Silicon nitride sintered body and wear-resistant member using same

Abstract

Raman imaging of a measurement area on a certain cross-section of the silicon nitride sintered body according to an embodiment of the present invention yields a mapping where (1) among a region of silicon nitride crystal particles oriented in a direction nearly aligned with a direction perpendicular to the certain cross-section in the measurement area and a region of silicon nitride crystal particles oriented in a direction nearly aligned with a direction parallel to the certain cross-section, the region of silicon nitride crystal particles having a smaller area ratio is defined as a first region, and (2) the region of silicon nitride crystal particles having a larger area ratio is defined as a second region; (3) a region of the grain boundary phase of a rare earth element-aluminum-oxygen system in the measurement area is defined as a third region; (4) a region of a substance including at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide in the measurement area is defined as a fourth region; and the area ratios of the first region, the second region, the third region, and the fourth region are 0.5%-8%, 70%-92%, 2%-16%, and 0.5%-8%, respectively.

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. 5100201 (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. 6416088 (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. This improves the wear resistance of the silicon nitride sintered body.

[0004] Patent No. 5100201 Patent No. 6416088

[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 bearing balls made of silicon nitride sintered bodies, there has been a demand for further improvement in the processability of silicon nitride sintered bodies, that is, for shortening the processing time.

[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] The silicon nitride sintered body according to the embodiment is subjected to Raman imaging in a measurement area of ​​20 μm×20 μm on a specific cross section of the silicon nitride sintered body, and the following are determined: (1) the region of silicon nitride crystal grains oriented in a direction close to the perpendicular direction of the specific cross section within the measurement area and the region of silicon nitride crystal grains oriented in a direction close to the parallel direction of the specific cross section, the region of silicon nitride crystal grains with the smaller area ratio is defined as a first region; (2) the region of silicon nitride crystal grains with the larger area ratio is defined as a second region; and (3) the rare earth element-aluminum ratio within the measurement area is determined as a second region. When the region of the titanium-oxygen-based grain boundary phase is defined as the third region, and (4) the region of a material consisting of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide in the measurement area is defined as the fourth region, when the total area ratio of the first region, the second region, the third region, and the fourth region is taken as 100%, the area ratios of the first region, the second region, the third region, and the fourth region are 0.5% to 8% inclusive, 70% to 92% inclusive, 2% to 16% inclusive, and 0.5% to 8% inclusive, respectively. In the silicon nitride sintered body, the difference in area ratio between the plurality of first regions among different measurement areas may be 2% or more, and the difference in area ratio between the plurality of fourth regions among different measurement areas may be 2% or more.

[0008] Fig. 1 is a schematic diagram showing an example of Raman imaging of a silicon nitride sintered body according to an embodiment. Fig. 2 is a diagram showing an example of Raman spectra in a first region and a second region of a silicon nitride sintered body according to an embodiment. Fig. 3 is a diagram showing another example of Raman imaging of a silicon nitride sintered body according to an embodiment. Fig. 4 is an external view showing an example of a bearing ball based on a silicon nitride sintered body according to an embodiment. Fig. 5 is an external view showing an example of a base sphere for a bearing ball made of a silicon nitride sintered body according to an embodiment. Embodiment

[0009] The silicon nitride sintered body according to the embodiment is subjected to Raman imaging in a measurement area of ​​20 μm×20 μm on a specific cross section of the silicon nitride sintered body, and the following are determined: (1) the region of silicon nitride crystal grains oriented in a direction close to the perpendicular direction of the specific cross section within the measurement area and the region of silicon nitride crystal grains oriented in a direction close to the parallel direction of the specific cross section, the region of silicon nitride crystal grains with the smaller area ratio is defined as a first region; (2) the region of silicon nitride crystal grains with the larger area ratio is defined as a second region; and (3) the rare earth element-aluminum ratio within the measurement area is determined as a second region. When the region of the titanium-oxygen-based grain boundary phase is defined as the third region, and (4) the region of a material consisting of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide in the measurement area is defined as the fourth region, when the total area ratio of the first region, the second region, the third region, and the fourth region is taken as 100%, the area ratios of the first region, the second region, the third region, and the fourth region are 0.5% to 8% inclusive, 70% to 92% inclusive, 2% to 16% inclusive, and 0.5% to 8% inclusive, respectively. In the silicon nitride sintered body, the difference in area ratio between the plurality of first regions among different measurement areas may be 2% or more, and the difference in area ratio between the plurality of fourth regions among different measurement areas may be 2% or more.

