Vitrified-bond superabrasive wheel

Abstract

Provided is a vitrified-bond superabrasive wheel comprising a base metal and a vitrified-bond superabrasive layer fixed thereto, wherein the superabrasive layer comprises superabrasive grains and a vitrified bond and has voids. The superabrasive grains have an average grain diameter of 0.02-1.0 μm and the voids include small voids having diameters of 0.10 μm or larger but smaller than 10 μm, the average value of the diameters of the small voids being 0.3-3.0 μm. The voids include large voids having diameters of 20-500 μm, the average value of the diameters of the large voids being 20-120 μm and the average value of void-to-void distances of the large voids being 40-300 μm.

Description

Vitrified bond super abrasive wheel

[0001] The present disclosure relates to a vitrified bond superabrasive wheel. This application claims priority to Japanese Patent Application No. 2024-113328, filed on July 16, 2024. The entire contents of said Japanese Patent Application are incorporated herein by reference.

[0002] Conventionally, vitrified bonded superabrasive wheels have been disclosed, for example, in Patent Document 1: JP 2012-152881 A, Patent Document 2: JP 2012-200831 A, Patent Document 3: JP 2010-521326 A, Patent Document 4: JP 2019-181614 A, Patent Document 5: JP 2018-510074 A, and Patent Document 6: JP 2019-59019 A.

[0003] Japanese Patent Laid-Open No. 2012-152881 Japanese Patent Laid-Open No. 2012-200831 Japanese Patent Laid-Open No. 2010-521326 Japanese Patent Laid-Open No. 2019-181614 Japanese Patent Laid-Open No. 2018-510074 Japanese Patent Laid-Open No. 2019-59019

[0004] A vitrified-bond superabrasive wheel according to the present disclosure has a vitrified-bond superabrasive layer fixed to a base metal. The superabrasive layer includes superabrasive grains, a vitrified bond, and pores. The average particle size of the superabrasive grains is 0.02 μm or more and 1.0 μm or less. The pores include small pores with diameters of 0.10 μm or more and less than 10 μm. The average diameter of the small pores is 0.3 μm or more and 3.0 μm or less. The pores include large pores with diameters of 20 μm or more and 500 μm or less. The average diameter of the large pores is 20 μm or more and 120 μm or less. The average distance between the large pores is 40 μm or more and 300 μm or less.

[0005] Fig. 1 is a diagram showing an image of the structure of a superabrasive grain layer 6 enlarged at a high magnification. Fig. 2 is a diagram showing an image of the structure of a superabrasive grain layer 6 enlarged at a low magnification. Fig. 3 is a schematic diagram of a superabrasive grain wheel 10 having a superabrasive grain layer 6. Fig. 4 is a Delaunay diagram expressed as a collection of Delaunay triangles for measuring the distance between large pores 7. Fig. 5 is a schematic diagram of a superabrasive grain wheel 20 and a table 110 shown to explain a grinding method using the superabrasive grain wheel 20.

[0006] [Problem to be Solved by the Present Disclosure] Conventional vitrified bonded superabrasive wheels have the problem that the sharpness increases with a high wear rate, and the sharpness decreases with a low wear rate.

[0007] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0008] Porous materials tend to aggregate, and poor dispersion of medium-sized or larger pores can lead to localized clogging, resulting in excessive grinding resistance for the abrasive layer as a whole. The reason for this is that wear-resistant superabrasive grain layers are prone to clogging because they are less likely to self-sharpen, but clogging can be eliminated by adding medium-sized or larger pore agents. On the other hand, if the amount of medium-sized or larger pore agent added is small, clogging can be eliminated around the pores, but clogging occurs in areas far from the pores.

[0009] Furthermore, adding too many small pores can lead to increased wear. The reason is that a certain level of abrasive layer strength is necessary when machining high-hardness materials such as SiC and sapphire, but adding too many small pores significantly reduces the abrasive layer strength and increases wear.

[0010] A vitrified-bond superabrasive wheel according to the present disclosure has a vitrified-bond superabrasive layer fixed to a base metal. The superabrasive layer includes superabrasive grains, a vitrified bond, and pores. The average particle size of the superabrasive grains is 0.02 μm or more and 1.0 μm or less. The pores include small pores with diameters of 0.10 μm or more and less than 10 μm. The average diameter of the small pores is 0.3 μm or more and 3.0 μm or less. The pores include large pores with diameters of 20 μm or more and 500 μm or less. The average diameter of the large pores is 20 μm or more and 120 μm or less. The average distance between the large pores is 40 μm or more and 300 μm or less.

