Silicon nitride sintered body and wear-resistant member using same

Abstract

A silicon nitride sintered body according to the embodiments comprises silicon nitride crystal particles and a grain boundary phase and includes metal compound particles in the grain boundary phase. The metal compound particles of the silicon nitride sintered body contain a principal component compound that comprises at least one of an oxide, a carbide, a nitride, a silicide, and a composite compound that includes at least one of tungsten and molybdenum as a principal component. The metal compound particles of the silicon nitride sintered body contain a dispersion component that comprises at least one of aluminum, cobalt, iron, and a rare earth element. The silicon nitride sintered body of the embodiments can be used for bearing balls.

Description

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

[0001] The embodiments described below generally relate to a silicon nitride sintered body and a wear-resistant member using the same.

[0002] Silicon nitride sintered bodies are used in wear-resistant members. Examples of wear-resistant members include bearing members, roll materials, compressor vanes, gas turbine blades, and engine parts. Examples of bearing members include bearing balls, inner rings of bearings, and outer rings of bearings. Examples of roll materials include those used in rolling mills and conveying. Examples of engine parts include cam rollers. In recent years, silicon nitride sintered bodies have been used in bearing balls as bearing members due to their excellent mechanical strength and wear resistance.

[0003] For example, Japanese Patent No. 5,100,201 (Patent Document 1) discloses a silicon nitride sintered body in which the aspect ratio and standard deviation of acicular silicon nitride crystal grains are controlled. Furthermore, Japanese Patent No. 6,416,088 (Patent Document 2) discloses a silicon nitride sintered body in which the variation in the area ratio of the grain boundary phase is suppressed. Patent Documents 1 and 2 disclose the uniform distribution of silicon nitride crystal grains and grain boundary phases, thereby improving the wear resistance of the silicon nitride sintered body. Furthermore, Japanese Patent No. 5,499,718 (Patent Document 3) discloses a silicon nitride sintered body to which boron nitride, cobalt, aluminum, and tungsten carbide are added. In Patent Document 3, the use of these additives improves the bonding strength between particles, resulting in excellent chipping resistance.

[0004] Patent No. 5100201 Patent No. 6416088 Patent No. 5499718

[0005] In recent years, silicon nitride sintered bodies have been used for bearing balls in electric vehicle motors. As a result, demand for bearing balls made of silicon nitride sintered bodies has grown significantly. However, silicon nitride sintered bodies are difficult to process. Therefore, in order to mass-produce silicon nitride sintered body balls, further improvements in the processability of silicon nitride sintered bodies, i.e., shortening of the processing time, have been required.

[0006] One of the problems to be solved by the embodiments is to provide a silicon nitride sintered body with improved processability and a wear-resistant member using the same.

[0007] According to an embodiment, a silicon nitride sintered body having silicon nitride crystal grains and a grain boundary phase has metal compound particles in the grain boundary phase. The metal compound particles of the silicon nitride sintered body contain a main component compound consisting of at least one of oxide, carbide, nitride, silicide, and composite compound, mainly composed of at least one of tungsten and molybdenum. The metal compound particles of the silicon nitride sintered body also contain a dispersed component consisting of at least one of aluminum, cobalt, iron, and rare earth elements.

[0008] 1 is a schematic diagram showing an example of a cross-sectional structure of a silicon nitride sintered body according to an embodiment, an external view showing an example of a bearing ball based on the silicon nitride sintered body according to an embodiment, and an external view showing an example of a base sphere for a bearing ball made of the silicon nitride sintered body according to an embodiment. Embodiment

[0009] According to an embodiment, a silicon nitride sintered body having silicon nitride crystal grains and a grain boundary phase has metal compound particles in the grain boundary phase. The metal compound particles of the silicon nitride sintered body contain a main component compound consisting of at least one of oxide, carbide, nitride, silicide, and composite compound, mainly composed of at least one of tungsten and molybdenum. The metal compound particles of the silicon nitride sintered body also contain a dispersed component consisting of at least one of aluminum, cobalt, iron, and rare earth elements.

