Silicon nitride sintered body and wear-resistant member using same

Abstract

The present invention provides a silicon nitride sintered body that exhibits excellent durability even when used in an environment where torque changes. According to an embodiment, in an XRD analysis result of an arbitrary cross section of a silicon nitride sintered body, when the highest peak intensities corresponding to a hexagonal α-SiAlON crystal that are detected at 20.5±0.3°, 22.8±0.3°, 34.3±0.3°, and 38.7±0.3° are represented respectively by I20.5°, I22.8°, I34.3°, and I38.7°, the highest peak intensities corresponding to a β-Si3N4 crystal that are detected at 33.6±0.3° and 36.1±0.3° are represented respectively by I33.6° and I36.1°, and the highest peak intensities corresponding to an R2Si3O3N4 crystal (where R is a rare earth element) that are detected at 33.6±0.3° and 36.1±0.3° are represented respectively by I31.8° and I37.2°, 0.001≤(I20.5°+I22.8°+I34.3°+I38.7°) / (I33.6°+I36.1°)≤0.300 is satisfied, and 0.002≤(I31.8°+I37.2°) / (I33.6°+I36.1°)≤0.100 is satisfied.

Description

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

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

[0002] Silicon nitride sintered bodies have excellent mechanical properties (hardness, toughness, strength, etc.). Utilizing these properties, silicon nitride sintered bodies are used in wear-resistant components and substrates for semiconductor devices. Wear-resistant material components include bearing balls, friction stir welding tool components, engine parts, etc. In recent years, silicon nitride sintered bodies have been used in bearing balls for electric vehicle motors, and demand for them is increasing.

[0003] In the mass production of silicon nitride sintered bodies, attempts have been made to use inexpensive silicon nitride powder. Silicon nitride powder is the raw material for silicon nitride sintered bodies and is mainly produced by the direct nitridation method or the imide decomposition method. The imide decomposition method can produce silicon nitride powder with few impurities, but it is expensive. On the other hand, the direct nitridation method is cheaper than the imide decomposition method, but the silicon nitride powder contains more impurities.

[0004] For example, Japanese Patent No. 5732037 (Patent Document 1) discloses silicon nitride powder produced by a direct nitriding method. The silicon nitride powder is used in silicon nitride sintered bodies. According to Patent Document 1, the silicon nitride powder contains 10 wtppm or more and 3500 wtppm or less of iron as an impurity. The silicon nitride sintered body described in Patent Document 1 has a Vickers hardness HV of about 1450, and therefore lacks mechanical strength.

[0005] In Japanese Patent No. 6334413 (Patent Document 2), β-Si ３ N ４ The XRD peak ratio between the Y crystal and the hexagonal α-SiAlON crystal is controlled. ２ Si ３ O １２ N (H phase), YSiO ２ N (K phase) or Y ２ Si ３ O ３ N ４According to Patent Document 2, the Vickers hardness HV of the silicon nitride sintered body is about 1500 to 1600.

[0006] Patent No. 5732037 Patent No. 6334413 Patent No. 5362758

[0007] Toshiba Review, Vol. 60, No. 11, (2005), pp. 41-44

[0008] For example, Toshiba Review, Vol. 60, No. 11 (2005), pp. 41-44 (Non-Patent Document 1) discloses a motor used in an electric vehicle (EV) or hybrid vehicle (HEV). According to Non-Patent Document 1, the maximum rotation speed of a passenger vehicle motor is said to reach 10,000 to 15,000 rpm. An electric vehicle repeatedly stops and starts. Therefore, the rotation speed of the motor varies within a range of 0 to 15,000 rpm.

[0009] As shown in Non-Patent Document 1, a change in rotational speed leads to a change in torque. In mechanics, torque is the moment of force acting around a fixed axis of rotation. A change in rotational speed is a change in the number of rotations per unit time. When the number of rotations changes, the torque (i.e., stress) acting on the bearing ball also changes. The bearing balls described in Patent Document 1 or Patent Document 2 may have reduced durability when used in an environment where torque changes.

[0010] The silicon nitride sintered body according to the embodiment is intended to address these issues, and aims to provide a silicon nitride sintered body that exhibits excellent durability even when used in an environment where the torque changes.

[0011] According to the embodiment, in the XRD analysis results of an arbitrary cross section of the silicon nitride sintered body, the strongest peak intensities corresponding to hexagonal α-SiAlON crystals detected at 20.5±0.3°, 22.8±0.3°, 34.3±0.3°, and 38.7±0.3° are respectively I ２０．５° , I ２２．８° , I ３４．３° , I ３８．７°and β-Si detected at 33.6±0.3° and 36.1±0.3°. ３ N ４ The strongest peak intensities corresponding to the crystals are I ３３．６° , I ３６．１° and R detected at 31.8±0.3° and 37.2±0.3° ２ Si ３ O ３ N ４ The strongest peak intensities corresponding to the crystal (R is a rare earth element) are I ３１．８° , I ３７．２° In this case, 0.001≦(I ２０．５° +I ２２．８° +I ３４．３° +I ３８．７° ) / (I ３３．６° +I ３６．１° )≦0.300 and 0.002≦(I ３１．８° +I ３７．２° ) / (I ３３．６° +I ３６．１° )≦0.100.

[0012] 1A and 1B are diagrams showing an example of an XRD analysis result of a silicon nitride sintered body according to an embodiment.

[0013] According to the embodiment, in the XRD analysis results of an arbitrary cross section of the silicon nitride sintered body, the strongest peak intensities corresponding to hexagonal α-SiAlON crystals detected at 20.5±0.3°, 22.8±0.3°, 34.3±0.3°, and 38.7±0.3° are respectively I ２０．５° , I ２２．８° , I ３４．３° , I ３８．７° and β-Si detected at 33.6±0.3° and 36.1±0.3°. ３ N ４ The strongest peak intensities corresponding to the crystals are I ３３．６° , I ３６．１° and R detected at 31.8±0.3° and 37.2±0.3° ２ Si ３ O ３ N ４ The strongest peak intensities corresponding to the crystal (R is a rare earth element) are I ３１．８° , I ３７．２°In this case, 0.001≦(I ２０．５° +I ２２．８° +I ３４．３° +I ３８．７° ) / (I ３３．６° +I ３６．１° )≦0.300 and 0.002≦(I ３１．８° +I ３７．２° ) / (I ３３．６° +I ３６．１° )≦0.100.

[0014] First, the conditions for XRD analysis will be described. The XRD device used is a BRUKER D8 ADVANCE or a device with equivalent performance. The measurement surface is a cross section of the sintered body. The measurement surface is a polished surface with a surface roughness Ra of 1 μm or less. XRD analysis uses a Cu target (Cu-Kα) with a tube voltage of 40 kV, a tube current of 40 mA, a scan speed of 2.0° / min, a slit (RS) of 0.15 mm, and a scanning range (2θ) of 10° to 60°. A wider scanning range (2θ) may be measured as long as it includes 10° to 60°. The strongest peak refers to the maximum peak intensity among the peak intensities appearing within a specific range.

[0015] The search range was set to 10° to 60° because the peaks of the silicon nitride sintered body appear strongly within this range. The silicon nitride sintered body according to the embodiment may have other peaks in addition to the peaks specified in this specification within the range of 10° to 60°. Furthermore, the silicon nitride sintered body according to the embodiment may have a peak outside the range of 10° to 60°.

[0016] The strongest peak intensities detected at 20.5±0.3°, 22.8±0.3°, 34.3±0.3°, and 38.7±0.3° were designated as I ２０．５° , I ２２．８° , I ３４．３° , I ３８．７°The peaks detected in these ranges correspond to hexagonal α-SiAlON crystals. It is sufficient that a peak is present in at least one of the ranges of 20.5±0.3°, 22.8±0.3°, 34.3±0.3°, and 38.7±0.3°. More preferably, peaks are present in all of 20.5±0.3°, 22.8±0.3°, 34.3±0.3°, and 38.7±0.3°. If no peak is detected in any range, the maximum peak intensity I in that range is zero.

