Silicon nitride sintered body and wear-resistant member using the same

Abstract

The silicon nitride sintered body of the embodiment having silicon nitride crystal grains and a grain boundary phase has metal compound particles at the grain boundary phase. The metal compound particles of the silicon nitride sintered body contain a main component compound including at least one of oxides, carbides, nitrides, silicides, and complex compounds of at least one of tungsten and molybdenum as a main component. The metal compound particles of the silicon nitride sintered body contain a dispersed component including at least one of aluminum, cobalt, iron, and rare earth elements. In addition, the silicon nitride sintered body of the embodiment is effective for use in bearing balls.

Description

Technical Field

[0001] The embodiments described later generally relate to silicon nitride sintered bodies and wear-resistant components using them. Background Technology

[0002] Silicon nitride sintered bodies are used in wear-resistant components. Examples of wear-resistant components include bearing components, rollers, compressor blades, gas turbine blades, and engine components. Examples of bearing components include bearing balls, bearing inner rings, and bearing outer rings. Furthermore, examples of rollers include rolling and conveying rollers. Examples of engine components include cam rolls. In recent years, due to its excellent mechanical strength and wear resistance, silicon nitride sintered bodies have been used as bearing balls in bearing components.

[0003] For example, Japanese Patent No. 5100201 (Patent Document 1) discloses a silicon nitride sintered body that controls the aspect ratio and standard deviation of needle-like silicon nitride grains. Furthermore, Japanese Patent No. 6416088 (Patent Document 2) discloses a silicon nitride sintered body that suppresses deviations in the area ratio of the grain boundary phase. Patent Documents 1 and 2 are techniques for uniformly distributing silicon nitride grains and grain boundary phases. This improves the wear resistance of the silicon nitride sintered body. Additionally, Japanese Patent No. 5499718 (Patent Document 3) discloses a silicon nitride sintered body containing boron nitride, cobalt, aluminum, and tungsten carbide. In Patent Document 3, by using these additives, the interparticle bonding force is improved, resulting in excellent resistance to chipping.

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 5100201 Patent Document 2: Japanese Patent No. 6416088 Patent Document 3: Japanese Patent No. 5499718 Summary of the Invention

[0005] The problem that the invention aims to solve In recent years, silicon nitride sintered bodies have been used in bearing balls for electric vehicle motors. Therefore, the demand for silicon nitride sintered body bearing balls is increasing significantly. On the other hand, silicon nitride sintered bodies are difficult to machine. Therefore, in order to mass-produce silicon nitride sintered body bearing balls, further improvements in the machinability of silicon nitride sintered bodies are required, i.e., a reduction in machining time.

[0006] One of the challenges to be addressed by the implementation method is to provide silicon nitride sintered bodies with improved processability and wear-resistant components using them.

[0007] Methods for solving problems The silicon nitride sintered body of the embodiment, comprising silicon nitride grains and a grain boundary phase, has metal compound particles in the grain boundary phase. These metal compound particles contain a main component compound, which includes at least one of oxides, carbides, nitrides, silicides, and composite compounds, with at least one of tungsten and molybdenum as the main component. Furthermore, the metal compound particles of the silicon nitride sintered body contain a dispersion component containing at least one of aluminum, cobalt, iron, and rare earth elements. Attached Figure Description

[0008] Figure 1 This is a schematic diagram illustrating an example of the cross-sectional microstructure of a silicon nitride sintered body according to an embodiment.

[0009] Figure 2 This is an external view showing an example of bearing balls of a silicon nitride sintered body based on an embodiment.

[0010] Figure 3 This is an external view showing an example of a raw material ball for bearings formed from a silicon nitride sintered body according to the embodiment. Detailed Implementation

[0011] The silicon nitride sintered body of the embodiment, comprising silicon nitride grains and a grain boundary phase, has metal compound particles in the grain boundary phase. These metal compound particles contain a main component compound comprising at least one of oxides, carbides, nitrides, silicides, and composite compounds, with at least one of tungsten and molybdenum as the main component. Furthermore, the metal compound particles of the silicon nitride sintered body contain a dispersed component comprising at least one of aluminum, cobalt, iron, and rare earth elements.

