Sintered body, bearing ball, and bearing

Abstract

A sintered body having β-SiAlON as a main phase, the half-value width of a peak corresponding to β phase (101) in an X-ray diffraction (XRD) spectrum being 0.20 or lower.

Description

Sintered body, bearing ball, and bearing

[0001] The present disclosure relates to a sintered body, a bearing ball, and a bearing.

[0002] Silicon nitride sintered bodies have excellent mechanical strength and wear resistance, and are therefore used in wear-resistant members, gas turbine blades, engine parts, etc. Among these, silicon nitride sintered bodies used in bearing members, which require high wear resistance, are, for example, silicon nitride sintered bodies containing Y. ２ O ３ , Al ２ O ３ The sintered body is sintered with the addition of sintering aids such as Y to form a liquid phase, thereby increasing the density and strength of the sintered body. ２ O ３ We use sintering aids containing rare earth elements such as

[0003] In addition, AlN is added 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 a slurry and granulate it, which increases costs and reduces the amount of SiAlON produced.

[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-stage heat treatment.

[0005] JP 2009-12985 A

[0006] Since sintered bodies are used as bearing balls and the like, improvements in lifespan, such as rolling life, are required. If a sintered body has a portion with low fracture toughness, that portion will be fractured, shortening the lifespan. Therefore, an object of one embodiment of the present disclosure is to provide a sintered body with little variation in fracture toughness, a bearing ball, and a bearing using the same.

[0007] Specific means for achieving the above object are as follows. <1> A sintered body having β-SiAlON as a main phase, in which the half-width of a peak corresponding to the β-phase (101) in an X-ray diffraction (XRD) spectrum is 0.20 or less. <2> The sintered body according to <1>, in which the liquid phase contains at least one element selected from the group consisting of Ca, Y, and Mg. <3> The sintered body according to <1> or <2>, further containing a dispersed phase containing carbon or at least one carbide selected from the group consisting of Ti, Zr, and W. <4> The sintered body according to <3>, in which the dispersed phase contains at least one carbide selected from the group consisting of Ti, Zr, and W. <5> The sintered body according to any one of <1> to <4>, which is a base sphere for a bearing ball. <6> A bearing ball composed of a mirror-finished product of the sintered body according to any one of <1> to <5>. <7> A bearing comprising the bearing ball according to <6>. <8> The bearing according to <7>, which is for an electric vehicle.

[0008] According to one embodiment of the present disclosure, a sintered body with little variation in fracture toughness, a bearing ball, and a bearing using the same are provided.

[0009] 1 is an example of an X-ray diffraction (XRD) spectrum of a sintered body. (A) and (B) are examples of Raman spectroscopy spectra of a sintered body. (A) and (B) are images of a cross section of a sintered body observed with a scanning electron microscope at 25,000 magnifications after mirror finishing, and are diagrams for explaining a solid solution state. 2 are schematic diagrams of a molded product having convex portions when a raw material composition is molded into a spherical shape.

[0010] Embodiments of the present disclosure are described in detail below. However, the present disclosure is not limited to the following embodiments. In this disclosure, the term "to" indicating a numerical range is used to mean that the numerical values ​​before and after it are included as the upper and lower limits. Unless otherwise specified, "to" is used in the following disclosure with the same meaning. In 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 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 in this disclosure with reference to drawings, 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 thereto.

[0011] 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: 45 kV-200 mA, scanning range: 10°-60°, optical system: focusing method, incident solar slit: 5°, length limiting slit: 10 mm, receiving slit 1: 8 mm, receiving slit 2: 13 mm, receiving parallel slit: 5.0°, attenuator open, scanning speed: 5° / min, step width: 0.005°

[0012] The 101 plane of β-SiAlON (hereinafter also referred to as the β(101) plane) appears as the maximum peak in the range of 2θ = 33 to 34°. When determining the half-width of the β(101) plane, the line connecting points where no peaks exist in the diffraction pattern between 30 and 40° in the XRD profile is used as the baseline. Absence of a peak means that the intensity is below the noise level. Noise can be automatically determined using the X-ray analysis software "PDXL2." The intensity of each peak is the length of the line segment drawn perpendicular to the peak top to the point where it intersects with the baseline.

