silicon nitride sintered body, a rolling element for a bearing, a silicon nitride ball, and a bearing. [Background technology]

[0002] Silicon nitride sintered bodies have excellent mechanical strength and wear resistance, and are therefore used in wear-resistant components, gas turbine blades, engine parts, etc. Silicon nitride sintered bodies used in bearing components, which require particularly high wear resistance, are prepared by adding sintering aids such as Y2O3 or Al2O3 to the silicon nitride raw material and then firing the resulting material to form a grain boundary phase, thereby increasing the density and strength of the sintered body. To obtain such dense sintered bodies, sintering aids containing rare earth elements such as Y2O3 are used.

[0003] Another method is to add AlN as a sintering aid to form a silicon nitride solid solution called SiAlON, which improves wear resistance. However, because AlN has low water resistance, this method requires the use of an organic solvent instead of water to prepare the slurry and granulate it, which increases costs and produces a small amount of SiAlON.

[0004] Therefore, it has been proposed to use β-SiAlON synthesized by combustion synthesis as a raw material and sinter it. For example, Patent Document 1 discloses a silicon nitride sintered body obtained by adding aluminum oxide and yttrium oxide as sintering aids to β-SiAlON powder synthesized by combustion synthesis and then performing a single-stage sintering process, and the maximum pore size, contact area ratio, and average grain size of the crystal grains are within specific ranges. Patent Document 1 states that the resulting silicon nitride sintered body has small grain size and is almost free of defects that could serve as fracture bases, and is produced by a single heat treatment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-12985 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the silicon nitride sintered body described in Prior Art Document 1 has low fracture toughness, which is thought to be due to the use of βSiAlON powder, which results in little intertwining of the matrix phases when the α phase transitions to the β phase during liquid phase sintering. The application fields of silicon nitride sintered bodies are expanding, including electric vehicles, and there is a demand for reducing the processing cost when processing bare balls into precision balls, particularly for rolling elements for bearings. Therefore, one embodiment of the present disclosure aims to provide a silicon nitride sintered body with few defects, a rolling element for a bearing, and a bearing using the same. Another embodiment of the present disclosure aims to provide a silicon nitride sintered body, a silicon nitride ball, a rolling element for a bearing, and a bearing using the same, which have good processability. [Means for solving the problem]

[0007] The specific means for achieving the above object are as follows: <1> The total content of at least one metal M selected from the group consisting of Mg, Ca, and Y is 0.2 to 8.0 mass%, the content of Al is 4.0 to 12.0 mass%, and the content of O is 4.0 to 12.0 mass%, and the fracture toughness value is 5.0 to 10.0 MPa m 1 / 2 A silicon nitride sintered body. <2> The alloy has a matrix phase and a grain boundary phase, and the total content of the metal M in the grain boundary phase is 2.0 to 40.0 mass%. <1> The silicon nitride sintered body according to claim 1. <3> the total content of the metal M in the matrix is ​​2.0 to 10 mass%; <2> The silicon nitride sintered body according to claim 1. <4> The metal M is Ca. <1> ~ <3> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <5> It is a solid solution of SiAlON. <1> ~ <4> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <6> In the Raman spectrum, 177 to 197 cm -1 The minimum peak intensity at 170-190 cm -1 The ratio of the maximum peak intensity at <1> ~ <5> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <7> In the Raman spectrum, 185 to 210 cm -1 The peak attributable to the β phase in the range of 187 to 199 cm -1 exists between <1> ~ <6> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <8> Thermal conductivity is 5 to 15 W / (m·K). <1> ~ <7> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <9> Density: 3.10~3.20g / cm 3 That is, <1> ~ <8> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <10> The proportion of β phase, expressed as (β(101) + β(120)) / (α(210) + α(201) + β(101) + β(120)) × 100, obtained from the heights of the peaks corresponding to α phase (210), α phase (201), β phase (101), and β phase (120) in the X-ray diffraction spectrum, is 5 to 100%. <1> ~ <9> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <11> When a unit area of ​​5 mm × 5 mm of a cross section of the silicon nitride sintered body is observed under an optical microscope in a bright field at a magnification of 10 to 200 times, no pores having a major axis of 10 μm or more are observed. <1> ~ <10> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <12> When a unit area of ​​5 mm × 5 mm of a cross section of the silicon nitride sintered body is observed under an optical microscope in a dark field at a magnification of 10 to 200 times, no snowflakes having a major axis of 25 μm or more are observed. <1> ~ <11> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <13> When a region within 250 μm from the surface of the silicon nitride sintered body in a cross section is observed with an optical microscope in a dark field at a magnification of 10 to 200 times, no snowflakes with a major axis of 50 μm or more are observed. <1> ~ <12> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <14> For wear-resistant components, <1> ~ <13> 1. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is a silicon nitride sintered body. <15> <1> ~ <14> A silicon nitride sintered body according to any one of the above, wherein the difference between the maximum and minimum diameters is 100 μm or less and the height of the band-like convex portion is 50 μm or less. <16> <1> ~ <14> 2. A rolling element for a bearing, comprising a mirror-finished silicon nitride sintered body according to any one of 1 to 11. <17> <16> A bearing comprising the rolling element for a bearing according to claim 1. <18> It is for electric vehicles, <17> The bearing described in [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, there are provided a silicon nitride sintered body, silicon nitride solid balls, and rolling elements for bearings with few defects, as well as a bearing using the same. According to another embodiment of the present disclosure, there are provided a silicon nitride sintered body, silicon nitride solid balls, and rolling elements for bearings with good processability, as well as a bearing using the same. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram of a molded product having protrusions when a raw material composition is molded into a spherical shape using a die. [Figure 2] (A) is a cross-section of the spherical silicon nitride sintered body of Example 2, and (B) is a cross-section of the spherical silicon nitride sintered body of Example 6. Each is a mirror-finished image (dark field) of the cross-section near the surface of the sphere, observed with an optical microscope at 10x magnification. [Figure 3] (A) is a cross section of the silicon nitride sintered body of Example 2, and (B) is a cross section of the silicon nitride sintered body of Example 6, both of which were mirror-finished and then observed with a scanning electron microscope at 25,000x magnification. [Figure 4] 1 is an XRD spectrum of the silicon nitride sintered body of Example 2. [Figure 5] (A) is the Raman spectrum of the silicon nitride sintered body of Example 2, and (B) is the Raman spectrum of the silicon nitride sintered body of Example 6. [Figure 6] 1 shows Raman spectra of silicon nitride sintered bodies of Examples 6, 11, 15, 18, and 26. [Figure 7] FIG. 1 is a diagram illustrating a calotest. [Figure 8] FIG. 1 is a schematic diagram of a thrust rolling test device. [Figure 9] 1 shows images of the surfaces of the silicon nitride sintered bodies of Examples 15 and 28 after a thrust rolling test, observed with a laser microscope. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments. In this disclosure, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. Unless otherwise specified, "to" will be used in the following disclosure in the same sense. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. When embodiments are described with reference to the drawings in this disclosure, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of components in each drawing are conceptual, and the relative size relationships between components are not limited to these.

[0011] In the present disclosure, the Vickers hardness is measured using a Vickers hardness tester in accordance with JIS R1610:2003. In the present disclosure, fracture toughness is measured by the indentation method (IF method) specified in JIS R 1607:1995, and calculated using the formula of Niihara et al. In the present disclosure, Young's modulus is measured by the static deflection method in accordance with JIS R1602:1995. In this disclosure, density is measured by the Archimedes method.

[0012] In this disclosure, crushing strength is measured using a Tensilon testing machine according to a method based on JIS B1501:2009. The crushing strength value is the average value when 10 samples are measured. The Weibull coefficient of crushing strength is the value when 10 samples are measured. In the present disclosure, the thermal expansion coefficient is measured using a thermomechanical analysis (TMA) measuring device in accordance with JIS R1618:2002. In this disclosure, the three-point bending strength is measured by preparing a test piece of 3 mm x 4 mm x 40 mm, with a span (distance between supports) of 30 mm and a load application rate of 0.5 mm / min. The three-point bending strength value is the average value obtained by measuring 10 test pieces. The Weibull modulus of the three-point bending strength is the value obtained by measuring 10 test pieces.

[0013] In the present disclosure, measurements by X-ray diffraction (XRD) are performed using an X-ray diffractometer (for example, Rigaku Corporation's "Smart lab," detector "D / teXUltra," and X-ray analysis software "PDXL2") under the following conditions. Output: 45kV-200mA, Scanning range: 10°-60°, Optical system: Concentration method, Incident Soller slit: 5°, Length limiting slit: 10mm, Receiving slit 1: 8mm, Receiving slit 2: 13mm, Receiving parallel slit: 5.0°, Attenuator open, Scanning speed: 5° / min, Step width: 0.005°

[0014] In the present disclosure, elemental analysis of silicon nitride sintered bodies is carried out using an electron probe microanalyzer (EPMA) (for example, a JXA-8500F manufactured by JEOL Ltd. and a standard sample) under the following conditions: The surface of the measurement sample is carbon-coated (30 nm, 10 flashes) before analysis. Acceleration voltage: 15 keV, probe current: 30 nA, beam diameter: 30 μm,

[0015] In the present disclosure, the contents of Mg, Ca, and Y in the grain boundary phase of a silicon nitride sintered body are determined by energy dispersive X-ray spectroscopy (EDS) using an EDS analyzer (e.g., Noran System 6 manufactured by Thermo Fisher Scientific, detector: Ultradry manufactured by Thermo Fisher Scientific) under the following conditions. The line analysis width is 1, the number of points is 100, and the point acquisition interval is 50 nm. The acquired net count is converted into a moving average of three points, including one before and one after. The converted data is normalized so that the maximum value is 1 and the minimum value is 0. The point where Si and O intersect is defined as the phase boundary, and measurements are taken at five points within 150 nm from the boundary toward the grain boundary phase, and the average value of the obtained values ​​is calculated. In the present disclosure, the Mg, Ca, and Y contents in the matrix phase of a silicon nitride sintered body are determined in the same manner as the Mg, Ca, and Y contents in the grain boundary phase, except that the average values ​​obtained at points within 150 nm from the boundary toward the matrix are calculated.