[0012] Figure 1 An example of the cross-sectional microstructure of a silicon nitride sintered body according to an embodiment is shown in the figure. In the figure, symbol 1 represents the silicon nitride sintered body, symbol 2 represents silicon nitride grains, symbol 3 represents grain boundary phases, and symbol 4 represents metal compound particles. The silicon nitride sintered body 1 has a structure in which multiple silicon nitride grains 2 are complexly intertwined. Furthermore, the silicon nitride sintered body 1 has a structure in which grain boundary phases 3 fill the gaps between the multiple silicon nitride grains 2. Additionally, at least a portion of the grain boundary phases 3 contains metal compound particles 4. Figure 1 In the middle, the metal compound particles are recorded in smaller circles 4.

[0013] Metal compound particles 4 contain at least one of the following main component compounds: oxides, carbides, nitrides, silicides, and composite compounds, with at least one of tungsten (W) and molybdenum (Mo) as the main component. The main component refers to the component that is most abundant in the metallic composition of metal compound particles 4 by mass ratio. Furthermore, composite compounds can include various compounds such as oxynitrides, oxycarbides, oxysilicides, and carbonitrides.

[0014] In addition to the main component compound, the metal compound particle 4 also contains at least one of aluminum (Al), cobalt (Co), iron (Fe), and rare earth elements. The component containing at least one of aluminum, cobalt, iron, and rare earth elements within the metal compound particle 4 is called the dispersed component. Here, "containing" indicates its presence within the metal compound particle 4. Therefore, the presence of the dispersed component within the metal compound particle 4 is not limited to components obtained through solid dissolution of the main component compound, but the case where the dispersed component is contained within the metal compound particle 4 through solid dissolution of the main component compound will be explained as an example. Maintaining the crystal structure of the metal compound particle 4 will not reduce the effect of strengthening the grain boundary phase 3.

[0015] The presence of a dispersion component within the metal compound particles 4 is effective. This results in a more robust structure for the metal compound particles 4. Furthermore, since the grain boundary phase 3 is difficult to detach, the processing speed of the silicon nitride sintered body 1 can be accelerated, thereby improving its machinability. Additionally, by containing a dispersion component within the metal compound particles 4, the strength of the metal compound particles 4 themselves can be increased. Therefore, the cutting amount generated by grinding of the silicon nitride grains 2 and the grain boundary phase 3 becomes more homogeneous, improving machinability.

[0016] The grain boundary phase 3 fills the gaps between the multiple silicon nitride grains 2. Furthermore, by containing metal compound particles 4 in at least a portion of the grain boundary phase 3, the grain boundary phase 3 is strengthened, thereby increasing the fracture toughness or hardness of the silicon nitride sintered body 1. Additionally, by containing dispersed components within the metal compound particles 4, the surface of the silicon nitride sintered body 1 can be easily removed by grinding.

[0017] The dispersion component of the metal compound particles 4 includes at least one of aluminum, cobalt, iron, and rare earth elements. Furthermore, the dispersion component preferably includes two or more of aluminum, cobalt, iron, and rare earth elements. Examples of rare earth elements include yttrium and lanthanides.

[0018] Aluminum, cobalt, iron, and rare earth elements are elements that readily dissolve in the main component compound of metal compound particles 4. Furthermore, metal compound particles 4 only need to be at least partially dissolved in the main component compound; alternatively, they may be partially dissolved in the main component compound.

[0019] In addition, the determination (presence or absence) of dispersed components in metal compound particles 4 was performed using TEM-EDS. The sample used in the determination was set to have a thickness of 0.05 μm or more and 0.5 μm or less. The TEM-EDS conditions were set as follows: accelerating voltage 200 kV, irradiation current 1.00 nA, spot size during analysis 1 nm, analysis time 30 seconds, and sample angles X=10° and Y=0°.

[0020] In any cross-section of the silicon nitride sintered body 1, an analysis point is selected near the center of the metal compound particles 4. If at least one of tungsten and molybdenum is detected as a dispersed component through this analysis, it is determined that the metal compound particles 4 contain dispersed components. Furthermore, if TEM-EDS is used, both qualitative and quantitative analysis can be performed.

[0021] In addition, FESEM-EDS can be used instead of TEM-EDS in determining the presence or absence of dispersed components. FESEM stands for Field Emission Scanning Electron.

[0022] Furthermore, the total content (mass percentage) of the dispersed component relative to the total metal compound particles 4 is preferably in the range of 1% by mass or more and 15% by mass or less. The content of the dispersed component in the metal compound particles 4 is set as the amount of the metal element being detected. The dispersed component itself is not limited to the metal element, but may also be contained in the form of compounds such as oxides.