[0017] The peak intensity is affected not only by the abundance and crystal composition, but also by the crystallite size and orientation. The detection of these four peaks indicates that the hexagonal α-SiAlON crystal has good crystallinity and good orientation. In addition to the four ranges of 20.5±0.3°, 22.8±0.3°, 34.3±0.3°, and 38.7±0.3° corresponding to the hexagonal α-SiAlON crystal, peaks in other ranges may also be present. Here, "orientation" refers to the dispersion of the crystals within the sintered body. The uniform dispersion of the crystals in various directions within the sintered body can improve various properties of the silicon nitride sintered body.

[0018] The strongest peak intensities detected at 33.6±0.3° and 36.1±0.3° are designated as I ３３．６° , I ３６．１° The peaks detected in these ranges are β-Si ３ N ４ The sintered body corresponds to the β-Si crystal. ３ N ４ If crystals are present, peaks are detected at 33.6±0.3° and 36.1±0.3°. In other words, if peaks are detected at 33.6±0.3° and 36.1±0.3°, the sintered body contains β-Si ３ N ４ This means that crystals exist. ３ N ４ In addition to the two peaks corresponding to the crystals in the ranges of 33.6±0.3° and 36.1±0.3°, there may be peaks in other ranges. ３３．６° and I ３６．１°The reason for using both peak intensities is to mitigate the influence of changes in peak intensity due to crystal orientation.

[0019] The strongest peak intensities detected at 31.8±0.3° and 37.2±0.3° are designated as I ３１．８° , I ３７．２° The peaks detected in these ranges are R ２ Si ３ O ３ N ４ It corresponds to the crystal. ２ Si ３ O ３ N ４ "R" in the crystal represents a rare earth element. The rare earth element is at least one element selected from the group consisting of yttrium and lanthanoid elements. ２ Si ３ O ３ N ４ is also called melilite. ３１．８° or I ３７．２° It is sufficient to detect at least one of these peaks, and it is more preferable to detect both of them. ２ Si ３ O ３ N ４ Not only is the crystallinity good, but ２ Si ３ O ３ N ４ This also indicates that the crystal orientation is good.

[0020] The silicon nitride sintered body according to the embodiment is made of hexagonal α-SiAlON crystal, β-Si ３ N ４ Crystal, and R ２ Si ３ O ３ N ４ The XRD peaks based on each of the crystals satisfy the following formulas 1 and 2. Formula 1: 0.001≦(I ２０．５° +I ２２．８° +I ３４．３° +I ３８．７° ) / (I ３３．６° +I ３６．１° ) ≦ 0.300 Formula 2: 0.002 ≦ (I ３１．８° +I ３７．２° ) / (I３３．６° +I ３６．１° )≦0.100

[0021] Formula 1 is β-Si ３ N ４ This ratio of 0.001 or more indicates that the hexagonal α-SiAlON crystal and the β-Si ３ N ４ This indicates the presence of β-Si crystals. ３ N ４ The amount of hexagonal α-SiAlON crystals is β-Si ３ N ４ This indicates that the size is sufficiently small compared to the amount of crystals.

[0022] Most hexagonal α-SiAlON crystals have an aspect ratio of less than 2. ３ N ４ Most of the crystals are columnar with an aspect ratio of 2 or more. ３ N ４ The presence of hexagonal α-SiAlON crystals in the gaps between the crystals is effective in improving the properties of the sintered body. ３ N ４ In a structure where hexagonal α-SiAlON crystals are mixed, crystal grains with different aspect ratios are mixed. ２０．５° , I ２２．８° , I ３４．３° , and I ３８．７° is affected not only by the amount present but also by the orientation. The fact that formula 1 is satisfied means that the orientation of the hexagonal α-SiAlON crystal and the β-Si ３ N ４ This indicates good crystal orientation. ３ N ４ The presence of well-oriented hexagonal α-SiAlON crystals in the gaps between the crystals can improve the wear resistance of the sintered body. The α-SiAlON crystals can also have a cubic crystal structure. It is preferable that no XRD peaks due to cubic α-SiAlON crystals are detected in the silicon nitride sintered body according to the embodiment.

[0023] Ratio (I ２０．５° +I ２２．８° +I ３４．３° +I ３８．７° ) / (I ３３．６° +I ３６．１° ) is less than 0.001, β-Si ３ N ４ When the ratio exceeds 0.300, the amount of hexagonal α-SiAlON crystals is insufficient relative to the amount of hexagonal α-SiAlON crystals. ３ N ４ The amount of crystals is insufficient. As a result, the properties of the sintered body may be deteriorated. ２０．５° +I ２２．８° +I ３４．３° +I ３８．７° ) / (I ３３．６° +I ３６．１° ) is preferably in the range of 0.001 or more and 0.300 or less, and more preferably in the range of 0.010 or more and 0.100 or less.

[0024] When the cross section of the silicon nitride sintered body is observed with a scanning electron microscope (SEM), depending on the orientation direction, β-Si ３ N ４ The aspect ratio of the crystals may appear to be less than 2. ３ N ４ The aspect ratio of the hexagonal α-SiAlON crystals present in the gaps between the crystals may appear to be 2 or more. ３ N ４ It is difficult to distinguish between the crystals and determine the orientation of each crystal. ３ N ４ The detection of XRD peaks is effective for evaluating the crystal orientation.

[0025] Formula 2 is β-Si ３ N ４ R for the maximum peak intensity based on the crystal ２ Si ３ O ３ N ４ This represents the condition of the ratio of the maximum peak intensity based on the crystal.２ Si ３ O ３ N ４ The fact that formula 2 is satisfied means that the sintered body contains melilite crystals and β-Si ３ N ４ For melilite crystals, the maximum peak intensity I ３１．８° and I ３７．２° is also affected by the orientation. If formula 2 is satisfied, it means that the melilite crystal and β-Si ３ N ４ This indicates that both orientations of the crystals are good.

[0026] The melilite crystals are composed of hexagonal α-SiAlON crystals and β-Si ３ N ４ The melilite crystals are present at the grain boundaries of the crystalline structure. Satisfying formula 2 indicates that the abundance, crystallinity, and orientation of melilite crystals are good. This further improves the wear resistance of the silicon nitride sintered body.

[0027] Ratio (I ３１．８° +I ３７．２° ) / (I ３３．６° +I ３６．１° ) is less than 0.002, β-Si ３ N ４ In addition, when the value of formula 2 exceeds 0.100, the amount of β-Si crystals is insufficient relative to the amount of melilite crystals. ３ N ４ The amount of crystals is insufficient. As a result, the properties of the sintered body may be deteriorated. ３１．８° +I ３７．２° ) / (I ３３．６° +I ３６．１° ) is preferably in the range of 0.002 or more and 0.100 or less, and more preferably in the range of 0.020 or more and 0.080 or less.

[0028] When any cross section of the silicon nitride sintered body according to the embodiment is subjected to XRD analysis, it satisfies both Formula 1 and Formula 2. In other words, the silicon nitride sintered body according to the embodiment satisfies both Formula 1 and Formula 2 no matter which cross section is analyzed.

[0029] The strongest peak intensities detected at 19.1±0.3°, 31.0±0.3°, and 32.5±0.3° are designated as I １９．１° , I ３１．０° , I ３２．５° The peaks detected in these ranges are R ４ Al ２ O ９ It is sufficient that a peak exists in at least one of the ranges of 19.1±0.3°, 31.0±0.3°, and 32.5±0.3°. ４ Al ２ O ９ In addition to the three ranges of 19.1±0.3°, 31.0±0.3°, and 32.5±0.3° that correspond to crystals, peaks may also be present in other ranges. ４ Al ２ O ９ Crystalline and β-Si ３ N ４ The XRD peaks based on each of the crystals preferably satisfy the following formula 3: 0≦(I １９．１° +I ３１．０° +I ３２．５° ) / (I ３３．６° +I ３６．１° )≦0.100

[0030] R ４ Al ２ O ９ R represents a rare earth element. The rare earth element is at least one element selected from the group consisting of yttrium and lanthanoid elements. The detection of XRD peaks at 19.1±0.3°, 31.0±0.3°, and 32.5±0.3° indicates that R ４ Al ２ O ９ indicates that it exists as a crystal. ４ Al ２ O ９ The crystal is also called a YAM crystal. Here, the term "YAM crystal" includes cases where "R" is an element other than yttrium.