[0010] Figure 1 shows an example of the cross-sectional structure of a silicon nitride sintered body according to an embodiment. In the figure, reference numeral 1 denotes a silicon nitride sintered body, reference numeral 2 denotes silicon nitride crystal grains, reference numeral 3 denotes a grain boundary phase, and reference numeral 4 denotes metal compound particles. The silicon nitride sintered body 1 has a structure in which a plurality of silicon nitride crystal grains 2 are intricately entangled. The silicon nitride sintered body 1 also has a structure in which the gaps between the plurality of silicon nitride crystal grains 2 are filled with a grain boundary phase 3. At least a portion of the grain boundary phase 3 contains metal compound particles 4. In Figure 1, the metal compound particles 4 are depicted as relatively small circles.

[0011] The metal compound particles 4 contain at least one main component compound selected from the group consisting of oxides, carbides, nitrides, silicides, and composite compounds containing at least one of tungsten (W) and molybdenum (Mo) as a main component. The main component refers to the component that is contained in the largest amount by mass among the metal components of the metal compound particles 4. The composite compound may be various compounds such as oxynitrides, oxycarbides, oxysilicides, and carbonitrides.

[0012] Furthermore, the metal compound particles 4 contain at least one of aluminum (Al), cobalt (Co), iron (Fe), and a rare earth element in addition to the main component compound. The component consisting of at least one of aluminum, cobalt, iron, and a rare earth element contained in the metal compound particles 4 is called a dispersed component. Here, "contained" refers to a state in which the dispersed component is present inside the metal compound particles 4. Therefore, the presence of the dispersed component in the metal compound particles 4 is not limited to that due to solid solution in the main component compound, but the following description will be given taking as an example a case in which the dispersed component is contained in the metal compound particles 4 by being solid-solved in the main component compound. As long as the crystal structure of the metal compound particles 4 is maintained, the effect of strengthening the grain boundary phase 3 is not reduced.

[0013] It is effective to include a dispersed component in the metal compound particles 4. This makes it possible to strengthen the structure of the metal compound particles 4. Furthermore, since the grain boundary phase 3 is less likely to fall off, the processing speed of the silicon nitride sintered body 1 can be increased, thereby improving the workability of the silicon nitride sintered body 1. Furthermore, by including a dispersed component in the metal compound particles 4, the strength of the metal compound particles 4 itself can be increased. Therefore, the amount of silicon nitride crystal grains 2 and grain boundary phase 3 removed by polishing becomes uniform, improving the workability.

[0014] The grain boundary phase 3 fills the gaps between the silicon nitride crystal grains 2. Furthermore, the inclusion of metal compound particles 4 in at least a portion of the grain boundary phase 3 has the effect of strengthening the grain boundary phase 3, thereby improving the fracture toughness or hardness of the silicon nitride sintered body 1. Furthermore, the presence of dispersed components in the metal compound particles 4 makes it easier to remove the surface of the silicon nitride sintered body 1 by polishing.

[0015] The dispersed components of the metal compound particles 4 are composed of at least one of aluminum, cobalt, iron, and a rare earth element. Preferably, the dispersed components are composed of two or more of aluminum, cobalt, iron, and a rare earth element. For example, rare earth elements include yttrium and lanthanoid elements.

[0016] Aluminum, cobalt, iron, and rare earth elements are elements that can be easily dissolved in the main component compound of the metal compound particles 4. In addition, the metal compound particles 4 may have at least the dispersed component dissolved in the main component compound, and may have a component other than the dispersed component dissolved in the main component compound.

[0017] The presence or absence of dispersed components in the metal compound particles 4 is measured using TEM-EDS. The thickness of the sample used for the measurement is 0.05 μm or more and 0.5 μm or less. The TEM-EDS conditions are an acceleration voltage of 200 kV, a probe current of 1.00 nA, a spot diameter during analysis of 1 nm, an analysis time of 30 seconds, and sample angles of X=10° and Y=0°.

[0018] In any cross section of the silicon nitride sintered body 1, an analysis spot is selected near the center of the metal compound particle 4. If at least one of tungsten and molybdenum and the dispersed component are detected by this analysis, it is determined that the dispersed component is contained in the metal compound particle 4. Furthermore, TEM-EDS can perform qualitative and quantitative analysis.

[0019] Furthermore, the presence or absence of dispersed components may be measured using FESEM-EDS instead of TEM-EDS. FESEM stands for Field Emission Scanning Electron.

[0020] Furthermore, the total content (mass ratio) of the dispersed components relative to the entire metal compound particles 4 is preferably within a range of 1 mass % to 15 mass %. The content of the dispersed components in the metal compound particles 4 is the amount of the detected elemental metal. The dispersed components themselves are not limited to elemental metals, and may be contained as compounds such as oxides.

