Method for producing silicon nitride sintered body, wear-resistant member, and method for producing bearing

Abstract

A silicon nitride sintered body according to an embodiment of the present invention comprises silicon nitride crystal particles and a grain boundary phase, and is characterized in that when a Raman spectrum analysis is performed in a 20 [mu] m * 20 [mu] m region in an arbitrary cross section of the silicon nitride sintered body, seven or more peaks are detected in the range of 400 cm-1 to 1200 cm-1, the strongest peak of the seven or more peaks is not in the range of 515 cm <-1 > or more and 525 cm <-1 > or less. It is preferable that at least three of the seven or more peaks are within the range of 530 cm <-1 > to 830 cm <-1 > (inclusive). It is preferable that at least one of the seven or more peaks is within the range of 440 cm <-1 > to 460 cm <-1 > (inclusive).

Description

[0001] This application is a divisional application of the invention patent application with the application date of March 28, 2022, application number 202280016624.5, and invention name "Silicon nitride sintered body, wear-resistant component and method for manufacturing silicon nitride sintered body". Technical Field

[0002] The embodiments described below mainly relate to a silicon nitride sintered body, a wear-resistant member, and a method for producing the silicon nitride sintered body. Background Art

[0003] Silicon nitride sintered compacts are used as wear-resistant components such as bearing balls and rollers due to their wear resistance. Conventional sintered compositions for silicon nitride sintered compacts include silicon nitride-yttrium oxide-aluminum oxide-aluminum nitride-titania systems (Patent Document 1: Japanese Patent Application Publication No. 2001-328869). Using yttrium oxide, aluminum oxide, aluminum nitride, and titanium oxide as sintering aids improves sinterability and produces a silicon nitride sintered compact with excellent wear resistance.

[0004] For example, a bearing has a structure in which bearing balls are arranged between an outer ring and an inner ring. The life of the bearing is affected by the lifespan of the bearing balls, the outer ring, and the inner ring. In Patent Document 1, the durability of the bearing balls is improved by using a sintered silicon nitride body. On the other hand, bearing steel (SUJ2) is used for the outer and inner rings. Even if the durability of the bearing balls is improved, the outer and inner rings may wear, thereby reducing the durability of the bearing.

[0005] Japanese Patent Application Laid-Open No. 2003-65337 (Patent Document 2) uses bearing balls made of a silicon nitride sintered body having high thermal conductivity. Improving the thermal conductivity of the silicon nitride sintered body improves heat dissipation.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-328869

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 2003-65337 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] Improving the heat dissipation of the bearing balls can suppress the thermal expansion of the outer and inner rings. However, further benefits were not achieved. Investigation into the cause revealed that the attack from the bearing balls on the mating components (outer and inner rings) was not sufficiently reduced, resulting in reduced durability.

[0012] The present invention is an invention for coping with such a problem, and provides a silicon nitride sintered body capable of improving the durability of a wear-resistant member.

[0013] Means for solving problems

[0014] The silicon nitride sintered body of the embodiment is characterized in that, when a Raman spectrum analysis is performed on an area of 20 μm×20 μm in any cross section of the silicon nitride sintered body including silicon nitride crystal particles and grain boundary phases, the peak at 400 cm -1 Over 1200cm -1 Peaks were detected at more than 7 locations within the following range, and the strongest peak within the above range was not at 515 cm -1 Over 525cm -1 Within the following range. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a diagram showing a part of the cross-sectional structure of a silicon nitride sintered compact according to an embodiment.

[0016] Figure 2 This is a diagram schematically illustrating the analysis results of the silicon nitride sintered body according to the embodiment using Raman spectroscopy.

[0017] Figure 3 This is a diagram showing an example of a bearing ball according to an embodiment.

[0018] Figure 4 This is a diagram showing an example of a bearing according to an embodiment. DETAILED DESCRIPTION

[0019] The silicon nitride sintered compact of the embodiment is characterized in that it comprises silicon nitride crystal particles and grain boundary phases, and when a Raman spectrum analysis is performed on a 20 μm×20 μm area in an arbitrary cross section of the silicon nitride sintered compact, the Raman spectrum at 400 cm -1 Over 1200cm -1 More than 7 peaks are detected within the following range, and the strongest peak of the above 7 or more peaks is not at 515cm -1 Over 525cm -1 Within the following range.

[0020] Figure 1 It is a diagram showing a part of the cross-sectional structure of a silicon nitride sintered compact according to an embodiment.

[0021] Figure 1 In FIG. 1 , 10 is a silicon nitride sintered body, 11 is a silicon nitride crystal particle, and 12 is a grain boundary phase. Figure 1As shown in FIG, the silicon nitride sintered body 10 of the embodiment includes silicon nitride crystal particles 11 and grain boundary phases 12. The grain boundary phases are formed by the reaction of sintering aid powders with each other or with impurities in the silicon nitride powder. The grain boundary phases fill the gaps between the silicon nitride crystal particles. This improves the strength of the sintered body.

[0022] When the silicon nitride sintered compact of the embodiment is subjected to Raman spectroscopy analysis of an area with a unit area of 20 μm×20 μm in an arbitrary cross section, the -1 Over 1200cm -1 More than 7 peaks are detected within the following range, and the strongest peak among the above 7 or more peaks is not at 515cm -1 Over 525cm -1 Within the following range.

[0023] Raman spectroscopy is a method for evaluating substances using Raman scattered light. Raman scattered light is a phenomenon in which light with a different wavenumber corresponding to the vibrational energy relative to the excitation light is scattered. The wavelength difference corresponds to the energy component of the molecular vibrations possessed by the substance. Raman scattered light with different wavelengths can be obtained between substances with different molecular structures. By examining Raman scattered light, it is possible to identify the vibrational modes of the atoms in the sample and obtain data related to the bonding state. For example, even if the composition is the same, the resulting Raman scattered light will be different if the orientation, crystallinity, etc. are different. Therefore, the Raman spectrum of silicon nitride powder is different from that of a sintered body. In addition, the appearance of the sintered body is opaque.

