Sialon powder, sialon sintered body, bearing ball, and bearing

Abstract

This SiAlON powder satisfies at least one of the following (1) and (2). (1) The powder is Cam / 2Si12-(m+n)Al(m+n)OnN16-n, in which m is less than 1.0. (2) The value of Ca / (Si+Al) determined by inductively coupled plasma (ICP) optical emission spectrometry is less than 0.0595.

Description

SiAlON powder, SiAlON sintered body, bearing ball, and bearing

[0001] The present disclosure relates to a SiAlON powder, a SiAlON 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 then fired with the addition of sintering aids, which form a grain boundary 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, improved strength is required. From the viewpoint of improving strength, a SiAlON sintered body with a high β ratio is required. Therefore, in one embodiment of the present disclosure, an object is to provide a SiAlON powder capable of forming a SiAlON sintered body with a high β ratio. In another embodiment of the present disclosure, an object is to provide a SiAlON sintered body with a high β ratio, and a bearing ball and a bearing using the same.

[0007] Specific means for achieving the above object are as follows: <1> Ca ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎ and m is less than 1.0. <2> The SiAlON powder according to <1>, wherein m is 0.6 or more. <3> The SiAlON powder, wherein the value of Ca / (Si+Al) determined by inductively coupled plasma (ICP) optical emission spectroscopy is less than 0.0595. <4> The SiAlON powder according to <1> or <2>, wherein the value of Ca / (Si+Al) determined by inductively coupled plasma (ICP) optical emission spectroscopy is less than 0.0595. <5> The SiAlON powder according to <3> or <4>, wherein the value of Ca / (Si+Al) is 0.0340 or more. <6> A SiAlON sintered body obtained by sintering the SiAlON powder according to any one of <1> to <5>. <7> The SiAlON sintered body according to <6>, which is a base sphere for a bearing ball. <8> A bearing ball, comprising a mirror-finished SiAlON sintered body according to <6>. <9> A bearing comprising the bearing ball according to <8>. <10> The bearing according to <9>, which is for use in an electric vehicle. <11> The bearing according to <9>, which is for use in industrial equipment, home appliances, aviation equipment, space equipment, or medical equipment.

[0008] According to one embodiment of the present disclosure, there is provided a SiAlON powder capable of forming a SiAlON sintered body with a high β ratio. According to another embodiment of the present disclosure, there are provided a SiAlON sintered body with a high β ratio, and a bearing ball and a bearing using the same.

[0009] 1 is an example of defects (pores) inside a sintered body photographed in a microscope, and an example of an XRD measurement spectrum of a sintered body.

[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: 40 kV-37 mA, scanning range: 10 to 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: 0.01°

[0012] In this disclosure, inductively coupled plasma (ICP) optical emission spectroscopy measurements are performed using a high-resolution ICP optical emission spectrometer (for example, Hitachi High-Tech Science's "PS-3520UVDDII"). Si is measured using alkali fusion / internal standard-ICP optical emission spectroscopy, and Ca and Al are measured using pressurized acid decomposition-ICP optical emission spectroscopy.

[0013] In this disclosure, the oxygen content in the SiAlON powder is measured using an oxygen analyzer conforming to the inert gas fusion-infrared absorption method, and the nitrogen content in the SiAlON powder is measured using a nitrogen analyzer conforming to the inert gas fusion-thermal conductivity method.

[0014] In this disclosure, D ５０ is the particle diameter (50% D) at 50% cumulative volume when a cumulative volume distribution curve is drawn from the smallest diameter side in a particle diameter distribution measured by a laser diffraction / scattering method. The volume-average particle diameter can be measured, for example, by a laser diffraction particle size distribution analyzer (e.g., SALD-3100J manufactured by Shimadzu Corporation) in a state where the powder is dispersed in purified water containing a surfactant.