[0013] In the present disclosure, fracture toughness is measured by the indentation method (IF method) specified in JIS R 1607: 1995 and calculated by the formula of Niihara et al. In the present disclosure, the variation in fracture toughness is measured for a spherical sintered body at a total of 10 points, including 5 arbitrary points near the center and 5 arbitrary points near the outer periphery, and the standard deviation of the 10 points is calculated.

[0014] In the present disclosure, the three-point bending strength is measured in accordance with JIS R 1601:2008, by preparing a test piece of 3 mm × 4 mm × 40 mm, under the conditions of 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 of 10 test pieces.

[0015] In the present disclosure, the main phase, liquid phase, and dispersed phase can be identified by observing a measurement sample that has been subjected to plasma etching using a backscattered electron image of a scanning electron microscope (SEM). When plasma etching is performed, the etching rates of the main phase and the liquid phase differ, resulting in a greater removal of either the main phase or the liquid phase. As a result, the main phase and the liquid phase can be identified using a backscattered electron image of the SEM. In the SEM, the liquid phase appears brighter than the main phase, and the dispersed phase appears even brighter than the liquid phase. In the present disclosure, confirmation that the dispersed phase contains carbon or at least one carbide selected from the group consisting of Ti, Zr, and W is performed using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer (Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy: SEM-EDS) in combination with Raman spectroscopy.

[0016] In the present disclosure, elemental analysis of the sintered body is carried out using an electron probe microanalyzer (EPMA) device (for example, "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

[0017] In the present disclosure, the contents of Mg, Ca, and Y in the liquid phase of the sintered body are determined by energy dispersive X-ray spectroscopy (EDS) using an EDS analyzer (e.g., Thermo Fisher Scientific's Noran System 6, detector: Thermo Fisher Scientific's Ultradry) under the following conditions: Line analysis width: 1, number of points: 100, point acquisition interval: 50 nm, and the acquired net count is converted to 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 of the boundary toward the liquid phase, and the average of the obtained values ​​is calculated. In the present disclosure, the contents of Mg, Ca, and Y in the matrix phase of the sintered body are determined in the same manner as the contents of Mg, Ca, and Y in the liquid phase, except that the average values ​​obtained at points within 150 nm from the boundary toward the matrix are calculated.

[0018] In the present disclosure, Raman spectroscopy is performed using a Raman spectroscopy device (for example, LabRAM HR Evolution manufactured by Horiba, Ltd.) under the following conditions: Measurement conditions: exposure time 1 second, 10 times accumulated, 100% neutral density filter (power 30 mW), 15 μm confocal hole, laser wavelength: 532 nm, 1200 grating rulings, 100x objective lens (NA = 0.6).

[0019] <Sintered body> The sintered body of the present disclosure has βSiAlON as the main phase, and the half-width of the peak corresponding to the β phase (101) in the X-ray diffraction (XRD) spectrum is 0.20 or less. A sintered body having the above configuration reduces the variation in fracture toughness. The reason why this effect is obtained is not clear, but is presumed as follows. SiAlON is a silicon nitride (Si ３ N ４) has a structure in which O is partially substituted for N and Al is partially substituted for Si. Here, it has been found that whether the Al substitution rate at each location of the sintered body is uniform can be confirmed using the half-width of the peak corresponding to the β phase (101) as an indicator. Since the sintered body of the present disclosure has a half-width of the peak corresponding to the β phase (101) of 0.20 or less and has a uniform Al substitution rate, it is presumed that the variation in fracture toughness is reduced.

[0020] The sintered body of the present disclosure has β-SiAlON as the main phase. SiAlON includes α-SiAlON, which exhibits an α-phase, and β-SiAlON, which exhibits a β-phase. α-SiAlON is believed to have a structure in which a metal atom M (M = Li, Mg, Ca, Y, La, etc.) is present within the crystal lattice. β-SiAlON does not have a metal atom M within the crystal lattice.

[0021] In the present disclosure, "βSiAlON is the main phase" when the β fraction of βSiAlON is 50% or more. The β fraction of βSiAlON is preferably 60% or more. The β fraction 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.

[0022] The β ratio is the ratio of the β phase to the total amount of the α phase and the β phase, which is determined from the heights of the peaks corresponding to the α phase (210), α phase (201), β phase (101), and β phase (120) in the X-ray diffraction spectrum. The ratio of the α phase to the total amount of the α phase and the β phase: α phase / (α phase + β phase) × 100 is also referred to as the α ratio (%).