[0024] The measurement area of the Raman spectroscopy analysis was set to a unit area of 20 μm × 20 μm. If it is of this size, both the silicon nitride crystal particles and the grain boundary phase can be included in the measurement area. The measurement device used for the Raman spectroscopy analysis was an inVia Reflex Leica microscope (resolution: 0.3 cm- 1) or a device with equivalent or better performance. For the excitation laser, an LD excitation green laser (wavelength 532nm, output power 100mW) was used. The irradiation laser beam diameter was set to 0.7μm. The exposure time was set to 1 second per measurement point, and the platform movement step was set to 0.4μm. For data analysis, multivariate curve resolution (MCR) using the image analysis software WiRe4Empty Modelling was used. Here, in the obtained Raman spectrum, the peak detected by the analysis software is used as the peak. In addition, the half-value width and peak intensity are also obtained by the above-mentioned analysis software. The peak intensity obtained here is the value obtained by subtracting the baseline value from the absolute intensity of the peak. The baseline value can also be obtained by the analysis software. In addition, the total number of measurement sites is 2601. By averaging the spectra of these total measurement sites, a spectrum with an improved SN ratio (the ratio of the size of the noise to the size of the spectrum) is obtained. In addition, by measuring while moving the platform, a Raman spectrum with less dependence on the measurement site is obtained. The air temperature during the measurement was set to 25 degrees Celsius (25℃).

[0025] In the case of the silicon nitride sintered body of the embodiment, at 400 cm -1 Over 1200cm -1 In the Raman spectroscopy analysis, more than 7 peaks were detected within the following wave number range. -1 Over 300cm -1 The strongest peak of silicon nitride crystal particles was detected in the range of 400 cm -1 Over 1200cm -1 The peaks in the following ranges are different from the strongest peaks of silicon nitride crystal particles. -1 Over 1200cm -1 The position of the strongest peak below is preferably not at 515 cm -1 Over 525cm -1 It should be noted that the strongest peak is the peak with the highest intensity. -1 Over 1200cm -1 The peaks in the range below 400 cm -1 Over 514cm -1 Below or 526cm -1 Over 1200cm -1 The strongest peak exists in the range below. As mentioned above, at 100 cm -1 Over 300cm -1 The strongest peak of silicon nitride crystal particles is detected in the following range. The silicon nitride sintered body of the embodiment is characterized by having a peak at 400 cm -1 Over 1200cm-1 The largest peak detected in the following range is not at 515 cm -1 Over 525cm -1 The following range.

[0026] As at 515cm -1 Over 525cm -1 The peaks detected in the following ranges include peaks due to free silicon. -1 Over 525cm -1 The peaks in the following range are large, which indicates that there is a large amount of free silicon. The intensity of the free silicon peak is at 400 cm -1 Over 1200cm -1 The maximum value in the following range indicates that the free silicon content is high. That is, the intensity of the free silicon peak is at 400 cm -1 Over 1200cm -1 If the maximum value is within the range below, the amount of free silicon may be excessive, and the strength of the silicon nitride sintered body may be reduced. -1 Over 1200cm -1 The position of the strongest peak below is not 515cm -1 Over 525cm -1 Within the following range.

[0027] As mentioned above, Raman spectroscopy detects peaks corresponding to the bonding state of atoms. Even if the composition is the same, the peaks will change depending on the bonding state. -1 Over 1200cm -1 The bonding state with more than 7 peaks detected in the following range can improve durability. In particular, it can stabilize the contact with the outer ring and inner ring in the bearing. -1 Over 1200cm -1 The upper limit of the number of peaks detected in the following range is not particularly limited, but is preferably 10 or less.

[0028] At 515cm -1 Over 525cm -1 If there is a peak in the range below, the peak is not 400 cm -1 Over 1200cm -1 The strongest peak in the following range: 515cm derived from free silicon -1 Over 525cm -1 The smaller the peak at the following wave number, the better. More preferably, the peak at 515cm -1 Over 525cm -1 There are no peaks below.

[0029] At 400cm -1 Over 1200cm -1 Among the seven or more peaks detected in the range below, preferably at least three peaks are present at 530 cm -1 Over 830cm -1 More preferably, at least three of the seven or more peaks are present at 530 cm -1 Over 800cm -1 Within the following range.

[0030] Furthermore, at least one of the seven or more peaks is preferably at 440 cm -1 Over 460cm -1 The intensity of the strongest peak in the first range is set to 1. When multiple peaks are detected, the peak with the largest intensity in the first range is set as the strongest peak. The strongest peak in the first range is the peak based on silicon nitride crystal particles. The number of peaks in the first range is not particularly limited, but is preferably 1 or more and 3 or less. If there are more than 4 peaks, it may become difficult to distinguish the true peak intensity of each peak. More preferably, the number of peaks in the first range is 1 or 2.

[0031] Furthermore, at least three of the seven or more peaks are preferably present at 500 cm -1 Over 830cm -1 The upper limit of the number of peaks detected is not particularly limited, but is preferably 6 or less. If the number of peaks is too large, it may become difficult to control the peaks exceeding 830 cm -1 and 1200cm -1 The number of peaks in the following third range: When the peak intensity of the strongest peak in the first range is set to 1, the peak intensity of each of the three or more peaks existing in the second range is preferably 0.8 or more and 2.0 or less.

[0032] Regarding the silicon nitride sintered body of the embodiment, the 400 cm outside the above range -1 ~1200cm -1 The peak detected in is not particularly limited. For example, it can be detected at 410 cm -1 Over 420cm -1 The following range, 715cm -1 Over 725cm -1 Peaks exist within the following ranges. In these ranges, peaks derived from iron or iron compounds are detected. Iron compounds are iron oxides, etc. -1 ~1200cm -1 In addition, it can also be 270cm -1 Over 280cm -1The following range, 1320cm -1 Over 1340cm -1 The following range, 1570cm -1 Above 1630cm -1 Peaks exist within the following ranges, etc. In these ranges, peaks derived from tungsten or tungsten compounds are detected. Tungsten compounds include tungsten oxide, etc.