[0031] The fact that formula 3 is satisfied means that β-Si ３ N ４This shows that the ratio of the amount of YAM crystals to the amount of YAM crystals is suppressed. １９．１° +I ３１．０° +I ３２．５° ) / (I ３３．６° +I ３６．１° ) exceeds 0.100, β-Si ３ N ４ In this case, there are too many YAM crystals compared to the β-Si crystals. ３ N ４ There is a possibility that the effects of improving strength and wear resistance due to the crystals may be difficult to obtain.

[0032] The YAM crystal is a rare earth aluminum oxide, and is formed by the reaction of a rare earth element component and an aluminum component. The rare earth element component and the aluminum component are added as sintering aids. The rare earth aluminum oxide is, for example, R ４ Al ２ O ９ crystal, R ３ Al ５ O １２ Crystalline and RAlO ３ In both cases, "R" is a rare earth element (yttrium or a lanthanoid element). ４ Al ２ O ９ The crystal is called a YAM crystal. ３ Al ５ O １２ The crystal is called a YAG crystal. ３ The crystal is called a YAL crystal. The YAL crystal is also called a YAP crystal. The terms "YAM crystal," "YAG crystal," and "YAL crystal" include cases where "R" is an element other than yttrium.

[0033] The melting point of YAM crystals is higher than that of YAG crystals and YAL crystals. The melting point of YAM crystals is 1950°C, that of YAG crystals is 1908°C, and that of YAL crystals is 1907°C. When a wear-resistant member contains YAM crystals, the durability of the sliding surface against frictional heat can be improved. Furthermore, YAG crystals and YAL crystals are more likely to cause the formation of white regions, as described below, than YAM crystals. In other words, when rare earth aluminum oxide crystals are present in a sintered body, it is preferable that the rare earth aluminum oxide crystals exist as YAM crystals. For this reason, the ratio (I １９．１° +I ３１．０° +I ３２．５° ) / (I ３３．６° +I ３６．１° ) is preferably in the range of 0 or more and 0.100 or less, and more preferably in the range of 0.001 or more and 0.090 or less.

[0034] R ３ Al ５ O １２ XRD peaks based on crystal (YAG crystal) and RAlO ３ It is preferable that XRD peaks due to YAG crystals and YAL crystals are not detected (including peaks below the detection limit). When peaks due to YAG crystals and YAL crystals are not detected, the sintered body is considered to be R. ３ Al ５ O １２ Crystalline and RAlO ３ This indicates that no crystals are present or that the amount of these crystals is so small that they cannot be detected by XRD. Therefore, the phrase "XRD peaks of YAG crystals and YAL crystals are not detected" includes values ​​below the detection limit.

[0035] Since YAG crystals and YAL crystals are not detected, the proportion of rare earth aluminum oxide crystals present as YAM crystals can be increased. As described above, when the wear-resistant member contains YAM crystals, the durability of the sliding surface against frictional heat can be improved. By increasing the proportion of YAM crystals, the effect of durability against frictional heat can be further improved.

[0036] R ３ Al ５ O １２ and RAlO３ In the silicon nitride sintered body according to the embodiment, R may be present as an amorphous phase. ４ Al ２ O ９ , R ３ Al ５ O １２ , and RAlO ３ One or more selected from may be present as an amorphous phase. ３ Al ５ O １２ and RAlO ３ is R ４ Al ２ O ９ In other words, R ４ Al ２ O ９ The amorphous phase is unlikely to become a white region. Therefore, when the silicon nitride sintered body contains an amorphous phase of rare earth aluminum oxide, the rare earth aluminum oxide is ４ Al ２ O ９ It is preferably present as an amorphous phase. ３ Al ５ O １２ Amorphous phase and RAlO ３ It is preferable that the amorphous phase is small.

[0037] For example, when yttrium is used, peaks due to YAG crystals are detected at 33.3°±0.3°, 55.1°±0.3°, 57.4°±0.3°, etc. Peaks due to YAL crystals are detected at 28.1°±0.3°, 32.9°±0.3°, 49.6°±0.3°, etc. To determine the presence or absence of XRD peaks due to a specific crystalline compound, refer to the PDF card. PDF cards are sometimes called JCPDS cards or ICDD cards. If it is difficult to distinguish between YAM crystals, YAG crystals, and YAL crystals from the XRD peaks, the crystals may be analyzed using a TEM or the like.

[0038] The strongest peak intensities detected at 36.5±0.3° and 42.4±0.3° are designated as I ３６．５° , I ４２．４°The peaks detected in these ranges correspond to titanium nitride. It is sufficient that a peak exists in at least one of the ranges of 36.5±0.3° and 42.4±0.3°. Peaks corresponding to titanium nitride may also exist outside the two ranges of 36.5±0.3° and 42.4±0.3°. Titanium nitride and β-Si ３ N ４ The XRD peaks based on each of the crystals preferably satisfy the following formula 4: Formula 4: 0.020≦(I ３６．５° +I ４２．４° ) / (I ３３．６° +I ３６．１° )≦0.050

[0039] The silicon nitride sintered body according to the embodiment preferably uses both a rare earth element component and an aluminum component as sintering aids. In addition to these components, one or more components selected from the group consisting of titanium (Ti), hafnium (Hf), molybdenum (Mo), tungsten (W), magnesium (Mg), and zirconium (Zr) can also be used as the sintering aid. The additional component selected from the group consisting of Ti, Hf, Mo, W, Mg, and Zr can be, for example, one or more compounds selected from the group consisting of oxides, nitrides, carbides, and silicides. The additional component can also be a complex compound. The complex compound can be, for example, an oxynitride. Silicon carbide (SiC) can also be added to the sintering aid. Ti, Hf, Mo, W, Mg, Zr, and SiC play a role in strengthening the grain boundary phase.

[0040] For example, Japanese Patent No. 5362758 (Patent Document 3) discloses a silicon nitride sintered body containing titanium nitride particles with an aspect ratio of 1.0 to 1.2. In Patent Document 3, the added titanium oxide becomes titanium nitride particles during the sintering process. That is, titanium changes from oxide to nitride during the sintering process. In the process of changing from oxide to nitride, titanium nitride can be dispersed as small particles in the sintered body. As a result, the grain boundary phase can be strengthened. Strengthening the grain boundary phase leads to improvements in wear resistance, strength, fracture toughness, etc. For this reason, it is preferable to include titanium nitride particles in the sintered body. In XRD analysis, I ３６．５° or I４２．４° The detection of ≈0.1 indicates that titanium nitride (TiN) is present as crystals.

[0041] Ratio (I ３６．５° +I ４２．４° ) / (I ３３．６° +I ３６．１° ) is less than 0.020, β-Si ３ N ４ The amount of titanium nitride is small relative to the amount of crystals, and the effect of titanium nitride may be insufficient. ３６．５° +I ４２．４° ) / (I ３３．６° +I ３６．１° ) exceeds 0.050, β-Si ３ N ４ The amount of titanium nitride may be too high relative to the amount of crystals, and if the amount of titanium nitride is too high, the proportion of melilite crystals in the grain boundary phase may be insufficient.

[0042] Equation 1 and Equation 2 are satisfied, and the ratio (I ３６．５° +I ４２．４° ) / (I ３３．６° +I ３６．１° ) is in the range of 0.020 or more and 0.050 or less, the grain boundary phase can be further strengthened. ３ N ４ By controlling the amount and orientation of the YAM crystals, hexagonal α-SiAlON crystals, and melilite crystals, the grain boundary phase can be strengthened. By satisfying formula 3 in addition to formulas 1, 2, and 4, it is possible to allow YAM crystals and titanium nitride to coexist in the grain boundary phase, which further strengthens the grain boundary phase.