[0023] In the present disclosure, the peaks corresponding to the α phase (210) and α phase (201) are used as the main peaks representing the α phase in the X-ray diffraction spectrum, and the peaks corresponding to the β phase (101) and β phase (120) are used as the main peaks representing the β phase. 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 °. An example of an X-ray diffraction spectrum is shown in FIG. 1.

[0024] In the present disclosure, the β ratio is calculated from the following formula: β ratio = (β(101) + β(120)) / (α(210) + α(201) + β(101) + β(120)) × 100 In the above formula, α(201) is the maximum value of the peak height in the range of 2θ = 30.5 to 32°, α(210) is the maximum value of the peak height in the range of 2θ = 35 to 36°, β(101) is the maximum value of the peak height in the range of 2θ = 33 to 34°, and β(120) is the maximum value of the peak height in the range of 2θ = 36 to 37°.

[0025] The sintered body of the present disclosure has a half-width of the peak corresponding to the β-phase (101) of 0.20 or less, preferably 0.19 or less, more preferably 0.17 or less, preferably 0.16 or less, and even more preferably 0.15 or less. There is no particular limit to the lower limit of the half-width, and the narrower the better. For example, the half-width may be 0.10 or more, 0.13 or more, or 0.14 or more.

[0026] SiAlON contains the elements Si, Al, O, and N. The Al content in the sintered body is preferably 3.0 mass% or more, 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 Al content in the 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.

[0027] The O content in the sintered body is preferably 3.0% by mass or more, preferably 3.5% by mass or more, preferably 4.0% by mass or more, preferably 4.5% by mass or more, preferably 5.0% by mass or more, preferably 5.5% by mass or more, and preferably 6.0% by mass. From the viewpoint of improving fracture toughness, the O content in the sintered body is preferably 15% by mass or less, preferably 14% by mass or less, preferably 12% by mass or less, preferably 11% by mass or less, preferably 10% 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, preferably 7.5% by mass or less, and preferably 7.0% by mass or less.

[0028] The Si content in the sintered body is preferably 30% by mass or more, preferably 40% by mass or more, preferably 42% by mass or more, preferably 43% by mass or more, preferably 44% by mass or more, and preferably 45% by mass or more. The Si content in the sintered body is preferably 60% by mass or less, preferably 58% by mass or less, preferably 56% by mass or less, preferably 54% by mass or less, preferably 52% by mass or less, preferably 50% by mass or less, preferably 49% by mass or less, preferably 48% by mass or less, preferably 47% by mass or less, and preferably 46% by mass or less.

[0029] The N content in the sintered body is preferably 25% by mass or more, preferably 27% by mass or more, preferably 29% by mass or more, preferably 31% by mass or more, preferably 33% by mass or more, and preferably 34% by mass. The N content in the sintered body is preferably 45% by mass or less, preferably 43% by mass or less, preferably 42% by mass or less, preferably 41% by mass or less, preferably 40% by mass or less, preferably 39% by mass or less, preferably 38% by mass or less, preferably 37% by mass or less, preferably 36% by mass or less, and preferably 35% by mass or less.

[0030] From the viewpoint of promoting sintering and densification, the liquid phase of the sintered body preferably contains at least one element selected from the group consisting of Ca, Y, and Mg, and more preferably contains at least 1 mass% of at least one element selected from the group consisting of Ca, Y, and Mg. The liquid phase may or may not contain Mg. When the sintered body contains Mg, the Mg content in the liquid phase 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. Furthermore, the Mg content in the liquid phase 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.

[0031] The liquid phase may or may not contain Ca, but preferably contains Ca from the viewpoint of promoting grain boundary sintering. When the liquid phase contains Ca, the Ca content in the liquid phase 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. Furthermore, from the viewpoint of strength, the Ca content in the liquid phase 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. In the sintered body of the present disclosure, the liquid phase preferably contains 1.0 mass% or more of Ca.

[0032] The liquid phase may or may not contain Y. When the liquid phase contains Y, the content of Y in the liquid phase may be 1.0 mass% or more, 1.5 mass% or more, 2.0 mass% or more, or 2.5 mass% or more. Furthermore, the content of Y in the liquid phase 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.

[0033] The liquid phase preferably contains 1.0% by mass or more of Mg, Ca, and Y in total, but may also contain 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 amount of Mg, Ca, and Y may also 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.