[0033] The peaks within the second range are peaks based on silicon nitride crystal particles or grain boundary phases. If the intensity of each peak within the second range is 0.8 times or more and 2.0 times or less of the intensity of the strongest peak within the first range, a balance can be achieved with the silicon nitride crystal particles showing the strongest peak within the first range. As a result, the orientation of the silicon nitride crystal particles can be controlled, and wear resistance can be improved.

[0034] In addition, at least 3 of the above 7 or more peaks are preferably present in the third range. The upper limit of the number of peaks detected in the third range is not particularly limited, but is preferably 6 or less. If the number of peaks is too large, it may become difficult to control the number of peaks in the second range. When the peak intensity of the strongest peak in the first range is set to 1, the peak intensity of each of the three or more peaks present in the third range is preferably 2.7 or more and 3.7 or less.

[0035] Peaks within the third range are peaks based on silicon nitride crystal particles or grain boundary phases. If the intensity of each peak within the third range is 2.7 times or more and 3.7 times or less of the intensity of the strongest peak within the first range, a balance can be achieved with the silicon nitride crystal particles exhibiting the strongest peak within the first range. As a result, the orientation of the silicon nitride crystal particles can be controlled, and wear resistance can be improved.

[0036] At least one of the seven or more peaks is preferably located at 500 cm -1 Over 600cm -1 Within the range below 10cm -1 Over 100cm -1 The full width at half maximum is more preferably 20 cm. -1 Over 80cm -1 Below, further preferably having 40cm -1 Over 70cm -1 Hereinafter, the "full width at half maximum" will be referred to as "full width at half maximum" for short.

[0037] At 500cm -1 Over 600cm -1 Within the range below 10cm -1 Over 100cm -1It is more preferable that any peak with a half-value width below 515 cm -1 Over 525cm -1 Within the range of 40cm -1 Over 70cm -1 It is further preferred that any peak with a half-value width below 515 cm -1 Over 525cm -1 In addition, it is preferably within the range of 530cm -1 Over 600cm -1 Within the range below, one or more objects with a length of 40 cm are detected. -1 Over 70cm -1 More preferably, the peak has a half-value width of 530 cm or less. -1 Over 600cm -1 Within the range below 40cm -1 Over 70cm -1 The number of peaks with the following half-value widths is more preferably only one. -1 Over 600cm -1 The half-value width of the peak in the range below is 40 cm -1 Over 70cm -1 Below, the half-value width is 70cm -1 The following indicates good crystallinity. If the crystallinity is good, it will lead to stabilization of the suppression of the aggressiveness to the target component. On the other hand, if the half-value width is less than 10cm -1 , there is a possibility that crystallization will progress excessively, which will have an adverse effect on impact resistance.

[0038] At 400cm -1 Over 1200cm -1 The peaks within the following ranges are mainly peaks of compounds based on silicon nitride crystal particles or grain boundary phases. The type of chemical bond can be determined by the position of the peak detected by Raman spectroscopy. In addition, the half-value width of the peak represents the degree of crystallinity. The smaller the half-value width of the peak, the higher the crystallinity. In addition, the peak intensity is affected by orientation and concentration. The peak shift value is affected by stress and strain. Even for materials with the same composition, the number, intensity, and half-value width of the peaks change depending on the bonding state, crystallinity, orientation, strain, etc.

[0039] In the case of a silicon nitride sintered body, the average particle size of the silicon nitride crystal particles is preferably 2 μm or less. The area ratio of silicon nitride crystal particles having an aspect ratio of 2 or greater is preferably within a range of 20% to 70%. Controlling the size of the silicon nitride crystal particles can homogenize the orientation and strain.

[0040] In determining the average particle size of silicon nitride crystalline particles, a scanning electron microscope (SEM) photograph of an arbitrary cross section is used. The maximum diameter of the silicon nitride crystalline particles photographed in the SEM photograph is set as the major diameter. The length of the line segment extending vertically from the center of the major diameter is set as the minor diameter. It is set to particle size = (major diameter + minor diameter) ÷ 2. The average value of the particle sizes of 50 silicon nitride crystalline particles is used as the average particle size. In addition, the particle size of particles that overlap with other silicon nitride crystalline particles and cannot be confirmed is calculated based on the observable portion.

[0041] The aspect ratio is also measured using an SEM photograph of an arbitrary cross section. The method for calculating the major and minor diameters is the same as for the particle size. Aspect ratio = major diameter / minor diameter. Calculate the area ratio of silicon nitride crystal particles with an aspect ratio of 2 or greater, captured within a 20 μm x 20 μm area in the SEM photograph. Similarly to the particle size, for particles that overlap with other silicon nitride crystal particles and whose outlines cannot be confirmed, calculate the particle size based on the observable portion.

[0042] When the outlines of the silicon nitride crystal particles cannot be clearly seen, the grain boundary phase may be removed by etching.

[0043] In addition, titanium nitride (TiN) particles are preferably present in the grain boundary phase. Titanium nitride particles are compounds that strengthen the grain boundary phase. In addition, titanium nitride particles are -1 Over 1200cm -1 Compounds that easily generate Raman spectral peaks within the following ranges.

[0044] Figure 2 This is a diagram schematically illustrating the analysis results of the silicon nitride sintered body according to the embodiment using Raman spectroscopy.

[0045] exist Figure 2 In the Raman spectrum RS shown in FIG, the horizontal axis represents the Raman shift (cm -1 ), the vertical axis represents the scattering intensity. When the silicon nitride sintered body of the embodiment is analyzed by Raman spectroscopy, for example, Figure 2 As shown in -1 Over 1200cm -1 Seven peaks P1 to P7 were detected in the following range. -1 Over 525cm -1 No peak was detected in the range below 440 cm -1 Over 460cm -1 In the first range below, peak P1 is detected. At 500 cm -1 Over 830cm -1 In the second range below, three peaks P2 to P4 were detected. -1and 1200cm -1 In the third range below, three peaks P5 to P7 are detected. The intensity of each of the peaks P2 to P4 in the second range is 0.8 times or more and 2.0 times or less of the intensity of the peak P1 in the first range. The intensity of each of the peaks P5 to P7 in the third range is 2.7 times or more and 3.7 times or less of the intensity of the peak P1. In addition, peak P2 is at 530 cm -1 Over 600cm -1 The half-value width of the peak is 40 cm -1 Over 70cm -1 the following.