[0021] If the content of the dispersed components relative to the total amount of the metal compound particles 4 is less than 1 mass %, the effect of strengthening the grain boundary phase 3 may be insufficient. Furthermore, if the content of the dispersed components exceeds 15 mass %, the crystal structure of the metal compound particles 4 may become unstable. This may result in a decrease in the strength of the grain boundary phase 3. Therefore, the total content of the dispersed components in the metal compound particles 4 is preferably in the range of 1 mass % to 15 mass %, and more preferably 2 mass % to 10 mass %.

[0022] Furthermore, the ratio of the number of metal compound particles 4 containing a dispersed component to the total number of metal compound particles 4 is preferably within the range of 50% to 100%. If the ratio of the number of metal compound particles 4 containing a dispersed component is 50% or less, the strengthening of the grain boundary phase 3 will not extend to the entire sintered body. Therefore, the ratio of the number of metal compound particles 4 containing a dispersed component is preferably 50% to 100%. Furthermore, the ratio of the number is preferably 60% to 90%. The ratio of the number of metal compound particles 4 containing a dispersed component is determined by measuring the presence or absence of dispersed components in metal compound particles 4 present in a measurement area of ​​50 μm × 50 μm.

[0023] The number ratio W of the metal compound particles 4 containing dispersed components was calculated according to the following formula (1): W = (metal compound particles containing dispersed components / total metal compound particles) × 100 (1)

[0024] In addition, when the main component of the metal compound particle 4 is at least one of tungsten and molybdenum, M, and oxygen, O, a compound MO ｘ It is preferable that the oxygen atomic ratio x (oxygen content) satisfies the following formula (2): 0.01≦x≦2.0 (2)

[0025] The metal compound particles 4 satisfying the formula (2) indicate that the metal compound particles 4 are oxides. In other words, the metal compound particles 4 contain at least one of tungsten oxide, molybdenum oxide, and tungsten molybdenum oxide. These oxides are likely to dissolve dispersed components. In addition, the compound MO ｘ may contain oxygen as a dispersed component.

[0026] Compound MO ｘ For example, WO ３ and MoO ３ The oxygen atomic ratio x is preferably in a range smaller than the theoretical value. ３ and MoO ３ In this case, it is preferable that the oxygen atomic ratio x is a value smaller than 3.

[0027] Furthermore, the content of the metal compound particles 4 relative to the entire silicon nitride sintered body 1 is preferably 0.1% by mass or more and 5% by mass or less. The metal compound particles 4 have the effect of strengthening the grain boundary phase 3. If the content of the metal compound particles 4 is less than 1% by mass, the effect of strengthening the grain boundary phase 3 may be insufficient. If the content of the metal compound particles 4 exceeds 5% by mass, the structure in which the silicon nitride crystal particles 2 are intricately entangled with each other may be impaired. For this reason, the content of the metal compound particles 4 is preferably within the range of 0.1% by mass or more and 5% by mass or less, and more preferably 1% by mass or more and 4% by mass or less.

[0028] The grain boundary phase 3 may 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 components are mainly composed of a sintering aid, which will be 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 to 15% by mass.

[0029] The silicon nitride crystal particles 2 preferably have an average major axis length of 0.1 μm or more and 10 μm or less, and an average aspect ratio of 2 or more and 10 or less. If the average major axis length is less than 0.1 μm, the silicon nitride crystal particles 2 may be too small, resulting in reduced durability. From the viewpoint of durability, it is more preferable that the average major axis length of the silicon nitride crystal particles 2 be 0.5 μm or more and 10 μm or less. If the average major axis length exceeds 10 μm, the gaps between the silicon nitride crystal particles 2 may become large, resulting in reduced strength.

[0030] The major axis of the silicon nitride crystal grains 2 is measured using an SEM photograph. An SEM photograph is taken of an arbitrary cross section of the silicon nitride sintered body 1. The cross section is a polished surface with a surface roughness Ra of 1 μm or less. The magnification of the SEM photograph is set to 1000 times or more. The recommended magnification of the SEM photograph is 4000 times. The measurement area is 300 μm × 300 μm.