[0015] <SiAlON Powder> The first SiAlON powder of the present disclosure is a powder containing Ca ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎ and m is less than 1.0. The second SiAlON powder of the present disclosure has a Ca / (Si+Al) value determined by inductively coupled plasma (ICP) atomic emission spectroscopy of less than 0.0595. The first SiAlON powder and the second SiAlON powder of the present disclosure are collectively referred to as the SiAlON powder of the present disclosure. The SiAlON powder of the present disclosure is capable of forming a SiAlON sintered body with a high β ratio. Although the reason for this is unclear, it has been experimentally confirmed that by setting the Ca content to a specific amount or less, a SiAlON powder with a high α phase content can be obtained, and when this powder is sintered, a SiAlON sintered body with a high β ratio can be obtained. Specific Ca amounts are those in which Ca, represented by m / 2 in the above composition formula, is less than 0.5, i.e., m is less than 1.0, or the Ca / (Si+Al) value is less than 0.0595.

[0016] (First SiAlON Powder) The first SiAlON powder is a powder containing Ca ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎand m is less than 1.0. From the viewpoint of obtaining a SiAlON sintered body having a higher β ratio, m is preferably 0.98 or less, preferably 0.95 or less, preferably 0.92, preferably 0.90 or less, preferably 0.85 or less, preferably 0.82 or less, preferably 0.80 or less, preferably less than 0.80, preferably 0.79 or less, preferably 0.78 or less, preferably 0.77 or less, preferably 0.76 or less, and preferably 0.75 or less.

[0017] When m is small enough, the SiAlON powder is likely to contain a β phase. From the viewpoint of increasing the β ratio of the sintered body obtained by sintering the SiAlON powder, the α ratio of the SiAlON powder is desirably 60 or more. From this viewpoint, m is preferably 0.55 or more, more preferably 0.60 or more, even more preferably greater than 0.60, even more preferably 0.61 or more, even more preferably 0.62 or more, and even more preferably 0.65 or more. In particular, when m is greater than 0.60, the occurrence of defects (pores) within the sintered body is suppressed, resulting in a homogeneous sintered body, which in turn tends to improve the strength of the sintered body. In the present disclosure, defects (pores) refer to black areas with a major axis of 10 μm or more when observed under the following conditions. Defects (pores) within the sintered body can be confirmed by mirror-finishing any cross section passing through the center of the sintered body and magnifying the mirror-finished cross section 10 to 20 times in the bright field (BF) of an optical microscope. In the image observed with the optical microscope, the position of the black portion in the observed image is confirmed, and the black portion is confirmed by magnifying it 100 to 200 times. Of the black portions that appear in the photograph taken under these conditions, black portions with a major axis of 10 μm or more are defects (pores). The major axis is defined as the longest diameter of a single black portion. The presence or absence of pores can be confirmed by repeating the above-described magnification, observation, and measurement procedures in any cross section passing through the center of the sintered body. Figure 1 shows an example of a defect (pore) inside a sintered body photographed by a microscope.

[0018] On the other hand, even if the SiAlON powder contains a β phase, it is possible to make the β ratio of the SiAlON sintered body higher than before. Therefore, in cases where the SiAlON powder may contain a certain amount of β phase or more, m may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more.

[0019] When n is larger than a certain level, the SiAlON powder is likely to contain a β phase. From the viewpoint of increasing the β ratio of a sintered body obtained by sintering the SiAlON powder, n may be 2.5 or less, 2.0 or less, 1.5 or less, 1.0 or less, less than 1.0, 0.9 or less, less than 0.9, 0.88 or less, 0.87 or less, 0.86 or less, 0.85 or less, 0.84 or less, 0.83 or less, 0.82 or less, 0.81 or less, or 0.8 or less. On the other hand, even if the SiAlON powder contains a β phase, it is possible to increase the β ratio of the SiAlON sintered body compared to conventional cases. Therefore, when the SiAlON powder may contain a certain amount of β phase or more, n may be 0.1 or more, 0.2 or more, 0.4 or more, 0.4 or more, 0.5 or more, more than 0.6, or in some cases 1.5 or more.