[0046] The flexural strength in the three-point bending test of the silicon nitride sintered body is preferably 700 MPa or more. If the strength is high, wear resistance can be improved. Therefore, the flexural strength is preferably 700 MPa or more, and then 900 MPa or more. It should be noted that the three-point bending test is carried out according to JIS-R-1601 (2008). In addition, the flexural strength in the three-point bending test is sometimes referred to as three-point bending strength. JIS-R-1601 (2008) corresponds to ISO 14704 (2000).

[0047] Utilizing a silicon nitride sintered body having the aforementioned Raman spectral peaks can improve wear resistance. Therefore, by using the silicon nitride sintered body of the embodiment in a wear-resistant component, durability can be improved. In particular, according to the embodiment, since aggressiveness toward the target component can be suppressed, the durability of the target component can also be improved. Examples of such wear-resistant components include bearing components, roller components, compressor components, pump components, engine components, and components for friction stir welding apparatuses.

[0048] A bearing is a combination of bearing components consisting of rolling elements and rings. Rolling elements are either spherical or roller-shaped. Components containing rolling elements are called bearing balls. Spherical elements are balls, while rollers are cylindrical. Bearings using spherical rolling elements are called ball bearings. Bearings using roller-shaped rolling elements are called roller bearings. Roller bearings also include needle bearings, cylindrical roller bearings, and spherical roller bearings. Rings also have outer and inner rings.

[0049] Examples of roller components include rolling rollers and rollers used as feed components in electronic equipment. Examples of compressor or pump components include impellers. A compressor is a device that increases pressure, while a pump is a device that reduces pressure. Examples of engine components include cam rollers, cylinders, pistons, and check balls. Examples of friction stir welding device components include tool components for friction stir welding devices.

[0050] Figure 3This is a diagram showing an example of a wear-resistant member (bearing ball) according to an embodiment. Figure 4 This is a diagram showing another example (bearing) of the wear-resistant member according to the embodiment.

[0051] Figure 3 and Figure 4 In the figure, 1 represents a bearing ball, 2 represents a bearing, 3 represents an inner ring, and 4 represents an outer ring. Bearing 2 has a structure in which bearing balls 1 are arranged between inner ring 3 and outer ring 4. Four or more bearing balls 1 are arranged in bearing 2. Inner ring 3 and outer ring 4 are the counterpart components of bearing balls 1.

[0052] The bearing ball 1 is made of the silicon nitride sintered body of the embodiment. As needed, it can also be ground in such a way that the surface roughness Ra becomes less than 0.1μm. Regarding bearing balls, the surface roughness Ra corresponding to the grade is specified in ASTM F2094 of the American Society for Testing and Materials. Therefore, it can also be ground to the surface roughness corresponding to the grade. It should be noted that ASTM is a standard specification issued by ASTM International. The old name of ASTM International is the American Society for Testing and Materials (ASTM). In addition, even if the silicon nitride sintered body is applied to a wear-resistant component other than a bearing ball, it can also be subjected to surface grinding as needed. In other words, the wear-resistant component of the embodiment preferably has a ground surface with a surface roughness Ra of less than 0.1μm, and further Ra of less than 0.02μm.

[0053] When the silicon nitride sintered compact of the embodiment is used in the bearing ball 1, the attack on the outer ring 4 and the inner ring 3 is reduced, thereby improving the durability of the bearing 2. The bearing 2 uses a plurality of bearing balls 1. By reducing the attack of each bearing ball 1 on the outer ring 4 and the inner ring 3, the durability of the bearing 2 can be improved.

[0054] In addition, if the bearing ball 1 of the embodiment is used, when the rolling life is measured with a thrust bearing tester under the conditions of a maximum contact pressure of 5.9 MPa and a rotation speed of 1200 rpm, the rolling life can be set to more than 600 hours. The bearing 2 also has the effect of suppressing the temperature rise during rotation and suppressing the increase in sliding noise. In recent years, inverter-driven motors have become popular. Inverter drive is a method of changing the speed of the motor. Generally speaking, the speed of the motor is within the range of 0 to 15000 rpm. 0 rpm is the state where the motor is stopped. The bearing rotates according to the speed of the motor. By reducing the aggressiveness, the durability is good even when the rotation speed changes. As such, the silicon nitride sintered body of the embodiment is suitable for use as a wear-resistant component of the object component.

[0055] Furthermore, the bearing ball 1 of the embodiment can reduce its aggressiveness toward the target component, thereby suppressing the occurrence of electrolytic corrosion. Electrolytic corrosion is a phenomenon in which localized discharges occur between the bearing ball and the inner ring, and between the bearing ball and the outer ring, corroding the surfaces of the inner and outer rings. In bearings, silicon nitride sintered bodies are used for the bearing balls, and metals such as bearing steel SUJ2 are used for the inner and outer rings. If electrolytic corrosion occurs, the metal inner and outer rings gradually corrode. As corrosion progresses, the bearing's performance deteriorates. This reduced performance can lead to, for example, an increase in sliding noise.

[0056] Generally speaking, in a bearing, grease is filled between the bearing ball and the inner ring, and between the bearing ball and the outer ring. Grease has lubricity and insulation properties. Grease includes various types such as lithium soap grease. If local discharge occurs between the bearing ball and the inner ring, and between the bearing ball and the outer ring, the grease deteriorates. If the grease deteriorates, the lubricity and insulation properties decrease. As a result, it becomes easy to cause electrical corrosion. If the grease deteriorates, the grease changes color. For example, in the case of lithium soap grease, it gradually changes from transparent to black. In the case of the bearing balls of the embodiment, since the aggressiveness to the target component is reduced, the deterioration of the grease can be suppressed. From this point of view, the life of the bearing can also be extended.

[0057] Causes of grease deterioration include physical factors, chemical factors, and the intrusion of foreign matter. The primary physical factor is aging. This deterioration occurs due to continued use. Other physical factors include mechanical shear and centrifugal force. The primary chemical factor is electrolytic corrosion. Other chemical factors include oxidation caused by heat. The primary cause of foreign matter intrusion is contact between the bearing balls and the inner or outer ring. Contact between the bearing balls and the inner or outer ring generates wear powder.