[0023] If the content of the dispersed component relative to the total metal compound particles 4 is less than 1% by mass, the effect of strengthening the grain boundary phase 3 may be insufficient. Furthermore, if the content of the dispersed component exceeds 15% by mass, the crystal structure of the metal compound particles 4 may become unstable. Therefore, the strength of the grain boundary phase 3 may decrease. Therefore, the total content of the dispersed component in the metal compound particles 4 is preferably 1% by mass or more and 15% by mass or less, and more preferably within the range of 2% by mass or more and 10% by mass or less.

[0024] Furthermore, the ratio of the number of metal compound particles 4 containing the dispersed component to the total number of metal compound particles 4 is preferably in the range of 50% or more and 100% or less. If the ratio of the number of metal compound particles 4 containing the dispersed component is 50% or less, the strengthening of the grain boundary phase 3 does not affect the sintered body as a whole. Therefore, the ratio of the number of metal compound particles 4 containing the dispersed component is preferably 50% or more and 100% or less. Furthermore, the ratio is preferably 60% or more and 90% or less. Moreover, the ratio of the number of metal compound particles 4 containing the dispersed component is determined by measuring the presence or absence of the dispersed component in the metal compound particles 4 present in the measurement area of ​​50 μm × 50 μm.

[0025] The proportion W of the number of metal compound particles 4 containing dispersed components is calculated according to the following formula (1).

[0026] W = (metal compound particles containing dispersed components / total metal compound particles) × 100…(1) In addition, when metal compound particle 4 is designated as M, which is at least one of tungsten and molybdenum as the main component, and oxygen is designated as O, the compound MO is selected. x The oxygen atom ratio x (oxygen content) is preferably satisfied by the following formula (2).

[0027] 0.01≤x≤2.0 …(2) The term "metal compound particle 4 satisfying formula (2)" indicates that the metal compound particle 4 is an oxide. That is, it indicates that the metal compound particle 4 contains at least one of tungsten oxide, molybdenum oxide, or tungsten-molybdenum oxide. These oxides readily disperse the components in solid solution. Additionally, compound MO... x It may contain oxygen as a dispersed component.

[0028] As compound MO x Examples include WO3 and MoO3. Furthermore, the oxygen atom ratio x is preferably in a range smaller than the theoretical value. For example, in WO3 or MoO3, the oxygen atom ratio x is preferably less than 3.

[0029] Furthermore, the content of metal compound particles 4 relative to the overall silicon nitride sintered body 1 is preferably 0.1% by mass or more and 5% by mass or less. Metal compound particles 4 have the effect of strengthening the grain boundary phase 3. If the content of metal compound particles 4 is less than 1% by mass, the effect of strengthening the grain boundary phase 3 may be insufficient. Additionally, if the content of metal compound particles 4 exceeds 5% by mass, it may hinder the complex entanglement of silicon nitride grains 2. Therefore, the content of metal compound particles 4 is preferably 0.1% by mass or more and 5% by mass or less, and more preferably within the range of 1% by mass or more and 4% by mass or less.

[0030] In addition, the grain boundary phase 3 may also contain components other than the metal compound particles 4. Examples of grain boundary phase components include rare earth compounds, aluminum compounds, titanium compounds, hafnium compounds, zirconium compounds, and silicon carbide. The grain boundary phase component is mainly composed of the sintering aids described later. The content of the grain boundary phase other than the metal compound particles 4 in the silicon nitride sintered body 1 is preferably in the range of 1% by mass or more and 15% by mass or less.

[0031] Furthermore, it is preferable that the average length of the major axis of the silicon nitride grain 2 is 0.1 μm or more and 10 μm or less, and the average aspect ratio is 2 or more and 10 or less. When the average length of the major axis is less than 0.1 μm, the silicon nitride grain 2 is too small, and durability may decrease. From the viewpoint of durability, the average length of the major axis of the silicon nitride grain 2 is more preferably 0.5 μm or more and 10 μm or less. In addition, if the average length of the major axis exceeds 10 μm, the gap between the silicon nitride grains 2 becomes larger, and the strength may decrease.

[0032] The major and minor axes of silicon nitride grains 2 were determined using SEM images. SEM images of any cross-section of the silicon nitride sintered body 1 were taken. The cross-section was set to a polished surface with a surface roughness Ra of less than 1 μm. The SEM image magnification was set to 1000x or higher. A magnification of 4000x is recommended. Additionally, the measurement area was set to 300 μm × 300 μm.