[0034] The sintered body of the present disclosure has a Raman spectrum of 177±2 cm －１ (177 cm －１ (also called "nearby"), 192±5 cm －１ (192 cm －１ (also called "nearby"), 219±3 cm －１ (219 cm －１ It is preferable that a peak corresponding to the β phase exists in the vicinity of 177 cm －１ Around 192 cm －１ The peak in the vicinity of 177 cm is preferably broad. Examples of the Raman spectrum of the sintered body are shown in Figures 2(A) and 2(B). The sintered body in Figure 2(A) has a peak at 177 cm －１ Around 192 cm －１ Near 219 cm －１ These peaks correspond to the β phase of the sintered body. In the Raman spectrum shown in FIG. 2(A), －１ Around 192 cm －１ The peak in the vicinity of 180 cm is broad, indicating that the sintered body is in a solid solution state. This suggests that a large amount of Al and O (oxygen) is dissolved in solid solution, resulting in low crystallinity. In contrast, the sintered body in Figure 2(B) has a peak in the vicinity of 180 cm －１ , 200 cm －１ , 223 cm －１ In the Raman spectrum shown in Figure 2(B), these peaks are sharp, which indicates that the sintered body is not in a solid solution state.

[0035] 177 cm in Raman spectroscopy －１Around 192 cm －１ The peaks around 177-197 cm are broad. －１ 170 to 190 cm relative to the minimum value of the peak intensity at －１ This 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.

[0036] The Raman spectrum shown in FIG. 2(A) shows the peak at 170-190 cm －１ The peak having a peak top at 177 to 197 cm －１ The ratio of the peak to the minimum value is 1.26, which indicates a broad peak and a solid solution state. In contrast, the sintered body shown in FIG. 2(B) has a peak of 170 to 190 cm －１ The peak having a peak top at 177 to 197 cm －１ Since the difference between the minimum value and the peak value exceeds 3.0, it can be said that the peak is sharp, indicating that the solid solution is not formed.

[0037] As the sintered body, solid solution SiAlON is preferred. In the present disclosure, whether or not the sintered body is in a solid solution state is confirmed by Raman spectroscopy as described above, but it may also be confirmed by a scanning electron microscope (SEM, for example, IM4000plus manufactured by Hitachi High-Technologies Corporation). For example, as shown in FIG. 3, the sintered body represented by (B) is confirmed to have a clear separation between the main phase and the liquid phase, while the sintered body represented by (A) is confirmed to have a solid solution state where the main phase and the liquid phase are not clearly separated. When the sintered body is in a solid solution state, the liquid phase region with low mechanical strength is reduced, thereby improving the mechanical strength. Furthermore, when the liquid phase is small, the occurrence of snowflakes tends to be more suppressed.

[0038] The sintered body of the present disclosure preferably further includes a dispersed phase containing carbon or at least one carbide selected from the group consisting of Ti, Zr, and W. Hereinafter, at least one carbide selected from the group consisting of Ti, Zr, and W is also referred to as a specific carbide. The dispersed phase is believed to have the function of enhancing wettability or lubricity at the boundary between the main phase and the liquid phase, which tends to suppress the occurrence of white spot-like defects called snowflakes. Snowflakes appear as amorphous white spots near the periphery of the sintered body and can be confirmed in dark-field (DF) images using an optical microscope. Since snowflakes are less dense than the surrounding area, sintered bodies containing snowflakes require a hot isostatic pressing (HIP) process to fill the defects, increasing production costs. Furthermore, since such defects tend to occur near the surface of the sintered body, grinding near the surface is required, increasing production costs. From the viewpoint of improving the fracture toughness of the sintered body, it is preferable that the dispersed phase contains at least one specific carbide selected from the group consisting of Ti, Zr and W.

[0039] The fracture toughness value of the sintered body is 5.0 MPa m １／２ Preferably, 5.2 MPa m １／２ More than 5.4 MPa m １／２ More than 5.6 MPa m １／２ More than 5.8 MPa m １／２ More than 6.0 MPa m １／２ More than 6.3 MPa m is preferable. １／２ More than 6.5 MPa m １／２ More than 7.0 MPa m １／２ The upper limit of the fracture toughness value is not particularly limited, but is preferably 10.0 MPa m １／２ or less, and may be 9.0 MPa m １／２ It may be 8.0 MPa m or less. １／２ It may be 7.5 MPa m or less. １／２ It may be the following:

[0040] The variation in fracture toughness of the sintered body is 0.5 MPa m １／２ Preferably less than 0.25 MPa m１／２ The lower limit of the variation in fracture toughness is not particularly limited, but is preferably less than 0.01 MPa m １／２ or more, and may be 0.05 MPa m １／２ It may be 0.1 MPa m or more. １／２ It may be more than that.