[0031] The longest diagonal line of the silicon nitride crystal particles 2 seen in the SEM photograph is taken as the major axis. The 50 largest silicon nitride crystal particles 2 seen in the 300 μm × 300 μm measurement area are selected, and their average value is taken as the average length of the major axis. The minor axis is taken as a line drawn perpendicularly from the midpoint of the major axis of the selected silicon nitride crystal particles 2. The aspect ratio is taken as the major axis / minor axis, and the average value is taken as the average aspect ratio. Image processing software such as ImageJ may be used to select the silicon nitride crystal particles 2.

[0032] The silicon nitride sintered body 1 as described above can have a three-point bending strength of 600 MPa or more, and even 900 MPa or more. Also, the fracture toughness value can be 6.0 MPa m １／２ or more, and even 7.0 MPa m １／２ Furthermore, the Vickers hardness can be set to 1400 or more, and further to 1500 or more.

[0033] Three-point bending strength is measured in accordance with JIS-R-1601 (2008). JIS-R-1601 corresponds to ISO 14704. Fracture toughness can be measured using the Niihara formula in accordance with the IF method of JIS-R-1607 (2015). JIS-R-1607 corresponds to ISO 15732. Vickers hardness can be measured in accordance with JIS-R-1610 (2003). JIS-R-1610 corresponds to ISO 14705.

[0034] The silicon nitride sintered body 1 according to the embodiment is also suitable for use as a wear-resistant member. The wear-resistant member preferably has a sliding surface with a surface roughness Ra of 0.1 μm or less. Examples of wear-resistant members include bearing members, roll materials, compressor vanes, gas turbine blades, and engine parts. Examples of bearing members include bearing balls, inner rings of bearings, and outer rings of bearings. Examples of roll materials include those for rolling and conveying. Examples of engine parts include cam rollers.

[0035] The wear-resistant member has a sliding surface that slides against a mating member. For example, a bearing ball is disposed between the inner and outer rings of a bearing. In the case of a bearing ball made of a ball-shaped silicon nitride sintered body 1, the entire spherical surface serves as the sliding surface. In the case of a roll made of a cylindrical silicon nitride sintered body 1, the roll surface serves as the sliding surface.

[0036] The silicon nitride sintered body 1 according to the embodiment includes metal compound particles 4 containing dispersed components. This improves the processability of the silicon nitride sintered body 1. Additionally, polishing the silicon nitride sintered body 1 to a surface roughness Ra of 0.1 μm or less is effective for improving the wear resistance of the sliding surface. For example, the surface roughness of bearing balls is specified in ASTM F2094. Depending on the application, bearing balls are graded according to ASTM F2094, ISO 26602, or JIS R1669. The bearing balls are polished to a surface roughness Ra according to the grade. With higher grades, some are mirror-finished to a surface roughness Ra of 0.01 μm or less. The silicon nitride sintered body 1 according to the embodiment also controls the surface roughness Ra of the silicon nitride sintered body 1, thereby improving processability while maintaining wear resistance. The polishing process to obtain a sliding surface with a surface roughness Ra of 0.1 μm or less can be efficiently performed.

[0037] FIG. 2 shows an example of a bearing ball, and FIG. 3 shows an example of a base sphere for a bearing ball (hereinafter simply referred to as a "base sphere"). Reference numeral 5 denotes a bearing ball, 6 denotes a base sphere, 7 denotes a spherical portion of the base sphere 6, and 8 denotes a band-shaped portion of the base sphere 6. FIG. 3(A) shows the base sphere 6 as viewed in a direction perpendicular to a line connecting the two poles G1 and G2 of the band-shaped portion 8 (two vertices when the surface including the band-shaped portion 8 is the bottom), and FIG. 3(B) shows the base sphere 6 as viewed in a direction connecting the two poles G1 and G2 of the band-shaped portion 8. The base sphere 6 is polished to form a bearing ball 5. While FIG. 3 illustrates a case in which the base sphere 6 has a band-shaped portion 8 on the circumference of the spherical portion 7, the base sphere 6 may not have a band-shaped portion 8. In other words, the base sphere 6 is what is polished to form a bearing ball 5.

[0038] Next, a method for manufacturing the silicon nitride sintered body 1 according to the embodiment will be described. The method for manufacturing the silicon nitride sintered body 1 according to the embodiment is not particularly limited as long as it has the above-mentioned configuration, but the method for obtaining it with a good yield is as follows.