[0016] In the present disclosure, the nitrogen content and oxygen content in the silicon nitride sintered body are measured using an oxygen analyzer in accordance with the inert gas fusion-infrared absorption method.

[0017] In the present disclosure, the major diameter of a pore is determined by observation and measurement in a bright field (BF) of an optical microscope. Specifically, a cross section of a silicon nitride sintered body is mirror-finished, and a region of 5 mm x 5 mm in area extending 2 mm or more from the surface of the mirror-finished cross section is magnified 10 to 20 times in a bright field (BF) to confirm the location of defects. The defect is then magnified 100 to 200 times to measure the major diameter of the pore. The longest diameter of a single pore is measured. Pores and pores are synonymous and are identified as defects with depth. Repeat the above magnification, observation, and measurement procedures to check for pores with a major axis of 10 μm or more in a unit area of ​​5 mm x 5 mm. If the sample size is less than 5 mm x 5 mm, observe multiple samples so that the total unit area is 5 mm x 5 mm.

[0018] In this disclosure, the major axis of a snowflake is determined by observation and measurement under a dark field (DF) of an optical microscope. Specifically, the cross section of the sintered body is polished to a mirror finish, and an arbitrary unit area of ​​5 × 5 mm on the polished cross section is magnified 10 to 20 times under a dark field (DF) to confirm the location of defects. The major axis of the snowflake is measured by magnifying the defects 100 to 200 times. The longest diameter of a single snowflake is measured. Repeat the above magnification, observation, and measurement procedures to check whether there are snowflakes with a major axis of 50 μm or more or 25 μm or more in a unit area of ​​5 mm × 5 mm. If the sample size is less than 5 mm × 5 mm, observe multiple samples so that the total unit area is 5 mm × 5 mm. "Snowflakes" are white spot-like defects that can be confirmed, for example, in dark-field (DF) images taken with an optical microscope, as shown in Figures 2(A) and 2(B). In the silicon nitride sintered compact shown in Figure 2(B), snowflakes appear as amorphous white spots near the periphery. Snowflakes are observed at any location on a sample of a silicon nitride sintered compact whose cross section has been mirror-polished, and in the surface layer region within 250 μm inward from the outer surface, which corresponds to the periphery of the sintered compact.

[0019] In the present disclosure, Raman spectroscopy is performed using a Raman spectrometer (for example, LabRAM HR Evolution manufactured by Horiba, Ltd.) under the following conditions. Measurement conditions: exposure time 1 second, 10 times accumulation, 100% neutral density filter (power 30 mW), 15 μm confocal hole, laser wavelength: 532 nm, 1200 grating lines, 100x objective lens (NA = 0.6)

[0020] The grinding rate is measured by pressing a #200 diamond metal grinding wheel at a constant pressure of 1.55 kg / cm2 onto a sample machined to a size of 15 mm square and 5 mm thick.

[0021] The arithmetic mean surface roughness Ra is measured in accordance with JIS B0601:2013 using a surface roughness measuring device (for example, a Surfcom measuring device) at a scanning speed of 1 mm / s and a scanning distance of 3 mm.

[0022] The volume resistivity is measured by processing a sample into a diameter of 20 mm and a thickness of 2 mm using a direct current three-terminal method in accordance with JIS C2141:1992.

[0023] The specific heat capacity is measured by DSC (differential scanning calorimetry). A sample with a diameter of 6 mm and a thickness of 0.75 mm is used. The thermal diffusivity is measured by the laser flash method using a sample with a diameter of 10 mm and a thickness of 2.0 mm. The thermal conductivity λ is calculated from the above-mentioned specific heat capacity Cp, density ρ, and thermal diffusivity α by the formula: λ=Cp×ρ×α.

[0024] The polishing rate is measured using the depth of polishing marks measured with a Calotest, the outline of which is shown in Figure 7. The deeper the polishing marks, the faster the polishing rate. As the Calotest, for example, a Calotest manufactured by Anton Paar is used. A silicon nitride sintered body is cut out, and the surface to be evaluated is mirror-finished to form a 2 mm-thick sample 10, which is attached to a surface plate 20. A 30 mm diameter steel ball 30 (precision ball, for example, SUJ2 ball (JIS grade G60) manufactured by Tsubaki Nakashima Co., Ltd.) is applied to the sample, and the sample is rotated on a rotating shaft 40 under the conditions described below while the following slurry is dropped on it. The depth of the depression (polishing mark) formed in the sample 10 is measured with a laser microscope. Three measurements are taken, and the average value is calculated. Stage angle: 25° Rotation speed: 1000 rpm ·Processing time: 60sec Slurry: 0.2 μm diamond abrasive grains Slurry amount: 3 drops initially, then 1 drop every 10 seconds

[0025] The fatigue test using the thrust rolling test is carried out under the following conditions. Testing machine: Thrust rolling contact fatigue testing machine (for example, manufactured by Fuji Testing Machinery Co., Ltd.). Figure 8 shows a schematic diagram of the thrust rolling contact testing device. Maximum Hertzian pressure: 5.2 GPa Spindle speed: 1200 rpm Spherical, Quantity: φ3 / 8 inch, 6 pieces Environment: Oil lubrication (e.g., JX Nippon Mining and Red Cross Kurisef Oil F8) Test piece: SUJ2 flat plate Stopping condition: 10 8 When the rotation is reached or when vibration due to the occurrence of spalling increases, but if no spalling is visually observed on the rolling elements, replace the SUJ2 plate and continue the test. In the thrust rolling test, the number of rotations when stopped is measured.

[0026] <Silicon nitride sintered body> The first silicon nitride sintered body of the present disclosure contains 3.0 mass% or more Al and 3.0 mass% or more O, and has a β-phase ratio of 5 to 100%, calculated from the heights of the peaks corresponding to the α-phase (210), α-phase (201), β-phase (101), and β-phase (120) in an X-ray diffraction spectrum, expressed as (β(101) + β(120)) / (α(210) + α(201) + β(101) + β(120)) × 100. The first silicon nitride sintered body having the above configuration has a small surface alteration layer due to sintering.

[0027] Commonly known sintered compositions for silicon nitride sintered bodies include silicon nitride-aluminum oxide and silicon nitride-rare earth oxide-aluminum oxide-titanium oxide. Sintering aids such as rare earth oxides are used to densify the sintered body and increase its strength. The sintering aids generate grain boundary phases consisting of Si-rare earth element-Al-ON, etc., during sintering.

[0028] However, when a sintering aid is used, some of the oxygen contained in the sintering aid evaporates during sintering, generating gas. If the gas remains in the silicon nitride sintered body, white spot-like defects called snowflakes occur. Because snowflakes are gas-induced regions, they are less dense than the surrounding area.

[0029] In contrast, the first silicon nitride sintered body of the present disclosure has the above-described structure and is therefore less likely to produce snowflakes.

[0030] Furthermore, silicon nitride sintered bodies having defects such as snowflakes and imperfections require hot isostatic pressing (HIP) to fill the defects, which increases the manufacturing cost. Furthermore, since such defects tend to occur near the surface of the silicon nitride sintered body, grinding near the surface is required, which increases the manufacturing cost.

[0031] The first silicon nitride sintered body of the present disclosure comprises the following: <1> It has the following configuration: <2> ~ <12> It is preferable that the structure be as follows: <1> A silicon nitride sintered body containing 3.0 mass% or more of Al and 3.0 mass% or more of O, in which the proportion of β phase, expressed as (β(101)+β(120)) / (α(210)+α(201)+β(101)+β(120))×100, calculated from the heights of the peaks corresponding to α phase (210), α phase (201), β phase (101), and β phase (120) in an X-ray diffraction spectrum, is 5 to 100%. <2> Contains at least one of Mg, Ca, and Y in an amount of 1 mass% or more; <1> The silicon nitride sintered body according to claim 1. <3> Contains 1% by mass or more of Ca, <1> or <2> The silicon nitride sintered body according to claim 1. <4> The cross section of the silicon nitride sintered body was examined under an optical microscope in a unit area of ​​5 mm x 5 mm. When observed under a microscope in a bright field at 10 to 200 times magnification, no defects with a major axis of 30 μm or more are found. <1> ~ <3> 1. The silicon nitride sintered body according to claim 1. <5> When a unit area of ​​5 mm × 5 mm of a cross section of the silicon nitride sintered body is observed under an optical microscope in a dark field at a magnification of 10 to 200 times, no snowflakes having a major axis of 50 μm or more are observed. <1> ~ <4> 1. The silicon nitride sintered body according to claim 1. <6> When a region within 250 μm from the surface of the silicon nitride sintered body in a cross section of the sintered body is observed with an optical microscope in a dark field at 10 to 200 magnifications, no snowflakes with a major axis of 50 μm or more are present. <1> ~ <5> 1. The silicon nitride sintered body according to claim 1. <7> When a region within 250 μm from the surface of the silicon nitride sintered body in a cross section of the sintered body is observed with an optical microscope in a dark field at 10 to 200 magnifications, no sintered layer having snowflakes with a major axis of 50 μm or more is present. <1> ~ <6> 1. The silicon nitride sintered body according to claim 1. <8> Fracture toughness value is 5.0 MPa m 1 / 2 That's all. <1> ~ <7> 1. The silicon nitride sintered body according to claim 1. <9> Young's modulus is 270 GPa or more, <1> ~ <8> 1. The silicon nitride sintered body according to claim 1. <10> It is a solid solution of SiAlON. <1> ~ <9> 1. The silicon nitride sintered body according to claim 1. <11> The silicon nitride sintered body in a spherical shape having a diameter of 10 mm has a crushing strength of 15 kN or more and a Weibull coefficient of the crushing strength of 7 or more. <1> ~ <10> 1. The silicon nitride sintered body according to claim 1. <12> In the Raman spectrum, 177±2cm -1 , 192±5cm -1 , and 219±3cm -1 There is a peak corresponding to the β phase in <1> ~ <11> 1. The silicon nitride sintered body according to claim 1.