[0043] β-Si ３ N ４ The range of 36.1°±0.3° in which the peaks due to the crystals can appear partially overlaps with the range of 36.5°±0.3° in which the peaks due to titanium nitride can appear. ３ N ４ is the base material of silicon nitride sintered body. ３ N ４ The peak due to β-Si is much larger than the peak due to titanium nitride. ３ N４ The peaks due to crystals and the peaks due to titanium nitride are distinguishable. For example, if a silicon nitride sintered body contains titanium nitride and no peaks are observed in the range of either 35.8° to 36.2° or 36.4° to 36.8°, multiple peaks may appear in the range of 36.2° to 36.4°. In this case, the largest peak appears in the range of 36.2° to 36.3°. This largest peak is called β-Si ３ N ４ The second largest peak appears in the range of 36.3° to 36.4°. This second peak is determined to be a peak due to titanium nitride crystals.

[0044] 1 is a diagram showing an example of the XRD analysis result of the silicon nitride sintered body according to the embodiment. As shown in FIG. ３ N ４ A peak P2 at 36.5°±0.3° due to titanium nitride is detected near the base of a peak P1 at 36.1°±0.3° due to the crystal.

[0045] The silicon nitride sintered body preferably contains 3% by mass or more and 7% by mass or less of Al and 2% by mass or more and 8% by mass or less of rare earth elements. The Al content is a value converted into simple Al. The rare earth element content is a value converted into simple rare earth elements. The Al in the silicon nitride sintered body may exist as a compound combined with other components. When multiple rare earth elements are added, the total amount of rare earth elements is preferably within the range of 2% by mass or more and 8% by mass or less. Al is a constituent element of hexagonal α-SiAlON crystal or YAM crystal. The rare earth elements are constituent elements of melilite crystal or YAM crystal.

[0046] The amount of oxygen in the silicon nitride sintered body is preferably in the range of 2.0% by mass to 4.0% by mass. The "amount of oxygen in the silicon nitride sintered body" refers to the total amount of oxygen contained in the silicon nitride sintered body. By controlling the amount of oxygen, it is possible to control the formation of each crystal. Therefore, the amount of oxygen in the silicon nitride sintered body is preferably in the range of 2.0% by mass to 4.0% by mass, and more preferably in the range of 2.5% by mass to 3.4% by mass.

[0047] The iron (Fe) content in the silicon nitride sintered body is preferably in the range of 10 wtppm to 3000 wtppm. Iron may be contained as an impurity in the silicon nitride powder or sintering aid powder. When iron alloys are used in the manufacturing equipment, iron may be mixed in as an impurity. The iron content in the silicon nitride sintered body is the content converted to elemental iron. Iron in the silicon nitride sintered body may also exist as a compound.

[0048] The chromium (Cr) content in the silicon nitride sintered body is preferably in the range of 10 wtppm to 3000 wtppm. Chromium may be contained as an impurity in the silicon nitride powder or sintering aid powder. Chromium may also be mixed in as an impurity when stainless steel is used in manufacturing equipment. The chromium content in the silicon nitride sintered body is the content converted to elemental chromium. Chromium in the silicon nitride sintered body may also exist as a compound.

[0049] The calcium (Ca) content in the silicon nitride sintered body is preferably in the range of 10 wtppm to 3000 wtppm. Calcium may be contained as an impurity in the silicon nitride powder or sintering aid powder. The calcium content in the silicon nitride sintered body is the content converted to elemental calcium. Calcium in the silicon nitride sintered body may also exist as a compound.

[0050] Fe, Cr, and Ca are mainly impurities in silicon nitride powder. These impurities cause uneven sintering. When the sintering is uneven, variations in grain growth occur, which can cause a decrease in strength or wear resistance. As mentioned above, hexagonal α-SiAlON crystal, β-Si ３ N ４ By controlling the XRD peaks of the crystalline silicon nitride and the melilite crystal, the properties of the sintered body can be improved even if these impurities are contained in the sintered body. In particular, silicon nitride powder produced by the direct nitriding method contains a large amount of the above impurities. According to the embodiment, the properties of the sintered body can be improved even if silicon nitride powder produced by the direct nitriding method is used.

[0051] The Fe content of the silicon nitride sintered body is preferably in the range of 10 wtppm to 3000 wtppm, more preferably in the range of 50 wtppm to 2000 wtppm. The Cr content of the silicon nitride sintered body is preferably in the range of 10 wtppm to 3000 wtppm, more preferably in the range of 50 wtppm to 2000 wtppm. The Ca content of the silicon nitride sintered body is preferably in the range of 10 wtppm to 3000 wtppm, more preferably in the range of 50 wtppm to 2000 wtppm. Note that as long as formulas 1 and 2 are satisfied, silicon nitride powder with fewer impurities may be used in the production of the silicon nitride sintered body according to the embodiment. For example, silicon nitride powder produced by the imide decomposition method has a small amount of impurities.

[0052] When an arbitrary cross section of a silicon nitride sintered body is observed with a laser microscope, the area ratio of white regions in a measurement area of ​​4000 μm × 4000 μm is preferably 70% or less. The cross section observed with the laser microscope may be the same as the measurement surface for XRD analysis.

[0053] The measurement conditions using a laser microscope are explained below. The laser microscope used is a Keyence VK-X1000 shape analysis laser microscope or an equivalent device. The magnification of the laser microscope is set to 20x, and a measurement area of ​​4000 μm x 4000 μm is observed in a dark field. The dark field image is analyzed to calculate the area ratio of the white region. In the image analysis, the image is binarized using the image analysis software Image-J.

[0054] The binarization method is as follows: A dark-field image (color image) taken with the laser microscope setting "brightness" set to 120 is converted into a grayscale image with 0 to 255 gradations. The binarization threshold is set to 230. Areas with pixel values ​​of 230 or greater are binarized as white areas, and areas with pixel values ​​less than 230 are binarized as black areas. The proportion of the area of ​​the white areas in the binary image is calculated.

[0055] The white areas are caused by structural defects, such as voids, segregation of sintering aids, segregation of impurities, and density variations.３ Al ５ O １２ and RAlO ３ is R ４ Al ２ O ９ Compared to R, it is more likely to cause the formation of white areas. ３ Al ５ O １２ and RAlO ３ Whether crystalline or amorphous, the area ratio of the white region is likely to cause the white region. It is most preferable that the area ratio of the white region is 0% (below the detection limit). On the other hand, as mentioned above, when a silicon nitride powder with a large amount of impurities is used, the white region is likely to be formed. By satisfying the above-mentioned formulas 1 and 2, the properties of the sintered body can be improved even if a white region exists. The area ratio of the white region is preferably in the range of 0% to 70% and more preferably in the range of 0% to 30%.

[0056] The area ratio of the white region may be 3% or more. Setting the area ratio of the white region to 0% may increase the burden of production control. By controlling the XRD peak ratios of the above-mentioned formulas 1 and 2, the wear resistance of the sintered body can be improved even if the area ratio of the white region is within the range of 3% to 70% or within the range of 3% to 30%.

[0057] When any cross section of a silicon nitride sintered body is observed with an SEM, it is preferable that a plurality of crystal grains with a major axis of 2.5 μm or more and an aspect ratio of 2.5 or more are present in a measurement area of ​​20 μm × 15 μm. Furthermore, it is preferable that the total area ratio of these crystal grains is in the range of 20% to 70%. The cross section observed with an SEM may be the same as the observation surface with a laser microscope or the measurement surface for XRD analysis.

[0058] The observation method using SEM will be explained. For the SEM, a JOEL JCM-7000, a JOEL JSM-7200F, or an equivalent or higher device is used. The magnification is set to 5000x. A measurement area of ​​20 μm x 15 μm is observed to obtain an SEM image. In the SEM image, crystal grains with a major axis of 2.5 μm or more and an aspect ratio of 2.5 or more are extracted. Crystal grains are observed to be darker than grain boundaries, and appear gray, for example. This makes them distinguishable from grain boundaries.