[0033] The longest diagonal of the silicon nitride grain 2 as shown in the SEM image is taken as the major axis. The area of ​​each of the 300 μm × 300 μm silicon nitride grains 2 is measured, and 50 grains are selected in descending order of size. The average of these 50 grains is taken as the average length of the major axis. Additionally, a line drawn perpendicularly from the midpoint of the major axis of each selected silicon nitride grain 2 is taken as the minor axis. The ratio of major axis to minor axis is defined as the aspect ratio, and the average of this ratio is taken as the average aspect ratio. Image processing software such as ImageJ can also be used for screening the silicon nitride grains 2.

[0034] The silicon nitride sintered body 1 described above can achieve a three-point bending strength of 600 MPa or more, and further, 900 MPa or more. Furthermore, it can achieve a fracture toughness of 6.0 MPa·m. 1 / 2 Above, and further 7.0 MPa·m 1 / 2 That's all. Furthermore, it can achieve a Vickers hardness of 1400 or higher, and even 1500 or higher.

[0035] Three-point bending strength is determined according to JIS-R-1601 (2008). It should be noted that JIS-R-1601 corresponds to ISO 14704. Furthermore, fracture toughness can be determined using the new formula according to the IF method of JIS-R-1607 (2015). JIS-R-1607 corresponds to ISO 15732. Additionally, Vickers hardness can be determined according to JIS-R-1610 (2003). JIS-R-1610 corresponds to ISO 14705.

[0036] Furthermore, the silicon nitride sintered body 1 of the embodiment is suitable for wear-resistant components. Moreover, the wear-resistant component preferably has a sliding surface with a surface roughness Ra of 0.1 μm or less. Examples of wear-resistant components include bearing components, rollers, compressor blades, gas turbine blades, and engine components. Examples of bearing components include bearing balls, bearing inner rings, and bearing outer rings. Furthermore, examples of rollers include rolling mill rollers and conveying rollers. Examples of engine components include cam rollers.

[0037] Wear-resistant components have sliding surfaces that slide against the target component. For example, bearing balls are disposed between the inner and outer rings of a bearing. The entire surface of the bearing ball formed from a spherical silicon nitride sintered body 1 serves as the sliding surface. Furthermore, the roller surface of a roller formed from a cylindrical silicon nitride sintered body 1 serves as the sliding surface.

[0038] The silicon nitride sintered body 1 of the embodiment includes metal compound particles 4 containing dispersed components. This improves the processability of the silicon nitride sintered body 1. Furthermore, to improve the wear resistance of the sliding surface, grinding the silicon nitride sintered body 1 to a surface roughness Ra of 0.1 μm or less is effective. For example, the surface roughness of bearing balls is specified in ASTM_F2094. Depending on the application, bearing balls adopt a grade according to ASTM_F2094, ISO_26602, or JIS_R1669. Grinding is performed to a surface roughness Ra according to that grade. If the grade is increased, a mirror finish with a surface roughness Ra of 0.01 μm or less may also be performed. In the silicon nitride sintered body 1 of the embodiment, by also controlling the surface roughness Ra of the silicon nitride sintered body 1, processability is improved while maintaining wear resistance. The grinding process for obtaining a sliding surface with a surface roughness Ra of 0.1 μm or less can be performed efficiently.

[0039] Figure 2 The image shows an example of bearing balls. Figure 3 The image shows an example of a raw ball for bearing ball bearings (hereinafter referred to as "raw ball"). Symbol 5 represents a bearing ball, symbol 6 represents a raw ball, symbol 7 represents the spherical surface of raw ball 6, and symbol 8 represents the strip-shaped portion of raw ball 6. Figure 3 (A) represents the raw material ball 6 viewed along a direction orthogonal to the straight line G1 and G2 connecting the two poles of the strip 8 (the two vertices in the case where the surface containing the strip 8 is the bottom). Figure 3 (B) This refers to the raw material ball 6 as viewed along the directions G1 and G2 of the two poles of the connecting strip 8. The raw material ball 6 is ground to produce the bearing ball 5. Furthermore, in Figure 3 In this example, the raw material ball 6 is illustrated with a strip-shaped portion 8 on the circumference of the spherical surface 7, but it may also be without the strip-shaped portion 8. In other words, the component before the bearing ball 5 is ground is called the raw material ball 6.

[0040] Next, the manufacturing method of the silicon nitride sintered body 1 according to the embodiment will be described. The manufacturing method of the silicon nitride sintered body 1 according to the embodiment is not particularly limited as long as it has the above-described structure, but a method for obtaining a good yield is described below.