[0010] 1 and 3 are schematic diagrams showing an example of Raman imaging of a silicon nitride sintered body according to an embodiment. In the figures, reference numeral 10 denotes the silicon nitride sintered body, reference numeral 1 denotes a first region of the silicon nitride sintered body 10, reference numeral 2 denotes a second region of the silicon nitride sintered body 10, reference numeral 3 denotes a third region of the silicon nitride sintered body 10, and reference numeral 4 denotes a fourth region of the silicon nitride sintered body 10. An example of the silicon nitride sintered body 10 is a base sphere 6 for a bearing ball shown in FIG. 5.

[0011] Fig. 1 shows the results of Raman imaging within a measurement area R (e.g., measurement area R1) on a specific cross section of a silicon nitride sintered body 10. Fig. 3 shows the results of Raman imaging within a measurement area R (e.g., measurement area R2) different from that shown in Fig. 1 within the silicon nitride sintered body 10. Measurement area R2 may be an area on a specific cross section different from that of measurement area R1, or may be an area on the specific cross section of measurement area R1 but different from that of measurement area R1. Furthermore, actual Raman imaging may be color mapped, unlike Figs. 1 and 3.

[0012] Raman imaging is a method for measuring information on a certain area within a 20 μm x 20 μm measurement area R in a specific cross section of a silicon nitride sintered body 10. The specific cross section may be any size that can secure the measurement area R (or 400 μm x 400 μm, as described below). The microscopic laser Raman device used is a LabRAM HR Evolution manufactured by Horiba, Ltd. or an equivalent device. The excitation laser wavelength is 532 nm, the laser output is 20.8 mW, and the grating is 600 gr / mm. The objective lens is 100x magnification. The exposure time is 1 second, the number of integrations is 3, the measurement area R is 20 μm x 20 μm, and the measurement pitch is 0.25 μm. 100 to 1700 cm －１ The data obtained by the Raman shift of the silicon nitride sintered body 10 is subjected to multivariate analysis to obtain Raman imaging. The measurement sample is an arbitrary cross section of the silicon nitride sintered body 10, and the polished surface is polished to a surface roughness Ra of 1 μm or less. For example, color mapping can be performed by displaying the first region 1 as blue, the second region 2 as green, the third region 3 as orange, and the fourth region 4 as red.

[0013] Raman imaging is performed on the following first region 1, second region 2, third region 3, and fourth region 4 within the measurement area R. First, the first region 1 is a region of silicon nitride crystal grains with a smaller area ratio between a region of silicon nitride crystal grains oriented in a direction close to the perpendicular direction of the specific cross section and a region of silicon nitride crystal grains oriented in a direction close to the parallel direction of the specific cross section. The second region 2 is a region of silicon nitride crystal grains with a larger area ratio among the multiple silicon nitride crystal grains within the measurement area R. Unless otherwise specified, the following description will be given assuming that the first region 1 is a region of silicon nitride crystal grains oriented in a direction close to the perpendicular direction of the specific cross section and the second region 2 is a region of silicon nitride crystal grains oriented in a direction close to the parallel direction of the specific cross section. The third region 3 is a region of a rare earth element-aluminum-oxygen-based grain boundary phase within the measurement area R. The fourth region 4 is a region of a material consisting of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide within the measurement area R.

[0014] In the silicon nitride sintered body 10 according to the embodiment, the total area ratio of the first region 1, the second region 2, the third region 3, and the fourth region 4 in the measurement area R is in the range of 95% to 100%. In other words, the area ratio of the regions other than the first to fourth regions 1 to 4 is 0% to 5%. It is preferable that the total area ratio of the first region 1, the second region 2, the third region 3, and the fourth region 4 is 100%.

[0015] The first region 1 and the second region 2 are regions of silicon nitride crystal grains. The silicon nitride crystal grains also include sialon crystal grains. The difference between the first region 1 and the second region 2 is the difference in the orientation direction. Figure 2 shows an example of the Raman spectra of the first region 1 and the second region 2. In Figure 2, the vertical axis represents the intensity (relative ratio) and the horizontal axis represents the Raman shift (cm －１ 2, the upper part shows the Raman spectrum of the first region 1 and the lower part shows the Raman spectrum of the second region 2.

[0016] As shown in FIG. 2, in the first region 1 and the second region 2, －１ 230cm or more －１ In the first region 1, the peak on the left side (184-190 cm －１In the second region 2, the middle peak (200 to 210 cm －１ The peak detected at 180 cm －１ 230cm or more －１ The difference in the detection position of the largest peak among the peaks detected between 180 cm and 180 cm is due to the difference in orientation. The orientation of silicon nitride crystal grains is classified as being closer to the vertical direction or the parallel direction by the detection position of the largest peak. －１ 230cm or more －１ Five or more peaks may be detected between

[0017] Silicon nitride crystal particles (including sialon crystal particles) are classified into β-type and α-type. β-type particles are columnar particles. α-type particles are spherical particles. Columnar particles have a relatively large aspect ratio. Spherical particles have a relatively small aspect ratio. α-type particles have an aspect ratio of 1.5 or less.

