Method for manufacturing a sliding member made of silicon nitride sintered body

Abstract

To provide a manufacturing method for a slide member made from a silicon nitride sintered body, capable of manufacturing a slide member showing stable durability even if a load is changed.SOLUTION: A manufacturing method related to one embodiment includes: a cracking step of obtaining a raw material blend by cracking and blending a silicon nitride powder, a sintering aid powder, and a binder; a molding step of molding the raw material blend; a degreasing step of obtaining a degreased body by degreasing the molded body; a sintering step of obtaining a silicon nitride sintered body by sintering the degreased body; a step of performing HIP treatment to the silicon nitride sintered body; and a processing step of processing the silicon nitride sintered body into a slide member. The sintering step is performed in a non-oxidative atmosphere and at a sintering temperature of 1650-2000°C. In the sintering step, changes in pressure due to a gas generated from the degreased body is 0.3 MPa or under. In any given 50-μm2 observation region of a specific cross section or surface, the slide member displays a ratio of 0-10% for silicon nitride crystal grains with internal dislocation defects out of any 50 silicon nitride crystal grains with their entire contours visible.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiments relate to a method for producing a sliding member made of a silicon nitride sintered body. [Background technology]

[0002] Wear-resistant sliding members made of silicon nitride sintered bodies are used in a variety of fields, including various roll materials for rolling mills, engine parts such as cam rollers, bearing members, compressor vanes, gas turbine blades, and friction stir welding tool members. These are used as members that slide against mating members. Silicon nitride sintered bodies are required to have strength and wear resistance. For example, Japanese Patent No. 5380277 (Patent Document 1) discloses a silicon nitride sintered body in which the silicon nitride crystal grain size and void size are controlled. The silicon nitride sintered body of Patent Document 1 has improved both strength and wear resistance. As a result, Patent Document 1 achieves a rolling life of more than 600 hours. Electric vehicles have become popular in recent years. Inverter-driven motors are now the norm for electric vehicles. With inverter-driven motors, the rotation speed of the motor can be changed by changing the frequency of the power supply that drives the motor. In other words, with inverter-driven motors, the rotation speed of the motor can be changed. Inverter-driven motors are becoming more common in a variety of fields, including electric vehicles and industrial equipment. By adopting inverter drive, the motor's rotation speed can be changed from 1,000 rpm to a maximum of around 15,000 rpm. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5380277 Summary of the Invention [Problem to be solved by the invention]

[0004] As mentioned above, inverter drive is a drive method that allows the rotational speed of a motor to be changed. In Patent Document 1, the durability test for bearing balls was conducted under conditions of a maximum contact pressure of 5.9 MPa and a rotational speed of 1200 rpm. Conventional durability tests are conducted at a constant rotational speed. With the spread of inverter drive, motors are increasingly being driven while varying their rotational speed. When the rotational speed changes, the load on the bearing balls and bearings becomes unstable. Conventional bearing balls made of sintered silicon nitride exhibited variations in durability when used in environments where the load changes. Furthermore, problems such as electrolytic corrosion also occurred. The present invention has been made to address such problems, and an object of the present invention is to provide a method for manufacturing a slide member made of a silicon nitride sintered body, which is capable of manufacturing a slide member that exhibits stable durability even when the load changes. [Means for solving the problem]

[0005] A method for producing a silicon nitride sintered sliding member according to an embodiment includes the following steps: a crushing step in which silicon nitride powder, sintering aid powder, and binder are crushed and mixed using a crusher to obtain a raw material mixture; a molding step in which the raw material mixture is molded; a degreasing step in which the molded body is degreased to obtain a degreased body; a sintering step in which the degreased body is sintered to obtain a silicon nitride sintered body; a hot isostatic pressing (HIP) step in which the silicon nitride sintered body is processed into a sliding member. The sintering step is carried out in a non-oxidizing atmosphere at a sintering temperature of 1650°C to 2000°C. The pressure change due to gas generated from the degreased body during the sintering step is 0.3 MPa or less. In the sliding member, the percentage of silicon nitride crystal grains having internal dislocation defects is 0% to 10% of any 50 silicon nitride crystal grains whose entire contours are visible in a 50 μm × 50 μm observation area on any cross section or surface. [Effects of the Invention]

[0006] The slide member manufactured by the method for manufacturing a slide member made of sintered silicon nitride according to the embodiment has a reduced proportion of silicon nitride crystal grains having dislocation defects. This allows the slide member to have excellent durability even when sliding conditions such as the rotation speed change. Furthermore, the occurrence of electrolytic corrosion can be suppressed. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a conceptual diagram illustrating a silicon nitride crystal grain having dislocation defects. [Figure 2] FIG. 2 is a conceptual diagram illustrating the major axis of a silicon nitride crystal particle. [Figure 3] FIG. 1 is a conceptual diagram showing an example of a bearing. [Figure 4] FIG. 1 is a conceptual diagram showing an example of a motor and a drive device including the motor. DETAILED DESCRIPTION OF THE INVENTION

[0008] The slide member manufactured by the method for manufacturing a slide member made of sintered silicon nitride according to the embodiment has a reduced proportion of silicon nitride crystal grains having dislocation defects. This allows the slide member to have excellent durability even when sliding conditions such as the rotation speed change. Furthermore, the occurrence of electrolytic corrosion can be suppressed.

[0009] Silicon nitride sintered bodies have silicon nitride crystal grains and a grain boundary phase. The grain boundary phase is mainly composed of sintering aid components. The grain boundary phase is formed by a reaction of the sintering aid during the sintering process. The reaction occurs between sintering aids, between the sintering aid and silicon nitride, or between the sintering aid and impurity oxygen. The sliding member according to the embodiment is characterized in that, in an observation area of ​​50 μm × 50 μm on any cross section or surface, the proportion of the number of silicon nitride crystal grains having dislocation defects therein is 0% or more and 10% or less among any 50 silicon nitride crystal grains whose entire contours are visible.

[0010] For the observation of dislocation defects, any cross section or surface of the silicon nitride sintered body is used. First, any cross section or surface of the silicon nitride sintered body is processed by ion milling or FIB (focused ion beam) processing so that the surface roughness Ra is 1 μm or less. The processed cross section or surface is used as the evaluation surface. Next, the evaluation surface is observed using a transmission electron microscope (TEM). The magnification during evaluation using a TEM is set to 10,000x or more. The area of ​​the evaluation surface is set to 50μm x 50μm. If it is not possible to observe a 50μm x 50μm area in a single field of view, the evaluation surface may be divided into multiple areas for observation. For example, observation may be performed in a field of view of 10μm x 10μm or less. For evaluation, after observing one observation area (50μm x 50μm), another area located 1000μm or more away from that area is observed. In other words, two or more 50μm x 50μm areas are observed, and the percentage of silicon nitride crystal grains with dislocation defects (defect particles) is calculated. The presence or absence of dislocation defects is determined by observing the TEM image in both dark and bright fields. Dislocation defects appear white in the dark field and appear inverted black in the bright field. In this way, the areas where the pixel color inverts when switching between dark and bright fields are considered to be dislocation defects.