[0039] First, raw material powders are prepared. The raw material powders are silicon nitride powder and sintering aid powder. The silicon nitride powder preferably has an average particle size of 3 μm or less. It is also preferable that the oxygen content is 3 mass% or less and the alpha conversion rate is 90% or more. Sialon powder may be used instead of silicon nitride powder. A mixture of silicon nitride powder and sialon powder may also be used.

[0040] Examples of sintering aid powders include rare earth element component powder, aluminum component powder (excluding aluminum component powder as dispersed component powder), main component powder (at least one component powder of tungsten component powder and molybdenum component powder) corresponding to the main component of the metal compound particles 4, and dispersed component powder (dispersed component powder consisting of at least one of aluminum, cobalt, iron, and rare earth element) corresponding to the dispersed component. For example, rare earth element component powder, tungsten component powder (or molybdenum component powder), and aluminum component powder are used as the sintering aid powder. Furthermore, it is preferable that the sintering aid powder have an average particle size of 4 μm or less.

[0041] The rare earth element component powder may be a powder of oxide, nitride, or oxynitride of a rare earth element. Yttrium and lanthanoid elements are preferred as rare earth elements. The aluminum component powder, which is the dispersion component powder, may be a powder of oxide, nitride, or oxynitride of aluminum. The main component powder may be a powder of oxide, nitride, carbide, sulfide, oxynitride, oxycarbide, or carbonitride. Of these, oxide or carbide is preferred. The oxide may be tungsten oxide (WO ３ ), molybdenum oxide (MoO ３ Examples of carbides include tungsten carbide (WC, W ２ C), molybdenum carbide (Mo ２ C) can be mentioned.

[0042] It is preferable to use a main component powder that contains a dispersed component powder made of at least one of aluminum, cobalt, iron, and a rare earth element. Examples of such a powder include compounds containing multiple metals as constituent elements. Examples include W-Al-O, W-Co-O, W-Fe-O, W-Y-O, Mo-Al-O, Mo-Co-O, Mo-Fe-O, and Mo-Y-O. Furthermore, a powder containing at least one of aluminum, cobalt, iron, and a rare earth element as an impurity may also be used.

[0043] The surface of the main component powder may be coated with a powder of at least one of aluminum, cobalt, iron, and a rare earth element. Coating methods include sputtering and mechanical alloying. By coating, the dispersed components can easily penetrate into the metal compound particles 4 during the sintering process.

[0044] Alternatively, the sintering aid powder may be a mixture of the main component powder and the dispersed component powder with carbon powder, followed by pulverization. The carbon powder functions as a reducing agent. By reducing the tungsten component powder or the molybdenum component powder, the dispersed component can be contained in the metal compound particles 4. The sintering aid contains not only the dispersed component but also the grain boundary phase component. The aluminum component powder added as a sintering aid is divided into aluminum component powder present in the grain boundary phase 3 other than the metal compound particles 4, and aluminum component powder as the dispersed component contained in the metal compound particles 4. The dispersed component aluminum component powder is preferably contained in or coated on the main component powder of the sintering aid.

[0045] When "silicon nitride powder" + "sintering aid powder", i.e., "silicon nitride powder" + "rare earth element component powder" + "aluminum component powder" + "main component powder (including dispersed component powder)" + "other component powder" is taken as 100% by mass, the "rare earth element component powder" is preferably 1% by mass or more and 13% by mass or less, the "aluminum component powder" is 1% by mass or more and 10% by mass or less, the "sintering aid powder consisting of at least one of tungsten and molybdenum" is 0.1% by mass or more and 7% by mass or less, the "other component powder" is 0% by mass or more and 8% by mass or less, and the remainder is preferably "silicon nitride powder". The aforementioned carbon powder is the other component powder. Furthermore, titania and hafnia may be used as the other component powders as needed.

[0046] Next, the raw material powder is mixed. The mixing process is performed using a disintegrating mixer such as a ball mill. The ball mill can disintegrate the raw material powder by optimizing the disintegrating media, solvent, etc. Disintegrating the raw material powder can suppress the remaining agglomerates. The ball mill may be either a wet type or a dry type. The mixing process may also be performed by adding an organic binder or a solvent to the raw material powder, if necessary.