[0058] These effects can cause poor lubrication and reduced insulation due to hardening of the grease.

[0059] The bearing balls of the embodiment can suppress the aggressiveness toward the counterpart member, thereby suppressing the generation of electrolytic corrosion and wear powder. As a result, the deterioration of the grease can be suppressed, and the life of the bearing can be extended.

[0060] Next, the method for producing the silicon nitride sintered body of the embodiment will be described. The method for producing the silicon nitride sintered body of the embodiment is not particularly limited as long as it has the above-described configuration. The following examples can be cited as methods for producing a silicon nitride sintered body with a good yield.

[0061] First, prepare silicon nitride powder. The silicon nitride powder preferably has an alpha-catalysis rate of 80% by mass or more and an average particle size D 50The particle size is 0.4 μm or more and 2.5 μm or less, and the impurity oxygen content is 2 mass% or less. The impurity oxygen content is preferably 2 mass% or less, and more preferably 1.0 mass% or less. More preferably, the impurity oxygen content is 0.1 mass% or more and 0.8 mass% or less. If the impurity oxygen content exceeds 2 mass%, there is a possibility that the impurity oxygen reacts with the sintering aid, forming a grain boundary phase more than necessary.

[0062] Next, prepare sintering aid powder. The amount of sintering aid added is preferably within a range of 3% by mass or more and 20% by mass or less. The amount of sintering aid added is calculated by setting the total of silicon nitride powder and sintering aid powder to 100% by mass. Regarding the sintering aid powder, the average particle size D 50 It is preferably 1.0 μm or less, and further preferably 0.4 μm or less.

[0063] The sintering aid powder is preferably one or more selected from rare earth compounds, aluminum compounds, and titanium compounds. The rare earth compound is preferably one or two selected from yttrium oxide or lanthanide oxide. The aluminum compound is preferably one or more selected from aluminum oxide, aluminum nitride, or aluminum oxynitride. The titanium compound is preferably one or more selected from titanium oxide, titanium nitride, or titanium oxynitride. In addition, the content of the rare earth compound is preferably 2% by mass or more and 10% by mass or less. The content of the aluminum compound is preferably 2% by mass or more and 10% by mass or less. The content of the titanium compound is preferably 0.1% by mass or more and 5% by mass or less. In addition to these, alkaline earth compounds and the like may also be added. The total amount of the sintering aid is adjusted so as to be within a range of 3% by mass or more and 20% by mass or less. In addition, iron compounds or tungsten compounds may also be used instead of titanium compounds.

[0064] Next, a raw material powder mixing step is performed to mix silicon nitride powder and sintering aid powder. This raw material powder mixing step is performed using a bead mill or a ball mill. Furthermore, the mixing step is performed using a raw material powder slurry mixed with a binder and a solvent.

[0065] First, the ball mill is described. A ball mill is a crusher that uses media with a diameter of 4 to 50 mm. In a ball mill, a raw material powder slurry and a medium are placed in a crushing chamber (stirring chamber) called a vessel and crushed while rotating. The raw material powder slurry and the medium collide with each other in accordance with the rotation of the vessel, and the raw material powder slurry is gradually crushed. The mixing process using a ball mill is preferably carried out for more than 20 hours. The ball mill can also be a pot drum type. As a ball mill, in addition to the pot drum type, a device that fixes both ends of the crushing chamber and rotates the crushing chamber can also be used. The pot drum type is a device in which a vessel is arranged on a roughly cylindrical drum with a controlled rotation speed, and the vessel rotates by the rotation of the drum. In addition, by controlling the rotation speed (rpm) of the vessel, the crushing condition can be controlled. Therefore, with respect to the ball mill, the "rotation speed in the stirring process" is defined as the rotation speed of the crushing chamber (vessel).

[0066] Next, the bead mill is described. A bead mill is a pulverizer that uses media with a diameter of 3 mm or less. Compared to a ball mill, the energy generated by the collision between the raw material powder slurry and the media in a bead mill is greater. The mixing process using a bead mill is preferably performed for at least 3 hours. In a bead mill, pulverization is performed by rotating a propeller-shaped agitator called a disc. The media is located around the disc. As the disc rotates, pulverization or stirring is performed.

[0067] When any mixing step is performed, the upper limit of the time is not particularly limited, but is preferably 100 hours or less. Even if it exceeds 100 hours, the above effects cannot be obtained, which may become a factor of cost increase.

[0068] The raw material powder slurry can be uniformly mixed by using a mixing process using a bead mill or a ball mill. The raw material powder is crushed or broken up into a uniformly mixed state. Afterwards, the uniformly mixed state can be maintained by performing a stirring process. If the uniformly mixed raw material powder slurry is left alone, the raw material powder gradually settles relative to the binder or solvent. If sedimentation occurs, the raw material powder will aggregate. The stirring process has the effect of preventing sedimentation. If the rotation speed of the stirring process in the ball mill is greater than 50 rpm and less than 150 rpm and is maintained for more than 12 hours, the uniformly mixed state of the raw material powder can be maintained.

[0069] Performing this ball mill stirring process allows for adjustment of the viscosity of the raw powder slurry. A rotational speed below 50 rpm may result in insufficient stirring force. Furthermore, a rotational speed exceeding 150 rpm may alter the uniform mixing achieved during the mixing process. Furthermore, stirring for at least 12 hours allows for control of the viscosity of the raw powder slurry. This maintains a uniform mixing of the raw powders.

[0070] The agitator used in the stirring process in the bead mill is a device that rotates a propeller-shaped stirrer at a certain speed and in one direction and stirs the tank. In addition, a device that does not mix the medium is preferably used. The device that does not mix the medium represents that the bead mill has a mechanism for separating the medium from the slurry, and the amount of the medium in the slurry after the stirring process is controlled to be less. The rotating speed of the stirrer in the bead mill is preferably more than 500rpm and less than 2000rpm. More preferably, the rotating speed of the stirrer is more than 500rpm and less than 1500rpm. If the rotating speed exceeds 2000rpm, it is possible that the motor that rotates the stirrer is excessively loaded. If the rotating speed is less than 500rpm, it is possible that the stirring process is excessively time-consuming.