[0041] First, prepare the raw material powders. The raw material powders consist of silicon nitride powder and sintering aid powder. The silicon nitride powder preferably has an average particle size of 3 μm or less. Furthermore, powders with an oxygen content of 3% by mass or less and an α-saturation rate of 90% or more are preferred. Alternatively, silane powder can be used instead of silicon nitride powder. A mixture of silicon nitride powder and silane powder can also be used.

[0042] Examples of sintering aid powders include: rare earth element powders, aluminum powders (excluding aluminum powders used as dispersion powders), main component powders corresponding to the main component of the metal compound particles 4 (at least one of tungsten powders and molybdenum powders), and dispersion powders corresponding to the dispersion component (dispersion powders containing at least one of aluminum, cobalt, iron, and rare earth elements). For example, rare earth element powders, tungsten powders (or molybdenum powders), and aluminum powders are used as sintering aid powders. Furthermore, the average particle size of the sintering aid powder is preferably 4 μm or less.

[0043] Examples of rare earth element powders include oxides, nitrides, and oxynitrides of rare earth elements. Yttrium and lanthanides are preferred as rare earth elements. Examples of aluminum powders as dispersing components include oxides, nitrides, and oxynitrides of aluminum. Examples of main component powders include oxides, nitrides, carbides, sulfides, oxynitrides, oxycarbides, and carbonitrides. Oxides or carbides are preferred. Examples of oxides include tungsten oxide (WO3) and molybdenum oxide (MoO3). Examples of carbides include tungsten carbide (WC, W2C) and molybdenum carbide (Mo2C).

[0044] As the main component powder, it is preferable to use a powder that pre-contains a dispersion component powder composed of at least one of aluminum, cobalt, iron, and rare earth elements. Examples of such substances include compounds with various metals as constituent elements. Examples include W-Al-O, W-Co-O, W-Fe-O, WYO, Mo-Al-O, Mo-Co-O, Mo-Fe-O, and Mo-YO systems. Furthermore, as impurities, substances containing at least one of aluminum, cobalt, iron, and rare earth elements can also be used.

[0045] Powder containing at least one of aluminum, cobalt, iron, and rare earth elements can be coated onto the surface of the main component powder. Examples of coating methods include sputtering and mechanical alloying. By coating, the dispersed components can easily enter the metal compound particles 4 during the sintering process.

[0046] Alternatively, as a sintering aid powder, a powder obtained by mixing carbon powder with the main component powder and the dispersing component powder and then pulverizing it can also be used. The carbon powder functions as a reducing agent. By reducing the tungsten component powder or the molybdenum component powder, the metal compound particles 4 can contain a dispersing component. The sintering aid contains not only a dispersing component but also a grain boundary phase component. Furthermore, the aluminum component powder added as a sintering aid is divided into aluminum component powder containing the grain boundary phase 3 outside the metal compound particles 4 and aluminum component powder containing the dispersing component within the metal compound particles 4. The dispersing component aluminum component powder is preferably contained in or coated with the main component powder of the sintering aid.

[0047] When the total weight of "silicon nitride powder" + "sintering aid powder," i.e., "silicon nitride powder" + "rare earth element powder" + "aluminum powder" + "main component powder (including dispersing component powder)" + "other component powders" is set to 100% by mass, preferably, "rare earth element powder" is 1% to 13% by mass, "aluminum powder" is 1% to 10% by mass, "sintering aid powder containing at least one of tungsten and molybdenum" is 0.1% to 7% by mass, "other component powders" is 0% to 8% by mass, and the remainder is "silicon nitride powder." The aforementioned carbon powder becomes the other component powders. Alternatively, titanium oxide and hafnium oxide may be used as other component powders as needed.

[0048] Next, the raw material powder is mixed. This mixing process is performed using a crushing mixer such as a ball mill. The ball mill can crush the raw material powder through optimization of the crushing media and solvents. By crushing the raw material powder, the presence of agglomerates can be suppressed. Furthermore, the ball mill can be either a wet or dry type. Additionally, organic binders and solvents can be added to the raw material powder as needed during the mixing process.

[0049] Next, the raw material after the mixing process is used in a molding process to obtain a silicon nitride molded body (hereinafter referred to as "molded body"). The raw material can be shaped after granulation. The molding process can be performed by die forming, roll granulation, cold isostatic pressing (CIP), scraper molding, injection molding, etc. When producing spheres, die forming, roll granulation, and CIP are preferred. In addition, CIP is also effective for molded bodies obtained by die forming or roll granulation. CIP is a molding method in which the pressurizing medium is set to a liquid. Since the liquid is pressurized isotropically, a molded body with a uniform density distribution can be obtained. In addition, the CIP pressure is preferably in the range of 40 MPa or more and 500 MPa or less.