[0018] The first region 1 is a region of silicon nitride crystal grains oriented in a direction close to the vertical direction of the specific cross section. In this case, the major axes of the β-type columnar particles are oriented in the vertical direction. The first region 1 may also contain at least a portion of α-type spherical particles. Since spherical particles have low orientation, they may be included in either the first region 1 or the second region 2. Furthermore, the orientation direction of the major axes of the β-type columnar particles is not limited to 90° (so-called vertical). 180 cm －１ 230cm or more －１ The determination is made based on the position where the largest peak is detected among the peaks detected between the two points.

[0019] The second region 2 is a region of silicon nitride crystal grains oriented in a direction close to the parallel direction of the specific cross section. In this region, the major axes of the β-type columnar grains are oriented in the parallel direction. The orientation direction of the major axes of the β-type columnar grains is not limited to 180° (so-called parallel). －１ 230cm or more －１ The determination is made based on the position where the largest peak is detected among the peaks detected between the two points.

[0020] The third region 3 is a region of a rare earth element-aluminum-oxygen system grain boundary phase. The rare earth element may be at least one of yttrium and a lanthanoid element. The lanthanoid element may be lanthanum (La), cerium (Ce), erbium (Er), ytterbium (Yb), dysprosium (Dy), lutium (Lu), or europium (Eu).

[0021] The rare earth element-aluminum-oxygen system grain boundary phase indicates a compound in which a rare earth element, aluminum, and oxygen are bonded. The rare earth element-aluminum-oxygen system grain boundary phase may also contain other elements as constituent elements of the rare earth element-aluminum-oxygen system compound. Examples of other constituent elements include nitrogen (N), magnesium (Mg), calcium (Ca), and hafnium (Hf).

[0022] The fourth region 4 is a region of a material consisting of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide. The material consisting of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide in the fourth region 4 is distributed as a metal element or a compound. Examples of the compound include at least one of oxide, nitride, carbide, sulfide, oxynitride, carbonate nitride, and carbonitride. The fourth region 4 may also be distributed within the third region 3. This indicates that the fourth region 4 may also be distributed within the grain boundary phase.

[0023] The area ratios of the first to fourth regions 1 to 4 satisfy the following conditions (A) to (D) when the total area ratios of the first region 1, the second region 2, the third region 3, and the fourth region is taken as 100%. Condition (A): The area ratio of the first region 1 is 0.5% or more and 8% or less. Condition (B): The area ratio of the second region 2 is 70% or more and 92% or less. Condition (C): The area ratio of the third region 3 is 2% or more and 16% or less. Condition (D): The area ratio of the fourth region 4 is 0.5% or more and 8% or less.

[0024] The fact that the first region 1 is 0.5% or more and 8% or less, the second region 2 is 70% or more and 92% or less, the third region 3 is 2% or more and 16% or less, and the fourth region 4 is 0.5% or more and 8% or less indicates that each region is present within the measurement area R.

[0025] The first region 1 and the second region 2 are both silicon nitride crystal grains with different orientation directions. The presence of silicon nitride crystal grains with different orientation directions can improve the strength of the silicon nitride sintered body 10.

[0026] The third region 3 becomes a grain boundary phase that fills the gaps between silicon nitride crystal grains. The presence of the grain boundary phase also improves the strength of the silicon nitride sintered body 10.

[0027] The fourth region 4 serves as a component that strengthens the third region 3. That is, by being distributed in the grain boundary phase, the grain boundary phase can be strengthened.

[0028] It is preferable that the silicon nitride sintered body 10 according to the embodiment further satisfies the following conditions (E) to (F) on a specific cross section. Here, the difference rate of the area ratio is a value obtained by dividing the difference in the area ratio by the average of the area ratio. Condition (E): There is a case where the difference rate of the area ratio between the plurality of first regions 1 between different plurality of measurement areas R is 2% or more. Condition (F): There is a case where the difference rate of the area ratio between the plurality of fourth regions 4 between different plurality of measurement areas R is 2% or more.

[0029] This shows that, when the area ratio of the first regions 1 within the measurement area R is set to 0.5% or more and 8% or less, there are locations where the difference in area ratio between the plurality of first regions 1 between different measurement areas R is 2% or more. Also, when the area ratio of the fourth regions 4 within the measurement area R is set to 0.5% or more and 8% or less, there are locations where the difference in area ratio between the plurality of fourth regions 4 between different measurement areas R is 2% or more. These show that there is variation in the distribution of the first regions 1 and the fourth regions 4 within the measurement area R, and therefore within the silicon nitride sintered body 10. By providing this distribution variation, the machinability of the silicon nitride sintered body 10 can be improved.