[0032] The first silicon nitride sintered body contains 3.0 mass% or more of Al. The Al content in the first silicon nitride sintered body is preferably 3.5 mass% or more, more preferably 4.0 mass% or more, more preferably 4.5 mass% or more, more preferably 5.0 mass% or more, more preferably 5.5 mass% or more, and more preferably 6.0 mass%. From the viewpoint of improving fracture toughness, the Al content in the first silicon nitride sintered body is preferably 15 mass% or less, preferably 14 mass% or less, preferably 12 mass% or less, preferably 11 mass% or less, preferably 10 mass% or less, preferably 9.0 mass% or less, preferably 8.5 mass% or less, preferably 8.0 mass% or less, preferably 7.5 mass% or less, and preferably 7.0 mass% or less.

[0033] The first silicon nitride sintered body contains 3.0 mass% or more of O. The O content in the first silicon nitride sintered body is preferably 3.5 mass% or more, preferably 4.0 mass% or more, preferably 4.5 mass% or more, preferably 5.0 mass% or more, preferably 5.5 mass% or more, and preferably 6.0 mass%. From the viewpoint of improving fracture toughness, the O content in the first silicon nitride sintered body is preferably 15 mass% or less, preferably 14 mass% or less, preferably 12 mass% or less, preferably 11 mass% or less, preferably 10 mass% or less, preferably 9.0 mass% or less, preferably 8.5 mass% or less, preferably 8.0 mass% or less, preferably 7.5 mass% or less, and preferably 7.0 mass% or less.

[0034] The Si content in the first silicon nitride sintered body is preferably 30 mass % or more, preferably 40 mass % or more, preferably 42 mass % or more, preferably 43 mass % or more, preferably 44 mass % or more, preferably 45 mass % or more. The Si content in the first silicon nitride sintered body is preferably 60 mass% or less, preferably 58 mass% or less, preferably 56 mass% or less, preferably 54 mass% or less, preferably 52 mass% or less, preferably 50 mass% or less, preferably 49 mass% or less, preferably 48 mass% or less, preferably 47 mass% or less, and preferably 46 mass% or less.

[0035] The N content in the first silicon nitride sintered body is preferably 25 mass % or more, preferably 27 mass % or more, preferably 29 mass % or more, preferably 31 mass % or more, preferably 33 mass % or more, preferably 34 mass %. The N content in the first silicon nitride sintered body is preferably 45 mass% or less, preferably 43 mass% or less, preferably 42 mass% or less, preferably 41 mass% or less, preferably 40 mass% or less, preferably 39 mass% or less, preferably 38 mass% or less, preferably 37 mass% or less, preferably 36 mass% or less, and preferably 35 mass% or less.

[0036] The first silicon nitride sintered body has a ratio of β phase to the total amount of α phase and β phase, determined from the heights of the peaks corresponding to α phase (210), α phase (201), β phase (101), and β phase (120) in an X-ray diffraction spectrum, of 5 to 100%. Hereinafter, the ratio of β phase to the total amount of α phase and β phase: β phase / (α phase + β phase) × 100 is also referred to as the β ratio (%). Also, the ratio of α phase to the total amount of α phase and β phase: α phase / (α phase + β phase) × 100 is also referred to as the α ratio (%).

[0037] In this disclosure, the main peaks representing the α phase in the X-ray diffraction spectrum are those corresponding to the α phase (210) and α phase (201), and the main peaks representing the β phase are those corresponding to the β phase (101) and β phase (120). In the X-ray diffraction spectrum, the peak corresponding to the α phase (210) appears at 2θ = 30.5 to 32°, the peak corresponding to the α phase (201) appears at 2θ = 35 to 36°, the peak corresponding to the β phase (101) appears at 2θ = 33 to 34°, and the peak corresponding to the β phase (120) appears at 2θ = 36 to 37°.

[0038] In the present disclosure, the β rate is calculated using the following formula. β rate = (β(101)+β(120)) / (α(210)+α(201)+β(101)+β(120))×100 In the above formula, α(201) is the maximum peak height in the range of 2θ=30.5 to 32°, α(210) is the maximum peak height in the range of 2θ=35 to 36°, β(101) is the maximum peak height in the range of 2θ=33 to 34°, and β(120) is the maximum peak height in the range of 2θ=36 to 37°. The average value in the range of 2θ=32 to 35° is taken as the baseline.

[0039] The β ratio of the first silicon nitride sintered body is 5% or more, preferably 10% or more, preferably 20% or more, preferably 30% or more, preferably 40% or more, preferably 50% or more, and preferably 60% or more, and the β ratio is 100% or less, preferably 95% or less, preferably 90% or less, preferably 85% or less, preferably 80% or less, preferably 75% or less, and preferably 70% or less.

[0040] The first silicon nitride sintered body preferably contains at least one of Mg, Ca and Y in an amount of 1 mass % or more. The first silicon nitride sintered body may or may not contain Mg. When the first silicon nitride sintered body contains Mg, the Mg content in the first silicon nitride sintered body is preferably 0.1 mass%, preferably 0.5 mass% or more, preferably 1.0 mass% or more, preferably 1.5 mass% or more, preferably 2.0 mass% or more, and preferably 2.5 mass% or more. The Mg content in the first silicon nitride sintered body is preferably 6.0 mass% or less, preferably 5.0 mass% or less, preferably 4.0 mass% or less, and preferably 3.0 mass% or less. The first silicon nitride sintered body may or may not contain Ca, but preferably contains Ca from the viewpoint of promoting grain boundary sintering. When the first silicon nitride sintered body contains Ca, the Ca content in the first silicon nitride sintered body is preferably 1.0 mass% or more, more preferably 1.5 mass% or more, even more preferably 2.0 mass% or more, and preferably 2.5 mass% or more. From the viewpoint of strength, the Ca content in the first silicon nitride sintered body is preferably 10 mass% or less, preferably 9.0 mass% or less, preferably 8.0 mass% or less, preferably 7.0 mass% or less, preferably 6.0 mass% or less, preferably 5.0 mass% or less, preferably 4.0 mass% or less, and preferably 3.0 mass% or less. The first silicon nitride sintered body of the present disclosure preferably contains 1.0 mass% or more of Ca. The first silicon nitride sintered body may or may not contain Y. When the first silicon nitride sintered body contains Y, the Y content in the first silicon nitride sintered body may be 1.0 mass% or more, 1.5 mass% or more, 2.0 mass% or more, or 2.5 mass% or more. The Y content in the first silicon nitride sintered body may be 10 mass% or less, 9.0 mass% or less, 8.0 mass% or less, 7.0 mass% or less, 6.0 mass% or less, 5.0 mass% or less, 4.0 mass% or less, or 3.0 mass% or less.

[0041] The first silicon nitride sintered body preferably has a total content of Mg, Ca, and Y of 1.0% by mass or more, but may also be 1.5% by mass or more, 2.0% by mass or more, 2.5% by mass or more, or 3.0% by mass or more. The total content of Mg, Ca, and Y may be 10% by mass or less, 9.0% by mass or less, 8.0% by mass or less, 7.0% by mass or less, 6.0% by mass or less, 5.0% by mass or less, 4.0% by mass or less, or 3.5% by mass or less.

[0042] The first silicon nitride sintered body is more preferably an oxynitride, SiAlON. SiAlON has a structure in which O partially substitutes for N in silicon nitride (Si3N4), and Al partially substitutes for Si. SiAlON exists as αSiAlON, which exhibits an α phase, and βSiAlON, which exhibits a β phase. αSiAlON is considered to have a structure in which a metal atom M (M = Li, Mg, Ca, Y, La, etc.) is present inside the crystal lattice. βSiAlON does not have a metal atom M inside the crystal lattice.

[0043] The first silicon nitride sintered body of the present disclosure has a Raman spectrum of 177±2 cm -1 (177cm -1 (also called "nearby"), 192±5cm -1 (192cm -1 (also called "nearby"), 219±3cm-1 (219cm -1 It is preferable that a peak corresponding to the β phase exists in the region around 177 cm -1 Around 192cm -1 The nearby peaks are preferably broad. Fig. 5(A) shows the Raman spectrum of an example of the first silicon nitride sintered body of the present disclosure (Example 2 described in the Examples below). Fig. 5(B) shows the Raman spectrum of an example of a conventional silicon nitride sintered body (Example 6 described in the Examples below). As shown in FIG. 5(A), the first silicon nitride sintered body of the present disclosure has a surface roughness of 177 cm -1 Around 192cm -1 Near 219cm -1 These peaks correspond to the β phase of the silicon nitride sintered body. In the Raman spectrum shown in Figure 5(A), -1 Around 192cm -1 The peak in the vicinity is broad, indicating that the first silicon nitride sintered body is in a solid solution state. This suggests that a large amount of Al and O (oxygen) are dissolved in solid solution, resulting in low crystallinity. In contrast, as shown in FIG. 5(B), the conventional silicon nitride sintered body has a 180 cm -1 , 200cm -1 , 223cm -1 In the Raman spectrum shown in Figure 5(B), these peaks are sharp, which indicates that the silicon nitride sintered body is not in a solid solution state.