[0020] m+n may be 0.2 or more, 0.5 or more, 1.0 or more, or 1.3 or more. Also, m+n may be 3.0 or less, 2.5 or less, 2.3 or less, 2.0 or less, 1.8 or less, or in some cases 1.3 or less.

[0021] As described above, the higher the α ratio of the SiAlON powder, the easier it is to produce a SiAlON sintered body with a high β ratio. From this viewpoint, the α ratio of the SiAlON powder is preferably 67% or more, preferably more than 67%, preferably 72% or more, preferably more than 72%, preferably 73% or more, preferably 74% or more, preferably 75% or more, preferably 76% or more, preferably 77% or more, preferably 78% or more, preferably 79% or more, preferably 80% or more, 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 a single phase (100%) is preferred.

[0022] The α-fraction is the proportion of the α-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 an X-ray diffraction spectrum. The proportion of the β-phase to the total amount of the α-phase and the β-phase: β-phase / (α-phase + β-phase) × 100 is also referred to as the β-fraction (%).

[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] The α rate is calculated using the following formula: α rate = (α(210) + α(201)) / (α(210) + α(201) + β(101) + β(120)) × 100

[0025] 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

[0026] 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°. After background subtraction is performed on X-ray analysis software (e.g., PDXL2), the average value in the range of 2θ=32 to 33° is used as the baseline.

[0027] When the first SiAlON powder is sintered, granular α-phase crystals transform into acicular β-phase crystals during firing, resulting in a β-SiAlON sintered body. Because acicular β-phase crystals have excellent strength, SiAlON with a high β fraction also has excellent strength. The first SiAlON powder contains Ca within the crystal lattice. This Ca forms grain boundary phases with Si, Al, O, etc. during sintering and transforms into β-SiAlON, resulting in a uniform, dense sintered body. Furthermore, Ca in the SiAlON powder may function as a sintering aid during sintering. Therefore, the use of a sintering aid can be omitted or the amount of sintering aid used can be reduced. The use of a sintering aid may result in the evaporation of some of the oxygen contained in the sintering aid during sintering, generating gas. If gas remains in the SiAlON sintered body, white spot-like defects called snowflakes occur. Snowflakes are gas-induced regions that are less dense than the surrounding area. Therefore, if a sintering aid is not used or the amount used is reduced, the generation of snowflakes in the SiAlON sintered body is likely to be suppressed. Furthermore, the composition of the grain boundary phase of the SiAlON sintered body varies depending on the composition of the first SiAlON powder used for sintering. SiAlON powder with a smaller m contains less Ca in the grain boundary phase formed during sintering, and the amount of volatilization of the grain boundary phase components is reduced, so the generation of snowflakes in the SiAlON sintered body is likely to be suppressed.

[0028] (Method for Producing First SiAlON Powder) The first SiAlON powder is preferably obtained by combustion synthesis from the viewpoints of productivity and ease of controlling the ratio of α phase to β phase. ２ powder, Al powder, and further SiAlON powder as a diluent. ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎ When preparing SiAlON powder in which m is less than 1, a part of the Si powder is replaced with SiO to adjust the oxygen content so that the composition formula is met. ２ Convert into powder. SiO ２ The powder may be crystalline or amorphous. The diluent for the SiAlON powder does not contribute to the combustion synthesis reaction itself, and therefore can prevent the temperature of the reaction site from rising above the expected level. It is preferable to use a SiAlON powder as the diluent that has the same composition as the target SiAlON powder obtained by the reaction.

[0029] The average particle diameter of the Si powder used as the powder raw material (D ５０ ) is about 1 to 20 μm, and D of Al powder ５０ is about 4 to 20 μm, and D of CaO powder ５０ is about 1 to 10 μm, and the D of SiAlON powder as a diluent ５０ and are preferably about 2 to 10 μm.