[0011] With this type of vitrified-bond superabrasive wheel, the pores formed by large pores ranging from 20 μm to 500 μm or more are dispersed and present with reduced variation, maximizing the chip removal effect. This allows a sharp abrasive cutting edge to always act on the workpiece, enabling highly efficient machining of the workpiece. Generally, if chips exist between the workpiece and the abrasive grains, workpiece removal will not progress. As a result, grinding resistance will be high and wear will increase. The abrasive grain layer according to the present disclosure can solve these problems.

[0012] The discharge of chips prevents clogging of the grinding surface, allowing for stable machining. Furthermore, the cooling of processing heat by retaining coolant prevents the abrasive grains from becoming dull due to processing heat, allowing for stable machining.

[0013] If the average inter-pore distance is large and the pore distribution varies widely, the desired effect cannot be achieved and stable processing cannot be achieved. If the average inter-pore distance is small, the chip cannot have sufficient strength and the desired effect cannot be achieved.

[0014] Furthermore, the pores are preferably spherical in shape in order to disperse the pores uniformly and to suppress variations in the distance between the pores.

[0015] The small pores create unevenness on the grinding surface, which has the effect of enabling stable processing without clogging.

[0016] Preferably, the standard deviation of the inter-pore distances of the large pores is not more than half the average value of the inter-pore distances of the large pores.

[0017] The standard deviation σ of the distance between large pores is calculated using the following formula: σ = [(1 / n){(W1-A) 2 +(W2-A) 2 +...+(Wn-A) 2}] 1 / 2 Here, the distances between the n large holes are W1, W2, ... Wn.

[0018] The average distance between n large pores is defined as A. A can be calculated using the following formula: A = (1 / n)(W1 + W2 + ... Wn) By making the standard deviation of the distance between large pores less than half the average value, the dispersion of the large pores is improved, making it easier to achieve the desired effect.

[0019] Preferably, the small pores have an average diameter of 1.0 μm or more and 2.0 μm or less. Preferably, the proportion of the small pores in the superabrasive layer is 5.0 volume % or more and 40.0 volume % or less.

[0020] Preferably, the large pores are spherical, and the ratio of the minor axis a to the major axis b (a / b) of the large pores is 0.5 or more and 1.0 or less. The spherical shape of the large pores can suppress variation in the distance between pores, thereby achieving the desired effect. To make the pores spherical, a spherical resin-based pore-forming material is used, and the large pores are formed by burning it off in a baking process.

[0021] Preferably, the ratio of the large pores to the superabrasive layer is 5.0% by volume or more and 50.0% by volume or less. If the large pores fall within this range, it is easy to form a uniform pore-to-pore distance at low cost.

[0022] Preferably, the superabrasive layer contains a filler, the filler containing at least one selected from the group consisting of silicon carbide, hBN, and alumina, and the filler content in the superabrasive layer is 2% by volume or more and 40% by volume or less. By adding a filler, the concentration of superabrasive particles in the superabrasive layer can be adjusted, preferably to a low concentration. This allows low grinding resistance to be achieved.

[0023] Preferably, the softening temperature of the vitrified bond is 600°C or higher and 900°C or lower. A vitrified bond with high self-sharpening properties desirably has a low softening point. The softening point is preferably between 600°C and 700°C. The softening point of the vitrified bond can be measured, for example, by the glass softening point measurement method specified in JIS R3101-1 (2001).

[0024] Preferably, the vitrified bonded superabrasive wheel is made of SiC, GaN, LiTaO ３ (lithium tantalate), or LiNbO ３ It is used for processing compound semiconductor wafers made of lithium niobate.

[0025] Figure 1 is a highly magnified image of the structure of the superabrasive layer. The vitrified-bond superabrasive wheel of the present disclosure has small pores on the order of several microns, as shown in Figure 1, formed in a bond called the abrasive layer. The superabrasive layer 6 has a vitrified bond 2, superabrasive grains 3 and filler 4 held by the vitrified bond 2, and small pores 5 surrounded by the vitrified bond 2, superabrasive grains 3, and filler 4. The superabrasive layer 6 is capable of grinding a workpiece 11 made of, for example, SiC.

[0026] The vitrified bond 2 has, for example, the following composition: SiO ２ :30 to 60% by mass, Al ２ O ３ :2 to 15% by mass, B ２ O ３ : 15 to 40 mass%, RO (RO is one or more oxides selected from CaO, MgO, and BaO): 1 to 10 mass%, R ２ O (R ２ O is Li ２ O, Na ２ O and K ２ O): 5 to 15 mass%, ZrO ２ : 0 to 8 mass%, others: 0 to 5 mass%.