[0044] 177cm in Raman spectroscopy -1 Around 192cm -1 The peaks in the vicinity of 177-197 cm are broad. -1 The minimum peak intensity at 170-190 cm -1This is confirmed from the ratio of the maximum peak intensities at 1.0 to 3.0. If this ratio is 1.0 to 3.0, it can be considered to be a solid solution. This ratio is preferably 1.0 or more, preferably 1.1 or more, preferably 1.2 or more, preferably 1.3 or more, preferably 1.4 or more, and preferably 1.5 or more. This ratio is preferably 4 or less, preferably 3.5 or less, preferably 3.0 or less, preferably 2.5 or less, preferably 2.0 or less, preferably 1.9 or less, and preferably 1.8 or less.

[0045] The Raman spectrum shown in FIG. 5(A) is an example of the Raman spectrum of the second silicon nitride sintered body (Example 2 described later in the Examples section), and has a peak intensity of 170 to 190 cm -1 The peak with a peak top at 177 to 197 cm -1 Since the ratio of the peak to the minimum value is 1.26, it can be said that the peak is broad, indicating that the solid solution is in a state. In contrast, the silicon nitride sintered body shown in FIG. 5(B) has a surface roughness of 170 to 190 cm -1 The peak with a peak top at 177 to 197 cm -1 Since the difference between the minimum value and the peak is more than 3.0, it can be said that the peak is sharp, indicating that it is not a solid solution.

[0046] The first silicon nitride sintered body is preferably a solid solution of SiAlON. In the present disclosure, whether or not the first silicon nitride sintered body is in a solid solution state is confirmed by Raman spectroscopy as described above, but may also be confirmed additionally by a scanning electron microscope (SEM, e.g., IM4000plus, manufactured by Hitachi High-Technologies Corporation). For example, as shown in FIG. 3, the silicon nitride sintered body shown in (B) is confirmed to have a clear separation between the matrix and the grain boundary phase, while the sintered body shown in (A) is confirmed to have an incomplete separation between the matrix and the grain boundary phase, resulting in a solid solution. When the first silicon nitride sintered body is in a solid solution state, the grain boundary phase region, which has low mechanical strength, is reduced, thereby improving mechanical strength. Furthermore, a reduced grain boundary phase tends to further suppress the occurrence of snowflakes. Conventional silicon nitride sintered bodies are obtained by adding sintering aids such as Al2O3 and Y2O3 to the raw material α-Si3N4 and firing it. α-Si3N4 alone does not form a solid solution even at high temperatures, so the grain boundary phase derived from the sintering aid fills the grain boundaries of the α-Si3N4. Conventional silicon nitride sintered bodies, in which the matrix and grain boundary phases are clearly separated, require a sufficient amount of sintering aid to obtain a dense sintered body. Because this grain boundary phase is likely to cause snowflakes that can reduce wear resistance, it is preferable that no more grain boundary phase than necessary be present. Furthermore, in conventional silicon nitride sintered bodies, if an excessive amount of O (oxygen) is contained, the crystal grains grow, increasing defects at the grain boundaries and leading to a decrease in strength, so the O content is set to less than 3 mass%.

[0047] The first silicon nitride sintered body of the present disclosure is less likely to have pores with a major axis of 30 μm or more, and preferably, when observed in a unit area of ​​5 × 5 mm under an optical microscope in a bright field at 10 to 200 magnifications, no pores with a major axis of 30 μm or more are observed. The maximum major axis of the pores is preferably 30 μm or less, preferably 25 μm or less, preferably 20 μm or less, preferably 15 μm or less, preferably 12 μm or less, and preferably 10 μm or less.

[0048] The first silicon nitride sintered body of the present disclosure is less likely to produce snowflakes with a major axis of 50 μm or more, and preferably does not show snowflakes with a major axis of 25 μm or more when observed in a unit area of ​​5 × 5 mm using an optical microscope in a dark field at 10 to 200 magnifications. The maximum major axis of the snowflakes of the first silicon nitride sintered body is preferably 50 μm or less, more preferably 40 μm or less, more preferably 30 μm or less, more preferably 20 μm or less, more preferably 15 μm or less, more preferably 12 μm or less, and more preferably 10 μm or less.

[0049] Generally, silicon nitride sintered bodies are prone to snowflake formation, especially near the surface. However, the first silicon nitride sintered body of the present disclosure is less prone to snowflake formation even near the surface, so the amount of surface cutting (grinding allowance) required to remove snowflakes is reduced, thereby suppressing manufacturing costs. When the first silicon nitride sintered body is observed in a region within 250 μm from the surface (also referred to as the outer periphery) under an optical microscope in a dark field at 10 to 200 magnifications, it is preferable that no snowflakes with a major axis of 50 μm or more are present in the magnified image. The maximum major axis of the snowflakes in the outer periphery of the first silicon nitride sintered body is preferably 50 μm or less, more preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less.

[0050] The first silicon nitride sintered body of the present disclosure preferably does not have a sinter-induced alteration layer in a region within 250 μm from the surface (also referred to as the outer periphery). The sinter-induced alteration layer is defined as a region within 250 μm from the surface of the sintered body before surface processing, in which snowflakes with a major axis of 50 μm or more are present when observed under a dark field of 10 to 200 times with an optical microscope.

[0051] The fracture toughness value of the first silicon nitride sintered body is 5.0 MPa m 1 / 2 More than 5.2 MPa m is preferable. 1 / 2 More than 5.4 MPa m is preferable. 1 / 2 More than 5.6 MPa m is preferable. 1 / 2 More than 5.8 MPa m is preferable. 1 / 2 More than 6.0 MPa m is preferable. 1 / 2 More than 6.3 MPa m is preferable. 1 / 2 More than 6.5 MPa m is preferable. 1 / 2 More than 7.0 MPa m is preferable. 1 / 2 The above is preferable. The upper limit of the first fracture toughness value is not particularly limited, but is preferably 10.0 MPa m 1 / 2 It may be less than 9.0 MPa m 1 / 2 It may be less than 8.0 MPa m 1 / 2 It may be 7.5 or less.

[0052] The Young's modulus of the first silicon nitride sintered body is preferably 270 GPa or more, preferably 280 GPa or more, preferably 290 GPa or more, and preferably 300 GPa or more. The upper limit of the Young's modulus is not particularly limited, but may be 350 GPa or less, 340 GPa or less, 330 GPa or less, 320 GPa or less, 315 GPa or less, or 310 GPa or less.

[0053] The density of the first silicon nitride sintered body is 3.00 g / cm 3 More than 3.05 g / cm is preferable. 3 More than 3.10 g / cm is preferable. 3 More than 3.15 g / cm is preferable. 3 More than 3.17 g / cm is preferable. 3 More than 3.19 g / cm is preferable. 3 The upper limit of the density is preferably 3.40 g / cm 3 Preferably less than 3.30 g / cm 3 Less than 3.25 g / cm is more preferable. 3 More preferably, 3.20 g / cm 3 The following is particularly preferred: 3.19 g / cm 3 may be less than 3.18 g / cm 3 may be less than 3.17 g / cm 3 may be less than 3.16 g / cm 3 It may be the following:

[0054] The thermal expansion coefficient of the first silicon nitride sintered body is preferably 3.5 ppm or less, preferably 3.4 ppm or less, preferably 3.3 ppm or less, preferably 3.2 ppm or less, preferably 3.1 ppm or less, and preferably 3.0 ppm or less. There is no particular lower limit to the thermal expansion coefficient, but it may be 2.5 ppm or more, 2.6 ppm or more, 2.7 ppm or more, 2.8 ppm or more, or 2.9 ppm or more.

[0055] The first silicon nitride sintered body is preferably an insulator, and has a volume resistivity of 1×10 at room temperature (25° C.). 10 Ω·cm or more is preferable, and 1×10 11 Ω·cm or more is preferable, and 1×10 12 Ω·cm or more is preferable, and 1×10 13 Ω·cm or more is preferable, and 1×10 14 Ω·cm or more is preferable, and 1×10 15 Ω·cm or more is preferable, and 1×10 16 Ω·cm or more is most preferable.

[0056] The first silicon nitride sintered body preferably has high thermal insulation performance, and its thermal conductivity is preferably 50 W / (m·K) or less, preferably 40 W / (m·K) or less, preferably 30 W / (m·K) or less, preferably 25 W / (m·K) or less, preferably 20 W / (m·K) or less, preferably 15 W / (m·K) or less, and preferably 10 W / (m·K) or less. For example, when used as a rolling element in a bearing, the temperature of the rolling element tends to rise due to frictional resistance between the outer and inner rings at high rotation speeds. Therefore, from the perspective of suppressing temperature increases due to frictional resistance, it is preferable that the thermal conductivity of the rolling element be low, which is also expected to suppress increases in friction due to thermal deformation. The first silicon nitride sintered body tends to have low thermal conductivity.