[0030] Each powder raw material was ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎ The powder raw material is weighed so that the element ratio is 100%. The powder raw material is then pulverized and mixed. The pulverization and mixing may be performed using a rolling ball mill, a vibration mill, or the like. The pulverization is performed by ５０ It is preferable to carry out this process until the thickness is 5 μm or less.

[0031] The pulverized and mixed powder raw materials are packed into a heat-resistant reaction vessel made of ceramics, graphite, or the like to form a powder packed bed. In this case, it is preferable to place graphite fibers, porous ceramic plates, silicon nitride powder, SiAlON powder, or the like on the upper surface of the powder raw materials and between the powder packed bed and the reaction vessel to encase the powder packed bed. This makes it difficult for heat generated in the combustion synthesis reaction in the next step to dissipate to the surroundings, allowing the reaction to proceed efficiently. It is preferable to use SiAlON powder with the same composition as the target SiAlON powder obtained by the reaction.

[0032] A heat-resistant reaction vessel filled with powdered raw materials is placed in a pressure-resistant sealed reaction vessel equipped with an ignition device and a gas supply / exhaust mechanism, and the powdered raw materials are ignited to carry out a combustion synthesis reaction of the powdered raw materials using the heat of self-reaction. The ignition method is not limited, and an ignition agent may be used. Examples of the ignition agent include powders of Ti, Al, etc. The amount of ignition agent used is preferably small enough so as not to affect the composition of the resulting SiAlON powder. The ignition agent may be placed at a portion of the powdered raw materials that serves as an ignition point. The ignition agent may be placed at the end, center, or any arbitrary position of the powder-filled layer, or may be placed at one or more positions. The method for igniting the ignition agent is not particularly limited. For example, ignition by arc discharge, laser heating, etc. may be used, or heat generated when a metal or carbon filament is heated electrically may be used.

[0033] The combustion synthesis reaction is preferably carried out in a pressurized environment. Specifically, it is preferably carried out at 1 kPaG to 880 KPaG. When the pressure is equal to or greater than the lower limit, the combustion synthesis reaction is likely to proceed. When the pressure is equal to or less than the upper limit, the reaction temperature is appropriately suppressed, and the generation of coarse silicon chunks is likely to be suppressed. The combustion synthesis reaction is carried out in a nitrogen reaction atmosphere, and a pressurized environment can be created by the nitrogen pressure supplied to the closed reactor. When ignited in a pressurized environment, the powder raw material self-combusts and the combustion diffuses in a short time, and an aggregate product (agglomerates of SiAlON) is obtained by the combustion synthesis reaction due to direct reaction with nitrogen.

[0034] The aggregate product has a target average particle diameter (D５０ ). Examples of the pulverizer include a jaw crusher, a hammer mill, a disk mill, a vibration mill, a bead mill, a jet mill, and a planetary ball mill. One type of pulverizer may be used alone, or two or more types may be used in combination. The pulverization may be performed in the order of coarse pulverization, medium pulverization, and fine pulverization. In coarse pulverization, the aggregated product is pulverized to a size of several mm, in medium pulverization, the product is pulverized to a size of about 100 μm, and in fine pulverization, the product may be pulverized to the desired size. For example, coarse pulverization may be performed using a jaw crusher or a hammer mill, medium pulverization may be performed using a disk mill or a vibration mill, and fine pulverization may be performed using a dry bead mill or a wet bead mill. Fine pulverization may be performed using a dry bead mill followed by a wet bead mill. Water is preferably used as the medium when using a wet bead mill. In addition, the wet bead mill may be performed after adding a dispersant, a pH adjuster, etc. to water to form a slurry.