[0071] Next, a forming process is performed to produce a formed body using raw material powder (including raw material powder slurry). As a forming method, a mold pressing method, a cold isostatic pressing (CIP) method, a sheet forming method, etc. can be applied. The sheet forming method is a doctor blade method, a roll forming method, etc. In addition, these forming methods can also be combined. As needed, a solvent such as toluene, ethanol, butanol can also be mixed in the raw material powder (including raw material powder slurry). In addition, as needed, the raw material powder (including raw material powder slurry) is mixed with an organic binder. As organic binders, butyl methacrylate, polyvinyl butyral, polymethyl methacrylate, etc. can be listed. In addition, when the raw material mixture (the total amount of silicon nitride powder and sintering aid powder) is set to 100 parts by mass, the amount of organic binder added is preferably more than 3 parts by mass and less than 17 parts by mass. When the amount of organic binder added is less than 3 parts by mass, the amount of binder is too small and becomes difficult to maintain the shape of the formed body. On the other hand, if the content exceeds 17 parts by mass, the pores of the compact (the compact after degreasing) become larger after the degreasing step, and a dense sintered body cannot be obtained.

[0072] Next, the compact is degreased. In this degreasing process, the compact is heated in a non-oxidizing atmosphere at a temperature of 500°C to 800°C for 1 to 4 hours to remove most of the pre-added organic binder. Examples of non-oxidizing atmospheres include nitrogen and argon. If necessary, treatment can be performed in an oxidizing atmosphere such as air to control the amount of organic matter remaining in the degreased compact.

[0073] Next, the degreased body (the degreased molded body) is placed in a sintering container and sintered in a non-oxidizing atmosphere in a sintering furnace. The sintering temperature is preferably within a range of 1650°C to 1950°C. A nitrogen atmosphere or a reducing atmosphere containing nitrogen is preferred as the non-oxidizing atmosphere. Furthermore, the pressure within the sintering furnace is preferably a pressurized atmosphere.

[0074] If the degreased body is sintered at a low temperature of less than 1650°C, the grain growth of the silicon nitride crystal particles is insufficient, and it is difficult to obtain a dense sintered body. On the other hand, if the sintering temperature is higher than 1950°C, the silicon nitride may be decomposed into Si and N2 when the pressure of the atmosphere in the furnace is low. Therefore, the sintering temperature is preferably controlled within the above range. In addition, the sintering time is preferably within the range of more than 3 hours and less than 12 hours. The atmosphere pressure in the furnace at this time is preferably above normal pressure and below 60 MPa. More preferably, the atmosphere pressure in the furnace is above 0.2 MPa and below 30 MPa.

[0075] After the sintering step, the sintered body is preferably subjected to hot isostatic pressing (HIP). The step of sintering the degreased body is referred to as a first sintering step, and the step of HIPing the sintered body is referred to as a second sintering step.

[0076] During the HIP process, the temperature is preferably within the range of 1600°C to 1900°C, and the pressure is preferably within the range of 80 MPa to 200 MPa. The HIP process can reduce pores (voids) within the sintered body. This allows for a dense sintered body. If the pressure is lower than 80 MPa, the effect of the load pressure is insufficient. Furthermore, if the pressure exceeds 200 MPa, the load on the manufacturing equipment may increase.

[0077] The obtained silicon nitride sintered body is subjected to grinding processing as needed. In addition, when obtaining a plurality of silicon nitride sintered bodies, the silicon nitride sintered bodies may also be subjected to cutting processing or the like.

[0078] (Example)

[0079] (Examples 1 to 4, Comparative Examples 1 and 2)

[0080] As raw material powders, the compositions shown in Table 1 were prepared. The silicon nitride powders used in Examples and Comparative Examples had an alpha-catalysis rate of 80% by mass or more, an average particle size D 50 The average particle size D of the sintering aid powder used in Examples 1 to 4 and Comparative Example 1 is 0.4 to 2.5 μm, and the impurity oxygen content is 2% by mass or less. 50 The average particle size D of the sintering aid powder used in Comparative Example 2 is 1.0 μm or less. 50 It is 1.4μm.

[0081] Table 1

[0082]

[0083] Next, the raw material powder mixing step and the stirring step were performed. In the raw material powder mixing step, a binder and a solvent were added to the raw material powder to prepare a raw material powder slurry. In Comparative Examples 1 and 2, stirring was not performed. The conditions for each step are shown in Table 2.

[0084] Table 2

[0085]

[0086] The obtained raw material powder slurry was used to perform a forming step. The forming step was performed by die forming. Two types of formed bodies were produced: a formed body for obtaining a bearing ball with a size of 3 / 8 inch (diameter 9.525 mm) and a formed body for measuring bending strength.

[0087] Next, the compact is subjected to a degreasing process at a temperature of 500°C to 800°C for a period of 1 hour to 4 hours. The degreased compact is then subjected to a first sintering process. In the first sintering process, sintering is performed at a temperature of 1750°C to 1870°C and a pressure of 0.1 MPa to 0.5 MPa for a period of 4 hours to 8 hours. The resulting sintered compact is subjected to a HIP treatment at a temperature of 1600°C to 1700°C and a pressure of 100 MPa to 200 MPa for a period of 3 hours to 5 hours. The sintered compact after the HIP treatment is polished to a surface roughness Ra of 0.02 μm or less.

[0088] Raman spectroscopy was performed on the examples and comparative examples. An arbitrary cross section of the silicon nitride sintered body was used for the Raman spectroscopy. An inVia Reflex Leica microscope (resolution: 0.3 cm) manufactured by RENISHAW was used for the Raman spectroscopy. -1 ). As an excitation laser, an LD excitation green laser (wavelength 532nm, output power 100mW) was used, the irradiation laser beam diameter was set to 0.7μm, the exposure time was set to 1 second per measurement point, and the platform movement step was set to 0.4μm. For data analysis, multivariate curve resolution (MCR) using image analysis software WiRe4Empty Modelling was used. The total number of measurement locations is 2601. In addition, locations away from the surface of the sintered body were measured. By averaging the spectra of these total measurement locations, a spectrum with an improved SN ratio (the ratio of the size of the noise to the size of the spectrum) was obtained. In addition, by performing the measurement while moving the platform, a Raman spectrum with less dependence on the measurement location was obtained.