[0059] The "major axis" is the distance between two points located on the outer edge of a crystal particle and furthest from each other. The dimension of the crystal particle passing through the midpoint of the major axis and perpendicular to the direction of the major axis is the "minor axis." The aspect ratio is calculated as the major axis / minor axis. In a measurement area of ​​20 μm × 15 μm, crystal particles with a major axis of 2.5 μm or more and an aspect ratio of 2.5 or more are extracted, and the sum of the areas of these crystal particles is calculated. The total area ratio is calculated by dividing the sum of the areas by the total area of ​​the SEM image. Three non-overlapping 20 μm × 15 μm areas are observed, and the total area ratio is calculated for each measurement area. The average of the three total area ratios is used as the final total area ratio. Even if the outline of a crystal particle is cut off in the measurement area, it is counted as long as it has a major axis of 2.5 μm or more and an aspect ratio of 2.5 or more. Here, crystal particles with a major axis of 2.5 μm or more and an aspect ratio of 2.5 or more are referred to as "long-axis crystal particles."

[0060] The long axis crystal grains are mainly β-Si ３ N ４ The presence of multiple long axis crystal grains in a measurement area of ​​20 μm × 15 μm indicates that there are multiple β-Si ３ N ４ It essentially indicates the presence of crystal grains. In addition, it is preferable that the total area ratio of the long axis crystal grains is in the range of 20% to 70%. According to an embodiment, the β-Si ３ N ４ The orientation of the crystal grains is controlled, which can further improve the wear resistance of the sintered body.

[0061] The long-axis crystal grains are intricately intertwined, and the presence of crystal grains with an aspect ratio of less than 2.5 between them improves the properties of the sintered body. ３ N ４ Crystal grains other than β-Si crystal grains may be counted as long-axis crystal grains. When the above formulas 1 and 2 are satisfied, most of the long-axis crystal grains are β-Si crystal grains. ３ N ４ It is a crystalline particle.

[0062] The silicon nitride sintered body having the above-mentioned characteristics can have a Vickers hardness HV of 1500 or more. １／２ or more. Vickers hardness (Hv) is measured at an indentation load of 20 kgf by a method conforming to JIS-R-1610. Fracture toughness is measured at an indentation load of 20 kgf by the indenter penetration method (IF method) of JIS-R-1607, and calculated using the Niihara formula. JIS-R-1610 corresponds to ISO14705. JIS-R-1607 corresponds to ISO15732.

[0063] Furthermore, according to the embodiment, it is possible to suppress the variation in Vickers hardness. It is also possible to suppress the variation in fracture toughness. When the Vickers hardness HV of 100 random silicon nitride sintered bodies is measured, the difference between the maximum value of Vickers hardness HV and the minimum value of Vickers hardness HV can be made 80 or less. Furthermore, when the fracture toughness of 100 random silicon nitride sintered bodies is measured, the difference between the maximum value of fracture toughness and the minimum value of fracture toughness can be made 0.8 MPa m １／２ It can be the following:

[0064] The silicon nitride sintered body according to the embodiment can be used for wear-resistant members. Examples of wear-resistant members include bearing balls, rollers, check balls, wear pads, plungers, rollers, and friction stir welding tool members. These wear-resistant members slide against mating members made of metal or ceramics. To improve the durability of the sliding surface, the surface roughness (Ra) of the wear-resistant member is preferably 0.5 μm or less, more preferably 0.1 μm or less, and most preferably 0.05 μm or less. By using a polished surface as the sliding surface, the surface roughness (Ra) of the sliding surface can be reduced.

[0065] According to the embodiment, the variation in hardness of the silicon nitride sintered body is suppressed, and therefore the variation in polishing efficiency is also suppressed, so that the same polished surface can be obtained in the same polishing time.

[0066] Here, a bearing ball will be described as an example of a wear-resistant member. Fig. 2 is a diagram showing an example of a bearing ball. Fig. 3 is a diagram showing an example of a bearing. In Figs. 2 and 3, 1 is a bearing ball. In Fig. 3, 2 is a bearing, 3 is an inner ring, and 4 is an outer ring.

[0067] The bearing ball 1 is a member made of sintered silicon nitride according to the embodiment. In the bearing 2, a plurality of bearing balls 1 are arranged between an inner ring 3 and an outer ring 4. In the example shown in Fig. 3, 16 bearing balls 1 are used in the bearing 2.

[0068] Non-Patent Document 1 discloses a motor for an electric vehicle (EV) or hybrid vehicle (HEV). The maximum rotational speed of a passenger vehicle motor is said to reach 10,000 to 15,000 rpm. Because electric vehicles repeatedly stop and start, the motor's rotational speed varies between 0 and 15,000 rpm. To accommodate this change in motor rotational speed, inverter motors have been developed. Inverter motors control the motor's rotational speed by controlling the frequency of the power supplied to the AC (alternating current) motor. As shown in Non-Patent Document 1, changes in rotational speed lead to changes in torque. In mechanics, torque is the moment of force acting around a fixed rotational axis. An environment in which the rotational speed changes is, in other words, an environment in which the torque (i.e., stress) acting on the bearing ball changes.

[0069] According to the embodiment, the silicon nitride sintered body has reduced variation in fracture toughness value. Fracture toughness value is an index showing resistance to fracture. Specifically, fracture toughness value indicates resistance to fracture when a mechanical load is applied to a member having a crack or a crack-like defect. Fracture toughness value is a type of specific index showing toughness. Toughness refers to the resistance of a material to fracture.

[0070] When the rotational speed of the bearing 2 changes, the torque changes. When the torque changes, the stress applied to the bearing balls 1 changes. That is, when the rotational speed changes, the stress applied to the bearing balls 1 changes as they slide. Eccentricity occurs particularly when the rotational speed is high. Eccentricity causes slight changes in the gaps between the bearing balls and the inner and outer rings. The change in the gaps leads to changes in the contact state between the bearing balls 1 and the inner and outer rings 3 and 4, and the load applied from the bearing balls 1 to the inner and outer rings 3 and 4 increases. As a result, wear resistance decreases and electrolytic corrosion can occur.

[0071] According to the embodiment, variation in fracture toughness value of the silicon nitride sintered body is suppressed. By suppressing variation in fracture toughness value, the load on the inner ring 3 and the outer ring 4 by the bearing ball 1 is stable, even in an environment where eccentricity may occur. This makes it possible to improve the durability of the bearing 2. According to the embodiment, it is possible to improve the durability of not only the bearing ball 1 but also the bearing 2. In other words, the wear-resistant member according to the embodiment is suitable for bearing balls used in bearings for inverter motors.

[0072] A method for producing a silicon nitride sintered body according to the embodiment will be described. The method for producing the silicon nitride sintered body according to the embodiment is not limited as long as it has the above-mentioned characteristics. Here, a method for obtaining a silicon nitride sintered body with a good yield will be described.

[0073] First, silicon nitride powder is prepared. The silicon nitride powder is α-phase silicon nitride (α-Si ３ N ４ The silicon nitride powder preferably contains 85 mass % or more of silicon nitride, and has an average particle size of 2 μm or less. The silicon nitride powder preferably contains 2 mass % or less of oxygen.

[0074] Silicon nitride powder having an impurity Fe content in the range of 10 wtppm to 3000 wtppm may be used. Silicon nitride powder having an impurity Cr content in the range of 10 wtppm to 3000 wtppm may be used. Silicon nitride powder having an impurity Ca content in the range of 10 wtppm to 3000 wtppm may be used. For example, silicon nitride powder produced by a direct nitridation method may contain impurities within the above range. Alternatively, in the method for producing a silicon nitride sintered body according to the embodiment, silicon nitride powder containing impurities less than the above range may be used. For example, silicon nitride powder produced by an imide decomposition method contains impurities less than the above range. Note that the silicon nitride sintered body according to the embodiment can also be produced using silicon nitride powder containing impurities greater than the above range.