[0011] Fig. 1 is a conceptual diagram illustrating a silicon nitride crystal grain having a dislocation defect. In Fig. 1, 1 is a silicon nitride crystal grain, and 2 is a dislocation defect. As shown in Fig. 1, in the silicon nitride sintered body of the slide member according to the embodiment, a dislocation defect 2 can exist inside the silicon nitride crystal grain 1. If dislocation defects exist within silicon nitride crystal grains, durability will decrease when sliding conditions change. Dislocation defects are crystal defects contained within crystals. Crystal defects are also called lattice defects. Crystal defects are caused by disturbances in the atomic arrangement or impurities. Dislocation defects cause defects in a stable crystal structure. For example, the rotational speed of an inverter-driven motor varies between 0 rpm and 15,000 rpm. A rotational speed of 0 rpm is when the motor is stopped. Inverter-driven motors can be driven while varying their rotational speed between 50 and 15,000 rpm. Accordingly, the load on the bearing balls used in the motor's bearings also varies. It has been found that when a strong load, such as that of a bearing ball, is applied to a silicon nitride sintered body, dislocation defects affect its durability. Silicon nitride sintered bodies are high-strength and highly wear-resistant materials. As in Patent Document 1, there are no problems when the surface of a sliding member slides against a mating member at a constant rotational speed. However, it has been found that if the sliding member slides while the load is applied in a changing manner, this affects the long-term life of the sliding member. The vibration frequency of a motor changes depending on the rotational speed. In other words, when the rotational speed changes, the vibration frequency also changes. Motor vibration leads to bearing vibration. Bearings resonate at a specific vibration frequency. Resonance is a phenomenon in which the amplitude of vibration increases when vibration equal to the natural frequency is applied to a vibrating body from the outside. Resonance occurs when the vibration frequency of a bearing is close to the natural frequency of the bearing. Under resonance, the load on the rolling elements (bearing balls) increases. In inverter-driven motors, the vibration frequency changes. If the vibration frequency passes through the vibration frequency band that causes bearing resonance during the process of changing, the load on the rolling elements increases. In this way, when the rotational speed changes, the sliding conditions change. As mentioned above, dislocation defects are crystal defects. Although they do not cause problems when the load applied to the silicon nitride sintered body is small, they do have an effect when the load applied to the silicon nitride sintered body is large. This is because silicon nitride sintered bodies with dislocation defects and silicon nitride sintered bodies without dislocation defects receive stress differently. In the silicon nitride sintered body of the sliding member according to the embodiment, the proportion of silicon nitride crystal grains having dislocation defects in any 50 μm × 50 μm microscopic region is 0% to 10%. The fact that the proportion in any 50 μm × 50 μm observation region is 0% to 10% means that the proportion is 0% to 10% no matter which 50 μm × 50 μm region is observed.

[0012] If the proportion of silicon nitride crystal grains with dislocation defects exceeds 10%, electrolytic corrosion becomes more likely to occur. When a bearing is placed near inverter-driven equipment or equipment that generates high frequency, current flows inside the bearing due to the influence of electromagnetic noise. This current damages the bearing raceway surface, a phenomenon known as electrolytic corrosion. The inside of the bearing is insulated by grease, etc., but if the current exceeds a certain level, a discharge phenomenon occurs. Dislocation defects in silicon nitride crystal grains are crystal defects. Potential differences are likely to occur at crystal defects, which are thought to easily serve as electrical discharge paths. When the proportion of silicon nitride crystal grains with dislocation defects exceeds 10%, the dislocation defects in the silicon nitride sintered body become electrical discharge paths, making it easier for electrical corrosion to occur on the bearing raceway.

[0013] Generally, the inside of a bearing (between the inner and outer rings) is filled with grease. Grease can improve the lubrication, heat resistance, water resistance, etc. of the bearing. When a motor is driven by an inverter, a voltage is generated on the rotating shaft. This voltage causes dielectric breakdown in the grease inside the bearing, resulting in electrolytic corrosion. Silicon nitride sintered body is an insulator, and its volume resistivity is 1 x 10 at room temperature. 14 Ω·cm or more. Insulators polarize when an electric field is applied. In inverter drive, the rotation speed can be changed by changing the frequency. For this reason, an AC electric field is generated in the inverter. Dislocation defects have defects. For this reason, electric field differences due to polarization phenomena are likely to occur. In the sliding member according to the embodiment, the number of dislocation defects is small, so the occurrence of electric field differences can be suppressed. Therefore, among the silicon nitride crystal grains present in a 50 μm × 50 μm observation area, the percentage of silicon nitride crystal grains with internal dislocation defects is preferably 0% to 10%, and even more preferably 0% to 3%. Most preferably, this percentage is 0%. In other words, the absence of silicon nitride crystal grains with dislocation defects enhances the effects of improving durability and suppressing electrolytic corrosion. Two or more regions separated by 1000 μm or more are observed. Furthermore, in a TEM photograph of at least a portion of the 50 μm × 50 μm observation area, silicon nitride crystal grains whose outlines are not fully visible are not used in calculating the number percentage. For example, silicon nitride crystal grains whose outlines are cut off at the edge of the photograph are not used in calculating the number percentage. Furthermore, once 50 silicon nitride crystal grains with their entire outlines visible have been confirmed, the percentage of silicon nitride crystal grains with dislocation defects among those 50 silicon nitride crystal grains is calculated. In other words, observations are continued until 50 silicon nitride crystal grains with their entire outlines visible have been confirmed. If 50 silicon nitride crystal particles with their entire outlines cannot be observed in one 50 μm × 50 μm observation area, 50 silicon nitride crystal particles with their entire outlines are observed in another 50 μm × 50 μm observation area. If more than 50 silicon nitride crystal particles are observed in a 50 μm × 50 μm observation area, 50 silicon nitride crystal particles are arbitrarily selected. The magnification for TEM observation of individual silicon nitride crystal particles is 10,000x. If a single silicon nitride crystal particle cannot fit in a single image, multiple images may be taken. In the silicon nitride sintered body for a sliding member according to the embodiment, the proportion of silicon nitride crystal particles with dislocation defects among any 50 silicon nitride crystal particles is 0% or more and 10% or less. This indicates that when more than 50 silicon nitride crystal grains are observed in an observation area of ​​50 μm × 50 μm, the proportion of silicon nitride crystal grains having dislocation defects is between 0% and 10%, regardless of which 50 silicon nitride crystal grains are selected.

[0014] In addition, at the dislocation defect, the components other than silicon, oxygen, and nitrogen are 1 μm 2It is preferable that the dislocation defects do not contain more than 10 mol % of components other than silicon, oxygen, and nitrogen. The components excluding silicon, oxygen, and nitrogen are the components that make up the grain boundary phase. The grain boundary phase is mainly composed of sintering aids. Therefore, the components excluding silicon, oxygen, and nitrogen correspond to the metal components of the sintering aid. For example, if yttrium oxide (Y2O3) is used as the sintering aid, the components excluding silicon, oxygen, and nitrogen are yttrium (Y). In addition, the components other than silicon, oxygen and nitrogen are 1 μm 2 The fact that the metal components that make up the grain boundary phase are not in a mass of 1 μm or more at the dislocation defect site means that 2 Less than (0 μm 2 Even when multiple sintering aids are used, the components other than silicon, oxygen, and nitrogen are within 1 μm. 2 It is preferable that the sintering aid components do not form nuclei for dislocation defects. Furthermore, the fact that components other than silicon, oxygen, and nitrogen are not detected at 10 mol% or more indicates that the metal components of the sintering aid are less than 10 mol% (including 0 mol%) in the dislocation defects. For example, when yttrium oxide (YO) is used as the sintering aid, this indicates that the yttrium (Y) is less than 10 mol% (including 0 mol%) in the dislocation defects. Furthermore, when multiple sintering aids are used, it is preferable that the total metal components of the sintering aids be less than 10 mol%. This indicates that the sintering aid components are not forming nuclei in the dislocation defects. In addition, the dislocation defect area is a region where the metal components that make up the grain boundary phase are 1 μm 2 Less than (0 μm 2 It is preferable that the content of the hydroxybenzoates is 10 mol % or less (including 0 mol %) and 10 mol % or less (including 0 mol %).