[0035] (Second SiAlON powder) The second SiAlON powder has a Ca / (Si+Al) value determined by inductively coupled plasma (ICP) emission spectroscopy of less than 0.0595, preferably 0.0580 or less, more preferably 0.0550 or less, even more preferably 0.0520 or less, particularly preferably 0.0500 or less, and extremely preferably 0.0460 or less. From the viewpoint of increasing the α rate of the SiAlON powder, the Ca / (Si+Al) value is preferably 0.0300 or more, more preferably 0.0340 or more, more preferably 0.0350 or more, more preferably 0.0355 or more, more preferably 0.0356 or more, more preferably 0.0360 or more, more preferably 0.0370 or more, more preferably 0.0400 or more, more preferably 0.0410 or more, and particularly preferably 0.0450 or more. In the case where the SiAlON powder may contain a certain amount of β phase or more, the value of Ca / (Si+Al) may be 0.0594 or less, 0.0580 or less, 0.0550 or less, 0.0500 or less, 0.0470 or less, or 0.0450 or less.

[0036] The second SiAlON powder may meet the requirements of the first SiAlON powder, and may contain Ca. ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎ and m may be less than 1.0. Regarding other requirements, reference can be made to the first SiAlON powder. Regarding the method for producing the second SiAlON powder, reference can be made to the method for producing the first SiAlON powder.

[0037] The average particle diameter (D ５０ From the viewpoint of increasing the β ratio of the SiAlON sintered body, the average particle diameter (D ５０ The lower limit of the particle size is not particularly limited, but from the viewpoint of appropriately suppressing the energy and time required for pulverization, it is preferably 0.2 μm or more, and more preferably 0.3 μm or more.

[0038] <SiAlON Sintered Body> The SiAlON sintered body of the present disclosure is obtained by sintering the SiAlON powder of the present disclosure. By using the SiAlON powder of the present disclosure, the resulting sintered body is a SiAlON sintered body with a high β ratio. The β ratio of the SiAlON sintered body of the present disclosure is preferably 20% or more, preferably 30% or more, preferably 40% or more, preferably 50% or more, and preferably 60% or more. Furthermore, the β ratio is 100% or less, and the higher the β ratio, the better, but it may be 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, or 70% or less.

[0039] The SiAlON sintered body of the present disclosure is suitable for use as a wear-resistant member, and may be used, for example, as a base sphere for a bearing ball.

[0040] <Method for manufacturing SiAlON sintered body> The sintered body of the present disclosure is obtained by sintering the SiAlON powder of the present disclosure. Conventional sintering methods can be applied as appropriate. One example of a method for manufacturing a SiAlON sintered body includes preparing a raw material composition containing the SiAlON powder of the present disclosure, granulating, molding, pressing, degreasing, and firing the raw material composition. Examples of additives added to the raw material composition include sintering aids, binders, solvents, and sintering accelerators. In the method for manufacturing a sintered body, processes other than firing may be omitted as appropriate. Furthermore, processes other than the above, such as classification and iron removal, may be added as appropriate. The SiAlON powder as a raw material may be used alone or in combination of two or more types.

[0041] Examples of sintering aids include compounds containing Li, Mg, Ca, Si, Y, La, etc., and specifically, SiO ２ , 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 powder already contains oxygen atoms as a constituent element, using water when using SiAlON powder as a raw material has little effect on the properties of the final product, thereby widening the options for manufacturing processes.

[0042] When a sintering aid is used, from the viewpoint of suppressing defects inside the sintered body due to volatilization of the sintering aid, the amount of the sintering aid added is preferably 6 mass % or less, more preferably 4.5 mass % or less, and even more preferably 3 mass % or less, calculated as oxide, relative to the SiAlON powder.

[0043] 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 enhance dispersibility in the crystalline structure, thereby improving the mechanical strength of the SiAlON 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 that colors the SiAlON sintered body black and imparts opacity.

[0044] When a sintering accelerator is used, from the viewpoint of making the most of the effect of the addition of the sintering accelerator, the amount of the sintering accelerator added, in oxide equivalent, 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, relative to the SiAlON powder. Also, from the viewpoint of further increasing the mechanical strength, the amount of the sintering accelerator added, in oxide equivalent, is preferably 5 mass % or less, preferably 3 mass % or less, preferably 2 mass % or less, and preferably 1 mass % or less, relative to the SiAlON powder.