[0075] Next, a sintering aid powder is prepared. The sintering aid powder is, for example, a rare earth element compound and an aluminum compound. The rare earth element compound is, for example, one or more selected from the group consisting of yttrium oxide, yttrium oxynitride, lanthanoid oxide, and lanthanoid oxynitride. By using a rare earth element oxide or rare earth element oxynitride, it is possible to obtain a hexagonal α-SiAlON crystal and R ２ Si ３ O ３ N ４ When the total amount of the silicon nitride powder and all the sintering aid powders is taken as 100 mass %, the amount of the rare earth element compound added is preferably within a range of 2 mass % to 8 mass % in terms of the rare earth element alone.

[0076] The aluminum compound is, for example, one or more selected from the group consisting of aluminum oxide, aluminum nitride, and aluminum oxynitride. When both aluminum nitride and aluminum oxide are used, the ratio of the amount of aluminum nitride added to the total amount of aluminum nitride added (mass) and aluminum oxide added is preferably within the range of 0.6 to 0.95. That is, it is preferable that 0.6≦amount of aluminum nitride added (mass%) / (amount of aluminum nitride added (mass%)+amount of aluminum oxide added (mass%))≦0.95. Aluminum nitride is represented by AlN, and aluminum oxide is represented by Al ２ O ３ The added AlN and Al ２ O ３ The mass ratio (AlN / (AlN+Al ２ O ３ )) to obtain a hexagonal α-SiAlON crystal and R ４ Al ２ O ９ Crystals are easily formed. ３ Al ５ O １２ Crystalline and RAlO ３ It is also possible to suppress the formation of crystals. Therefore, the mass ratio (AlN / (AlN+Al ２ O ３) is preferably in the range of 0.6 to 0.95, more preferably in the range of 0.75 to 0.85. When the total of the silicon nitride powder and all sintering aid powders is taken as 100 mass%, the amount of the aluminum compound added is preferably in the range of 3 to 7 mass% in terms of aluminum alone.

[0077] If necessary, in addition to the rare earth element compound and the aluminum compound, one or more components selected from the group consisting of titanium (Ti), hafnium (Hf), molybdenum (Mo), W (tungsten), magnesium (Mg), and zirconium (Zr) may be added as a sintering aid. The component selected from the group consisting of titanium (Ti), hafnium (Hf), molybdenum (Mo), tungsten (W), magnesium (Mg), and zirconium (Zr) is, for example, one or more compounds selected from the group consisting of oxides, nitrides, carbides, and silicides. When the total of the silicon nitride powder and all sintering aid powders is taken as 100 mass%, the total amount of sintering aids added, excluding the rare earth element compound and the aluminum compound, is preferably in the range of 0.1 mass% to 10 mass%, more preferably in the range of 0.2 mass% to 5 mass%. If necessary, silicon carbide (SiC) or silicon oxide (SiO ２ ) may be added to the sintering aid. The amount of silicon carbide or silicon oxide added is preferably within the range of 0.1 mass % to 10 mass %. The amount of silicon carbide or silicon oxide added is a value when the total of the silicon nitride powder and all sintering aid powders (including silicon carbide or silicon oxide) is taken as 100 mass %.

[0078] When the total of the silicon nitride powder and all sintering aid powders is taken as 100% by mass, the oxygen content is preferably in the range of 2.0% by mass to 4.0% by mass. This "oxygen content" refers to the oxygen content in the raw material powder, and is, for example, the sum of the oxygen content of the silicon nitride powder, the oxygen content of the rare earth oxide powder, and the oxygen content of the aluminum oxide powder. Controlling the oxygen content in the raw material powder leads to controlling the oxygen content in the silicon nitride sintered body. This allows for control of the formation of each crystal. For this reason, the oxygen content in the raw material powder is preferably in the range of 2.0% by mass to 4.0% by mass, and more preferably in the range of 2.5% by mass to 3.4% by mass.

[0079] In addition, the amount of oxygen is controlled, and the mass ratio AlN / (AlN+Al ２ O ３ ) and the above, it becomes easier to control the formation of each crystal. In this way, in the production of the silicon nitride sintered body according to the embodiment, it is preferable to mix at least three kinds of powders, namely, silicon nitride powder, rare earth element compound powder, and aluminum compound powder, and to react the respective components to form each crystal. When the raw material powder contains hexagonal α-SiAlON powder or R ２ Si ３ O ３ N ４ Compared to using powder, the crystals can be distributed more uniformly.

[0080] Next, the silicon nitride powder and the sintering aid powder are mixed and subjected to a crushing process using a crusher such as a ball mill, and a binder and a solvent are added to the crushed mixed powder as needed.

[0081] Next, a molding step is carried out. The molding step is, for example, die molding, cold isostatic pressing (CIP), injection molding, rolling granulation, or sheet molding. When producing a spherical silicon nitride sintered body, die molding or rolling granulation is used. When producing a silicon nitride sintered body to be used for a bearing ball, the molded body obtained by die molding may be subjected to a cold isostatic pressing (CIP) treatment. By carrying out the molding step, a molded body is obtained.

[0082] The obtained molded body is subjected to a debinding step. In the debinding step, binders and the like are removed. The debinding step is preferably carried out at a temperature in the range of 300 to 600°C. The atmosphere in the debinding step is not particularly limited, and may be air or a non-oxidizing atmosphere. The non-oxidizing atmosphere is, for example, a nitrogen atmosphere or an argon atmosphere. A debound body is obtained by the debinding step.

[0083] The degreased body is then sintered in a sintering step. The sintering temperature is preferably in the range of 1700°C to 1900°C. If the sintering temperature is lower than 1700°C, the reaction of each component may be insufficient, resulting in insufficient formation of each crystal. If the sintering temperature exceeds 1900°C, the β-Si ３ N ４ There is a possibility that the crystal grains may grow excessively. Therefore, the sintering temperature is preferably in the range of 1700°C or higher and 1900°C or lower, and more preferably in the range of 1775°C or higher and 1825°C or lower.

[0084] The sintering step may be either pressureless sintering or pressure sintering. The sintering step is preferably carried out in a non-oxidizing atmosphere, such as a nitrogen atmosphere or an argon atmosphere.

[0085] If necessary, after the sintering step, it is preferable to perform a hot isostatic pressing (HIP) treatment at 30 MPa or more in a non-oxidizing atmosphere. The non-oxidizing atmosphere is, for example, a nitrogen atmosphere or an argon atmosphere. The temperature of the HIP treatment is preferably in the range of 1500°C to 1900°C. By performing the HIP treatment, it is possible to reduce (e.g., eliminate) pores in the silicon nitride sintered body. If the HIP treatment pressure is less than 30 MPa, such an effect cannot be fully obtained. Therefore, the pressure is preferably 30 MPa or more. There is no particular upper limit for the HIP treatment pressure, but it is preferably 200 MPa or less. If the pressure is higher than 200 MPa, it may increase the burden on the equipment.

[0086] In addition, by performing HIP treatment, the ratio (I １９．１° +I ３１．０° +I ３２．５° ) / (I ３３．６°+I ３６．１° ) can be reduced. In other words, the XRD peaks due to YAM crystals can be reduced. Similarly, the XRD peaks due to YAG crystals and the XRD peaks due to YAL crystals can also be reduced. Therefore, the HIP treatment also has the effect of preventing the XRD peaks due to YAG crystals and the XRD peaks due to YAL crystals from being detected. This is thought to be because the HIP treatment incorporates part or all of the YAM, YAG, and YAL into the hexagonal α-SiAlON crystals.

[0087] For example, when titanium oxide powder is added, the titanium oxide powder reacts with silicon nitride powder during the sintering process to form titanium nitride particles. By subjecting a silicon nitride sintered body containing titanium nitride to HIP treatment, the ratio (I ３６．５° +I ４２．４° ) / (I ３３．６° +I ３６．１° ) can be easily controlled within the range of 0.020 or more and 0.050 or less. This is thought to be because the crystallinity of the titanium nitride particles is improved by performing the HIP treatment.

[0088] The silicon nitride sintered body thus produced is polished where necessary to obtain a wear-resistant member. The polishing is preferably carried out using diamond abrasive grains. By polishing, a polished surface with a surface roughness (Ra) of 0.5 μm or less can be obtained. By adjusting the size of the abrasive grains, a polished surface with a surface roughness (Ra) of 0.1 μm or less, or even 0.05 μm or less can be obtained.