[0030] The strength of silicon nitride sintered body 10 is improved by the presence of silicon nitride crystal grains (first region 1 and second region 2) with different orientation directions and a grain boundary phase strengthening component (fourth region 4). A uniform structure, as in Patent Documents 1 and 2, improves mechanical properties such as strength. However, there is a limit to how much improvement can be made in the machinability of silicon nitride sintered body 10. To improve the machinability of silicon nitride sintered body 10 while maintaining strength, it is better to have variation in the distribution of first region 1, second region 2, and fourth region 4.

[0031] It is also preferable that the silicon nitride sintered body 10 further satisfies the following conditions (G) to (H) on a specific cross section: Condition (G): Within 400 μm×400 μm, there is a measurement area R in which the difference in area ratio between a plurality of first regions 1 is 2% or more and the difference in area ratio between a plurality of fourth regions 4 is 2% or more; Condition (H): Within 400 μm×400 μm, there are adjacent measurement areas R in which the difference in area ratio between the first regions 1 is 2% or more and the difference in area ratio between the fourth regions 4 is 2% or more.

[0032] When the above conditions (G) to (H) are satisfied, the distribution variation between the first region 1 and the fourth region 4 within a relatively narrow region of 400 μm × 400 μm can further improve the machinability of the silicon nitride sintered body 10. Furthermore, even in adjacent measurement areas R within 400 μm × 400 μm, it is preferable that there are locations where the difference in area ratio between the first regions 1 is 2% or more and the difference in area ratio between the fourth regions 4 is 2% or more. It is preferable that the upper limit of the difference in area ratio between the first region 1 and the fourth region 4 is 6% or less.

[0033] The measurement area R is divided into four equal parts to form the reduced area. The four reduced areas divided into four from the measurement area R are measured. The measurement area R preferably includes at least one minute area in which the difference in area ratio between the first regions 1 is 2% or more, and the difference in area ratio between the fourth regions 4 is 2% or more. In other words, it is preferable that the difference in area ratio exists while satisfying a predetermined distribution.

[0034] It is preferable that there are multiple first regions 1 in the measurement area R. The presence of multiple first regions 1 in the measurement area R indicates the presence of multiple small first regions 1. The presence of multiple small first regions 1 allows the formation of a structure in which the silicon nitride crystal particles in the second region 2 are intricately intertwined. This further improves the strength of the silicon nitride sintered body 10. There is no particular upper limit on the number of first regions 1 present in the measurement area R, but it is preferable that it be 15 or less. If the number exceeds 15, it may become difficult to control the area ratio of the first regions 1 within the range of 0.5 to 8%. For this reason, it is preferable that the number of first regions 1 in the measurement area R be between 2 and 15.

[0035] It is preferable that a plurality of fourth regions 4 exist in the measurement area R. The presence of a plurality of fourth regions 4 in the measurement area R indicates the presence of a plurality of small fourth regions 4. The fourth regions 4 are components that strengthen the third region (grain boundary phase) 3. The distribution of a plurality of small fourth regions 4 can increase the amount of strengthened grain boundary phase. Furthermore, although there is no particular upper limit on the number of fourth regions 4 present in the measurement area R, it is preferable that it be 30 or less. If the number exceeds 30, it may be difficult to control the area ratio of the fourth regions 4 within the range of 0.5 to 8%. For this reason, it is preferable that the number of fourth regions 4 present in the measurement area R be in the range of 2 to 30.

[0036] The number of first regions 1 and fourth regions 4 is determined using the aforementioned Raman imaging. In the color-mapped image, connected first regions 1 are counted as one. Similarly, connected fourth regions 4 are counted as one in the color-mapped image. Furthermore, the third regions 3, which are made of a rare earth element-aluminum-oxygen-based grain boundary phase, preferably have an amorphous phase. If the grain boundary phase is amorphous, it will easily penetrate into the gaps between silicon nitride crystal grains. This makes it easier to form a silicon nitride sintered body 10 with fewer pores.

[0037] The material comprising at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide present in the fourth region 4 preferably includes a material present as a crystalline compound. A crystalline compound can be easily distributed in the grain boundary phase as small particles, which makes it easier to impart the function of strengthening the grain boundary phase.

[0038] It is preferable that the third region 3 is an amorphous grain boundary phase and the fourth region 4 is a crystalline compound. In this case, it is possible to form a silicon nitride sintered body 10 with few pores and a strengthened grain boundary phase.

[0039] The silicon nitride sintered body 10 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 It can be more than that.

[0040] The three-point bending strength is measured in accordance with JIS-R-1601 (2008). JIS-R-1601 corresponds to ISO 14704. The fracture toughness value 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.

[0041] The silicon nitride sintered body 10 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.

[0042] 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 10, the entire spherical surface serves as the sliding surface. In the case of a roll made of a cylindrical silicon nitride sintered body 10, the roll surface serves as the sliding surface.