[0045] 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.

[0046] 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.

[0047] Degreasing may be carried out in either a non-oxidizing or oxidizing atmosphere. When degreasing is carried out in a non-oxidizing atmosphere, a temperature of 550 to 800°C is preferred, and when degreasing is carried out 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.

[0048] The SiAlON powder or molded product is preferably heated under reduced pressure, and is preferably heated 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.

[0049] 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.

[0050] The α phase undergoes a phase transition to the β phase due to oxygen present on the surface during sintering. When Ca-αSiAlON undergoes a phase transition to βSiAlON, the Ca incorporated within the lattice migrates from the lattice to the grain boundaries outside the lattice, forming a solid solution between the crystal grains. As a result, the sintered body of Ca-αSiAlON becomes uniform and dense.

[0051] After firing, 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.

[0052] <Bearing Ball> The bearing ball of the present disclosure is formed from a mirror-finished product of the sintered body of the present disclosure. The bearing ball can be obtained by subjecting the sintered body of the present disclosure to mirror finishing or the like. Any method for mirror finishing may be used.

[0053] <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 electric vehicles. 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 industrial equipment, home appliances, aviation equipment, space equipment, or medical equipment.

[0054] The present invention will be described below using examples, but the present invention is not limited thereto. Examples 1 to 3 and 11 to 18 are working examples, and Example 4 is a comparative example.

[0055] In addition, when measuring the oxygen and nitrogen amounts by the inert gas fusion method, an oxygen, nitrogen, and hydrogen analyzer "ONH836" manufactured by LECO was used. For X-ray diffraction measurement, a Smart Lab manufactured by Rigaku Corporation was used, a D / teXUltra manufactured by Rigaku Corporation was used as the detector, and PDXL2 manufactured by Rigaku Corporation was used as the X-ray analysis software. For inductively coupled plasma (ICP) optical emission spectroscopy measurement, a high-resolution ICP optical emission spectrometer "PS-3520UVDDII" manufactured by Hitachi High-Tech Science Corporation was used.

[0056] [Example 1] SiAlON powder, CaO powder, Si powder, SiO powder were used as powder raw materials so as to have the element ratios shown in Table 1. ２ The powder and Al powder were weighed, and these powders were filled into a reaction vessel, which was then placed in a pressure-resistant sealed reaction vessel equipped with an ignition device and a gas supply / exhaust mechanism. The reactor was depressurized and degassed, and then nitrogen gas was supplied to replace the atmosphere. When the pressure reached 0.7 MPa, the ignition agent in the reaction vessel was ignited, and a combustion synthesis reaction was carried out, resulting in the formation of Ca, ０．３５ Si １０．５ Al １．５ O ０．８ N １５．２ A bulk product having an α ratio of 96% (m=0.7) was obtained. The Ca / (Si+Al) ratio of the bulk product was calculated by the above-mentioned method using ICP emission spectroscopy, and was found to be 0.0420.

[0057] The obtained aggregate product was crushed to a size of about several centimeters using a jaw crusher, and then crushed in a hammer mill.５０ The powder was then crushed in a planetary ball mill until the particle size was 5 to 20 μm. ５０ The powder was pulverized to a particle size of 2 to 4 μm. Just before the start of the planetary ball mill pulverization, an appropriate amount of ethanol was added as a pulverization aid, and the pulverizer was sealed and pulverized. After that, the powder was pulverized in a wet bead mill using alumina-based pulverization media. ５０ The powder was pulverized to a size of 0.531 μm to obtain a SiAlON powder.

[0058] The obtained SiAlON powder was molded by a uniaxial press, subjected to CIP molding and degreasing, and then sintered at 1775°C for 5 hours in a nitrogen atmosphere at 6 atmospheres. The β ratio of the obtained SiAlON sintered body was 67%.