[0041] The three-point bending strength of the sintered body is preferably 700 MPa or more, preferably 750 MPa or more, preferably 800 MPa or more, and preferably 850 MPa or more. The upper limit of the three-point bending strength is not particularly limited, but may be 1200 MPa or less, 1100 MPa or less, 1050 MPa or less, 1000 MPa or less, 980 MPa or less, or 930 MPa or less.

[0042] <Applications> The sintered body of the present disclosure is suitably used for applications as a wear-resistant member, and may be used, for example, as a base sphere for a bearing ball.

[0043] <Method for manufacturing sintered body> The method for manufacturing a sintered body according to the present disclosure is not particularly limited as long as it can produce a sintered body having βSiAlON as a main phase and having a half-width of a peak corresponding to the β phase (101) in an X-ray diffraction (XRD) spectrum of 0.20 or less.

[0044] One example of a method for producing a sintered body includes preparing a raw material composition containing a silicon nitride material as a raw material, granulating, molding, pressing, degreasing, and firing. Examples of additives added to the raw material composition include sintering aids, binders, solvents, and sintering accelerators. In the method for producing a sintered body, processes other than firing may be omitted as appropriate. Furthermore, processes other than those mentioned above, such as classification, may be added as appropriate.

[0045] As a silicon nitride material used as a raw material, αSi ３ N ４ , βSi ３ N ４ , βSiAlON, and M-αSiAlON. The silicon nitride material as a raw material may be used alone or in combination of two or more. From the viewpoint of sinterability, the silicon nitride material as a raw material is preferably αSi３ N ４ , βSiAlON, and M-αSiAlON are preferred, and βSiAlON or M-αSiAlON is more preferred. ３ N ４ When using AlN and Al in the liquid phase, ２ O ３ is Si during sintering ３ N ４ However, since the composition is determined by the liquid phase components adjacent to SiAlON, the amounts of Al and O dissolved in the solid solution tend to vary for each SiAlON particle (parent phase), which can lead to a decrease in homogeneity. On the other hand, since βSiAlON or M-αSiAlON are SiAlON before sintering and have excellent homogeneity, it is easy to adjust the half-width of the peak corresponding to the β phase (101) of the sintered body to 0.20 or less.

[0046] From the viewpoint of improving fracture toughness due to the transition from granular α-phase crystals to acicular β-phase crystals during liquid-phase sintering, M-αSiAlON is more preferable as the silicon nitride material used as the raw material. Furthermore, M-αSiAlON is also preferable as the silicon nitride material used as the raw material because it allows the elimination of the use of sintering aids and results in a homogeneous, dense sintered body in a solid solution state. From the viewpoint of easily adjusting the half-width of the peak corresponding to the β-phase (101) of the sintered body to 0.20 or less, it is preferable to use M-αSiAlON synthesized by combustion synthesis using raw material powder in which predetermined elements are homogeneously mixed in a predetermined ratio. The method for mixing the raw material powder is not particularly limited, and examples include methods such as a tumbling ball mill and a vibrating ball mill. To homogeneously mix the raw material powder, for example, it is preferable to mix the raw material powder for a long time. The mixing time of the raw material powder may be 2 hours or more, 4 hours or more, or 10 hours or more.

[0047] M-αSiAlON is αSiAlON in which a metal atom M (M = Li, Mg, Ca, Y, La, etc.) exists within the crystal lattice. When the metal atom transforms into βSiAlON during liquid-phase sintering, the metal element forms a liquid phase with Si, Al, O, etc., resulting in a uniform and dense sintered body.

[0048] The M-αSiAlON may be a commercially available product or may be manufactured. The M-αSiAlON may be manufactured by, for example, a combustion synthesis method. When manufacturing M-αSiAlON by a combustion synthesis method, for example, Si, Al, and metal M or a compound containing metal M are mixed as raw material powders, and then the mixture is subjected to a combustion synthesis reaction. M-αSiAlON is made of αSi ３ N ４ , AlN, Al ２ O ３ and a metal M or a compound containing metal M, and then calcining the mixture.