[0043] To improve the wear resistance of the sliding surface, it is effective to polish the surface to a surface roughness Ra of 0.1 μm or less. The silicon nitride sintered body 10 according to the embodiment controls the area ratio of the first to fourth regions 1-4, and then provides variation in the distribution of the first region 1 and the fourth region 4. This improves machinability. For example, the surface roughness of bearing balls is specified in ASTM F2094. Bearing balls are graded according to ASTM F2094, ISO 26602, or JIS R1669 depending on the application. They are polished to a surface roughness Ra according to that grade. Higher grades may be mirror-finished to a surface roughness Ra of 0.01 μm or less. The silicon nitride sintered body 10 according to the embodiment maintains wear resistance while improving machinability. The polishing process to obtain a sliding surface with a surface roughness Ra of 0.1 μm or less can be efficiently performed.

[0044] FIG. 4 shows an example of a bearing ball, and FIG. 5 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. 5(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. 5(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. 5 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. The base sphere 6 is the one before being polished to form a bearing ball 5.

[0045] Next, a method for manufacturing the silicon nitride sintered body 10 according to the embodiment will be described. The method for manufacturing the silicon nitride sintered body 10 according to the embodiment is not particularly limited as long as it has the above-described configuration, but the method for obtaining the silicon nitride sintered body 10 with a good yield is as follows.

[0046] 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. Furthermore, it is preferable that the oxygen content be 3 mass% or less and the alpha conversion rate be 90% or more.

[0047] The sintering aid powder may be a rare earth element powder, an aluminum powder, or at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide powder. The sintering aid powder preferably has an average particle size of 4 μm or less.

[0048] It is also preferable that the average particle size of the silicon nitride powder and the sintering aid powder are different from each other. It is also preferable that the average particle size of the silicon nitride powder is smaller than that of the sintering aid powder. By making the average particle sizes different, it is possible to create differences in the area ratio between the multiple first regions 1 and the area ratio between the multiple fourth regions 4.

[0049] The rare earth element component powder includes powders of oxides, nitrides, and oxynitrides of rare earth elements. Furthermore, yttrium and lanthanoid elements are preferred as rare earth elements. The aluminum component powder includes powders of oxides, nitrides, and oxynitrides of aluminum. Furthermore, the aluminum component powder includes at least aluminum oxide (Al ２ O ３ It is preferable to use powder of

[0050] It is also preferable to use both a rare earth oxide powder and an aluminum oxide powder. This allows the formation of a rare earth element-aluminum-oxygen grain boundary phase, which becomes the third region. Furthermore, by using oxygen as a constituent element, the rare earth element-aluminum-oxygen grain boundary phase can be made into an amorphous phase.

[0051] The powder of at least one of titanium, hafnium, tungsten, and molybdenum may be an oxide, nitride, carbide, oxynitride, oxycarbide, or carbonitride. Silicon carbide is preferably added as silicon carbide powder. These components form the fourth region.

[0052] Among these, oxides or carbides are preferred. Examples of oxides include titanium oxide (TiO ２ ), hafnium oxide (HfO ２ ), tungsten oxide (WO ３ ), molybdenum oxide (MoO３ If it is an oxide, it will react with silicon nitride to form a nitride. For example, titanium oxide (TiO ２ ) becomes titanium nitride (TiN). At this time, it can be distributed in the grain boundary phase as titanium nitride particles. This strengthens the grain boundary phase. In addition, by converting oxides into nitrides, it can become a crystalline phase.

[0053] Carbides include titanium carbide (TiC), hafnium carbide (HfC), tungsten carbide (WC), and molybdenum carbide (Mo ２ C). Carbide particles act as a component that strengthens the grain boundary phase. Silicon carbide acts as a component that strengthens the grain boundary phase as SiC particles. Therefore, by adding carbide particles, which are crystalline compounds, they can be distributed as crystalline compounds. The same applies when added as nitrides.

[0054] When "silicon nitride powder" + "rare earth element component powder" + "aluminum component powder" + "powder of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide components" is taken as 100% by mass, it is preferable that the "rare earth element component powder" be 1% by mass or more and 13% by mass or less, the "aluminum component powder" be 1% by mass or more and 10% by mass or less, the "powder of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide components" be 0.1% by mass or more and 7% by mass or less, and the remainder be "silicon nitride powder." Controlling the mixing ratio leads to controlling the area ratios of the first to fourth regions.

[0055] Next, a step of mixing the raw material powders is performed. The mixing step is performed using a grinder such as a ball mill. The ball mill can mix the raw material powder with media to crush the raw material powder. Crushing the raw material powder can suppress the generation of agglomerates. The ball mill may be either a wet or dry type. It is also preferable to mix materials under different ball mill conditions. The ball mill conditions include the rotation speed of the ball mill, the amount of raw material powder added, and the processing time. The difference between wet and dry milling may also be used. Mixing materials under different conditions means mixing raw material powder processed under first conditions with raw material powder processed under second conditions. There may be three or more raw material powders under different conditions.