[0089] (Examples) (Examples 1 to 23, Comparative Examples 1 to 3) The oxygen content was 2 mass % or less, and the α-phase silicon nitride (α-Si ３ N ４A silicon nitride powder containing 85% or more by mass of rare earth element (rare earth element) was prepared. The average particle size of the silicon nitride powder was 2 μm or less. In all examples, silicon nitride powder produced by direct nitriding was used. In Examples 1 to 13, Examples 17 to 23, and Comparative Examples 1 to 3, the Fe, Cr, and Ca contents of the silicon nitride powder were all within the range of 50 wtppm to 1000 wtppm. In Examples 14 to 16, the Fe, Cr, and Ca contents of the silicon nitride powder all exceeded 1000 wtppm. Next, the sintering aids shown in Table 1 were prepared. In all examples, when the total of the silicon nitride powder and all sintering aid powders is taken as 100% by mass, the amount of rare earth element compound added was within the range of 2% to 8% by mass, calculated as the rare earth element alone, and the Al content was within the range of 3% to 7% by mass, calculated as the Al alone.

[0090]

[0091] The raw material powder was crushed in a ball mill, and then a binder was added. Then, molding and CIP treatment were performed to produce a spherical compact having a band-shaped portion. The band-shaped portion is a portion that exists on the outer periphery of the spherical compact and protrudes outward. A debinding process was performed on the spherical compact having the band-shaped portion to obtain a debound body. The debound body was then subjected to a sintering process and a HIP process. In the sintering process, pressure sintering was performed in a nitrogen atmosphere. The temperature and pressure in the sintering process and the temperature and pressure in the HIP process are as shown in Table 2.

[0092]

[0093] Silicon nitride sintered bodies according to the examples and comparative examples were manufactured using the above steps. An arbitrary cross section of each silicon nitride sintered body was subjected to XRD analysis. Peaks based on each crystal were identified from the XRD analysis results, and their respective maximum peak intensities were recorded. Using these maximum peak intensities, the maximum peak intensity ratios identified by Equations 1 to 4 were calculated. The presence or absence of peaks based on YAG crystals and peaks based on YAL crystals was also confirmed. The conditions for the XRD analysis were as described above. The results are shown in Table 3.

[0094]

[0095] In Table 3, "Equation 1" represents the maximum peak intensity ratio (I ２０．５° +I ２２．８° +I ３４．３° +I ３８．７° ) / (I ３３．６° +I ３６．１° ) "Equation 2" represents the maximum peak intensity ratio (I ３１．８° +I ３７．２° ) / (I ３３．６° +I ３６．１° ) Equation 3 represents the maximum peak intensity ratio (I １９．１° +I ３１．０° +I ３２．５° ) / (I ３３．６° +I ３６．１° ) Equation 4 represents the maximum peak intensity ratio (I ３６．５° +I ４２．４° ) / (I ３３．６° +I ３６．１° ) is shown.

[0096] All of the silicon nitride sintered bodies according to the examples satisfied formulas 1 to 4. Furthermore, in all of the examples, neither the XRD peak of a YAG crystal nor the XRD peak of a YAL crystal was detected. Furthermore, in all of the examples, the XRD peak based on a cubic α-SiAlON crystal was not detected. In contrast, the silicon nitride sintered bodies according to the comparative examples did not satisfy either formula 1 or formula 2.

[0097] Next, the Fe content, Cr content, and Ca content in the silicon nitride sintered body were measured. Furthermore, an arbitrary cross section of the silicon nitride sintered body was observed with a laser microscope. From the results of the observation with the laser microscope, the total area ratio of the white region was measured. An arbitrary cross section of the silicon nitride sintered body was observed with a SEM. From the results of the observation with the SEM, the total area ratio of long-axis crystal grains with a major axis of 2.5 μm or more and an aspect ratio of 2.5 or more was calculated. The respective measurement methods were as described above. The results are shown in Table 4.

[0098]

[0099] The silicon nitride sintered bodies according to the examples contained impurities of Fe, Cr, and Ca. In Examples 1 to 13 and 17 to 23, the total area ratio of the white regions was within the range of 0% to 70%. In addition, multiple long-axis crystal grains were present, and the total area ratio was within the range of 20% to 70%. In Examples 1 to 3, where the white regions were 0%, neither the YAG amorphous phase nor the YAL amorphous phase was detected.

[0100] The Fe, Cr, and Ca contents of the silicon nitride sintered body according to the comparative example were equivalent to those of the silicon nitride sintered body according to the example, while the total area ratio of the white regions and the total area ratio of the long-axis crystal grains of the comparative example exceeded the preferred ranges.

[0101] Next, the Vickers hardness HV and fracture toughness of the silicon nitride sintered bodies were measured. The methods for measuring the Vickers hardness HV and fracture toughness were as described above. 100 silicon nitride sintered bodies were prepared for each of the examples and comparative examples. The average, minimum, and maximum values ​​were investigated. The results are shown in Table 5.

[0102]

[0103] In the examples, the average Vickers hardness HV of the silicon nitride sintered body was 1500 or more. The variation was within the range of ±50. The fracture toughness value was 6.0 MPa m １／２ The variation is ±0.8 MPa m １／２ was within the range.

[0104] In contrast, in the comparative example, although the average value of Vickers hardness HV was 1500 or more, the variation was large. Similarly, the variation in fracture toughness value was also large.

[0105] Next, durability tests were conducted using bearing balls made of sintered silicon nitride according to the examples and comparative examples. The diameter of the bearing balls used was 9.525 mm (3 / 8 inch). The bearing balls were polished to a surface roughness Ra of 0.013 μm or less. Sixteen bearing balls were assembled between an inner ring and an outer ring to produce a bearing. The inner ring and outer ring were made of bearing steel SUJ2. The durability and electrolytic corrosion resistance of each bearing were investigated.

[0106] In the durability test, the bearing was continuously driven while changing the rotational speed. The conditions for changing the rotational speed were as follows: "50 rpm for 1 hour" → "increase from 50 rpm to 2000 rpm over 1 hour" → "2000 rpm for 1 hour" → "increase from 2000 rpm to 13000 rpm over 1 hour" → "13000 rpm for 1 hour" → "decrease from 13000 rpm to 50 rpm over 1 hour." This set was repeated. The sliding noise (dB) was measured when the continuous driving reached 100 hours, 400 hours, and 800 hours. The ratio of the sliding noise after 400 hours to the sliding noise after 100 hours and the ratio of the sliding noise after 800 hours to the sliding noise after 100 hours were calculated as the increase rate of the sliding noise.

[0107] Silicon nitride sintered bodies with an increase rate of 10% or less were recorded as "best" (double circle). Silicon nitride sintered bodies with an increase rate of more than 10% but less than 20% were recorded as "good" (circle). Silicon nitride sintered bodies with an increase rate of more than 20% were recorded as "poor" (cross). This test makes it possible to check for changes in the sliding condition due to damage to the bearing balls or seizure of the raceway rings. The sliding noise was measured in accordance with JIS-B-1548. Furthermore, the presence or absence of electrolytic corrosion after 800 hours was checked to determine electrolytic corrosion resistance. The results are shown in Table 6.

[0108]

[0109] In the examples, the rate of increase in the sliding noise of the bearing balls was suppressed. In examples 10 and 14-16, the rate of increase in the sliding noise after 800 hours was slightly higher than in the other examples. This is thought to be due to the high area ratio of the white region. Furthermore, in many examples, the occurrence of electrolytic corrosion of the bearing balls was suppressed. From these results, it was found that, according to the embodiment, it is possible to improve the properties of silicon nitride sintered bodies manufactured from silicon nitride powder with a high impurity content. In examples 14-16, although the wear resistance was good, the occurrence of electrolytic corrosion was confirmed. This is because the amount of impurities (Fe content, Cr content, or Ca content) was higher than in the other examples. In contrast, in the comparative example, the rate of increase in the sliding noise after 800 hours was larger. The occurrence of electric lighting was also confirmed.