[0059] [Example 2] A lump product was obtained in the same manner as in Example 1, except that the powder raw material was weighed so as to obtain the element ratios shown in Table 1. The α ratio of the lump product was 98%. The Ca / (Si+Al) ratio of the lump product was calculated by the above-mentioned ICP emission spectroscopy and was found to be 0.0472. The lump product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. The D of the SiAlON powder ５０ The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 68%.

[0060] [Example 3] Agglomerated product was obtained in the same manner as in Example 1, except that the powder raw materials were weighed so as to have the element ratios shown in Table 1. The α ratio of the agglomerated product was 99%. The Ca / (Si+Al) ratio of the agglomerated product was 0.0524. The agglomerated product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. The D of the SiAlON powder ５０ The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 27%.

[0061] [Example 4] Agglomerated product was obtained in the same manner as in Example 1, except that the powder raw materials were weighed so as to have the element ratios shown in Table 1. The α ratio of the agglomerated product was 99%. The Ca / (Si+Al) ratio of the agglomerated product was 0.0595. The agglomerated product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. D of the SiAlON powder５０ The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 17%.

[0062] [Example 11] Agglomerated product was obtained in the same manner as in Example 1, except that the powder raw materials were weighed so as to have the element ratios shown in Table 1. The α ratio of the agglomerated product was 72%. The Ca / (Si+Al) ratio of the agglomerated product was 0.0355. The agglomerated product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. ５０ The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 99%.

[0063] [Example 12] Agglomerated product was obtained in the same manner as in Example 1, except that the powder raw materials were weighed so as to have the element ratios shown in Table 1. The α ratio of the agglomerated product was 67%. The Ca / (Si+Al) ratio of the agglomerated product was 0.0356. The agglomerated product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. The D of the SiAlON powder ５０ The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 99%.

[0064] [Example 13] Agglomerated product was obtained in the same manner as in Example 1, except that the powder raw materials were weighed so as to have the element ratios shown in Table 1. The α ratio of the agglomerated product was 99%. The Ca / (Si+Al) ratio of the agglomerated product was 0.0413. The agglomerated product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. ５０ The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 98%.

[0065] [Example 14] Agglomerated product was obtained in the same manner as in Example 1, except that the powder raw materials were weighed so as to have the element ratios shown in Table 1. The α ratio of the agglomerated product was 96%. The Ca / (Si+Al) ratio of the agglomerated product was 0.0414. The agglomerated product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. ５０The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 99%.

[0066] [Example 15] Agglomerated product was obtained in the same manner as in Example 1, except that the powder raw materials were weighed so as to have the element ratios shown in Table 1. The α ratio of the agglomerated product was 100%. The Ca / (Si+Al) ratio of the agglomerated product was 0.0562. The agglomerated product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. ５０ The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 79%.

[0067] [Example 16] Agglomerated product was obtained in the same manner as in Example 1, except that the powder raw materials were weighed so as to have the element ratios shown in Table 1. The α ratio of the agglomerated product was 99%. The Ca / (Si+Al) ratio of the agglomerated product was 0.0562. The agglomerated product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. ５０ The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 73%.

[0068] [Example 17] Agglomerated product was obtained in the same manner as in Example 1, except that the powder raw materials were weighed so as to have the element ratios shown in Table 1. The α ratio of the agglomerated product was 99%. The Ca / (Si+Al) ratio of the agglomerated product was 0.0564. The agglomerated product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. ５０ The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 74%.

[0069] [Example 18] Agglomerated product was obtained in the same manner as in Example 1, except that the powder raw materials were weighed so as to have the element ratios shown in Table 1. The α ratio of the agglomerated product was 98%. The Ca / (Si+Al) ratio of the agglomerated product was 0.0564. The agglomerated product was pulverized in the same manner as in Example 1 to obtain SiAlON powder. The D of the SiAlON powder ５０The SiAlON powder obtained was sintered in the same manner as in Example 1. The β ratio of the obtained SiAlON sintered body was 75%.