[0056] By mixing raw material powders having different crushed states, it is possible to create differences in the area ratio between the plurality of first regions 1 and the area ratio between the plurality of fourth regions 4. Furthermore, the mixing step may be performed by adding an organic binder or a solvent to the raw material powder, as necessary.

[0057] Next, a molding process is carried out using the raw material powder that has been mixed to obtain a silicon nitride molded body (hereinafter simply referred to as a "molded body"). The molding process can be carried out by die molding, rolling granulation, cold isostatic pressing (CIP), doctor blade method, injection molding, or the like. When producing spheres, die molding, rolling granulation, or CIP is preferably used. It is also effective to CIP the molded body obtained by die molding or rolling granulation. CIP is a molding method that uses a liquid as the pressurizing medium. Because isotropic pressurization is performed by the liquid, a molded body with a uniform density distribution can be obtained. The CIP pressure is preferably in the range of 50 MPa to 500 MPa.

[0058] 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.

[0059] 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.

[0060] Next, the compact, for example, the degreased body, is subjected to a sintering process. The sintering process is preferably performed at a temperature in the range of 1600°C to 2000°C. 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. Pressure sintering refers to sintering at atmospheric pressure (1 atm = 0.1 MPa). Pressure sintering refers to sintering by applying a pressure higher than atmospheric pressure. Uniaxial pressure sintering is sometimes called hot pressing. HIP is a sintering method that uses gas isostatic pressing.

[0061] This reduces internal defects such as voids and cracks in the silicon nitride sintered body 10. The HIP is preferably performed at a pressure in the range of 10 MPa to 200 MPa. Alternatively, atmospheric pressure sintering, pressure sintering, and HIP may be combined. When used for a wear-resistant member, it is preferable to use either one or both of pressure sintering and HIP. Sintering under pressure makes it possible to obtain a silicon nitride sintered body 10 (e.g., a raw sphere 6) with few internal defects.

[0062] The sintering step can produce a silicon nitride sintered body 10. A wear-resistant member is produced by polishing the sliding surface of the silicon nitride sintered body 10. For example, in the case of a ball-shaped silicon nitride sintered body 10 (e.g., base ball 6) for producing a bearing ball, the entire surface becomes the sliding surface.

[0063] The surface roughness Ra of the sliding surface of the silicon nitride sintered body 10 is preferably 0.1 μm or less. By making the surface of the silicon nitride sintered body 10 substantially flat, the wear resistance of the silicon nitride sintered body 10 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 10 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 10 can be shortened.

[0064] Furthermore, it is possible to improve the durability of the grindstone used to polish the silicon nitride sintered body 10. Diamond grindstones are generally used in the polishing process of the silicon nitride sintered body 10. 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 10 with improved processability.

[0065] Examples (Examples 1 to 5, Comparative Examples 1 to 2) Silicon nitride powder and sintering aid powder were prepared as raw material powders. The raw material powders for the silicon nitride sintered bodies 10 according to Examples 1 to 5 and the raw material powders for the silicon nitride sintered bodies 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%. In the examples, the silicon nitride powder used had an average particle size smaller than that of the sintering aid powder.

[0066]

[0067] The raw material powders were mixed using a ball mill. The mixing corresponding to the examples was performed under different ball mill conditions. The mixing corresponding to the comparative examples was performed using only the same ball mill conditions. An organic binder and a solvent were added to the raw material powders and mixed in a 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 then subjected to a drying process and a debinding process. The drying process was performed at 120°C. The debinding process was performed in the range of 400 to 650°C. The resulting debound compacts were then subjected to a sintering process. The sintering process was performed in two stages. The sintering conditions are as shown in Table 2.

[0068]

[0069] The above steps resulted in the production of a silicon nitride sintered body 10 according to the example and a silicon nitride sintered body according to the comparative example. A specific cross section of the resulting silicon nitride sintered body (e.g., a bare sphere) was subjected to Raman imaging measurement. A measurement area R was set from a cross-sectional structure of 400 μm × 400 μm. A reduced area was also set by dividing the measurement area R into four equal parts. The measurement conditions were as described above. The area ratios of each of regions 1 to 4 are those when the total area ratio of the first region 1, second region 2, third region 3, and fourth region 4 is 100%. The results are shown in Table 3. In Table 3, the area ratios that satisfy the conditions are marked "YES," and the area ratios that do not satisfy the conditions are marked "NO."