[0015] Since the sintering aid components do not become the nuclei of dislocation defects, resistance to electrolytic corrosion is improved. Furthermore, when a discharge phenomenon that leads to electrolytic corrosion occurs, heat is generated. Because the sintering aid components form compounds with low melting points, they are prone to internal fracture of silicon nitride crystal particles. Therefore, it is preferable that the sintering aid components do not become the nuclei of dislocation defects. The size and concentration of components other than silicon, oxygen, and nitrogen in dislocation defects are analyzed by EDX (energy dispersive X-ray analysis) or WDS (wavelength dispersive X-ray analysis). Analysis may also be performed in combination with EPMA (electron probe microanalyzer).

[0016] Furthermore, the ratio of the number of silicon nitride crystal grains with dislocation defects occupying an area ratio of 5% or less to the number of silicon nitride crystal grains with dislocation defects is preferably 70% or more. As mentioned above, if the number of silicon nitride crystal grains with dislocation defects is small, they will not cause electrolytic corrosion. On the other hand, if a single silicon nitride crystal grain contains large dislocation defects, mechanical durability may be reduced. For this reason, the area ratio of dislocation defects within a single silicon nitride crystal grain is preferably 5% or less. Furthermore, if the ratio of the number of silicon nitride crystal grains with dislocation defects occupying an area ratio of 5% or less to the number of silicon nitride crystal grains with dislocation defects is 70% or more, the effects of improving durability and suppressing electrolytic corrosion can be enhanced. This ratio is also determined within an observation area of ​​50 μm × 50 μm. Specifically, first, 50 random silicon nitride crystal particles whose entire contours are visible are observed in one 50 μm × 50 μm observation region. Next, the presence of dislocation defects is confirmed in each of the 50 observed silicon nitride crystal particles. The proportion of silicon nitride crystal particles having dislocation defects among the 50 observed silicon nitride crystal particles is calculated. This proportion is preferably between 0% and 10%. Next, if silicon nitride crystal particles having dislocation defects are present, the area ratio of dislocation defects is calculated for each of those silicon nitride crystal particles. The proportion of silicon nitride crystal particles whose area ratio of dislocation defects is 5% or less is calculated relative to the number of silicon nitride crystal particles having dislocation defects. This proportion is preferably 70% or more. If there are no 50 silicon nitride crystal particles whose entire contours are visible in one 50 μm × 50 μm observation region, 50 silicon nitride crystal particles whose entire contours are visible are searched for in another 50 μm × 50 μm observation region. After measuring the proportion of silicon nitride crystal grains with dislocation defects and the area ratio of dislocation defects in a 50 μm × 50 μm observation area, another 50 μm × 50 μm observation area at least 1000 μm away from the first observation area is observed. In the silicon nitride sintered body of the sliding member according to the embodiment, in any 50 μm × 50 μm observation area in any cross section, the proportion of silicon nitride crystal grains with dislocation defects is between 0% and 10%. Furthermore, the proportion of silicon nitride crystal grains with an area ratio of dislocation defects of 5% or less is 70% or more. In other words, the size of dislocation defects in silicon nitride crystal grains is controlled even in a tiny 50 μm × 50 μm area.

[0017] Furthermore, the dark-field image of the TEM photograph mentioned above is used to measure the area ratio of dislocation defects within a single silicon nitride crystal grain. In a dark-field image, dislocation defects appear white. The total area of ​​the white and black regions of a single silicon nitride crystal grain observed in the dark-field image is taken to be the area of ​​that silicon nitride crystal grain. The area of ​​the white regions in the dark-field image is taken to be the area of ​​dislocation defects. The area ratio of dislocation defects is calculated as (area of ​​dislocation defects / area of ​​silicon nitride crystal grain) x 100 (%). Furthermore, image processing software is used to measure this area ratio. Image analysis software such as Image-j or software with equivalent or higher resolution is used. The percentage of silicon nitride crystal grains with an area ratio of dislocation defects of 5% or less is calculated by photographing 50 silicon nitride crystal grains whose outlines are all visible in an observation area of ​​50 μm×50 μm.

[0018] In addition, in an observation area of ​​300 μm×300 μm of any cross section of the silicon nitride sintered body, the major axis of the silicon nitride crystal grains is preferably 25 μm or less. In an observation area of ​​300 μm×300 μm of any cross section of the silicon nitride sintered body, the average major axis of the silicon nitride crystal grains is preferably in the range of 1 μm or more and 10 μm or less. In an observation area of ​​300 μm×300 μm of any cross section of the silicon nitride sintered body, the area of ​​each grain boundary phase is preferably 9 μm or less. 2 The area of ​​the grain boundary phase means the area of ​​a region surrounded by a plurality of silicon nitride crystal grains. The fact that the major axis of the silicon nitride crystal grains is 25 μm or less means that there are no silicon nitride crystal grains with a major axis exceeding 25 μm. In other words, it means that there are no coarse grains exceeding 25 μm. As mentioned above, by reducing the number of dislocation defects, durability and electrolytic corrosion resistance are improved. By eliminating large coarse grains, local variations in mechanical strength can be suppressed. For this reason, the major axis of the silicon nitride crystal grains is preferably 25 μm or less, and more preferably 15 μm or less. The average major axis of the silicon nitride crystal particles is preferably in the range of 1 μm to 10 μm. If the average major axis is less than 1 μm, the silicon nitride crystal particles may be too small, resulting in reduced durability. If the average major axis is more than 10 μm, the gaps between the silicon nitride crystal particles may become large, resulting in reduced strength. In addition, in an observation area of ​​300 μm × 300 μm of an arbitrary cross section of a silicon nitride sintered body, the area of ​​each grain boundary phase is 9 μm 2 It is preferable that the area of ​​the grain boundary phase is 9 μm or less. 2 If the area exceeds 9 μm, it may cause variations in insulation. The grain boundary phase and silicon nitride crystal grains have different insulation properties. Therefore, if the grain boundary phase is too large, the effect of suppressing dislocation defects in the silicon nitride crystal grains will be reduced. For this reason, the area of ​​each grain boundary phase should be 9 μm 2 Below 5 μm 2 Most preferably, the area of ​​each grain boundary phase is less than 1 μm 2 The following is the result.