[0050] For the molded body, a drying process is set to be performed as needed. The drying process has the effect of removing the solvent that was used during wet mixing in the mixing process. Examples of drying processes include natural drying and heated drying. Heated drying is preferably set within a temperature range of 80°C to 200°C. Below 80°C, drying efficiency may decrease. Furthermore, if the temperature exceeds 200°C, uneven drying may occur. Therefore, the drying temperature is preferably within a range of 80°C to 200°C, and further, 100°C to 160°C.

[0051] Next, for the molded body, a degreasing process is performed as needed. By performing the degreasing process, organic binders can be removed from the molded body. Furthermore, the degreasing temperature is preferably in the range of 400°C or higher and 700°C or lower. Examples of degreasing processes include atmospheric conditions and nitrogen atmospheres. Sometimes, the molded body obtained through the degreasing process is also referred to as a degreased body.

[0052] Next, the shaped body, such as a degreased body, undergoes a sintering process. The sintering temperature is preferably in the range of 1600°C or higher and 2000°C or lower. The sintering time is preferably 1 hour or more and 12 hours or less. Furthermore, the sintering process can use atmospheric pressure sintering, pressure sintering, hot isostatic pressing (HIP), etc. Examples of sintering processes include atmospheric pressure, non-oxidizing atmosphere, reducing atmosphere, and vacuum. Atmospheric pressure sintering refers to sintering under 1 atmosphere of pressure (0.9~1.1 atm = 0.09~0.11 MPa). Pressure sintering involves applying pressure higher than atmospheric pressure. Uniaxial pressure sintering is sometimes also referred to as hot pressing. HIP is a sintering method that uses gas to apply isotropic pressure.

[0053] This reduces internal defects such as voids and cracks within the silicon nitride sintered body 1. The HIP pressure is preferably in the range of 10 MPa or higher and 200 MPa or lower. Atmospheric pressure sintering, pressure sintering, and HIP can also be combined. Furthermore, it is preferable to perform two or more stages in combination. In the case of wear-resistant components, it is preferable to use either or both of pressure sintering and HIP. By applying pressure during sintering, a silicon nitride sintered body 1 (e.g., raw material sphere 6) with fewer internal defects can be obtained. Additionally, the holding time at the sintering temperature is preferably 1 hour or more. In other words, the sintering temperature refers to a temperature held for 1 hour or more in the range of 1600°C or higher and 2000°C.

[0054] A silicon nitride sintered body 1 can be obtained through a sintering process. Sometimes, the sliding surface of the silicon nitride sintered body 1 is also ground to produce a wear-resistant component. For example, in a spherical silicon nitride sintered body 1 (e.g., raw material ball 6) used to obtain bearing balls, the entire surface becomes a sliding surface.

[0055] The surface roughness Ra of the sliding surface of the silicon nitride sintered body 1 is preferably set to 0.1 μm or less. By making the surface of the silicon nitride sintered body 1 substantially flat, the wear resistance of the silicon nitride sintered body 1 can be improved. Therefore, the surface roughness Ra of the sliding surface is preferably 0.1 μm or less, and further, 0.01 μm or less. The silicon nitride sintered body 1 of the embodiment has excellent machinability, thus improving the machinability of wear-resistant parts. That is, the grinding time for manufacturing wear-resistant parts from the silicon nitride sintered body 1 can be shortened.

[0056] Furthermore, the durability of the grinding wheel used for grinding the silicon nitride sintered body 1 can be improved. Diamond grinding wheels are generally used in the grinding process of the silicon nitride sintered body 1. Improving the durability of the grinding wheel is effective not only in achieving cost reduction but also in improving the manufacturing efficiency (machinability) of wear-resistant parts. Therefore, a silicon nitride sintered body 1 with improved machinability can be provided.

[0057] (Example) (Examples 1-6, Comparative Examples 1-2) Silicon nitride powder and sintering aid powder were prepared as raw material powders. The raw material powders of the silicon nitride sintered bodies 1 according to Examples 1 to 6 and the raw material powders of the silicon nitride sintered bodies according to Comparative Examples 1 to 2 were mixed under the conditions shown in Table 1. The mixing ratio is expressed as silicon nitride powder + sintering aid powder = 100% by mass.

[0058] [Table 1]

[0059] In addition, for the WO3 powder and MoO3 powder of Examples 1 to 6, the powders shown in Table 2 were used.