[0047] Next, the raw materials that have been mixed are subjected to a molding process to obtain a silicon nitride molded body (hereinafter simply referred to as a "molded body"). The raw materials may be granulated before molding. The molding process can be carried out by mold molding, rolling granulation, cold isostatic pressing (CIP), doctor blade method, injection molding, or the like. When producing spheres, mold molding, rolling granulation, or CIP is preferably used. It is also effective to CIP the molded body obtained by mold molding or rolling granulation. CIP is a molding method that uses a liquid as the pressurizing medium. Because isotropic pressure is applied by the liquid, a molded body with a uniform density distribution can be obtained. The CIP pressure is preferably in the range of 40 MPa to 500 MPa.

[0048] The molded body is subjected to a drying process as necessary. The drying process has the effect of removing the solvent used in the wet mixing process. Examples of the drying process include natural drying and heat drying. Heat drying is preferably performed at a temperature in the range of 80°C or higher and 200°C or lower. If the temperature is lower than 80°C, the drying efficiency may decrease. If the temperature exceeds 200°C, uneven drying may occur. For this reason, the drying temperature is preferably in the range of 80°C or higher and 200°C or lower, and more preferably in the range of 100°C or higher and 160°C or lower.

[0049] Next, the compact is subjected to a degreasing process as necessary. By carrying out the degreasing process, the organic binder can be removed from the compact. The degreasing temperature is preferably in the range of 400°C or higher and 700°C or lower. The degreasing process can be carried out in air, a nitrogen atmosphere, or the like. The compact obtained by the degreasing process is sometimes called a degreased body.

[0050] Next, the compact, e.g., the degreased body, is subjected to a sintering process. The sintering temperature in the sintering process is preferably in the range of 1600°C to 2000°C. The sintering time is preferably 1 hour to 12 hours. The sintering process can be performed using atmospheric sintering, pressure sintering, hot isostatic pressing (HIP), or the like. The sintering process can be performed in air, a non-oxidizing atmosphere, a reducing atmosphere, or a vacuum. Atmospheric pressure sintering refers to sintering under controlled conditions of 1 atmosphere (0.9 to 1.1 atm = 0.09 to 0.11 MPa). Pressure sintering refers to sintering under pressure higher than atmospheric pressure. Uniaxial pressure sintering is sometimes called hot pressing. HIP is a sintering method that uses gas isostatic pressure.

[0051] This reduces internal defects such as voids and cracks in the silicon nitride sintered body 1. The HIP pressure is preferably in the range of 10 MPa to 200 MPa. Normal pressure sintering, pressure sintering, and HIP may be combined. It is also preferable to combine these processes in two or more stages. When used for a wear-resistant component, it is preferable to use either one or both of pressure sintering and HIP. Sintering under pressure can produce a silicon nitride sintered body 1 (e.g., a raw sphere 6) with few internal defects. Furthermore, the sintering time is preferably maintained at the sintering temperature for one hour or more. In other words, the sintering temperature is a temperature maintained for one hour or more within the range of 1600°C to 2000°C.

[0052] The sintering step can produce a silicon nitride sintered body 1. In some cases, the sliding surface of the silicon nitride sintered body 1 is polished to form a wear-resistant member. For example, in the case of a ball-shaped silicon nitride sintered body 1 (e.g., a base ball 6) for producing a bearing ball, the entire surface serves as the sliding surface.

[0053] The surface roughness Ra of the sliding surface of the silicon nitride sintered body 1 is preferably 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. For this reason, the surface roughness Ra of the sliding surface is preferably 0.1 μm or less, and more preferably 0.01 μm or less. The silicon nitride sintered body 1 according to the embodiment has excellent machinability, which improves its processability into wear-resistant members. In other words, the polishing time required to produce wear-resistant members from the silicon nitride sintered body 1 can be shortened.

[0054] Furthermore, it is possible to improve the durability of the grindstone used to polish the silicon nitride sintered body 1. Diamond grindstones are generally used in the polishing process of the silicon nitride sintered body 1. Improving the durability of the grindstone not only reduces costs but is also effective in improving the manufacturing efficiency (improving processability) of wear-resistant members. Therefore, it is possible to provide a silicon nitride sintered body 1 with improved processability.