[0070]

[0071] The first region 1 is a region of silicon nitride crystal grains oriented in a direction close to the perpendicular direction of the specific cross section. The second region 2 is a region of silicon nitride crystal grains oriented in a direction close to the parallel direction of the specific cross section. The third region 3 is a region of a rare earth element-aluminum-oxygen system grain boundary phase. The fourth region 4 is a region of a material consisting of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide.

[0072] The Raman shift of the first region 1 is 180 cm －１More than 230cm －１ As shown in Figure 2, there are four peaks detected between －１ The Raman shift of the second region 2 was the largest at 180 cm －１ More than 230cm －１ As shown in Figure 2, there are three peaks detected between －１ The highest incidence was detected in

[0073] As shown in Table 3, the blank spheres 6 according to Examples 1 to 5 satisfied the above-mentioned conditions (A) to (D) for the area ratio, i.e., the area ratio of the first region 1 was 0.5% or more and 8% or less, the area ratio of the second region 2 was 70% or more and 92% or less, the area ratio of the third region 3 was 2% or more and 16% or less, and the area ratio of the fourth region 4 was 0.5% or more and 8% or less. Furthermore, the blank spheres 6 according to Examples 1 to 5 also satisfied the above-mentioned conditions (A) to (D) in another measurement area R. Furthermore, the blank spheres 6 according to Examples 1 to 5 also satisfied the above-mentioned conditions (E) to (F) for the difference rate of the area ratio, i.e., there was at least one region in the cross-sectional structure of 400 μm × 400 μm in the first region 1 and the fourth region 4 where the variation in the area ratio was 2% or more.

[0074] On the other hand, as shown in Table 3, the blank ball according to Comparative Example 1 satisfied the area ratio conditions (A) to (D), as did the blank ball 6 according to Examples 1 to 5. However, in the blank ball according to Comparative Example 1, the area ratio conditions (E) to (F), i.e., the variation in the first region 1 and the fourth region 4, was less than 2%. In other words, the blank ball according to Comparative Example 2 had a uniform structure with little variation. Furthermore, although the blank ball according to Comparative Example 2 satisfied conditions (B) to (F), there were some locations where the area ratio of the first region 1 exceeded 8%.

[0075] Next, the presence or absence of an amorphous phase in the third region and the presence or absence of a crystalline compound in the fourth region were examined for the blank spheres 6 of Examples 1 to 5 and the blank spheres of Examples 1 and 2. The presence or absence of a difference in the area ratio between the first region 1 and the fourth region 4 between adjacent reduced areas was also examined. The results are shown in Table 4.

[0076]

[0077] In both the example and the comparative example, the rare earth element-aluminum-oxygen system grain boundary phase (third region 3) contained amorphous phase portions.

[0078] Furthermore, in both the example and the comparative example, crystalline compounds were present in the fourth region 4. Titanium nitride (TiN) crystal particles were present in the element balls 6 of examples 1, 3, and 5 and the element balls of comparative examples 1 and 2. Tungsten carbide (WC) crystal particles were present in the element ball 6 of example 2. Molybdenum carbide (Mo) crystal particles were present in the element ball 6 of example 4. ２ C) Crystal grains and silicon carbide (SiC) crystal grains were present. In the examples, there was a measurement area R in which the difference in area ratio between the first region and the fourth region was 2% or more (condition (G)), and there were adjacent measurement areas R in which the difference in area ratio between the first region and the fourth region was 2% or more (condition (H)). Furthermore, in the reduced areas obtained by dividing the measurement area R into four, there were also regions in which the difference in area ratio between the first region and the fourth region was 2% or more.

[0079] Furthermore, because the base sphere of Comparative Example 1 had a uniform structure, there were no adjacent reduced areas in which the difference in area ratio of the first region 1 was 2% or more, or no areas in which the difference in area ratio of the fourth region 4 was 2% or more, or both.

[0080] 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 9.5250 mm). Furthermore, both blank balls had a band-like portion on the circumference of the sphere.

[0081] Next, the base ball 6 of the example and the base ball of 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 for the base ball 6 of the example were expressed as a ratio, with the replacement interval of the diamond grinding wheel for the base ball of comparative example 1 being set at 100. The larger the number, the longer the replacement interval of the grinding wheel and the better the durability of the grinding wheel. The results are shown in Table 5.

[0082]

[0083] As can be seen from Table 5, the grinding wheel replacement interval for the blank balls according to the examples was improved by about 10%, and the machinability was improved. This is because the grinding wheel durability was improved due to the improved machinability.

[0084] Furthermore, the durability of the bearing balls obtained by polishing in the examples and comparative examples was evaluated. In the durability test, the rolling life was measured using a thrust-type rolling fatigue tester under conditions of a maximum contact pressure of 5.9 GPa and a rotational speed of 1200 rpm. The mating member was a plate made of bearing steel SUJ2. The measurement time was 400 hours, and the presence or absence of surface peeling of the bearing balls was measured. No surface peeling was observed in bearing ball 5 of examples 1 to 5 and the bearing ball of comparative example 1. On the other hand, some surface peeling was observed in the bearing ball of comparative example 2. As a result, it was found that the durability of the bearing balls obtained by polishing in the examples was good.