[0057] The Vickers hardness of the first silicon nitride sintered body is preferably 1300 GPa or more, preferably 1350 GPa or more, preferably 1370 GPa or more, preferably 1400 GPa or more, preferably 1420 GPa or more, and preferably 1450 GPa or more. The upper limit of the Vickers hardness is not particularly limited, but may be 2000 GPa or less, 1900 GPa or less, 1800 GPa or less, 1700 GPa or less, 1600 GPa or less, or 1550 GPa or less.

[0058] The first silicon nitride sintered body preferably has a crushing strength of 15 kN or more when formed into a sphere having a diameter of 10 mm, and a Weibull coefficient of the crushing strength of 7 or more. The crushing strength of the first silicon nitride sintered body is preferably 15 kN or more, preferably 16 kN or more, preferably 17 kN or more, preferably 18 kN or more, preferably 19 kN or more, and preferably 20 kN or more. The upper limit of the crushing strength is not particularly limited, but may be 40 kN or less, 35 kN or less, 30 kN or less, 28 kN or less, 25 kN or less, or 24 kN or less. The Weibull coefficient of crushing strength of the first silicon nitride sintered body is preferably 7 or more, preferably 8 or more, preferably 9 or more, preferably 11 or more, preferably 12 or more, and preferably 13 or more. The upper limit of the Weibull coefficient of crushing strength is not particularly limited, but may be 40 or less, 30 or less, 25 or less, 20 or less, 18 or less, or 15 or less.

[0059] The three-point bending strength of the first silicon nitride sintered body is 500 MPa m 1 / 2 More than 600 MPa m is preferable. 1 / 2 More than 700 MPa m is preferable. 1 / 2 More than 750 MPa m is preferable. 1 / 2 More than 800 MPa m is preferable. 1 / 2 More than 850 MPa m is preferable. 1 / 2 The upper limit of the three-point bending strength is not particularly limited, but is preferably 1200 MPa m 1 / 2 may be less than 1100 MPa m 1 / 2 may be less than 1050 MPa m 1 / 2 may be less than 1000 MPa m 1 / 2 It may be less than 980 MPa m 1 / 2 It may be less than 930 MPa m 1 / 2 It may be the following: The Weibull coefficient of three-point bending strength of the first silicon nitride sintered body is preferably 5 or more, more preferably 6 or more, more preferably 7 or more, more preferably 8 or more, more preferably 9 or more, and more preferably 10 or more. The upper limit of the Weibull coefficient of three-point bending strength is not particularly limited, but may be 15 or less, 14 or less, 13 or less, 12 or less, or 11 or less.

[0060] <Second silicon nitride sintered body> The second silicon nitride sintered body of the present disclosure has a total content of at least one metal M selected from the group consisting of Mg, Ca, and Y of 0.2 to 8.0 mass%, an Al content of 4.0 to 12.0 mass%, and an O content of 4.0 to 12.0 mass%, and has a fracture toughness value of 5.0 to 10.0 MPa m 1 / 2 The second silicon nitride sintered body having the above-mentioned structure is characterized by excellent workability.

[0061] The second silicon nitride sintered body has a total content of metal M of 0.2% by mass or more, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2.0% by mass or more. The second silicon nitride sintered body has a total content of metal M of 8.0% by mass or less, preferably 7.5% by mass or less, preferably 7.0% by mass or less, preferably 6.5% by mass or less, preferably 6.0% by mass or less, preferably 5.5% by mass or less, preferably 5.0% by mass or less, preferably 4.5% by mass or less, preferably 4.0% by mass or less, preferably 3.5% by mass or less, and preferably 3.0% by mass or less.

[0062] In the second silicon nitride sintered body, the metal M is preferably Ca from the viewpoints of improving fracture toughness and achieving a low density. When the second silicon nitride sintered body contains Ca, the Ca content in the second silicon nitride sintered body is preferably 0.2% by mass or more, preferably 0.5% by mass or more, preferably 1.0% by mass or more, or may be 1.5% by mass or more, 2.0% by mass or more, 2.5% by mass or more, 3.0% by mass or more, or even 3.5% by mass or more. From the viewpoint of strength, the Ca content in the second silicon nitride sintered body is 8.0% by mass or less, or may be 7.5% by mass or less, or may be 7.0% by mass or less, or may be 6.5% by mass or less, or may be 6.0% by mass or less, or may be 5.5% by mass or less, or may be 5.0% by mass or less, or may be 4.5% by mass or less, or may be 4.0% by mass or less, or may be 3.5% by mass or less.

[0063] The second silicon nitride sintered body may or may not contain Mg. When the second silicon nitride sintered body contains Mg, the Mg content in the second silicon nitride sintered body may be 0.1% by mass, 0.5% by mass or more, 1.0% by mass or more, 1.5% by mass or more, 2.0% by mass or more, or 2.5% by mass or more. The Mg content in the second silicon nitride sintered body may be 8.0% by mass or less, 7.5% by mass or less, 7.0% by mass or less, 6.5% by mass or less, 6.0% by mass or less, 5.5% by mass or less, 5.0% by mass or less, 4.5% by mass or less, 4.0% by mass or less, or 3.5% by mass or less.

[0064] The second silicon nitride sintered body may or may not contain Y. When the second silicon nitride sintered body contains Y, the Y content in the second silicon nitride sintered body may be 1.0 mass% or more, 1.5 mass% or more, 2.0 mass% or more, or 2.5 mass% or more. The Y content in the second silicon nitride sintered body may be 8.0 mass% or less, 7.5 mass% or less, 7.0 mass% or less, 6.5 mass% or less, 6.0 mass% or less, 5.5 mass% or less, 5.0 mass% or less, 4.5 mass% or less, 4.0 mass% or less, or 3.5 mass% or less.

[0065] The second silicon nitride sintered body has an Al content of 4.0% by mass or more, and from the viewpoint of sinterability, preferably 4.5% by mass or more, preferably 5.0% by mass or more, preferably 5.5% by mass or more, preferably 6.0% by mass or more, preferably 6.5% by mass or more, and preferably 7.0% by mass or more. The second silicon nitride sintered body has a total Al content of 12.0% by mass or less, preferably 11.5% by mass or less, preferably 11.0% by mass or less, preferably 10.5% by mass or less, preferably 10.0% by mass or less, preferably 9.5% by mass or less, preferably 9.0% by mass or less, preferably 9.5% by mass or less, preferably 9.0% by mass or less, preferably 8.5% by mass or less, preferably 8.0% by mass or less, and preferably 7.5% by mass or less.

[0066] The second silicon nitride sintered body has an O content of 4.0% by mass or more, and from the viewpoint of processability, preferably 4.5% by mass or more, more preferably 5.0% by mass or more, preferably 5.5% by mass or more, more preferably 6.0% by mass or more, and even more preferably 6.5% by mass or more. The second silicon nitride sintered body has a total O content of 12.0% by mass or less, and from the viewpoint of improving fracture toughness, preferably 11.0% by mass or less, preferably 10.0% by mass or less, preferably 9.0% by mass or less, preferably 8.0% by mass or less, and preferably 7.0% by mass or less.

[0067] The Si content and N content of the second silicon nitride sintered body are the same as the Si content and N content of the first silicon nitride sintered body.

[0068] The fracture toughness value of the second silicon nitride sintered body is 5.0 MPa m 1 / 2 and above 5.2 MPa m 1 / 2 More than 5.4 MPa m is preferable. 1 / 2 More than 5.6 MPa m is preferable. 1 / 2 More than 5.8 MPa m is preferable. 1 / 2 More than 6.0 MPa m is preferable. 1 / 2 More than 6.3 MPa m is preferable. 1 / 2 More than 6.5 MPa m is preferable. 1 / 2 More than 7.0 MPa m is preferable. 1 / 2 The above is preferable.

[0069] The upper limit of the fracture toughness value of the second silicon nitride sintered body is 10.0 MPa m 1 / 2 is less than 9.0 MPa m 1 / 2 It may be less than 8.0 MPa m 1 / 2 It may be 7.5 or less.

[0070] The total content of metal M in the grain boundary phase is preferably 2.0 to 40.0 mass %, more preferably 2.0 to 30.0 mass %, from the viewpoint of improving fracture toughness. The total content of metal M in the grain boundary phase may be 3.0% by mass or more, 4.0% by mass or more, 5.0% by mass or more, 6.0% by mass or more, 7.0% by mass or more, 8.0% by mass or more, 9.0% by mass or more, 10.0% by mass or more, or 11.0% by mass or more. The total content of metal M in the grain boundary phase may be 25.0 mass% or less, 20.0 mass% or less, 18.0 mass% or less, 17.0 mass% or less, 16.0 mass% or less, 15.0 mass% or less, 14.0 mass% or less, 13.0 mass% or less, or 12.0 mass% or less.

[0071] The total content of metal M in the matrix is ​​preferably 2.0 to 10.0 mass %, more preferably 2.0 to 8.0 mass %, from the viewpoint of improving fracture toughness. The total content of metal M in the matrix may be 2.5% by mass or more, 3.0% by mass or more, 3.5% by mass or more, or 4.0% by mass or more. The total content of metal M in the matrix may be 7% by mass or less, 6.5% by mass or less, 6.0% by mass or less, 5.5% by mass or less, 5.0% by mass or less, 4.5% by mass or less, or 4.0% by mass or less.

[0072] The second silicon nitride sintered body is preferably a solid solution of SiAlON. The term "SiAlON" has the same meaning as that described for the first silicon nitride sintered body. The term "solid solution" also has the same meaning as that described for the first silicon nitride sintered body.