[0055] Examples (Examples 1 to 6, Comparative Examples 1 and 2) Silicon nitride powder and sintering aid powder were prepared as raw material powders. The raw material powder for silicon nitride sintered body 1 according to Examples 1 to 6 and the raw material powder for silicon nitride sintered body according to Comparative Examples 1 and 2 were mixed under the conditions shown in Table 1. The mixing ratio is shown as silicon nitride powder + sintering aid powder = 100 mass%.

[0056]

[0057] In addition, WO in Examples 1 to 6 ３ Powder, MoO ３ The powders used were those shown in Table 2.

[0058]

[0059] The raw material powders were mixed using a ball mill. An organic binder and a solvent were also added to the raw material powders and mixed in the ball mill. The raw material powders after ball mill mixing were then granulated, molded, and subjected to CIP. The resulting ball-shaped compacts had band-like portions around the periphery of the spheres. These compacts were intended to obtain the base spheres 6 after sintering. The compacts were subjected to a debinding process. The debinding process was carried out in the range of 400 to 650°C. The resulting debound compacts were then subjected to a sintering process. The sintering process was carried out in two stages. The sintering conditions are as shown in Table 3.

[0060]

[0061] As shown in Table 3, Examples 1, 2, and 4 were held at 1500°C for 3 hours or more. Example 3 was held at 800°C for 3 hours or more. Examples 5 and 6 were held at 800°C and 1500°C for 3 hours or more, respectively. Comparative Examples 1 and 2 did not undergo any intermediate holding steps. Through the above steps, silicon nitride sintered body 1 according to the example and a silicon nitride sintered body according to the comparative example were obtained.

[0062] For the silicon nitride sintered body 1 according to the example, the metal compound particles 4 containing the dispersed component were analyzed relative to the total metal compound particles 4 containing the dispersed component. The average length of the major axis of the silicon nitride crystal particles 1 was also analyzed. The analysis method was as described above. The results are shown in Table 4. The analysis results for the silicon nitride sintered body according to the comparative example are also shown in Table 3.

[0063]

[0064] As can be seen from Table 4, the silicon nitride sintered body 1 of the example contained metal compound particles 4 containing dispersed components. In addition, in the silicon nitride sintered body 1 of the example and the silicon nitride sintered body of the comparative example, the average length of the major axis of the silicon nitride crystal particles was 0.1 μm or more and 10 μm or less, and the average aspect ratio was 2 or more and 10 or less.

[0065] Next, the three-point bending strength, fracture toughness, and Vickers hardness of the silicon nitride sintered body were measured under the same conditions as described above. The results are shown in Table 5.

[0066] In addition, when the main component of the metal compound particles is at least one of tungsten and molybdenum, M, and oxygen is O, a compound Mo is ｘ It was confirmed whether the oxygen atomic ratio x of each metal compound particle satisfied the above formula (2). The confirmation method was to examine three random metal compound particles, and if all three metal compound particles satisfied the above formula (2), it was rated as "A", and if even one metal compound particle did not satisfy the above formula (2), it was rated as "B". The results are shown in Table 5.

[0067]

[0068] As can be seen from Table 5, there was no significant difference in fracture toughness between the Examples and Comparative Examples. Furthermore, the three-point bending strength and Vickers hardness were slightly higher in the Examples. Furthermore, the amount of oxygen contained in the metal compound particles, MO ｘ Regarding , all of the Examples were within the range of 0.01 or more and 2 or less, while all of the Comparative Examples were outside the range. Note that the three-point bending strength was measured not using the raw sphere 6 but using plate-shaped silicon nitride sintered bodies 1 manufactured under the same conditions as the raw sphere 6.

[0069] A blank ball 6 according to the example and a blank ball according to the comparative example were prepared. Both the blank ball 6 according to the example and the blank ball according to the comparative example were intended to obtain bearing balls of 3 / 8 inch (diameter 9.525 mm). Furthermore, both blank balls had a band-like portion on the circumference of the sphere.

[0070] Next, the base ball 6 according to the example and the base ball according to the comparative example were polished to a surface roughness Ra of 0.01 μm using a diamond grinding wheel. The replacement intervals of the diamond grinding wheels were compared between the example and the comparative example. The replacement intervals of the diamond grinding wheels of the example were shown as a ratio when the replacement interval of the diamond grinding wheel of comparative example 1 was set to 100. The larger the number, the longer the replacement interval of the grinding wheel and the better the durability of the grinding wheel.