[0049] The metal atom M in M-αSiAlON may function as a sintering aid during sintering. Therefore, the content of the metal atom M in M-αSiAlON is 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%. Furthermore, from the viewpoint of suppressing the precipitation of crystal phases other than M-αSiAlON, the content of the metal atom M in M-αSiAlON is 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 5.5 mass% or less, preferably 5 mass% or less, preferably 4.5 mass% or less, and preferably 4.0 mass% or less.

[0050] The more α-phase M-αSiAlON, the better. α-phase SiAlON has superior sinterability compared to β-phase SiAlON. The α-ratio 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 preferably a single phase (100%).

[0051] 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 rate.

[0052] Examples of sintering aids include compounds containing Li, Mg, Ca, Y, La, Al, etc., and specifically, Al ２ O ３ , Y ２ O ３ , AlN, MgAl ２ O ４ Examples of binders include organic materials. Examples of solvents include water, alcohol, and hydrocarbons. Conventional silicon nitride sintered bodies are made using αSi as a raw material. ３ N ４ However, if a solvent containing oxygen atoms such as water is used, Si ３ N ４ Oxygen atoms may enter the silicon nitride sintered body, affecting the properties of the final product. Therefore, when manufacturing conventional silicon nitride sintered bodies, it is preferable to select an appropriate solvent. On the other hand, since SiAlON already contains oxygen atoms as a constituent element, the use of water when using SiAlON as a raw material has little effect on the properties of the final product, thereby widening the options for manufacturing processes.

[0053] When a sintering aid is used, from the viewpoint of obtaining the effect of the addition of the sintering aid, the amount of the sintering aid added is preferably 0.5 mass % or more, preferably 1 mass % or more, preferably 2 mass % or more, and preferably 3 mass % or more, calculated as oxide, relative to the silicon nitride material. Also, from the viewpoint of further increasing the mechanical strength, the amount of the sintering accelerator added is preferably 10 mass % or less, preferably 8 mass % or less, preferably 7 mass % or less, and preferably 6 mass % or less, calculated as oxide, relative to the silicon nitride material.

[0054] Examples of sintering accelerators include compounds containing Ti, Hf, Zr, W, Mo, Nb, Cr, etc., including oxides, carbides, nitrides, silicides, borides, etc. of these elements. The elements of the sintering accelerator may also function to increase dispersibility in the crystalline structure and improve the mechanical strength of the sintered body. When the dispersed phase is composed of a specific carbide, it is preferable to use a compound containing Ti, W, or Zr as the sintering accelerator. Compounds containing Ti, W, or Zr also function as light-blocking agents that color the sintered body black and impart opacity.

[0055] When a sintering accelerator is used, from the viewpoint of obtaining the effect of the addition of the sintering accelerator, the amount of the sintering accelerator added 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, calculated as oxide, relative to the silicon nitride material. Also, from the viewpoint of further increasing the mechanical strength, the amount of the sintering accelerator added is preferably 5 mass % or less, preferably 3 mass % or less, preferably 2 mass % or less, and preferably 1 mass % or less, calculated as oxide, relative to the silicon nitride material.

[0056] 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.

[0057] 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 a protrusion 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 4 is obtained. When removing this protrusion, it is preferable to grind it before firing, and when the molded product is subjected to CIP treatment, it is preferable to grind it after CIP treatment and before firing. When degreasing is performed before firing, it is preferable to grind the protrusion before degreasing.

[0058] When stripping is performed before firing, the height of the strip-shaped convex portions is preferably 500 μm or less, more preferably 40 μm or less, more preferably 30 μm or less, more preferably 20 μm or less, more preferably 10 μm or less, and most preferably 0 μm.

[0059] 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.

[0060] Degreasing may be performed in either a non-oxidizing or oxidizing atmosphere. When degreasing is performed in a non-oxidizing atmosphere, a temperature of 550 to 800°C is preferred, and when degreasing is performed in an oxidizing atmosphere such as air, a temperature of 400 to 650°C is preferred. The heating time at these temperatures is preferably 1 to 2 hours. By controlling the heating temperature and holding time, the amount of carbon remaining from the added binder component can be controlled, thereby preventing the localization of the dispersed phase in the sintered body or molded product. From this perspective, the carbon content before sintering is preferably 500 to 2000 mass ppm, and more preferably 800 to 1500 mass ppm.

[0061] 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 the vacuum is preferably 800 to 1500°C, and the holding time at this heating temperature is preferably 1 to 10 hours.