[0027] The superabrasive grains 3 are made of, for example, diamond, CBN, or a mixture thereof. The filler 4 is an auxiliary material added to reduce the concentration of the superabrasive grains 3.

[0028] When the superabrasive grains 3 of the superabrasive grain layer 6 grind the workpiece 11 , chips 12 are generated and adhere to the surface of the superabrasive grain layer 6 .

[0029] Figure 2 is a highly magnified image of the vitrified-bond superabrasive grain structure. As shown in Figure 2, the superabrasive grain layer 6 has large pores 7 on the order of tens to hundreds of microns. By uniformly dispersing the large pores 7, the average inter-pore distance between the large pores 7 is in the range of 100 μm to 300 μm. Furthermore, by dispersing the large pores uniformly, the standard deviation is less than half of the average value.

[0030] Figure 3 is a schematic diagram of a superabrasive wheel 10 having a superabrasive layer 6 and a workpiece 11. As shown in Figure 3, in the superabrasive wheel 10, a plurality of segment-shaped superabrasive layers 6 are fixed to a base metal 9. An adhesive layer may be provided between the superabrasive layer 6 and the base metal 9. The superabrasive wheel 10 is a so-called grinding wheel, and the superabrasive layer 6 is provided on the axial surface or the radial surface. In other words, the superabrasive wheel 10 may be either a surface grinding wheel or a cylindrical grinding wheel.

[0031] The present disclosure relates to a wheel used for precision grinding of, for example, SiC wafers, and the average particle size of the superabrasive grains 3 made of diamond is in the range of 0.02 μm to 1.00 μm.

[0032] (Manufacturing Method) A method for manufacturing such a superabrasive wheel 10 will now be described.

[0033] (Step 1) First, various compositions of superabrasive grains 3 made of diamond, vitrified bond 2, which is a glass binder, filler 4, pore-forming material with an average particle size of Φ0.3 to 3.0 μm, and binder are blended and wet-mixed to obtain a first mixture. At this time, these raw materials are mixed at a constant rotation speed (15-400 rpm) for 120 hours to ensure uniform mixing. The first mixture is dried and pulverized to obtain a pulverized product. At this time, pulverization is performed at a constant rotation speed (15-400 rpm) for 48 hours or more to obtain a pulverized product with an average particle size of 50 μm or less.

[0034] (Step 2) Next, in a separate container, pore-forming materials with average particle diameters of 30 μm to 300 μm are mixed in various compositions and mixed at a constant rotation speed (15-400 rpm) for 60 hours to obtain a second mixture of uniform pore-forming materials. To uniformly mix the ground material and the second mixture, the mixture is mixed at a constant rotation speed (15-400 rpm) for 120 hours to obtain a third mixture.

[0035] The third mixture is pressure molded into chips of a specified size, and the chips are fired to burn off the pore-forming material and binder, producing a superabrasive layer 6 as a fired chip composed of superabrasive grains 3, vitrified bond 2, filler 4, small pores 5, and large pores 7. The fired chip is bonded to base metal 9, which is a metal body, and the chip is ground to the specified size, thereby producing a vitrified-bond superabrasive wheel 10.

[0036] The pore-forming material used is a spherical resin, and the traces of the pore-forming material that have been burned off retain their original state, so that roughly spherical pores remain in the vitrified bond 2 after firing.

[0037] [Details of the embodiment of the present disclosure] (Production of vitrified bonds of sample numbers 1 to 17)

[0038]

[0039] Vitrified bonded superabrasive wheels of sample numbers 2 to 5, 9 to 13, and 15 to 17 were manufactured according to the above "(Manufacturing Method)." Furthermore, vitrified bonded superabrasive wheels of sample numbers 1, 6, 7, 8, and 14 were manufactured by a method different from the above "(Manufacturing Method)." In the manufacturing method of sample number 1, a pore-forming material with an average particle diameter of Φ0.2 μm was used in step 1. In the manufacturing method of sample number 6, a pore-forming material with an average particle diameter of Φ3.5 μm was used in step 1. In the manufacturing method of sample number 7, a pore-forming material with an average particle diameter of Φ12 μm was used in step 1.