[0110] The embodiments of the present invention include the following features: (Feature 1) In the XRD analysis results of an arbitrary cross section, the strongest peak intensities corresponding to hexagonal α-SiAlON crystals detected at angles of 20.5±0.3°, 22.8±0.3°, 34.3±0.3°, and 38.7±0.3° are respectively expressed as I ２０．５° , I ２２．８° , I ３４．３° , I ３８．７° and β-Si detected at 33.6±0.3° and 36.1±0.3°. ３ N ４ The strongest peak intensities corresponding to the crystals are I ３３．６° , I ３６．１° and R detected at 31.8±0.3° and 37.2±0.3° ２ Si ３ O ３ N ４ The strongest peak intensities corresponding to the crystal (R is a rare earth element) are I ３１．８° , I ３７．２° In this case, 0.001≦(I ２０．５° +I ２２．８° +I ３４．３° +I ３８．７° ) / (I ３３．６° +I ３６．１° )≦0.300 and 0.002≦(I ３１．８° +I ３７．２° ) / (I ３３．６° +I ３６．１°)≦0.100. (Feature 2) In the XRD analysis results, R detected at 19.1±0.3°, 31.0±0.3°, and 32.5±0.3° are ４ Al ２ O ９ (R is a rare earth element) is expressed as I １９．１° , I ３１．０° , I ３２．５° In this case, 0≦(I １９．１° +I ３１．０° +I ３２．５° ) / (I ３３．６° +I ３６．１° )≦0.100. (Feature 3) In the XRD analysis results, the strongest peak intensities corresponding to titanium nitride detected at 36.5±0.3° and 42.4±0.3° are expressed as I ３６．５° , I ４２．４° In this case, 0.020≦(I ３６．５° +I ４２．４° ) / (I ３３．６° +I ３６．１° )≦0.050. (Feature 4) R ３ Al ５ O １２ XRD peaks based on crystals and RAlO ３A silicon nitride sintered body according to any one of Features 1 to 3, in which no XRD peaks due to crystals are detected (including those below the detection limit). (Feature 5) A silicon nitride sintered body according to any one of Features 1 to 4, containing 3% by mass or more and 7% by mass or less of Al and 2% by mass or more and 8% by mass or less of rare earth elements. (Feature 6) A silicon nitride sintered body according to any one of Features 1 to 5, in which the iron content is in the range of 10 wtppm or more and 3000 wtppm or less. (Feature 7) A silicon nitride sintered body according to any one of Features 1 to 6, in which, when the cross section is observed with a laser microscope, the area ratio of white regions in a measurement area of ​​4000 μm × 4000 μm is 70% or less. (Feature 8) The silicon nitride sintered body according to any one of Features 1 to 7, wherein, when the cross section is observed by SEM, a plurality of crystal grains having a major axis of 2.5 μm or more and an aspect ratio of 2.5 or more are present in a measurement area of ​​20 μm×15 μm, and the total area ratio of the plurality of crystal grains is in the range of 20% to 70%. (Feature 9) The silicon nitride sintered body according to any one of Features 1 to 8, having a Vickers hardness HV of 1500 or more. (Feature 10) A fracture toughness value of 6.0 MPa m １／２ The silicon nitride sintered body according to any one of Features 1 to 9. (Feature 11) A wear-resistant member using the silicon nitride sintered body according to any one of Features 1 to 10. (Feature 12) The wear-resistant member according to Feature 11, which is a bearing ball.

[0111] 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.

[0112] 1...Bearing ball 2...Bearing 3...Inner ring 4...Outer ring

Claims

1. In the XRD analysis results of any cross section, the strongest peak intensities corresponding to hexagonal α-SiAlON crystals detected at 20.5±0.3°, 22.8±0.3°, 34.3±0.3°, and 38.7±0.3° are defined as I ２０．５° , I ２２．８° , I ３４．３° , I ３８．７° β-Si detected at 33.6±0.3° and 36.1±0.3° ３ N ４ The strongest peak intensities corresponding to the crystals are I ３３．６° , I ３６．１° R detected at 31.8±0.3° and 37.2±0.3° ２ S ３ O ３ N ４ The strongest peak intensities corresponding to the crystals (R is a rare earth element) are I ３１．８° , I ３７．２° In this case, 0.001≦(I ２０．５° +I ２２．８° +I ３４．３° +I ３８．７° ) / (I ３３．６° +I ３６．１° )≦0.300 and 0.002≦(I ３１．８° +I ３７．２° ) / (I ３３．６° +I ３６．１° ) ≦0.

100.

2. In the XRD analysis results, Rs detected at 19.1±0.3°, 31.0±0.3°, and 32.5±0.3° ４ A ２ O ９ (R is a rare earth element) １９．１° , I ３１．０° , I ３２．５° In this case, 0≦(I １９．１° +I ３１．０° +I ３２．５° ) / (I ３３．６° +I ３６．１° 2. The silicon nitride sintered body according to claim 1, which satisfies the following:

3. In the XRD analysis results, the strongest peak intensities corresponding to titanium nitride detected at 36.5±0.3° and 42.4±0.3° are designated as I ３６．５° , I ４２．４° In this case, 0.020≦(I ３６．５° +I ４２．４° ) / (I ３３．６° +I ３６．１° 3. The silicon nitride sintered body according to claim 1 or 2, which satisfies the following: )≦0.

050.

4. R ３ A ５ O １２ XRD peaks based on crystals and RAlO ３ 3. The silicon nitride sintered body according to claim 1, wherein no XRD peaks due to crystals are detected (including peaks below the detection limit).

5. R ３ A ５ O １２ XRD peaks based on crystals and RAlO ３ 4. The silicon nitride sintered body according to claim 3, in which no XRD peaks due to crystals are detected (including peaks below the detection limit).

6. A silicon nitride sintered body according to claim 1 or 2, containing 3 mass % or more and 7 mass % or less of Al and 2 mass % or more and 8 mass % or less of rare earth elements.

7. A silicon nitride sintered body according to claim 5, containing 3% by mass or more and 7% by mass or less of Al and 2% by mass or more and 8% by mass or less of rare earth elements.

8. A silicon nitride sintered body according to claim 1 or 2, wherein the iron content is within the range of 10 wtppm or more and 3000 wtppm or less.

9. The silicon nitride sintered body according to claim 5, wherein the iron content is within the range of 10 wtppm or more and 3000 wtppm or less.

10. A silicon nitride sintered body according to claim 1 or 2, wherein when the cross section is observed with a laser microscope, the area ratio of white regions in a measurement area of ​​4000 μm × 4000 μm is 70% or less.

11. A silicon nitride sintered body according to claim 1 or claim 2, wherein, when the cross section is observed with an SEM, in a measurement area of ​​20 μm × 15 μm, there are a plurality of crystal grains having a major axis of 2.5 μm or more and an aspect ratio of 2.5 or more, and the total area ratio of the plurality of crystal grains is within the range of 20% or more and 70% or less.

12. A silicon nitride sintered body as described in claim 6, wherein, when the cross section is observed with an SEM, in a measurement area of ​​20 μm × 15 μm, there are a plurality of crystal grains having a major axis of 2.5 μm or more and an aspect ratio of 2.5 or more, and the total area ratio of the plurality of crystal grains is within the range of 20% or more and 70% or less.

13. A silicon nitride sintered body as described in claim 7, wherein, when the cross section is observed with an SEM, in a measurement area of ​​20 μm × 15 μm, there are a plurality of crystal grains having a major axis of 2.5 μm or more and an aspect ratio of 2.5 or more, and the total area ratio of the plurality of crystal grains is within the range of 20% or more and 70% or less.

14. The silicon nitride sintered body according to claim 1 or 2, which has a Vickers hardness HV of 1,500 or more.

15. Fracture toughness value is 6.0 MPa·m １／２ 3. The silicon nitride sintered body according to claim 1 or 2.

16. A wear-resistant member using the silicon nitride sintered body according to claim 1.

17. A wear-resistant member using the silicon nitride sintered body according to claim 14.

18. The wear-resistant member according to claim 16 which is a bearing ball.

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