[0089] The results are shown in Table 3. The wave numbers (cm -1)This is the value obtained by rounding off the decimal point.

[0090] Table 3

[0091]

[0092] As can be seen from Table 3, a preferred Raman peak was detected for the silicon nitride sintered compacts of the Examples. -1 Over 1200cm -1 The position of the strongest peak below is not 515cm -1 Over 525cm -1 In addition, within 515cm -1 Over 525cm -1 In the range below, no peak was detected.

[0093] Furthermore, for the silicon nitride sintered bodies of Examples 1 to 3, at 500 cm -1 Over 830cm -1 Among the peaks detected in the following range, three or more peaks are detected at 530 cm -1 Over 800cm -1 In addition, the intensity of each of these three or more peaks is detected within the range of 440 cm -1 Over 460cm -1 When the intensity of the strongest peak below is set to 1, it is 0.8 or more and 2.0 or less.

[0094] For Example 4, at 530 cm -1 Over 830cm -1 Three or more peaks were detected in the following range. -1 Over 460cm -1 When the intensity of the strongest peak is set to 1, the peak intensity ratio is 530 cm -1 Over 830cm -1 The number of peaks within the following ranges is less than 3. Therefore, in Table 3, Example 4 is described as "different intensity ratios."

[0095] For Comparative Examples 1 and 2, at 400 cm -1 Over 1200cm -1 In the range below 500 cm, only 6 peaks were detected. -1 Over 830cm -1 In the range below, only two peaks were detected.

[0096] 500cm -1 Over 600cm -1The strongest peak among the peaks within the following range is at 530 cm in all of Examples 1 to 4 and Comparative Example 1. -1 Over 600cm -1 The following was observed. For Examples 1 to 3, the half-value width of the strongest peak was 40 cm -1 Over 70cm -1 On the other hand, in Example 4 and Comparative Example 1, the half-value width of the strongest peak is 40 cm -1 Over 70cm -1 In addition, in Comparative Example 2, at 500 cm -1 Over 600cm -1 No peaks were detected in the range below.

[0097] Next, the average particle size of the silicon nitride crystalline particles and the area ratio of the silicon nitride crystalline particles with an aspect ratio of 2 or more are measured. First, an SEM photograph of an arbitrary cross section is taken. The maximum diameter of the silicon nitride crystalline particles taken in the SEM photograph is set as the major diameter. The length of the line segment extending vertically from the center of the major diameter is set as the minor diameter. Set as particle size = (major diameter + minor diameter) ÷ 2, and take the average value of the particle size of 50 quantities as the average particle size. Set as aspect ratio = major diameter / minor diameter. In an area of 20μm×20μm, calculate the area ratio of silicon nitride crystalline particles with an aspect ratio of 2 or more. In addition, the three-point bending strength is investigated. The three-point bending strength is determined by the bending strength of the three-point bending test according to JIS-R-1601 (2008). In addition, the Vickers hardness is measured according to JIS-R-1610 (2003) with a test load of 9.807N (HV1). JIS-R-1610 (2003) corresponds to ISO 14705:2000.

[0098] The results are shown in Table 4.

[0099] Table 4

[0100]

[0101] In the Examples, the average particle size of the silicon nitride crystal particles was 2 μm or less. Furthermore, the area ratio of the silicon nitride crystal particles having an aspect ratio of 2 or greater was within a range of 20% to 70%. Furthermore, in both the Examples and the Comparative Examples, the three-point bending strength was 600 MPa or greater. Furthermore, in the Examples, the Vickers hardness (HV1) was 1490 or greater.

[0102] Next, a durability test was performed using the bearing balls of the embodiment and the comparative example. The durability test was performed by measuring the rolling life using a thrust rolling fatigue testing machine under the conditions of a maximum contact pressure of 5.9 MPa and a rotation speed of 1200 rpm. It should be noted that the target component used a plate made of bearing steel SUJ2. The time until the surface of the bearing ball peeled off was measured. It should be noted that the measurement time was set to 600 hours as the upper limit. In the test results, the bearing balls for which no surface peeling was confirmed even after 600 hours were recorded as "more than 600 hours". The results are shown in Table 5.

[0103] Table 5

[0104] Durability test Example 1 More than 600 hours Example 2 More than 600 hours Example 3 More than 600 hours Example 4 More than 600 hours Comparative Example 1 More than 600 hours Comparative Example 2 More than 450 hours

[0105] As can be seen from the table, the bearing balls of Examples 1 to 4 and Comparative Example 1 exhibited excellent durability. On the other hand, the bearing balls of Comparative Example 2 exhibited reduced durability compared to Examples 1 to 4 and Comparative Example 1. This is presumably due to a lower proportion of silicon nitride crystal particles having an aspect ratio of 2 or greater in Examples 1 to 4 and Comparative Example 1 compared to Comparative Example 2.

[0106] Next, bearings were produced using the bearing balls of the examples and comparative examples. The inner ring and outer ring may be any material, but in this test, they were produced from bearing steel SUJ2. Various greases can be used, but in this test, lithium soap grease, which is widely used as a general-purpose material, was used. Among these lithium soap greases, lithium soap grease with an original transparent color was particularly used. When using a grease with an original transparent color, deterioration of the grease can be observed in the form of a change in color. Furthermore, the bearings were assembled using 16 bearing balls. The rate of change in the sliding sound of the bearing and the presence or absence of discoloration of the grease were measured.

[0107] A rotating shaft was mounted in the bearing and rotated at 1200 rpm. The sliding noise change rate was measured after 10 consecutive hours and 400 consecutive hours. The sliding noise change rate between 10 and 400 consecutive hours in Comparative Example 1 was set to 1. The sliding noise change of the bearings in Examples 1 to 4 and Comparative Example 2 was compared with this change rate. If the change in sliding noise is small, the change rate is less than 1.