[0070] (Evaluation of defects in sintered bodies) Any cross section passing through the center of the sintered bodies obtained in Examples 1 to 4 and 11 to 18 was mirror-polished, and any field of view of the mirror-polished cross section was magnified 10 to 20 times in the bright field (BF) of an optical microscope to confirm the position of the black part, and the black part was observed at a magnification of 100 to 200 times to confirm the presence or absence of defects (pores). Table 1 shows the evaluation of defects in the sintered bodies. A indicates that no defects (pores) were found, and B indicates that defects (pores) were found.

[0071]

[0072] As shown in Table 1, Ca ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎ It can be seen that in Examples 1 to 3 and 11 to 18, in which m is less than 1.0 or the value of Ca / (Si+Al) is less than 0.0595, the β ratio of the SiAlON sintered body is significantly improved compared to Example 4.

[0073] As shown in Table 1, in Examples 1 to 3 and 13 to 18 where m was greater than 0.6 and less than 1.0, no defects (pores) were found in the sintered body.

[0074] Therefore, Ca ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎ When m is less than 1.0 or the value of Ca / (Si+Al) is less than 0.0595, the β-modulus of the SiAlON sintered body is significantly improved, and when m is more than 0.6 and less than 1.0, an additional effect of suppressing the generation of defects (pores) in the sintered body is obtained.

[0075] [Examples 5 to 7] The same method as in Example 1 was used, except that the powder raw materials were weighed so as to have the element ratios shown in Table 2, and the D ５０The α-ratio of the aggregated product of Example 5 was 96%, that of the aggregated product of Example 6 was 98%, and that of the aggregated product of Example 7 was 99%.

[0076]

[0077] As shown in Table 2, the D of SiAlON powder ５０ Even if the thickness is around 0.35 μm, Ca ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎ It can be seen that in Examples 5 to 7, where m is less than 1.0 or the value of Ca / (Si+Al) is less than 0.0595, the β ratio of the SiAlON sintered body is high.

[0078] [Examples 8 to 10] The same method as in Example 1 was used, except that the powder raw materials were weighed so as to have the element ratios shown in Table 3, and the D ５０ The α-ratio of the aggregated product of Example 8 was 96%, that of Example 9 was 98%, and that of Example 10 was 99%.

[0079]

[0080] As shown in Table 3, the D of SiAlON powder ５０ Even if the thickness is around 0.7 μm, Ca ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎ It can be seen that, in Examples 8 to 10 in which m is less than 1.0 or the value of Ca / (Si+Al) is less than 0.0595, the β ratio of the SiAlON sintered body is higher than that of Example 4.

[0081] The SiAlON powder 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.

[0082] The disclosure of Japanese Patent Application No. 2024-123714 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. Ca ｍ／２ Si １２－（ｍ＋ｎ） Al （ｍ＋ｎ） O ｎ N １６－ｎ and m is less than 1.

0.

2. The SiAlON powder according to claim 1, wherein m is 0.6 or more.

3. SiAlON powder having a Ca / (Si+Al) value of less than 0.0595 as determined by inductively coupled plasma (ICP) emission spectroscopy.

4. The SiAlON powder according to claim 1, wherein the value of Ca / (Si+Al) determined by inductively coupled plasma (ICP) emission spectrometry is less than 0.0595.

5. The SiAlON powder according to claim 3 or 4, wherein the value of Ca / (Si+Al) is 0.0340 or more.

6. A SiAlON sintered body obtained by sintering the SiAlON powder according to claim 1 or 3.

7. The SiAlON sintered body according to claim 6, which is a base sphere for a bearing ball.

8. A bearing ball made of the mirror-finished SiAlON sintered body according to claim 6.

9. A bearing comprising the bearing ball according to claim 8.

10. The bearing of claim 9, which is for an electric vehicle.

11. The bearing according to claim 9, which is for use in industrial equipment, home appliances, aircraft equipment, space equipment, or medical equipment.

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