[0062] 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 further improved, and when made into a bearing ball, 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) can be used.

[0063] The α phase undergoes a phase transition to the β phase due to oxygen present on the surface during sintering. When M-αSiAlON undergoes a phase transition to βSiAlON, metal atoms M incorporated within the lattice migrate from the lattice to the grain boundaries outside the lattice, forming a solid solution between the crystal grains. Therefore, a sintered body obtained by sintering M-αSiAlON is uniform and dense, as shown in Figure 3(A), for example. Carbon components remaining during degreasing tend to disperse homogeneously in the liquid phase or at the interface between the liquid phase and βSiAlON (main phase), providing lubrication to the main phase from the liquid phase, improving sinterability, suppressing the occurrence of snowflakes, and improving toughness. Furthermore, these carbon components combine with Ti, W, or Zr added as sintering accelerators to form metal carbides, further improving the toughness of the sintered body. While the above explanation explains that Ti, W, or Zr are added as sintering accelerators, this is not a limitation.

[0064] After sintering, the resulting 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 sintered body to hot isostatic pressing (HIP) treatment, defects that can be the starting point of fatigue fracture can be reduced, and when the sintered body is made into a bearing ball, the sliding properties and rolling life properties are further improved.

[0065] <Bearing Ball> The bearing ball of the present disclosure is composed of a mirror-finished product of the sintered body of the present disclosure. The bearing ball is obtained by subjecting the sintered body of the present disclosure to mirror finishing or the like. Any mirror finishing method is acceptable as long as the arithmetic mean surface roughness Ra can be made 0.5 μm or less. The arithmetic mean surface roughness Ra of the bearing ball is preferably 0.5 μm or less, more preferably 0.4 μm or less, more preferably 0.3 μm or less, more preferably 0.2 μm or less, more preferably 0.1 μm or less, more preferably 0.08 μm or less, more preferably 0.06 μm or less, and more preferably 0.05 μm or less. The smaller the arithmetic mean surface roughness Ra of the bearing ball, the better, and it may even be 0 μm.

[0066] The surface layer may be cut prior to mirror finishing, but since the sintered body of the present disclosure has fewer defects such as snowflakes and pores in the surface layer compared to conventional sintered bodies, cutting of the surface layer may be omitted. Alternatively, the amount of cutting of the surface layer may be reduced.

[0067] <Bearing> The bearing of the present disclosure includes the bearing ball of the present disclosure. The bearing ball of the present disclosure uses a sintered body with few defects or a sintered body with good processability, and is therefore suitable as a bearing for an electric vehicle.

[0068] The present invention will be described below using examples, but the present invention is not limited thereto. Examples 1 to 8 are working examples, and Examples 9 and 10 are comparative examples.

[0069] The raw materials, sintering accelerators, and organic binders listed in Table 1 were prepared. Ca-αSiAlON, Y-αSiAlON, and Mg-αSiAlON used as raw materials in Examples 1, 3, and 8 were mixed in a vibration mill for 5 hours before combustion synthesis, and then synthesized by combustion synthesis. Ca-αSiAlON used as raw material in Example 2 was mixed in a vibration mill for 4 hours before combustion synthesis, and then synthesized by combustion synthesis. αSi ３ N ４ is a product name 9FWS manufactured by Denka Co., Ltd. The Ca-αSiAlON used as the raw material in Example 10 was synthesized by the combustion synthesis method after mixing with a vibration mill for 1 hour before the combustion synthesis.

[0070] In Examples 1 and 2, a solvent and an organic binder were added to the raw materials and mixed for 48 hours to prepare a slurry. In Example 3, a solvent was added to the raw materials, but no organic binder was added, to prepare a slurry. In Examples 4 to 8 and 10, a sintering accelerator, a solvent and an organic binder were added to the raw materials, and mixed for 48 hours to prepare a slurry. In Example 9, a sintering aid (Al ２ O ３ , AlN), a solvent, and an organic binder were added and mixed for 48 hours to prepare a slurry. The organic binder used was a polycarboxylic acid compound, paraffin wax, and a fatty acid. The solvent used was water.

[0071] The resulting slurry was spray-dried to obtain a granulated powder, which was then 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, followed by CIP treatment.