[0060] [Table 2]

[0061] The raw material powder is mixed using a ball mill. Alternatively, organic binders and solvents are added to the raw material powder during ball mill mixing.

[0062] Next, the ball-milled raw material powder is granulated, molded, and CIP (Computer Injection Process). The resulting spherical molded body has a strip-shaped portion on the circumference of the sphere. This molded body is used to obtain raw material sphere 6 after sintering.

[0063] A degreasing process is performed on the molded body. The degreasing process is carried out in the range of 400–650°C. The resulting molded body, i.e., the degreased body, is then subjected to a sintering process. The sintering process is carried out in two stages. The sintering conditions are shown in Table 3.

[0064] [Table 3]

[0065] As shown in Table 3, Examples 1, 2, and 4 were held at 1500°C for more than 3 hours. Example 3 was held at 800°C for more than 3 hours. Examples 5 and 6 were held at 800°C and 1500°C for more than 3 hours each, respectively. Comparative Examples 1 and 2 did not undergo an intermediate holding process. Through the above processes, silicon nitride sintered bodies 1 of the Examples and silicon nitride sintered bodies of the Comparative Examples were obtained.

[0066] For the silicon nitride sintered body 1 of the embodiment, the metal compound particles 4 containing dispersed components were analyzed relative to the overall dispersed components of the metal compound particles 4. Additionally, the average length of the major axis of the silicon nitride grains 1 was also analyzed. The analytical method is as described above. The results are shown in Table 4. Furthermore, the analytical results of the silicon nitride sintered body of the comparative example are also shown in Table 3.

[0067] [Table 4]

[0068] As shown in Table 4, the silicon nitride sintered body 1 in the embodiment contains metal compound particles 4 including dispersed components. Furthermore, in the silicon nitride sintered body 1 of the embodiment and the silicon nitride sintered body of the comparative example, the average length of the major axis of the silicon nitride grains is 0.1 μm or more and 10 μm or less, and the average aspect ratio is 2 or more and 10 or less.

[0069] Next, the three-point bending strength, fracture toughness, and Vickers hardness of the silicon nitride sintered body were measured. The measurement conditions were as described above. The results are shown in Table 5.

[0070] Furthermore, it was confirmed that when the main component of the metal compound particles containing at least one of tungsten and molybdenum is set as M and oxygen is set as O, the compound Mo is obtained. x The oxygen atom ratio x is checked to see if it satisfies equation (2). The confirmation method is to investigate any three metal compound particles. If all three metal compound particles satisfy equation (2), it is set as "A"; if at least one metal compound particle does not satisfy equation (2), it is set as "B". The results are shown in Table 5.

[0071] [Table 5]

[0072] As shown in Table 5, there were no significant differences in fracture toughness values ​​between the examples and comparative examples. However, the examples showed slightly higher three-point bending strength and Vickers hardness. Additionally, the oxygen content (MO) in the metal compound particles was also observed. xAll the examples fell within the range of 0.01 to 2, while the comparative examples all deviated from this range. It should be noted that the three-point bending strength was not measured using the raw material ball 6, but rather using a plate-shaped silicon nitride sintered body 1 manufactured under the same conditions as the raw material ball 6.

[0073] The raw material ball 6 involved in the preparation examples and the raw material ball involved in the comparative examples are both raw material balls used to obtain 3 / 8-inch (9.525 mm in diameter) bearing balls. Furthermore, both raw material balls have a strip-shaped portion on their circumference.

[0074] Next, the raw material balls 6 of the examples and the raw material balls of the comparative examples were ground using diamond grinding wheels until the surface roughness Ra was 0.01 μm. In the examples and comparative examples, the replacement frequency of the diamond grinding wheels was compared. The replacement frequency of the diamond grinding wheels in the examples is expressed as a ratio to the replacement frequency of the diamond grinding wheel in Comparative Example 1 being set to 100. A larger number indicates a longer replacement frequency and better wheel durability.

[0075] In addition, the time required to grind with a diamond wheel to a surface roughness Ra of 0.01 μm was measured. The grinding time of the examples is expressed as a ratio to the grinding time of Comparative Example 1 when it is set to 100. The smaller the number, the shorter the grinding time. The results are shown in Table 6.

[0076] [Table 6]

[0077] As shown in Table 6, the grinding time in the embodiment was shortened by approximately 10-20%, and the machinability of the silicon nitride sintered body 1 was improved. This is because the machinability of the silicon nitride sintered body 1 was improved. Furthermore, in the embodiment, the grinding wheel replacement period was improved by approximately 10%. Therefore, the durability of the grinding wheel was improved. In addition, the bearing balls 5 obtained by grinding the raw material balls 6 exhibited good durability.