[0040] In the manufacturing method of sample No. 8, a pore-forming material with an average particle size of Φ20 μm was used in step 2. In the manufacturing method of sample No. 14, a pore-forming material with an average particle size of Φ180 μm was used in step 2. In all samples, the composition of the vitrified bond was as follows:

[0041] SiO ２ :30 to 60% by mass, Al ２ O ３ :2 to 15% by mass, B ２ O ３ : 15 to 40 mass%, RO (RO is one or more oxides selected from CaO, MgO, and BaO): 1 to 10 mass%, R ２ O (R ２ O is Li ２ O, Na ２ O and K ２ O): 5 to 15 mass%, ZrO ２ : 0 to 8 mass%, others: 0 to 5 mass%.

[0042] (Method of measuring the average particle size of the superabrasive grains 3) To measure the average particle size of the superabrasive grains 3 contained in the vitrified bond superabrasive grain wheel, the superabrasive grain layer 6 was dissolved with an acid or the like to remove the superabrasive grains 3. When the superabrasive grain wheel was large, the superabrasive grain layer 6 was dissolved in a predetermined volume (for example, 0.5 cm ３The cut-out superabrasive layer 6 is dissolved in acid or the like to extract the superabrasive particles, which are then measured with a laser diffraction particle size distribution analyzer (for example, the SALD series manufactured by Shimadzu Corporation) to determine the average particle size. The average particle size in this case refers to the D50 value.

[0043] (Method for measuring the diameter of small pores 5) The diameter of small pores 5 was measured as follows: The superabrasive layer 6 was cut with a diamond cutter, and the cut surface was polished by ion milling (for example, a CROSSSECTION POLISHER IB-19530 manufactured by JEOL Ltd.), and then three or more images were taken with an FE-SEM (for example, a JEOL Ltd. JSM-IT800 with a lens magnification of ×5000).

[0044] In the images, the small pores 5 appear as a grayish black or out of focus. The images were analyzed by an observer using image analysis software (e.g., WinROOF manufactured by Mitani Shoji Co., Ltd.) to measure the length and identify the long diameter. Regions with a long diameter of 0.1 μm or more and 10 μm or less were defined as small pores 5, and 100 or more small pores 5 were extracted. The long diameter of the extracted small pores 5 was defined as the diameter, and the diameter of the small pores 5 was measured.

[0045] (Measurement of the diameter of large pores 7) The large pores 7 in the abrasive grain layer were extracted by image analysis using the following image analysis software on three images (taken so that no part of each image overlaps) taken at three different locations using a stereomicroscope (e.g., a KEYENCE VHX7000 with a lens magnification of ×50). More specifically, the original images were converted to grayscale, and the boundaries were extracted. More than 300 regions corresponding to pores were extracted by image binarization. These regions were filtered to have an aspect ratio (minimum diameter / maximum diameter) of 0.5 to 1.0, and within the region with an aspect ratio of 0.5 to 1.0, those with a minimum circumscribed circle diameter of 20 μm to 500 μm were defined as large pores 7. The lower limit of the diameter of these large pores, 20 μm, was set because the lower limit of the diameter recognizable in the image taken here was around 20 μm.

[0046] The original pore-forming material was spherical and fell within the above aspect ratio, and since the spherical shape remained even after molding, only a very small amount was excluded by filtering the aspect ratio.

[0047] (Calculation of the volume ratio of large pores 7) The total area of ​​the images photographed in the above "(Measurement of the diameter of large pores 7)" was defined as S1, and the total area of ​​the measured large pores was defined as S2. The average value of S2 / S1 calculated for each of the three images was taken as the volume ratio of large pores 7.

[0048] (Calculation of the volume ratio of small pores 5) The total area of ​​the images photographed in the above "(Measurement of the diameter of small pores 5)" was defined as S3, and the total area of ​​the measured small pores was defined as S4. The average value of S4 / S3 calculated for each of three or more images was defined as the volume ratio of small pores 5.

[0049] (Measurement of distance between pores) The distance between the large pores 7 was defined as the distance between the pore centroids of the large pores 7. The centroid of the large pore 7 was the center of the smallest circumscribing circle of the large pore 7.

[0050] The distance between pore centers was calculated using a Delaunay diagram, where the distance between the pore centers of the large pores extracted above was expressed as a collection of Delaunay triangles.

[0051] 4 is a Delaunay diagram expressed as a collection of Delaunay triangles for measuring the distance between large pores 7. The centroids 7G of multiple large pores 7 are connected by lines 7A, forming multiple Delaunay triangles 7T. Each of these multiple lines 7A is the distance between the large pores 7.