[0085] In the examples and comparative examples, it was confirmed that the workability of the base sphere 6 (which becomes a bearing ball after polishing) is improved, which is an example of the silicon nitride sintered body 10. However, this effect is not limited to the case where the silicon nitride sintered body 10 is the base sphere 6, and it is believed that this effect can also be obtained with silicon nitride sintered body 10 other than the base sphere 6 (which becomes a wear-resistant member other than a bearing ball after polishing) as long as the above conditions (A) to (F) are satisfied.

[0086] According to at least one of the embodiments described above, it is possible to provide a silicon nitride sintered body 10 (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 10, it is possible to provide a silicon nitride sintered body 10 with improved processability while maintaining wear resistance, and a wear-resistant member using the same.

[0087] 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. By Raman imaging in a measurement area of 20 μm × 20 μm on a specific cross-section of a silicon nitride sintered body, (1) taking the region of silicon nitride crystal particles oriented in a direction close to the vertical direction of the specific cross-section within the measurement area and the region of silicon nitride crystal particles oriented in a direction close to the parallel direction of the specific cross-section, and designating the region of silicon nitride crystal particles with the smaller area ratio as the first region, (2) designating the region of silicon nitride crystal particles with the larger area ratio as the second region, (3) designating the region of a rare earth element-aluminum-oxygen-based grain boundary phase within the measurement area as the third region, and (4) mapping the region of a substance composed of at least one or more of titanium, hafnium, tungsten, molybdenum, and silicon carbide within the measurement area as the fourth region, when the sum of the area ratios of the first region, the second region, the third region, and the fourth region is 100%, the area ratios of the first region, the second region, the third region, and the fourth region are respectively 0.5% or more and 8% or less, 70% or more and 92% or less, 2% or more and 16% or less, and 0.5% or more and 8% or less, and there may be a case where the difference rate of the area ratios of a plurality of the first regions is 2% or more between different measurement areas, and there may be a case where the difference rate of the area ratios of a plurality of the fourth regions is 2% or more. A silicon nitride sintered body characterized by this.

2. Among 400 μm × 400 μm on the specific cross-section, there is a measurement area where the difference rate of the area ratios of the first regions is 2% or more and the difference rate of the area ratios of the fourth regions is 2% or more. The silicon nitride sintered body according to claim 1, characterized by this.

3. The silicon nitride sintered body according to claim 1 or claim 2, characterized in that there are a plurality of the first regions in the measurement area.

4. The silicon nitride sintered body according to claim 1 or claim 2, characterized in that there are a plurality of the fourth regions in the measurement area.

5. The silicon nitride sintered body according to claim 3, characterized in that there are a plurality of the fourth regions in the measurement area.

6. The silicon nitride sintered body according to claim 1 or claim 2, characterized in that the third region has an amorphous phase.

7. The silicon nitride sintered body according to claim 5, characterized in that the third region has an amorphous phase.

8. The silicon nitride sintered body according to claim 1 or claim 2, wherein the substance composed of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide present in the fourth region includes those present as crystalline compounds.

9. The silicon nitride sintered body according to claim 5, wherein the substance composed of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide present in the fourth region includes those present as crystalline compounds.

10. The silicon nitride sintered body according to claim 7, wherein the substance composed of at least one of titanium, hafnium, tungsten, molybdenum, and silicon carbide present in the fourth region includes those present as crystalline compounds.

11. An abrasion-resistant member characterized by being made of the silicon nitride sintered body according to claim 1 or claim 2.

12. An abrasion-resistant member characterized by being made of the silicon nitride sintered body according to claim 5.

13. An abrasion-resistant member characterized by being made of the silicon nitride sintered body according to claim 7.

14. An abrasion-resistant member characterized by being made of the silicon nitride sintered body according to claim 10.

15. The abrasion-resistant member according to claim 11, characterized by having a sliding surface with a surface roughness Ra of 0.1 μm or less.

16. The abrasion-resistant member according to claim 12, characterized by having a sliding surface with a surface roughness Ra of 0.1 μm or less.

17. The abrasion-resistant member according to claim 13, characterized by having a sliding surface with a surface roughness Ra of 0.1 μm or less.

18. The abrasion-resistant member according to claim 15, characterized in that the abrasion-resistant member is a bearing ball.

19. The abrasion-resistant member according to claim 16, characterized in that the abrasion-resistant member is a bearing ball.

20. The abrasion-resistant member according to claim 17, characterized in that the abrasion-resistant member is a bearing ball.

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