[0073] The second silicon nitride sintered body has a Raman spectrum of 177 to 197 cm -1 The minimum peak intensity at 170-190 cm -1 The ratio of the maximum peak intensities in the range of 1.0 to 3.0 is preferred, and within this range, the SiAlON particles are sufficiently solid-dissolved. The ratio is preferably 1.0 or more, preferably 1.1 or more, preferably 1.2 or more, preferably 1.3 or more, preferably 1.4 or more, and preferably 1.5 or more. The ratio is preferably 3.0 or less, preferably 2.5 or less, preferably 2.0 or less, preferably 1.9 or less, and preferably 1.8 or less.

[0074] In the Raman spectrum, 185 to 210 cm -1 The peak attributable to the β phase in the range of 187 to 199 cm -1 It is preferred that the saturation voltage is between 0.1 and 0.2 V.

[0075] The thermal conductivity of the second silicon nitride sintered body is preferably 5 to 15 W / (m·K). The thermal conductivity of the second silicon nitride sintered body may be 6 W / (m·K) or more, or 7 W / (m·K) or more. The thermal conductivity of the second silicon nitride sintered body may be 14 W / (m·K) or less, 13 W / (m·K) or less, or 12 W / (m·K) or less.

[0076] The density of the second silicon nitride sintered body is 3.10 to 3.20 g / cm 3 is preferred. The density of the second silicon nitride sintered body is 3.11 g / cm 3 It may be 3.12 g / cm or more. 3 or more, 3.13 g / cm 3 The density of the second silicon nitride sintered body may be 3.19 g / cm or more. 3 may be less than 3.18 g / cm 3 may be less than 3.17 g / cm 3 may be less than 3.16 g / cm 3 It may be the following:

[0077] The second silicon nitride sintered body preferably has a ratio of 5 to 100% of the β phase to the total amount of the α phase and the β phase, as determined from the heights of the peaks corresponding to the α phase (210), α phase (201), β phase (101), and β phase (120) in an X-ray diffraction spectrum. The β ratio (%) and α ratio (%) in the second silicon nitride sintered body are the same as the β ratio (%) and α ratio (%) in the first silicon nitride sintered body, respectively.

[0078] The second silicon nitride sintered body is preferably resistant to the generation of pores with a major axis of 10 μm or more, and when observed in a unit area of ​​5 × 5 mm under an optical microscope in a bright field at 10 to 200 magnifications, no defects with a major axis of 10 μm or more are found. The maximum major axis of the defect is preferably less than 10 μm, preferably 9 μm or less, preferably 8 μm or less, more preferably less than 7 μm, more preferably 6 μm or less, and more preferably 5 μm or less.

[0079] The second silicon nitride sintered body is less likely to produce snowflakes with a major axis of 25 μm or more, and it is preferable that when an area of ​​5 × 5 mm is observed under an optical microscope in a dark field at 10 to 200 magnifications, no snowflakes with a major axis of 25 μm or more are observed. The maximum length of the snowflakes of the second silicon nitride sintered body is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less.

[0080] When the second silicon nitride sintered body is observed in a region within 250 μm from the surface (also called the outer periphery) using an optical microscope in a dark field at 10 to 200 magnifications, it is preferable that no snowflakes with a major axis of 50 μm or more are observed in the enlarged image. The maximum major axis of the snowflakes in the outer periphery of the second silicon nitride sintered body is preferably 50 μm or less, more preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less.

[0081] From the viewpoint of processability, the depth of polishing marks of the second silicon nitride sintered body, as an index of the polishing rate measured by Calotest, is preferably 3.6 μm or more, preferably 3.7 μm or more, preferably 3.8 μm or more, preferably 3.9 μm or more, preferably 4.0 μm or more, preferably 4.1 μm or more, more preferably 4.2 μm or more, even more preferably 4.3 μm or more, preferably 4.4 μm or more, more preferably 4.5 μm or more, and even more preferably 4.6 μm or more. From the viewpoint of wear resistance, the second silicon nitride sintered body preferably has a depth of polishing marks measured by Calotest of 8.0 μm or less, preferably 7.0 μm or less, preferably 6.0 μm or less, preferably 5.0 μm or less, preferably 4.9 μm or less, preferably 4.8 μm or less, and preferably 4.7 μm or less.

[0082] The Young's modulus, thermal expansion coefficient, volume resistivity, Vickers hardness, crushing strength, Weibull coefficient of crushing strength, three-point bending strength, and Weibull coefficient of three-point bending strength of the second silicon nitride sintered body are similar to the Young's modulus, thermal expansion coefficient, volume resistivity, Vickers hardness, crushing strength, Weibull coefficient of crushing strength, three-point bending strength, and Weibull coefficient of three-point bending strength of the first silicon nitride sintered body, respectively.

[0083] <Application> The first silicon nitride sintered body and the second silicon nitride sintered body (hereinafter, the first silicon nitride sintered body and the second silicon nitride sintered body are also collectively referred to as silicon nitride sintered bodies) are suitably used for wear-resistant members, for example, as rolling elements for bearings.

[0084] <Method for manufacturing silicon nitride sintered body> There are no particular limitations on the method for producing the first silicon nitride sintered body, as long as it can produce a sintered body containing 3 mass % or more of Al, 3 mass % or more of O, and having a β ratio of 5 to 100%. The second method for producing a silicon nitride sintered body is to produce a silicon nitride sintered body having a total content of at least one metal M selected from the group consisting of Mg, Ca, and Y of 0.2 to 8.0 mass%, an Al content of 4.0 to 12.0 mass%, an O content of 4.0 to 12.0 mass%, and a fracture toughness value of 5.0 to 10.0 MPa m 1 / 2 There are no particular limitations on the manufacturing method as long as the sintered body can be obtained.

[0085] One example of a method for producing a silicon nitride sintered body involves preparing a raw material composition containing a silicon nitride material as a raw material, granulating, molding, pressing, degreasing, and firing. Examples of additives that can be added to the raw material composition include sintering aids, binders, solvents, and sintering accelerators. Processes other than firing may be omitted as appropriate. Furthermore, processes other than those mentioned above, such as classification, may be added as appropriate. Another example of a method for producing a silicon nitride sintered body is to sinter a silicon nitride material alone as a raw material. However, when a molded silicon nitride sintered body is to be obtained, it is preferable to prepare and use a raw material composition.

[0086] Examples of silicon nitride raw materials include αSi3N4, βSi3N4, M-αSiAlON, and βSiAlON. From the viewpoint of sinterability, αSi3N4 and M-αSiAlON are preferred. βSiAlON and M-αSiAlON are preferred because they have low or no hydrolysis and can be used in oxygen-containing solvents such as water. M-αSiAlON is preferred as a silicon nitride raw material because it improves fracture toughness by transforming granular α-phase crystals into acicular β-phase crystals during liquid-phase sintering. Furthermore, M-αSiAlON is preferred as a silicon nitride raw material because it can omit the use of sintering aids and produce a homogeneous, dense silicon nitride sintered body in a solid solution state. M-αSiAlON is αSiAlON in which metal atoms M (M = Li, Mg, Ca, Y, La, etc.) exist within the crystal lattice, and when it transforms into βSiAlON during liquid-phase sintering, the metal elements form grain boundary phases with Si, Al, O, etc., resulting in a uniform and dense sintered body. The silicon nitride material used as the raw material may be used alone or in combination of two or more types.

[0087] M-αSiAlON may be a commercially available product or may be manufactured. M-αSiAlON can be obtained by firing a mixture of αSi3N4, AlN, Al2O3, and metal M or a compound containing metal M. Alternatively, M-αSiAlON can be synthesized by combustion synthesis using raw material powders in which predetermined elements are mixed in predetermined ratios.

[0088] The metal atom M in M-αSiAlON may function as a sintering aid during sintering, and therefore the content of the metal atom M in M-αSiAlON is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, more preferably 1.5 mass% or more, more preferably 2.0 mass% or more, and more preferably 2.5 mass%. In addition, from the viewpoint of suppressing the precipitation of crystalline phases other than M-αSiAlON, the content of metal atom M in M-αSiAlON is preferably 9.0 mass%, preferably 8.0 mass% or less, preferably 7.0 mass% or less, preferably 6.0 mass% or less, preferably 5.5 mass% or less, preferably 5 mass% or less, preferably 4.5 mass% or less, and preferably 4.0 mass% or less.

[0089] The more α-phase SiAlON there is, the better. It has superior sinterability compared to ON. The α fraction of M-αSiAlON is preferably 81% or more, preferably 82% or more, preferably 83% or more, preferably 84% or more, preferably 85% or more, preferably 86% or more, preferably 87% or more, preferably 88% or more, preferably 89% or more, preferably 90% or more, preferably 91% or more, preferably 92% or more, preferably 93% or more, preferably 94% or more, preferably 95% or more, preferably 96% or more, preferably 97% or more, preferably 98% or more, preferably 99% or more, and is preferably a single phase (100%).

[0090] The α rate is calculated using the following formula. α rate=(α(210)+α(201)) / (α(210)+α(201)+β(101)+β(120))×100 In the above formula, α(201), α(210), β(101), and β(120) are synonymous with α(201), α(210), β(101), and β(120), respectively, in the β ratio.

[0091] Examples of sintering aids include compounds containing Li, Mg, Ca, Y, La, etc., and specific examples include Al2O3, Y2O3, AlN, and MgAl2O4. The binder may be an organic binder. Examples of solvents include water, alcohol, and hydrocarbons. Conventional silicon nitride sintered bodies use α-Si3N4 as the raw material, but if a solvent containing oxygen atoms, such as water, is used as the solvent, oxygen atoms may enter the Si3N4, affecting the properties of the final silicon nitride sintered body. Therefore, when manufacturing conventional silicon nitride sintered bodies, it is preferable to select the solvent appropriately. On the other hand, since SiAlON already contains oxygen atoms as a constituent element, using water when using SiAlON as the raw material has little effect on the properties of the final product, thereby widening the options for the manufacturing process.