[0019] The major axis of silicon nitride crystal grains and the area of ​​the grain boundary phase are measured using SEM photographs. Take an SEM photograph of any cross section of the silicon nitride substrate. The cross section should be a polished surface with a surface roughness Ra of 1 μm or less. The magnification of the SEM photograph should be set to 1000x or more. The recommended magnification of the SEM photograph is 4000x. If it is not possible to photograph an area of ​​300 μm x 300 μm in a single field of view, it is acceptable to photograph multiple 300 μm x 300 μm areas. If the length in one direction of the cross section is less than 300 μm, make the length of the observation area in that direction as long as possible, and then measure it to 90,000 μm. 2 The major axis of the silicon nitride crystal grains is 90,000 μm. 2 Measurements are made based on the observation results in the observation area. As shown in Figure 2, the major axis is the length of the longest line segment obtained by connecting any two points on the outer edge of a single silicon nitride crystal particle. In Figure 2, 3 indicates the major axis of silicon nitride crystal particle 1. The average major axis of each silicon nitride crystal particle seen in an SEM photograph with an observation area of ​​300 μm × 300 μm is measured. Silicon nitride crystal particles whose outlines are cut off at the edge of the SEM photograph and are not visible in their entirety are excluded from the count. The major axis is determined using only those silicon nitride crystal particles for which the longest line segment can be observed in the SEM photograph. In SEM images, silicon nitride crystal grains and the grain boundary phase can be distinguished by the difference in contrast. Silicon nitride crystal grains appear dark gray, and the grain boundary phase appears light gray. The area of ​​the grain boundary phase can be determined by image analysis of SEM images. Specifically, the binarized image is analyzed using image analysis software. In the binary image, silicon nitride crystal grains appear black, and the grain boundary phase appears white. The area of ​​the grain boundary phase is determined as the area surrounded by three or more silicon nitride crystal grains. In other words, the area is determined excluding the grain boundary phase that exists between two silicon nitride crystal grains. In addition, Image-j or software with equivalent or higher resolution is used as image analysis software.

[0020] The above-mentioned structure makes it possible to provide a sliding member with excellent durability and electrolytic corrosion resistance. In addition, as a silicon nitride sintered body, it has a three-point bending strength of 900 MPa or more and a fracture toughness of 5.5 MPa m 1 / 2 This means that the durability and electrolytic corrosion resistance can be improved while maintaining the strength of the material. The three-point bending strength is measured in accordance with JIS-R-1601. The fracture toughness is measured using the Niihara formula in accordance with the IF method of JIS-R-1607. For JIS-R-1601, ISO 14704 can be used as a reference. For JIS-R-1607, ISO 15732 can be used as a reference. The content of the sintering aid is preferably 20 mass% or less in terms of oxide. If the content of the sintering aid exceeds 20 mass%, the proportion of the grain boundary phase increases. If the grain boundary phase increases, the three-point bending strength or fracture toughness value may decrease. Furthermore, the effect of reducing the proportion of silicon nitride crystal grains having dislocation defects decreases.

[0021] That is, the silicon nitride sintered body preferably contains 20 mass% or less of additional components other than silicon nitride, and the additional components preferably contain three or more elements selected from Y, lanthanoid elements, Al, Mg, Si, Ti, Hf, Mo, and C.

[0022] That is, the silicon nitride sintered body contains 20 mass% or less of an additive component. The additive component refers to a component other than silicon nitride. In the case of a silicon nitride sintered body, the additive component other than silicon nitride refers to a sintering aid component. The sintering aid component constitutes the grain boundary phase. If the additive component is excessively high, exceeding 20 mass%, the grain boundary phase will become excessive. The silicon nitride sintered body has a structure in which elongated β-silicon nitride crystal grains are intricately entangled. If the sintering aid component is too high, portions where the silicon nitride crystal grains do not have the intricately entangled structure will be formed, which is undesirable. By having a larger amount of the intricately entangled structure, the three-point bending strength and fracture toughness value can be improved.

[0023] The amount of the additive component is preferably 3% by mass or more and 15% by mass or less. If the amount of the additive component is less than 3% by mass, the grain boundary phase may be insufficient, which may result in a decrease in the density of the silicon nitride sintered body. The grain boundary phase is a component that fills the gaps between silicon nitride crystal grains. Therefore, by setting the amount of the additive component to 3% by mass or more, it becomes easier to form a sintered body with a relative density of 95% or more. Furthermore, by setting the amount of the additive component to 5% by mass or more, it becomes easier to form a sintered body with a relative density of 98% or more.

[0024] The silicon nitride sintered body preferably contains three or more elements selected from the group consisting of Y (yttrium), lanthanoids, Al (aluminum), Mg (magnesium), Si (silicon), Ti (titanium), Hf (hafnium), Mo (molybdenum), and C (carbon) as additive components. The silicon nitride sintered body may contain any of the additive components Y (yttrium), lanthanoids, Al (aluminum), Mg (magnesium), Si (silicon), Ti (titanium), Hf (hafnium), Mo (molybdenum), and C (carbon) as constituent elements. Examples of the additive components include oxides (including composite oxides), nitrides (including composite nitrides), oxynitrides (including composite oxynitrides), and carbides (including composite carbides). The lanthanoid element is preferably one selected from the group consisting of Yb (ytterbium), Er (erbium), Lu (ruthenium), and Ce (cerium).

[0025] As will be described later, when added as a sintering aid in the manufacturing process, oxides (including composite oxides), nitrides (including composite nitrides), and carbides (composite carbides) are preferred. When Y element is used, yttrium oxide (YO) is preferred. Furthermore, as a lanthanoid element, one selected from ytterbium oxide (YbO), erbium oxide (ErO), ruthenium oxide (LuO), and cerium oxide (CeO) is preferred. The Y element and the lanthanoid element can promote the formation of elongated columnar β-silicon nitride crystal grains.

[0026] When Al element is used, aluminum oxide (Al2O3), aluminum nitride (AlN), MgO·Al2O3 spinel, or mullite (Al2O3-SiO2) is preferred. When Mg element is used, magnesium oxide (MgO), MgO·Al2O3 spinel, or talc (MgO-SiO2) is preferred. When Si element is used, silicon oxide (SiO2) or silicon carbide (SiC) is preferred. Furthermore, Al element, Mg element and Si element have the effect of lowering the sintering temperature and improving the sinterability.

[0027] When Ti element is used, titanium oxide (TiO2) or titanium nitride (TiN) is preferred. When Hf element is used, hafnium oxide (HfO2) is preferred. When Mo element is used, molybdenum oxide (MoO2) or molybdenum carbide (Mo2C) is preferred. As for C element, it is preferred to add it as silicon carbide (SiC), titanium carbide (TiC), or titanium carbonitride (TiCN). The elements Ti, Hf, Mo, and C function as components that strengthen the grain boundary phase, thereby increasing the strength and toughness of the silicon nitride sintered body.

[0028] By adding two or more of these additive components in combination, it is possible to form a grain boundary phase containing three or more elements selected from Y, lanthanoid elements, Al, Mg, Si, Ti, Hf, Mo, and C. Furthermore, the following combinations of sintering aids are preferred for addition in the manufacturing process.

[0029] The first combination contains 2-8 mass% Y2O3, 1-6 mass% Al2O3, 1-6 mass% AlN, and 0.5-4 mass% TiO2. Although Al2O3 and AlN are added, the components added to the silicon nitride sintered compact are counted as a single element, Al. Therefore, according to the first combination, three elements, Y, Al, and Ti, are added.