[0108] Furthermore, after 400 hours, the bearings were disassembled and the color change of the grease was examined. Grease color change indicates grease degradation. Grease color change is measured using lightness. A higher lightness value indicates a brighter grease color, while a lower lightness value indicates a darker grease color.

[0109] The results are shown in Table 6. Regarding Table 6, a lightness of 9.5 or less and 9 or greater is defined as "light gray." A lightness of less than 9 and 4 or greater is defined as "dark gray." A lightness of less than 4 is defined as "black." The Munsell color system is used as a standard for these lightness values. The Munsell color system corresponds to JIS Z8721 (1993). As grease deterioration progresses, the lightness decreases.

[0110] Table 6

[0111] Rate of change of glissando Grease color Example 1 0.8 light gray Example 2 0.7 light gray Example 3 0.7 light gray Example 4 0.9 light gray Comparative Example 1 1 Dark gray Comparative Example 2 1.2 black

[0112] As shown in Table 6, the sliding noise change rate and grease discoloration were improved in the Examples. While no significant differences were observed in the thrust test, differences were observed in the sliding noise change and grease discoloration tests. This is due to a reduction in the aggressiveness of the bearings to the mating components.

[0113] While several embodiments of the present invention have been illustrated above, these embodiments are provided as examples and are not intended to limit the scope of the invention. These novel embodiments may be implemented in various other ways, and various omissions, substitutions, and modifications may be made without departing from the gist of the invention. Modifications of these embodiments are included within the scope and gist of the invention, and are also included within the scope of the invention described in the patent claims and their equivalents. Furthermore, the above-mentioned embodiments may be implemented in combination with each other.

[0114] Explanation of symbols

[0115] 1…Bearing ball

[0116] 2…Bearings

[0117] 3…Inner Ring

[0118] 4…Outer Ring

[0119] 10…Silicon nitride sintered body

[0120] 11…Silicon nitride crystal particles

[0121] 12…Grain Boundary

[0122] RS…Raman spectroscopy

[0123] P1~P6…peak

Claims

1. A method for producing a silicon nitride sintered body, characterized in that: It has the following processes: a stirring step of mixing silicon nitride powder, 2% to 10% by mass of a rare earth compound, 2% to 10% by mass of an aluminum compound, and 0.1% to 5% by mass of one selected from a titanium compound, an iron compound, and a tungsten compound to form a raw material powder, stirring the raw material powder using a ball mill or a bead mill. When a ball mill is used, the raw material powder is stirred by rotating a stirring chamber at a speed of 50 rpm to 150 rpm for 12 hours or more. When a bead mill is used, the raw material powder is stirred by rotating a stirring bar at a speed of 500 rpm to 2000 rpm for 3 hours or more. a forming step of producing a formed body using the stirred raw material powder; a degreasing step of degreasing the formed body to produce a degreased body; and The first sintering step is to sinter the degreased body at a temperature of 1650° C. to 1950° C. to produce a silicon nitride sintered body.

2. The method for producing a silicon nitride sintered body according to claim 1, wherein: When a Raman spectrum analysis is performed on a 20 μm×20 μm region in an arbitrary cross section of the silicon nitride sintered body, the Raman spectrum at 400 cm -1 Over 1200cm -1 More than 7 peaks were detected in the following range, At least one of the seven or more peaks is at 440 cm -1 Over 460cm -1 Within the following range, And at 515cm -1 Over 525cm -1 There is no peak in the range below.

3. The method for producing a silicon nitride sintered body according to claim 2, wherein: At least three of the seven or more peaks are at 530 cm -1 Over 830cm -1 Within the following range.

4. The method for producing a silicon nitride sintered body according to claim 2 or 3, wherein: At least one of the seven or more peaks is at 500 cm -1 Over 600cm -1 Within the range below and with 10cm -1 Over 100cm -1 The full width at half maximum is as follows.

5. The method for producing a silicon nitride sintered body according to claim 2 or 3, wherein: Regarding the seven or more peaks, at 500 cm -1 Over 830cm -1 The intensity of at least three peaks within the following range is at 440 cm -1 Over 460cm -1 The intensity of the strongest peak in the following range is 0.8 times or more and 2.0 times or less.

6. The method for producing a silicon nitride sintered body according to claim 4, wherein: Regarding the seven or more peaks, at 500 cm -1 Over 830cm -1 The intensity of at least three peaks within the following range is at 440 cm -1 Over 460cm -1 The intensity of the strongest peak in the following range is 0.8 times or more and 2.0 times or less.

7. The method for producing a silicon nitride sintered body according to claim 6, wherein: Regarding the seven or more peaks, the peaks exceeding 830 cm -1 and 1200cm -1 The intensity of at least three peaks within the following range is at 440 cm -1 Over 460cm -1 The intensity of the strongest peak in the following range is 2.7 times or more and 3.7 times or less.

8. The method for producing a silicon nitride sintered body according to claim 1 or 2, wherein: After the first sintering step, the silicon nitride sintered body is subjected to hot isostatic pressing treatment in which the silicon nitride sintered body is heated at a temperature of 1600° C. to 1900° C. while applying a pressure within a range of 80 MPa to 200 MPa.

9. The method for producing a silicon nitride sintered body according to claim 6, wherein: The silicon nitride sintered body obtained by the first sintering step is subjected to hot isostatic pressing at a temperature of 1600° C. to 1900° C. and a pressure of 80 MPa to 200 MPa. 10 . A method for producing a wear-resistant member, comprising producing the silicon nitride sintered body by the production method according to claim 1 , and producing the wear-resistant member using the silicon nitride sintered body.

11. The method for manufacturing a wear-resistant member according to claim 10, wherein: The silicon nitride sintered body is polished so that the surface roughness Ra becomes 0.1 μm or less.

12. The method for manufacturing a wear-resistant member according to claim 11, wherein: The wear-resistant component is a bearing ball. 13 . A method for producing a bearing, comprising producing the silicon nitride sintered compact by the method according to claim 1 , and producing a bearing using the silicon nitride sintered compact.

14. The method for manufacturing a bearing according to claim 13, wherein: The bearing comprises: Inner ring, Outer ring, and Bearing balls formed of the silicon nitride sintered body and grease are arranged between the inner ring and the outer ring.

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