[0092] Examples of sintering accelerators include compounds containing Ti, Hf, Zr, W, Mo, Nb, Cr, etc., including oxides, carbides, nitrides, silicides, and borides of these elements. The elements in the sintering accelerator may enhance dispersion in the crystalline structure, thereby improving the mechanical strength of the silicon nitride sintered body. The sintering accelerator is preferably a compound containing Ti or Mo. Compounds containing Ti or Mo also function as a light-blocking agent, coloring the silicon nitride sintered body black and imparting opacity.

[0093] When a sintering aid is used, from the viewpoint of achieving the effect of adding the sintering accelerator, the amount of the sintering accelerator added, in terms of oxide, is preferably 0.1 mass% or more, preferably 0.2 mass% or more, preferably 0.3 mass% or more, preferably 0.4 mass% or more, and preferably 0.5 mass% or more, based on the silicon nitride material. Also, from the viewpoint of further increasing the mechanical strength, the amount of the sintering accelerator added, in terms of oxide, is preferably 5 mass% or less, preferably 3 mass% or less, preferably 2 mass% or less, and preferably 1 mass% or less, based on the silicon nitride material.

[0094] The raw material composition may be molded into a desired shape before firing for sintering. Known molding methods such as uniaxial pressing, mold pressing, doctor blade pressing, rubber pressing, and cold isostatic pressing (CIP) can be used. The molded product may be further compressed by CIP or the like. The molded product may then be degreased before firing.

[0095] When molding into a spherical shape using upper and lower molds, the molds are often designed so that there is some slack between them when they are closed, and in this case, the molded product obtained has protrusions due to the slack. For example, when a hemispherical upper mold and a hemispherical lower mold are used, a molded product such as that shown in Figure 1 is obtained. To remove these protrusions, it is preferable to grind them before firing, and if the molded product is subjected to CIP treatment, it is preferable to grind them after CIP treatment and before firing. If degreasing is performed before firing, it is preferable to grind the protrusions before degreasing.

[0096] When stripping is performed before firing, the height of the strip-shaped convex portions is preferably 500 μm or less, preferably 40 μm or less, preferably 30 μm or less, preferably 20 μm or less, preferably 10 μm or less, and most preferably zero.

[0097] Alternatively, the mixture may be granulated before molding, and the granulated mixture may be used for molding. The granulation method is not particularly limited, and examples thereof include spray drying.

[0098] Degreasing may be carried out in either a non-oxidizing or oxidizing atmosphere. When degreasing is carried out in a non-oxidizing atmosphere, the temperature is preferably 550 to 800° C., and when degreasing is carried out in an oxidizing atmosphere such as air, the temperature is preferably 400 to 650° C. The heating time at these temperatures is preferably 1 to 2 hours.

[0099] The silicon nitride material or molded product is preferably heated under reduced pressure, preferably in a vacuum of 0.01 Pa or less. The heating temperature in vacuum is preferably 1200 to 1500°C, and the holding time at this heating temperature is preferably 1 to 10 hours.

[0100] After heating under reduced pressure or vacuum, it is preferable to sinter in an inert gas atmosphere such as nitrogen gas or argon gas. Either atmospheric pressure sintering or pressure sintering may be used, and the sintering temperature is preferably 1600 to 1850°C. If the sintering temperature is 1600°C or higher, the sintered body will be sufficiently densified, the defect rate will be low, the mechanical strength will be improved, and when used as a rolling element for a bearing, the rolling life will be improved. If the sintering temperature is 1850°C or lower, it will be easier to obtain a sintered body with the desired composition. As the pressure sintering method, various pressure sintering methods such as atmospheric pressure sintering, hot pressing, and hot isostatic pressing (HIP) are used.

[0101] During firing, the α phase transforms into the β phase due to the oxygen present on the surface. When M-αSiAlON transforms into βSiAlON, the metal atoms M incorporated within the lattice migrate from within the lattice to the grain boundaries outside the lattice, forming a solid solution between the crystal grains. For this reason, the sintered body of M-αSiAlON becomes uniform and dense, as shown in Figure 3(A), for example.

[0102] After sintering, the resulting silicon nitride sintered body is preferably subjected to hot isostatic pressing (HIP) treatment in a non-oxidizing atmosphere of 300 atmospheres or more at a temperature of 1600°C to 1850°C. By subjecting the body to hot isostatic pressing (HIP) treatment, defects that can be the starting point for fatigue fracture can be reduced, and when the body is used as a rolling element for a bearing, the sliding properties and rolling life properties are further improved.

[0103] <Silicon nitride sphere> The silicon nitride solid spheres of the present disclosure may be formed from the silicon nitride sintered body of the present disclosure. An example of the silicon nitride solid spheres of the present disclosure is a sphere having a difference between the maximum and minimum diameters of 100 μm or less and a band-like protrusion height of 50 μm or less. Because the second silicon nitride sintered body of the present disclosure has excellent processability, it is possible to obtain spheres having a difference between the maximum and minimum diameters of 100 μm or less and a band-like protrusion height of 50 μm or less even in the raw sphere state. The height of the protrusions in the silicon nitride solid sphere as an example of the present disclosure is 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, more preferably 20 μm or less, even more preferably 10 μm or less, and particularly preferably zero. The silicon nitride sphere as an example of the present disclosure has a difference between the maximum and minimum diameters of 100 μm or less, preferably 90 μm or less, preferably 80 μm or less, preferably 70 μm or less, preferably 60 μm or less, and preferably 50 μm or less.

[0104] <Bearing rolling elements> The rolling elements for bearings according to the present disclosure are made of the silicon nitride sintered body according to the present disclosure. The rolling elements for bearings can be obtained by subjecting the silicon nitride sintered body according to the present disclosure to a mirror finish or the like. Any mirror finish method is acceptable as long as it can achieve an arithmetic mean surface roughness Ra of 0.5 μm or less. The arithmetic mean surface roughness Ra of the rolling elements for bearings is preferably 0.5 μm or less, preferably 0.4 μm or less, preferably 0.3 μm or less, preferably 0.2 μm or less, preferably 0.1 μm or less, preferably 0.08 μm or less, preferably 0.06 μm or less, preferably 0.05 μm or less.

[0105] The surface layer may be cut prior to mirror finishing, but since the silicon nitride sintered body of the present disclosure has fewer defects such as snowflakes and pores in the surface layer than conventional silicon nitride sintered bodies, cutting of the surface layer may be omitted, or the amount of cutting of the surface layer may be reduced.

[0106] <Bearings> The bearing of the present disclosure includes the rolling element for a bearing of the present disclosure. Because the rolling element for a bearing of the present disclosure uses a silicon nitride sintered body with few defects or a silicon nitride sintered body with good processability, the bearing is also suitable for use in electric vehicles. [Example]

[0107] The present invention will be described below using examples, but the present invention is not limited thereto. Examples 1 to 5 and 10 to 27 are working examples, and Examples 6 to 9 and 28 are comparative examples.

[0108] The raw materials and sintering aids listed in Tables 1 to 5 were prepared. The Ca-αSiAlON and Y-αSiAlON used as raw materials were synthesized by combustion synthesis, and the α ratios were as shown in Tables 1 to 5. The αSi3N4 used as raw material in Examples 6 to 9 was manufactured by Denka Co., Ltd., and synthesized by direct nitriding, and was available under the trade name 9FWS. It had an average particle size (D50) of 0.7 μm and an α ratio of 91%.

[0109] A solvent was added to the raw materials and sintering aids in the formulations shown in Tables 1 to 5, and the mixture was mixed for 48 hours to obtain a slurry. In Tables 1 to 5, blank cells indicate that no component was added. In Example 5, a mixture was obtained by adding an organic binder to the raw materials without adding any sintering aids or solvents. This slurry or mixture was spray-dried to obtain a granulated powder.

[0110] The obtained granulated powder was placed in a mold and press-molded under molding pressure into a rectangular parallelepiped of 60 mm x 50 mm x 10 mm thick or a sphere of 13.5 mm diameter, and then subjected to CIP treatment.

[0111] The obtained molded product was degreased by heating at 600°C for 1 hour in an air atmosphere. -2 The temperature was raised from room temperature under a vacuum of 100 Pa or less, and held at 1400°C for 2 hours, and then pressure sintered at 1750°C for 4 or 5 hours under a nitrogen gas atmosphere of 0.6 MPa to obtain a sintered body.

[0112] Furthermore, for Examples 2, 6, and 8 to 27, the obtained sintered bodies were subjected to a hot isostatic pressing (HIP) treatment in which they were heated at 1650°C to 1800°C for 1 hour under a pressure of 100 MPa in a nitrogen gas atmosphere.

[0113] In Example 3, after the degreasing treatment, instead of the pressure sintering, the material was fired at 1800° C. for 2 hours under a nitrogen gas atmosphere with a hot press while being pressurized at 40 MPa to obtain a sintered body. Example 28 is a commercially available silicon nitride ball (manufactured by Tsubaki Nakashima Co., Ltd.). The composition of the obtained silicon nitride sintered body was analyzed using EPMA (JXA-8500F manufactured by JEOL Ltd. and a standard sample). The results are shown in Tables 1 to 5.