[0072] The obtained molded product was heated in an air atmosphere at 600°C for 1 hour for degreasing treatment, and then －２ The temperature was raised from room temperature under a vacuum of 1000°C or less and held at 1000°C for 2 hours, and then sintered at 1750°C for 5 hours under a nitrogen gas atmosphere of 0.6 MPa to obtain a sintered body.

[0073] Furthermore, the obtained sintered body was subjected to a hot isostatic pressing (HIP) treatment in which it was heated at 1650° C. to 1800° C. for 1 hour under a pressure of 100 MPa in a nitrogen gas atmosphere.

[0074] The main phase components and β ratio, the half-width of the peak corresponding to the β phase (101), the liquid phase cation components, and the dispersed phase components of the obtained sintered bodies were confirmed and measured using the methods described above. In Table 1, "-" indicates that the values ​​were below the detection limit. For X-ray diffraction measurements, a Rigaku Corporation "Smart Lab" was used, a Rigaku Corporation "D / teXUltra" detector was used, and a Rigaku Corporation "PDXL2" X-ray analysis software was used. For elemental analysis of the sintered bodies, a JEOL Ltd. "JXA-8500F" electron probe microanalyzer (EPMA) was used, and a JEOL Ltd. standard sample was used. For elemental analysis of the powder, a Rigaku Corporation ZSX Primus II was used. For Raman spectroscopy measurements, a Horiba Ltd. LabRAM HR Evolution was used. The scanning electron microscope (SEM) was an SU6600 manufactured by Hitachi High-Technologies Corporation, and the conditions were as follows: 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: Ultradry manufactured by Thermo Fisher Scientific, map resolution: 512 × 384, map pixel size: 0.01 μm, magnification: 25,000 times, kernel size: 5 × 5, minimum valid intensity: high, filter fit type: high precision, quantitative peak separation method: standard-less filter method, and correction method: Proza (Phi-Rho-Z).

[0075] The sintered bodies thus obtained were evaluated for fracture toughness, the variation in fracture toughness, and three-point bending strength as strength. The results are shown in Table 1.

[0076] The variation in fracture toughness was evaluated according to the following criteria: A: Standard deviation is 0.25 MPa m １／２ Less than B: Standard deviation is 0.25 MPa m １／２ 0.50MPa・m or more １／２Less than C: Standard deviation is 0.50 MPa m １／２ End

[0077] The fracture toughness was evaluated according to the following criteria: A: 6.0 MPa m １／２ or more B: 5.5MPa・m １／２ 6.0MPa・m or more １／２ Less than C: 5.0 MPa m １／２ 5.5MPa・m or more １／２ Less than D: 5.0 MPa m １／２ less than

[0078] The strength was evaluated based on three-point bending strength according to the following criteria: A: 900 MPa or more B: 700 MPa or more and less than 900 MPa C: Less than 700 MPa

[0079]

[0080] The results in Table 1 show that the sintered bodies of Examples 1 to 8, which have βSiAlON as the main phase and in which the half-width of the peak corresponding to the β phase (101) in the X-ray diffraction (XRD) spectrum is 0.20 or less, have less variation in fracture toughness than the sintered bodies of Examples 9 and 10. In particular, the sintered bodies of Examples 4 to 8, which have a dispersed phase containing at least one carbide selected from the group consisting of Ti, Zr, and W, are also excellent in fracture toughness and strength.

[0081] The sintered body of the present disclosure is useful as a wear-resistant member, and can be suitably used in particular as a bearing ball and a bearing member.

[0082] The disclosure of Japanese Patent Application No. 2024-123712 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards in this disclosure are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A sintered body having βSiAlON as the main phase, in which the half-width of the peak corresponding to the β phase (101) in the X-ray diffraction (XRD) spectrum is 0.20 or less.

2. The sintered body according to claim 1, wherein the liquid phase contains at least one element selected from the group consisting of Ca, Y and Mg.

3. The sintered body according to claim 1 or 2, further comprising a dispersed phase comprising carbon or at least one carbide selected from the group consisting of Ti, Zr and W.

4. The sintered body according to claim 3, wherein the dispersed phase contains at least one carbide selected from the group consisting of Ti, Zr and W.

5. The sintered body according to claim 1 or 2, which is a base sphere for a bearing ball.

6. A bearing ball made of the mirror-finished sintered body according to claim 1 or 2.

7. A bearing comprising the bearing ball according to claim 6.

8. The bearing according to claim 7, which is for use in an electric vehicle.

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