[0071] The time required for polishing to a surface roughness Ra of 0.01 μm using a diamond grinding wheel was also measured. The polishing times of the examples are shown as a ratio when the polishing time of Comparative Example 1 is set to 100. The smaller the number, the shorter the polishing time. The results are shown in Table 6.

[0072]

[0073] As can be seen from Table 6, the polishing time in the examples was reduced by about 10 to 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. In addition, the replacement period of the grinding stone was improved by about 10% in the examples. This improved the durability of the grinding stone. Furthermore, the durability of the bearing balls 5 obtained by polishing the base balls 6 was good.

[0074] In the examples and comparative examples, it was confirmed that the wear resistance was maintained and the processability was improved for the base spheres 6 (which can be polished to become bearing balls), which are an example of the silicon nitride sintered body 1. However, this effect is not limited to the case where the silicon nitride sintered body 1 is the base spheres 6, and it is thought that this effect can also be obtained for silicon nitride sintered bodies 1 other than the base spheres 6 (which can be polished to become wear-resistant members other than bearing balls) as long as the metal compound particles 4 contain the above-mentioned main component compound and dispersed components.

[0075] According to at least one of the embodiments described above, it is possible to provide a silicon nitride sintered body 1 (e.g., base ball 6) with improved processability and a wear-resistant member using the same (e.g., bearing ball 5). Furthermore, by controlling the surface roughness Ra of the sliding surface of the silicon nitride sintered body 1, it is possible to provide a silicon nitride sintered body 1 with improved processability while maintaining wear resistance, and a wear-resistant member using the same.

[0076] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

Claims

1. A silicon nitride sintered body comprising silicon nitride crystal grains and a grain boundary phase, wherein the grain boundary phase contains metal compound particles, the metal compound particles containing a main component compound consisting of at least one of oxide, carbide, nitride, silicide, and composite compound containing at least one of tungsten and molybdenum as a main component, and the metal compound particles containing a dispersed component consisting of at least one of aluminum, cobalt, iron, and rare earth elements.

2. The silicon nitride sintered body according to claim 1, wherein the metal compound particles contain two or more of aluminum, cobalt, iron, and rare earth elements as the dispersed components.

3. A silicon nitride sintered body according to claim 1 or 2, wherein the total content of the dispersed components relative to the total amount of the metal compound particles is within the range of 1% by mass to 15% by mass.

4. The metal compound particles contain an oxide containing at least one of tungsten and molybdenum as the main component compound, and the main component of the metal compound particles is M and oxygen is O, which is a compound MO ｘ 3. The silicon nitride sintered body according to claim 1, wherein the oxygen atomic ratio x satisfies 0.01≦x≦2.

0.

5. The metal compound particles contain an oxide containing at least one of tungsten and molybdenum as a main component, and MO when the main component of the metal compound particles is M. ｘ 4. The silicon nitride sintered body according to claim 3, wherein the oxygen content satisfies 0.01≦x≦2.

0.

6. A silicon nitride sintered body according to claim 1 or 2, characterized in that it contains 0.1 mass % to 5 mass % of said metal compound particles.

7. The silicon nitride sintered body according to claim 3, characterized in that it contains 0.1 mass % to 5 mass % of said metal compound particles.

8. A silicon nitride sintered body according to claim 5, characterized in that it contains 0.1 mass % to 5 mass % of said metal compound particles.

9. A silicon nitride sintered body according to claim 1 or 2, characterized in that the silicon nitride crystal grains have an average major axis length of 0.1 μm or more and 10 μm or less and an average aspect ratio of 2 or more and 10 or less.

10. The silicon nitride sintered body according to claim 8, wherein the silicon nitride crystal grains have an average major axis length of 0.1 μm or more and 10 μm or less and an average aspect ratio of 2 or more and 10 or less.

11. A wear-resistant member comprising the silicon nitride sintered body according to claim 1.

12. A wear-resistant member comprising the silicon nitride sintered body according to claim 8.

13. A wear-resistant member comprising the silicon nitride sintered body according to claim 10.

14. The wear-resistant member according to claim 13, characterized in that it is a bearing ball.

15. A method for producing a silicon nitride sintered body as described in claim 1, comprising a mixing step of mixing a silicon nitride component powder and a sintering aid powder, wherein the mixing step uses as the sintering aid powder a main component powder corresponding to the main component of the metal compound particles containing a dispersed component powder corresponding to the dispersed component.

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