[0030] The second combination contains 2 to 8 mass% Y2O3, 0.1 to 3 mass% Al2O3, 1 to 6 mass% AlN, 0.5 to 3 mass% HfO2, and 0.1 to 3 mass% Mo2C. According to the second combination, five elements, Y, Al, Hf, Mo, and C, are added. The third combination contains 2 to 8 mass% Y2O3, 1 to 5 mass% Al2O3, 1 to 6 mass% AlN, 0.5 to 3 mass% HfO2, 0.1 to 3 mass% Mo2C, and 1 to 6 mass% SiC. According to the third combination, six types of elements are added: Y, Al, Hf, Mo, C, and Si. The fourth combination contains 0.2 to 3 mass% Y2O3, 0.5 to 5 mass% MgO·Al2O3 spinel, 2 to 6 mass% AlN, 0.5 to 3 mass% HfO2, and 0.1 to 3 mass% Mo2C. According to the fourth combination, six elements, namely Y, Mg, Al, Hf, Mo, and C, are added. In the first to fourth combinations, an oxide of a lanthanoid element may be used in place of Y2O3.In the first to fourth combinations, the total content of the sintering aid components is 15 mass % or less.

[0031] Of the first to fourth combinations, the first combination is preferred. The first combination uses both Al2O3 and AlN as the Al element. This facilitates the formation of Y-Al-Si-ON compounds in the grain boundary phase. Y-Al-Si-ON compounds are a reaction product of Y2O3, Al2O3, AlN, and silicon nitride (Si3N4). In other words, the sintering process can promote the reaction between the sintering aid powder and the silicon nitride powder. Furthermore, the addition of AlN allows the impurity oxygen in the silicon nitride powder to be utilized in the formation of Y-Al-Si-ON compounds. This suppresses the formation of dislocation defects in the silicon nitride crystal grains. Furthermore, TiO2 becomes TiN (titanium nitride) during the sintering process. TiN particles function as a component that strengthens the grain boundary phase. Furthermore, the long diameter of the silicon nitride crystal particles can suppress abnormal grain growth. This allows for the production of a dense sintered body. Therefore, according to the first combination, the three-point bending strength is 1000 MPa or more and the fracture toughness is 6.5 MPa m 1 / 2 It can be more than that.

[0032] The second to fourth combinations include the addition of HfO2. HfO2 reacts with Y2O3 to form Hf-Al-YO compounds. This acts as a low-melting-point liquid phase, improving sinterability. This prevents dislocation defects from forming in the silicon nitride crystal grains. Additionally, Mo2C or SiC functions as a component to strengthen the grain boundary phase. As a result, the second to fourth combinations have a three-point bending strength of 900 MPa or more and a fracture toughness of 5.5 MPa m 1 / 2 The silicon nitride sintered body described above can be obtained. The first combination has an average three-point bending strength that is approximately 100 MPa higher than the second to fourth combinations. The first combination converts TiO2 into TiN (titanium nitride) particles, allowing for fine dispersion of particles of 1 μm or less. TiO2, Mo2C, and SiC are dispersed in the grain boundary phase in the form of particles. TiO2 is easily dispersed as fine particles in the grain boundary phase of the silicon nitride sintered body because it is accompanied by a change to TiN (titanium nitride) particles. This makes it possible to strengthen the grain boundary phase while reducing its size. According to the first combination, the area of ​​the grain boundary phase can be reduced to 5 μm 2 Below that, even 1 μm 2 It can be the following: A silicon nitride sintered body having the desired strength and fracture toughness can be used depending on the environment in which the sliding member will be used. The sliding surface of the silicon nitride sintered body preferably has a surface roughness Ra of 1 μm or less.

[0033] A slide member comprising the silicon nitride sintered body as described above exhibits excellent durability. The slide member also has electrolytic corrosion resistance. Examples of the slide member include bearing members, roll members, compressor members, pump members, engine members, and friction stir welding device members. A bearing includes a combination of rolling elements and raceways. The rolling elements are spherical or roller-shaped. Here, the rolling elements are called bearing balls. A spherical shape is a ball, and a roller shape is a cylinder. Bearings that use spherical rolling elements are called ball bearings. Bearings that use roller-shaped rolling elements are called roller bearings. Roller bearings also include needle bearings, tapered roller bearings, and spherical roller bearings. Raceways include an outer ring and an inner ring. Examples of roll members include rolling rollers and rollers for feeding parts of electronic devices. Examples of compressor or pump members include vanes. Here, compressors are distinguished as those that increase pressure, while pumps are those that decrease pressure. Examples of engine members include cam rollers, cylinders, pistons, and check balls. Examples of friction stir welding device members include tool members for friction stir welding devices. The sliding members according to the embodiments have excellent durability and can be applied to various fields such as those described above. With regard to sliding members in the above fields, at least one of the sliding member and a mating member slides against the other. For example, in a bearing, the position of the rolling element in the bearing does not change. However, a portion of the surface of the rolling element contacts a portion of the surface of the mating member, and a portion of the surface of the rolling element slides against the mating member. The sliding members according to the embodiments have excellent durability due to the small number of dislocation defects. In particular, the sliding members according to the embodiments are suitable as sliding members that slide on surfaces. Furthermore, they are suitable for use in environments where the sliding conditions change. An example of such a sliding member is a bearing mounted in an inverter-driven motor.

[0034] JIS-B-1518 specifies the measurement methods for the dynamic load rating and rating life of rolling bearings. The formula for calculating rating life in JIS-B-1518 uses the load rating. In this way, the life of a general bearing is measured by load and rotational speed. For this reason, it cannot be said that sufficient consideration has been given to operating environments where the rotational speed changes. Regarding JIS-B-1518, ISO 281 can be used as a reference. Here, we will explain the torque of an inverter-driven motor. Let the motor's synchronous speed be Ns (r / min), the motor's rated rotation speed (r / min) be N, the slip (%) be s, the power supply frequency (Hz) be f, and the motor's number of poles be p. The motor's synchronous speed Ns is given by Ns = (2f / p) x 60. The rotor generates torque at a rotational speed with a slight slip above the synchronous speed Ns. A load corresponding to this torque is applied to the bearings. The rated rotation speed N (r / min) of a motor is expressed as N = Ns (1-s) = (120f / p) (1-s). The slip s (%) is expressed as s = ((Ns-N) / Ns) x 100. As can be seen from these formulas, changing the frequency of the power supply is an effective way to change the rotation speed of an inverter-driven motor. The unit r / min refers to rpm. Measuring sliding noise is an effective way to measure the durability of bearings in operating environments where sliding conditions change. JIS-B-1548 specifies a method for measuring the noise level of rolling bearings. As mentioned above, torque changes in inverter-driven motors. Changes in torque lead to changes in stress on the bearing ball surface. Damage to the bearing ball surface causes changes in sliding noise. For this reason, changes in sliding noise are an effective way to measure the durability of bearing balls. The sliding member according to the embodiment has few dislocation defects. Therefore, even when the sliding member according to the embodiment is used in applications where the sliding conditions change, damage to the sliding member or electrolytic corrosion can be suppressed, and the sliding member has excellent sliding characteristics. For example, the motor can be inverter-driven while changing the rotation speed of the motor within a range of about 50 to 15,000 rpm. Even under usage conditions where the rotation speed changes by 1,000 rpm or more, the sliding member according to the embodiment exhibits excellent durability.