[0114] The obtained silicon nitride sintered body was evaluated for physical properties using the above-mentioned measuring methods. The results are shown in Tables 1 to 5. Note that ND indicates not measured. Blanks in the metal M content of the matrix and grain boundary phase indicate that the content was below the detection limit.

[0115] The "Raman peak intensity ratio" in Tables 1 to 5 indicates the peak intensity ratio between 177 and 197 cm in the Raman spectrum. -1 The minimum peak intensity at 170-190 cm -1 The ratio of the maximum peak intensity to the maximum peak intensity at The "Raman peak position" in Tables 1 to 5 indicates the peaks from 177 to 197 cm in the Raman spectrum. -1 This represents the position of the peak top in In Tables 1 to 5, the item "Presence or absence of sintered altered layer" is marked as "present" if snowflakes of 50 μm or more are confirmed within a region 250 μm inward from the surface of the sintered body, and marked as "absent" if they are not confirmed.

[0116] For the X-ray diffraction measurement, Smart Lab manufactured by Rigaku Corporation was used, as the detector D / teXUltra manufactured by Rigaku Corporation was used, and as X-ray analysis software PDXL2 manufactured by Rigaku Corporation was used. Elemental analysis of silicon nitride sintered bodies was performed using an electron probe microanalyzer (EPMA) "JXA-8500F" manufactured by JEOL Ltd., and standard samples manufactured by JEOL Ltd. Elemental analysis of powders was performed using ZSX Primus II manufactured by Rigaku Corporation. The Raman spectroscopy was measured using LabRAM HR Evolution manufactured by Horiba Ltd. The polishing rate was measured using a Calotest manufactured by Anton Paar. Scanning electron microscopy (SEM) was performed using a Hitachi High-Technologies Corporation SU6600 under the following conditions: acceleration voltage: 6 kV, probe current: Medium, emission current: 29 μA, extraction voltage: 1.70 kV, detector conditions: backscattered electrons, suppressor voltage: 300 V, WD: 15 mm, and C-coat: approximately 24 nm. The EDS analyzer used was a Noran system 6 manufactured by Thermo Fisher Scientific, with a detector: Thermo Fisher Scientific Ultradry, map resolution: 512 × 384, map pixel size: 0.01 μm, magnification: 25,000x, kernel size: 5 × 5, minimum valid intensity: high, filter fit type: high precision, quantitative peak separation method: standardless filter method, and correction method: probe (Phi-Rho-Z). The thrust rolling test was carried out using a device manufactured by Fuji Testing Machinery Co., Ltd.

[0117] [Table 1]

[0118] [Table 2]

[0119] [Table 3]

[0120] [Table 4]

[0121] [Table 5]

[0122] Figures 2(A) and (B) show optical microscope photographs of the cross sections of the silicon nitride sintered bodies of Examples 2 and 6, taken in a dark field at 10x magnification. Example 2 is shown in Figure 2(A), and Example 6 in Figure 2(B). The silicon nitride sintered body of Example 2 was homogeneous, but defects such as snowflakes were observed on the periphery of the silicon nitride sintered body of Example 6.

[0123] 3(A) and (B) show photographs of mirror-finished cross sections of the silicon nitride sintered bodies of Examples 2 and 6, observed with a scanning electron microscope at 25,000 magnifications. Example 2 is shown in Figure 3(A), and Example 6 in Figure 3(B).

[0124] FIG. 4 shows the XRD spectrum of the silicon nitride sintered body obtained in Example 2. Peaks marked with ● (2θ = 30.5 to 32°) are peaks representing α(201), peaks marked with ▲ (2θ = 33 to 34°) are peaks representing β(101), peaks marked with ▼ (2θ = 35 to 36°) are peaks representing α(210), and peaks marked with ■ (2θ = 36 to 37°) are peaks representing β(120).

[0125] Raman spectra are shown in Figures 5(A) and 5(B) and Figure 6. Figure 5(A) shows the Raman spectrum of the silicon nitride sintered body obtained in Example 2, and Figure 5(B) shows the Raman spectrum of the silicon nitride sintered body obtained in Example 6. Figure 6 shows the Raman spectra of the silicon nitride sintered bodies obtained in Examples 6, 11, 15, 18 and 26.

[0126] From the results in Tables 1 to 5, it can be seen that the total content of at least one metal M selected from the group consisting of Mg, Ca, and Y is 0.2 to 8.0 mass%, the content of Al is 4.0 to 12.0 mass%, the content of O is 4.0 to 12.0 mass%, and the fracture toughness value is 5.0 to 10.0 MPa m 1 / 2 It can be seen that the silicon nitride sintered bodies of Examples 1 to 5 and 10 to 27 have higher polishing rates by Calotest and are superior in processability compared to Examples 6 to 9 and 28.

[0127] A thrust rolling test was carried out on the silicon nitride sintered bodies of Examples 10, 15, and 28. As a control sample, a similar test was also carried out on high carbon chromium steel (SUJ2) used as a rolling element in bearings. The test for the SUJ2 ball was terminated at 69 million revolutions because the test machine stopped due to increased vibration and flaking was confirmed on the rolling elements and test specimen. For the silicon nitride sintered body of Example 10, vibration increased at 45 million revolutions, and the test was terminated. When the silicon nitride sintered bodies were observed after the test, flaking was confirmed in one of the six bodies, and the remaining five bodies showed no noticeable wear. When the silicon nitride sintered body of Example 10 was observed in cross section with an optical microscope using the method described above, pores of up to 12 μm were confirmed, and it is presumed that flaking occurred from the pores. The silicon nitride sintered bodies of Examples 15 and 28 did not show an increase in vibration up to 100 million revolutions. When the appearance of the silicon nitride sintered bodies was observed after the test, no noticeable wear was visually observed in either Example 15 or Example 28. The results of laser microscope observation of the surfaces of the silicon nitride sintered bodies of Examples 15 and 28 after the thrust rolling test are shown in Figure 9. When observed with the laser microscope, Example 28 showed the presence of aggregates of minute peelings measuring approximately 80 μm in diameter and 0.5 μm in depth. On the other hand, no wear was observed with the laser microscope in Example 15, confirming its high wear resistance as a rolling element for bearing balls. Example 15 was found to have excellent wear resistance and excellent processability. [Industrial Applicability]

[0128] The silicon nitride sintered body of the present disclosure is useful as a wear-resistant member, and can be suitably used in particular as a rolling element for a bearing and a bearing member.

[0129] The disclosure of Japanese Patent Application No. 2023-014185 is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards in this disclosure are incorporated by reference into this disclosure to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. The total content of at least one metal M selected from the group consisting of Mg, Ca, and Y is 0.2 to 8.0 mass%, the content of Al is 4.0 to 12.0 mass%, and the content of O is 4.0 to 12.0 mass%, and the fracture toughness value is 5.0 to 10.0 MPa m １／２ and The β rate is 60% or more, A silicon nitride sintered body having a thermal conductivity of 5 to 15 W / (m·K).

2. The total content of at least one metal M selected from the group consisting of Mg, Ca, and Y is 0.2 to 8.0 mass%, the content of Al is 4.0 to 12.0 mass%, and the content of O is 4.0 to 12.0 mass%, and the fracture toughness value is 5.0 to 10.0 MPa m １／２ and The β rate is 60% or more, A silicon nitride sintered body that is a solid solution of SiAlON.

3. 3. The silicon nitride sintered body according to claim 1, which has a matrix phase and a grain boundary phase, and the total content of said metal M in said grain boundary phase is 2.0 to 40.0 mass %.

4. 4. The silicon nitride sintered body according to claim 3, wherein the total content of said metal M in said matrix is ​​2.0 to 10 mass %.

5. 3. The silicon nitride sintered body according to claim 1, wherein said metal M is Ca.

6. In the Raman spectrum, 177 to 197 cm －１ 170 to 190 cm relative to the minimum value of the peak intensity at －１ 3. The silicon nitride sintered body according to claim 1, wherein the ratio of the maximum peak intensity to the maximum peak intensity is 1.0 to 3.

0.

7. In the Raman spectrum, 185 to 210 cm －１ The peak attributable to the β phase is 187 to 199 cm －１ 3. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body is present between the above.

8. Density: 3.10 to 3.20 g / cm ３ 3. The silicon nitride sintered body according to claim 1, wherein

9. 3. The silicon nitride sintered body according to claim 1, wherein when a unit area of ​​5 mm x 5 mm of a cross section of the silicon nitride sintered body is observed under an optical microscope in a bright field at a magnification of 10 to 200 times, no pores having a major axis of 10 μm or more are observed.

10. 3. The silicon nitride sintered body according to claim 1, wherein when a unit area of ​​5 mm x 5 mm of a cross section of the silicon nitride sintered body is observed under a dark field of view at 10 to 200 magnifications with an optical microscope, no snowflakes with a major axis of 25 μm or more are observed.

11. 3. The silicon nitride sintered body according to claim 1, wherein when a region within 250 μm inward from the surface of the sintered body in a cross section of the silicon nitride sintered body is observed with an optical microscope in a dark field at 10 to 200 magnifications, no snowflakes with a major axis of 50 μm or more are observed.

12. 3. The silicon nitride sintered body according to claim 1, which is used for a wear-resistant member.

13. 3. A silicon nitride sintered body according to claim 1, wherein the difference between the maximum and minimum diameters is 100 μm or less and the height of the band-like protrusions is 50 μm or less.

14. 3. A rolling element for a bearing, comprising the silicon nitride sintered body according to claim 1 or 2, which has been subjected to a mirror finish.

15. A bearing comprising the rolling element for a bearing according to claim 14.

16. 16. The bearing of claim 15 for use in an electric vehicle.

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