[0078] Furthermore, in the examples and comparative examples, it can be confirmed that the wear resistance and processability of the raw material ball 6 (which is ground to become a bearing ball) as an example of silicon nitride sintered body 1 are maintained and improved. However, the effect is not limited to the case where the silicon nitride sintered body 1 is the raw material ball 6. As long as the metal compound particles 4 contain the above-mentioned main component compound and dispersion component, it is believed that even if the silicon nitride sintered body 1 is other than the raw material ball 6 (a wear-resistant component other than the bearing ball that is ground to become a bearing ball), it can be obtained.

[0079] According to at least one embodiment described above, a silicon nitride sintered body 1 with improved workability (e.g., raw material ball 6) and a wear-resistant component using the same (e.g., bearing ball 5) can be provided. Furthermore, by controlling the surface roughness Ra of the sliding surface of the silicon nitride sintered body 1, a silicon nitride sintered body 1 that maintains wear resistance and improves workability, and a wear-resistant component using the same, can be provided.

[0080] The above embodiments of the present invention have been illustrated, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and are also included within the scope of the invention as described in the claims and its equivalents. Furthermore, the above-described embodiments can be combined with each other for implementation.

Claims

1. A silicon nitride sintered body, characterized in that, It is a sintered silicon nitride body containing silicon nitride grains and grain boundary phases. The grain boundary phase contains metallic compound particles. The metal compound particles contain a main component compound, which includes at least one of oxides, carbides, nitrides, silicides, and composite compounds with at least one of tungsten and molybdenum as the main component. The metal compound particles contain a dispersed component comprising at least one of aluminum, cobalt, iron, and rare earth elements.

2. The silicon nitride sintered body according to claim 1, characterized in that, The metal compound particles contain two or more of the following as dispersion components: aluminum, cobalt, iron, and rare earth elements.

3. The silicon nitride sintered body according to claim 1 or 2, wherein, The total content of the dispersed component relative to the total content of the metal compound particles is in the range of 1% by mass or more and 15% by mass or less.

4. The silicon nitride sintered body according to claim 1 or 2, characterized in that, The metal compound particles comprise an oxide with at least one of tungsten and molybdenum as the main component. Compound MO is formed when the main component of the metal compound particles is set to M and oxygen is set to O. x The oxygen atom ratio x satisfies 0.01≤x≤2.

0.

5. The silicon nitride sintered body according to claim 3, characterized in that, The metal compound particles comprise an oxide with at least one of tungsten and molybdenum as the main component. MO when the principal component of the metal compound particles is set to M. x The oxygen content satisfies 0.01≤x≤2.

0.

6. The silicon nitride sintered body according to claim 1 or 2, characterized in that, It contains 0.1% by mass or more and 5% by mass of the aforementioned metal compound particles.

7. The silicon nitride sintered body according to claim 3, characterized in that, It contains 0.1% by mass or more and 5% by mass of the aforementioned metal compound particles.

8. The silicon nitride sintered body according to claim 5, characterized in that, It contains 0.1% by mass or more and 5% by mass of the aforementioned metal compound particles.

9. The silicon nitride sintered body according to claim 1 or 2, characterized in that, The average length of the major axis of the silicon nitride grain is greater than 0.1 μm and less than 10 μm, and the average aspect ratio is greater than 2 and less than 10.

10. The silicon nitride sintered body according to claim 8, characterized in that, The average length of the major axis of the silicon nitride grain is greater than 0.1 μm and less than 10 μm, and the average aspect ratio is greater than 2 and less than 10.

11. A wear-resistant component, characterized in that, It is formed from the silicon nitride sintered body as described in claim 1.

12. A wear-resistant component, characterized in that, It is formed from the silicon nitride sintered body as described in claim 8.

13. A wear-resistant component, characterized in that, It is formed from the silicon nitride sintered body as described in claim 10.

14. A wear-resistant component, characterized in that, The wear-resistant component of claim 13 is a bearing ball.

15. A method for manufacturing a silicon nitride sintered body, characterized in that, It is a method for manufacturing the silicon nitride sintered body according to claim 1. This includes a mixing process that combines silicon nitride powder and sintering aid powder. In the mixing process, the sintering aid powder is a powder that contains a dispersion component powder corresponding to the dispersion component in the main component powder corresponding to the main component of the metal compound particles.

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