[0035] Next, a method for manufacturing the slide member according to the embodiment will be described. The method for manufacturing the slide member is not particularly limited as long as the slide member has the above-described configuration. Here, the following example will be given as a method for obtaining the slide member according to the embodiment with a good yield. First, raw material powder is prepared. The raw material powder includes silicon nitride powder and sintering aid powder. The sintering aids described above are preferably used. The sintering aid preferably satisfies any one of the first to fourth combinations. The total amount of the sintering aids, calculated as oxides of the metal elements, is 20% by mass or less. The lower limit of the amount of sintering aids added is preferably 2% by mass or more.

[0036] The silicon nitride powder preferably has an alpha conversion rate of 80% by mass or more, an average particle size of 0.4 to 2.5 μm, and an impurity oxygen content of 2% by mass or less. The impurity oxygen content is preferably 2% by mass or less, and more preferably 1.0% by mass or less. More preferably, the impurity oxygen content is 0.1 to 0.8% by mass. If the impurity oxygen content is greater than 2% by mass, a reaction between the impurity oxygen and the sintering aid may occur, resulting in the formation of more grain boundary phase than necessary. In addition, the average particle size D of the sintering aid powder 50 The particle size is preferably 1.0 μm or less, and more preferably 0.4 μm or less. During the grain growth process of silicon nitride crystal particles, it is effective to create a state in which the sintering aid component can be easily coordinated to the surface of the silicon nitride crystal particles. For this reason, the sintering aid powder is preferably in the form of a fine powder.

[0037] The raw material powders are mixed and a binder is added to prepare a raw material mixture. The raw material powder is a mixed powder of silicon nitride powder and sintering aid powder. The raw material mixture with the binder added to the mixed powder becomes a slurry. In order to control the grain growth of silicon nitride crystal particles in the sintering process, it is preferable that the mixed powder is mixed uniformly. In the mixing process, the powder is crushed and mixed using a grinder such as a ball mill. If the crushing stress is too large, dislocation defects will be formed in the silicon nitride powder, and these will likely remain in the silicon nitride particles after sintering. For this reason, in the mixing process, the average particle size D is adjusted under a soft stress that will not cause dislocation defects to be formed in the silicon nitride powder. 50 It is preferable to crush the powder so that the average particle size D is 1 μm or less. 50 One method is to make the particle size 1 μm or less. In addition, in order to perform the mixing process under soft stress, it is possible to slow down the rotation speed of the grinder such as a ball mill, reduce the amount of media, or use light media. The media is put into the grinder together with the mixed powder. By using media, the mixed powder can be efficiently crushed. For this reason, the media is also called grinding media. By crushing under soft stress, it is possible to achieve both high crushing efficiency and defect suppression. The rotation speed of the grinder is preferably 20% to 40% of the critical rotation speed. For example, the critical rotation speed of a ball mill is Nc=42.3 D -1 / 2 This is expressed by the theoretical formula: Nc is the critical rotation speed (rpm), and D is the pot inner diameter (m). This theoretical formula defines the critical state as the state in which gravity and centrifugal force acting on the ball are balanced at the apex of the mill cylinder. The optimum rotation speed for a typical ball mill is said to be approximately 55 to 85% of the critical rotation speed. By setting the rotation speed to 40% or less of the critical rotation speed, the mixing process can be carried out under gentle stress. Furthermore, even if the rotation speed is less than 20% of the critical rotation speed, gentle stress will be achieved, but the mixing time will be too long, reducing mass productivity. For this reason, it is preferable that the rotation speed of the mill be 40% or less of the critical rotation speed, and especially 20% to 40%. The amount of media is preferably 10% by mass or less relative to 100% by mass of the mixed powder of silicon nitride powder and sintering aid powder. When using light media, it is preferable that the media have a specific gravity four times or less than that of the slurry. By reducing the amount of media or the specific gravity, a soft stress can be achieved. The above points of "taking 20 hours or more," "keeping the rotation speed at 40% or less of the critical rotation speed," "reducing the amount of media," and "using media with a low specific gravity" may be combined.

[0038] Next, a molding process is performed to mold the raw material mixture. Examples of methods for molding the raw material mixture include die pressing, cold isostatic pressing (CIP), and sheet molding. Examples of sheet molding methods include doctor blade and roll molding. These molding methods may also be combined. If necessary, the raw material mixture may be mixed with a solvent such as toluene, ethanol, or butanol. If necessary, the raw material mixture may be mixed with an organic binder. Examples of organic binders include butyl methacrylate, polyvinyl butyral, and polymethyl methacrylate. Furthermore, when the raw material mixture (the total amount of silicon nitride powder and sintering aid powder) is taken as 100% by mass, the amount of organic binder added is preferably 3 to 17% by mass. If the amount of organic binder added is less than 3% by mass, the amount of binder is too small and it becomes difficult to maintain the shape of the compact.If the amount of organic binder added exceeds 17% by mass, the voids in the compact after the debinding step (the compact after the debinding treatment) become large, and a dense sintered body cannot be obtained. Next, the compact is subjected to a debinding process. In the debinding process, the compact is heated in a non-oxidizing atmosphere at a temperature of 500 to 800°C for 1 to 4 hours to debinding most of the organic binder that was added beforehand. Examples of non-oxidizing atmospheres include a nitrogen gas atmosphere and an argon gas atmosphere. If necessary, the compact may be treated in an oxidizing atmosphere such as air to control the amount of organic matter remaining in the debound compact. Next, the degreased body (the degreased compact) is fired. furnace The sintered product is placed in a firing furnace and sintered in a non-oxidizing atmosphere. The temperature during the sintering process is preferably in the range of 1650°C to 2000°C. The non-oxidizing atmosphere is preferably a nitrogen gas atmosphere or a reducing atmosphere containing nitrogen gas. The pressure inside the firing furnace is preferably a pressurized atmosphere.

[0039] If the degreased body is sintered at a low temperature below 1650°C, the grain growth of silicon nitride crystal particles is insufficient, making it difficult to obtain a dense sintered body. On the other hand, if the degreased body is sintered at a temperature higher than 2000°C, there is a risk of decomposition into Si and N2 if the atmospheric pressure in the furnace is low. For this reason, it is preferable to control the sintering temperature within the above range. In addition, it is preferable that the sintering time be within the range of 3 hours to 12 hours.

[0040] In the sintering process, it is preferable to keep the heating rate at 50°C / h or less within the range of 1300°C to 1500°C. In this temperature range, a liquid phase consisting mainly of the sintering aid is generated. Controlling the heating rate can promote diffusion to the surfaces of the silicon nitride crystal particles. It is preferable to set the heating rate from 1500°C to the sintering temperature to 50°C / h or less. Setting the heating rate to 50°C / h or less promotes uniform grain growth, suppresses the generation of coarse grains, and also suppresses the formation of dislocation defects in the silicon nitride crystal grains. Furthermore, it is preferable that the amount of change in pressure is 0.3 MPa or less. By suppressing the amount of change in pressure, it is possible to suppress the formation of dislocation defects in the silicon nitride crystal grains. The change in pressure affects the grain growth of the silicon nitride crystal grains. Whether the sintering step is carried out at normal pressure or under pressure, it is preferable that the amount of change in pressure is 0.3 MPa or less, and more preferably 0.1 MPa or less. In order to control the amount of pressure change, it is effective to control the gas pressure in the sintering atmosphere. Gas is easily generated during the sintering process of silicon nitride sintered bodies. In the sintering process, the binder in the compact, the sintering aid, and the impurity oxygen in the silicon nitride powder become gas components. The pressure of the sintering atmosphere changes depending on the generated gas components. In other words, even in atmospheric sintering, where no particular pressure is applied, the pressure of the sintering atmosphere changes depending on the generated gas components. For this reason, it is effective to control the atmosphere pressure during the sintering process by removing the generated gas components, etc.

[0041] In this way, abnormal grain growth of silicon nitride crystal grains can be suppressed by controlling the rate of temperature rise or suppressing pressure changes. This allows the maximum long diameter of silicon nitride crystal grains to be controlled to 25 μm or less in an observation area of ​​300 μm×300 μm on any cross section of the silicon nitride sintered body. Furthermore, the average long diameter of silicon nitride crystal grains can be controlled to within a range of 1 μm to 10 μm in an observation area of ​​300 μm×300 μm on any cross section of the silicon nitride sintered body. Furthermore, because abnormal grain growth can be suppressed, the area of ​​each grain boundary phase can be controlled to 9 μm or less in an observation area of ​​300 μm×300 μm on any cross section of the silicon nitride sintered body. 2 Below 5 μm 2 It can be controlled as follows: Furthermore, after the sintering step, it is preferable to subject the sintered body to HIP (hot isostatic pressing). Here, the step of sintering the degreased body is called the first sintering step, and the step of HIPing the sintered body is called the second sintering step. The HIP treatment is preferably carried out at a temperature of 1600°C to 1900°C and a pressure of 80 MPa to 200 MPa. The HIP treatment can reduce the pores in the sintered body, thereby producing a dense sintered body. If the pressure is less than 80 MPa, the effect of applying pressure is insufficient. If the pressure is higher than 200 MPa, the load on the manufacturing equipment may increase.

[0042] The heat treatment temperature in the second sintering step is preferably lower than the heat treatment temperature in the first sintering step. By lowering the heat treatment temperature in the second sintering step, grain growth of silicon nitride crystal grains can be suppressed. Furthermore, according to the above manufacturing method, the formation of dislocation defects is suppressed in the first sintering step. Therefore, even if a HIP process that applies pressure is performed, the increase in dislocation defects can be suppressed. In other words, it is important to prevent the formation of dislocation defects in the silicon nitride crystal grains in the first sintering step. The resulting silicon nitride sintered body is then processed into a sliding member. Examples of processing include surface polishing, cutting, machining, and electrical discharge machining. In surface polishing, the portion of the silicon nitride sintered body that will become the sliding surface is processed so that the surface roughness Ra is 1 μm or less. By reducing the surface roughness Ra of the sliding surface to 1 μm or less, or even 0.2 μm or less, the durability of the sliding member is improved. Furthermore, aggressiveness toward the mating member can be reduced, thereby improving durability in this respect as well.

[0043] An example of a bearing is shown in Figure 3. In Figure 3, 10 is a bearing, 11 is a bearing ball, 12 is an inner ring, and 13 is an outer ring. Bearing 10 has a structure in which bearing balls 11 are arranged between inner ring 12 and outer ring 13. For example, the sliding member according to the embodiment is used for the bearing balls (rolling elements) 11. The bearing rings (inner ring 12 and outer ring 13) are made of bearing steel SUJ2. These components make up the bearing 10. The entire surface of the bearing ball is the sliding surface. For this reason, the entire surface of the sphere is polished. By reducing the surface roughness Ra of the bearing ball, it is possible to reduce the aggressiveness of the bearing rings. In other words, it is possible to prevent the sliding surface of the bearing rings from being worn away as the bearing balls slide. This improves the durability of the entire bearing.

[0044] Fig. 4 shows a motor using a bearing and a drive device using that motor. In Fig. 4, 20 is a motor, 10 is a bearing, 14 is a rotating shaft, 15 is a rotor, 16 is a stator, and 17 is a case. Also, 30 is a drive device, and 25 is a control unit. The motor 20 according to the embodiment has the bearing 10 according to the embodiment. The drive device 30 according to the embodiment has the motor 20 and control unit 25 according to the embodiment. The bearings are provided around one end and the other end of the rotating shaft. As the rotating shaft rotates, the inner ring of the bearing rotates, sliding against the surface of the bearing balls. The bearing balls also rotate, sliding against the surface of the bearing balls. A rotor is also provided around the rotating shaft. The rotor is located between the bearings. A stator is provided around the rotor. The bearings, part of the rotating shaft, the rotor, and the stator are housed inside a case. The stator is fixed to the case. The rotor is fixed to the rotating shaft, and the rotating shaft and rotor rotate inside the stator. The control unit is electrically connected to the stator. The control unit supplies AC current to the stator, which drives the rotating shaft of the motor via an inverter. The rotation speed of the motor can be changed by changing the frequency of the AC current. The motor and drive device according to the embodiment have bearings with improved durability, which can extend the life of the motor and drive device and improve reliability. Furthermore, the rotational speed of the motor corresponds to the rotational speed of the bearing, the rotating shaft, and the rotor. By applying the sliding member according to the embodiment to the bearing ball, the reliability of the motor and the drive device in which the bearing rotational speed is 50 rpm or more can be improved. Even if the motor and the drive device are configured so that the bearing rotational speed changes by 1000 rpm or more, the reliability of the motor and the drive device can be improved.

[0045] (Example) (Examples 1 to 7, Comparative Example 1) A mixed raw material powder was prepared by mixing silicon nitride powder and sintering aid powder. The mixed raw material powder was then crushed and mixed to prepare mixed raw material powders 1 to 6. The crushing and mixing was carried out using a ball mill. For mixed raw powders 1 to 5, the average particle size D 50 The crushing step was carried out for 20 hours or more until the particle size became 1 μm or less. For mixed raw material powder 6, the crushing step was carried out for a short time of 10 hours. Furthermore, the first combination was used for mixed raw material powders 1-2 and mixed raw material powder 6. The second combination was used for mixed raw material powder 3. The third combination was used for mixed raw material powder 4. The fourth combination was used for mixed raw material powder 5. The results are shown in Table 1.

[0046] [Table 1]

[0047] Next, 5 to 10 wt% of a binder was added to the mixed raw material powder to prepare a mixed raw material paste. The mixed raw material paste was then molded in a mold. The molded body was then subjected to a debinding process at 500 to 800°C for 1 to 4 hours to prepare a debound body. Next, the first sintering step shown in Table 2 was carried out in a nitrogen atmosphere. The pressure of 0.1 MPa indicates atmospheric pressure.

[0048] [Table 2]

[0049] After the first sintering step was completed, the obtained sintered body was cooled to room temperature. Then, the second sintering step was carried out. The second sintering step was a HIP treatment. The HIP treatment conditions are as shown in Table 3.

[0050] [Table 3]

[0051] The silicon nitride sintered body obtained was subjected to surface polishing to a surface roughness of Ra 0.01 μm or less. Silicon nitride sintered body samples of the size specified by JIS were prepared and their three-point bending strength and fracture toughness were measured. Furthermore, bearing balls with a diameter of 9.525 mm (3 / 8 inch) were prepared from the silicon nitride sintered body and their wear resistance was tested.

[0052] Next, the dislocation defects, the major axis of the silicon nitride crystal grains, the area of ​​the grain boundary phase, the three-point bending strength, and the fracture toughness value were measured for the examples and comparative examples. For the measurement of dislocation defects, an arbitrary cross section was processed by ion milling to a surface roughness Ra of 1 μm or less and used as the evaluation surface. The evaluation surface was observed using a TEM. A 50 μm × 50 μm area on the evaluation surface was observed and photographed using the TEM. A second area 1,000 μm away from one observation area was also observed and photographed. Thus, dislocation defects were measured in a total of two areas. The TEM magnification was set to 10,000x, and bright-field and dark-field images were taken. White areas in the dark-field images were identified as dislocation defects. The presence and area ratio of dislocation defects within a single silicon nitride crystal grain were determined by comparing the bright-field and dark-field images. Note that silicon nitride crystal grains cut off at the edge of the TEM image (i.e., grains whose outlines were not fully visible) were excluded from the count. The area ratio of dislocation defects was measured by binarizing the dark-field image using image processing software and calculating the area ratio of the white and black areas. In addition, the elements at the core of the dislocation defects were analyzed. The dislocation defects were analyzed using EDX. This revealed that elements other than silicon, oxygen, and nitrogen were present within 1 μm of the dislocation defects. 2It was measured whether or not the particles formed agglomerates of 10 mol % or more and whether or not they were detected at 10 mol % or more.

[0053] To measure the longest diameter of silicon nitride crystal particles, arbitrary cross sections were observed using an SEM. The magnification of the SEM photograph was set to 3000x, and a 300 μm × 300 μm area was observed and photographed. For one silicon nitride crystal particle shown in the SEM photograph, the longest distance between the two longest points on the outer edge was taken as the longest diameter. The average longest diameter of the silicon nitride crystal particles shown in the 300 μm × 300 μm observation area in the SEM photograph was calculated. The longest longest diameter was taken as the maximum longest diameter. The largest area of ​​the grain boundary phase shown in the SEM photograph was also calculated. The three-point bending strength was measured in accordance with JIS-R-1601. The fracture toughness was measured in accordance with the IF method of JIS-R-1607 and calculated using the Niihara formula. The results are shown in Tables 4 and 5.

[0054] [Table 4]

[0055] [Table 5]

[0056] As can be seen from the table, the proportion of dislocation defects was small in the examples. In addition, excellent values ​​were obtained for the three-point bending strength and fracture toughness. Next, a durability test was conducted on the bearing balls. A set of 16 bearing balls was assembled into raceways (inner and outer rings) to create bearings. The durability and electrolytic corrosion resistance of each bearing was investigated. For the durability test, the bearing was continuously driven under one set of conditions: "50 rpm for 1 hour" → "increase from 50 rpm to 1000 rpm over 1 hour" → "1000 rpm for 1 hour" → "increase from 1000 rpm to 10,000 rpm over 1 hour" → "10,000 rpm for 1 hour" → "decrease from 10,000 rpm to 50 rpm over 1 hour." The rate of change in sliding noise after 400 or 800 hours of continuous driving compared to 100 hours of continuous driving was determined. An increase in sliding noise of 10% or less was rated as best (◎), an increase of more than 10% but less than 20% was rated as good (○), and an increase of more than 20% was rated as poor (×). This test was conducted to check for changes in the sliding condition due to damage to the bearing balls or seizure of the raceway ring. The sliding noise measurements were conducted in accordance with JIS-B-1548. The electrolytic corrosion resistance was also investigated by determining whether or not electrolytic corrosion occurred after 800 hours. The results are shown in Table 6.

[0057] [Table 6]

[0058] As described above, the bearing balls according to the examples were excellent in durability and galvanic corrosion resistance. In particular, Examples 1 to 4, which used the first combination of sintering aids, were excellent in both durability and galvanic corrosion resistance. In contrast, Comparative Example 1 showed the same durability after about 400 hours, but deteriorated after 800 hours. It also showed electrolytic corrosion. It was found that the presence of a certain amount of dislocation defects can affect the sliding characteristics in a usage environment where the rotational speed changes.

[0059] Although several embodiments of the present invention have been described above, these embodiments are merely examples 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. These embodiments and their modifications 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. [Explanation of symbols]

[0060] 1...Silicon nitride crystal particles 2...Dislocation defect 3...Long diameter of silicon nitride crystal grain 10...Bearing 11...Bearing ball 12...Inner circle 13...Outer ring 14...Rotation axis 15...Rotor 16...Stator 17…Case 20...Motor 25...Control unit 30...Driver

Claims

1. a crushing step of crushing and mixing the silicon nitride powder, the sintering aid powder, and the binder using a crusher to obtain a raw material mixture; a molding step of molding the raw material mixture; a degreasing step of degreasing the compact at 500 to 800°C to obtain a degreased body; a sintering step of placing the degreased body in a sintering furnace and heat-treating the degreased body in the sintering furnace to obtain a silicon nitride sintered body; a step of subjecting the silicon nitride sintered body to a hot isostatic press (HIP) treatment; a processing step of processing the silicon nitride sintered body into a sliding member; Equipped with In the sintering step, the degreased body is sintered in a non-oxidizing atmosphere at a sintering temperature of 1650°C or higher and 2000°C or lower, In the sintering step, the change in pressure in the sintering furnace is suppressed to 0.3 MPa or less by removing gas generated from the degreased body; The method for manufacturing a sliding member made of sintered silicon nitride, wherein the sliding member is such that, in an observation area of ​​50 μm × 50 μm in which any cross section or surface has been subjected to ion milling to reduce the surface roughness Ra to 1 μm or less, the proportion of the number of silicon nitride crystal grains having dislocation defects therein among any 50 silicon nitride crystal grains whose entire contours are visible is 0% or more and 10% or less.

2. 2. The method for producing a silicon nitride sintered slide member according to claim 1, wherein in the sintering step, the rate of temperature increase within the range of 1300° C. to 1500° C. is 50° C. / h or less, and the rate of temperature increase from 1500° C. to the sintering temperature is 50° C. / h or less.

3. The crushing step is performed to crush the raw material mixture to an average particle size D ５０ 3. The method for producing a sliding member made of sintered silicon nitride according to claim 1, wherein the step is carried out for 20 hours or more so that the grain size is 1 μm or less.

4. 4. The method for producing a silicon nitride sintered slide member according to claim 1, wherein the HIP treatment is carried out at a temperature of 1600° C. to 1900° C. and at a pressure of 80 MPa to 200 MPa.

5. 5. The method for producing a slide member made of sintered silicon nitride according to claim 1, wherein in the processing step, the sliding surface of the slide member is surface-processed so as to have a surface roughness Ra of 1 μm or less.

6. 6. The method for producing a slide member made of sintered silicon nitride according to claim 1, wherein in any cross section or surface, a ratio of the number of silicon nitride crystal grains in which the area ratio of dislocation defects is 5% or less to the number of silicon nitride crystal grains having dislocation defects is 70% or more.

7. 7. The method for producing a sliding member made of sintered silicon nitride according to claim 1, wherein said sliding member is a bearing ball.

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