[0052] In order to measure the distance between the large pores 7, the large pores 7 exposed on the surface of the superabrasive grain layer 6 were extracted. At least 300 large pores 7 were extracted.

[0053] As a precaution when taking photographs, the surface of the chip with the superabrasive grain layer 6 after firing was roughly polished with #400 abrasive paper. After that, the chip surface was additionally polished with #1200 abrasive paper, and three surface photographs were taken using a KEYENCE VHX7000 with a lens magnification of ×50 so that the fields of view did not overlap.

[0054] (Image analysis software and commands used) For the above (measurement of large pore diameter) and (measurement of inter-pore distance), the commands in Table 2 were used, which were created for this analysis using the multipurpose image processing tool MultiImageTool, manufactured by System In Frontier Co., Ltd. Image analysis was performed using this software, and the large pore diameter and inter-pore distance were calculated.

[0055]

[0056] (Measurement of the volume fraction of filler 4) The volume fraction of filler 4 was measured using the following procedure. The superabrasive layer 6 was cut with a diamond cutter, and the cut surface was polished by ion milling (e.g., JEOL CROSSSECTION POLISHER IB-19530). Three or more images were then taken using a FE-SEM (e.g., JEOL JSM-IT800 with a lens magnification of 5000). In the images, filler 4 appears grayish white. Using image analysis software (e.g., WinROOF manufactured by Mitani Shoji Co., Ltd.), an observer extracted the white-gray areas and measured their areas. The volume fraction of filler 4 was calculated as the average value of S6 / S5 calculated for each of the three or more images, where S5 is the area of ​​the image taken and S6 is the area of ​​the measured filler 4.

[0057] (Machining Test) A plurality of superabrasive wheels 10 were fabricated with the shape shown in Fig. 3 and a diameter D of 250 mm. Each superabrasive wheel had a superabrasive layer 6 corresponding to each of sample numbers 1-13. Using this superabrasive wheel 10 attached to a Tokyo Seimitsu HRG200X high-rigidity grinding machine, machining was carried out to a thickness equivalent to that of ten 6-inch single-crystal SiC wafers.

[0058] 5 is a schematic diagram of superabrasive wheel 10 and table 110 shown to explain a grinding method using superabrasive wheel 10. In grinding method 100, workpiece 11, which is a SiC wafer, is fixed on table 110. Here, table 110 is rotatable in the direction indicated by arrow 110R. Superabrasive wheel 10 is rotatable in the direction indicated by arrow 1R. Furthermore, the direction indicated by arrow 1F is the cutting direction.

[0059] The machining conditions are spindle speed 1250 min－１ , work rotation speed 300 min －１ The grinding conditions were: feed rate 0.3 μm / sec, machining allowance 10 μm, and spark-out time 10 sec. During the grinding process, the wear rate (change in height of superabrasive layer 6 before and after wear / change in thickness of ground portion of workpiece (wafer) before and after grinding) × 100), the load current value for rotating superabrasive wheel 10, and the normal resistance in the direction indicated by arrow 11F in FIG. 5 were measured. The results are shown in Table 3.

[0060]

[0061] The grinding results in Table 3 are the average values ​​for 10 pieces. From Table 3, taking into consideration the grinding efficiency and grinding quality required in the actual market, products that met all the performance requirements of a wear rate of 200% or less, a load current value of 4 A or less, and a normal resistance of 30 kgf or less were deemed to be good products. It was found that sample numbers 2 to 5, 9 to 13, and 15 to 17 had a wear rate of 200% or less, a load current value of 4 A or less, and a normal resistance of 30 kgf or less. It was found that sample numbers 1, 6, 7, 8, and 14 had high wear rates, load current values, or normal resistance.

[0062] These results indicate that the average diameter of small pores must be 0.3 μm or more and 3 μm or less, the average diameter of large pores must be 20 μm or more and 120 μm or less, and the average distance between large pores must be 40 μm or more and 300 μm or less. (Appendix 1) A vitrified-bond superabrasive wheel having a vitrified-bond superabrasive layer fixed to a base metal, wherein the superabrasive layer has superabrasive grains, a vitrified bond, and pores, the average grain size of the superabrasive grains is 0.02 μm or more and 1.0 μm or less, the pores include small pores having a diameter of 0.10 μm or more and less than 10 μm, the average diameter of the small pores is 0.3 μm or more and 3.0 μm or less, the pores include large pores having a diameter of 20 μm or more and 500 μm or less, the average diameter of the large pores is 20 μm or more and 120 μm or less, and the average distance between the large pores is 40 μm or more and 300 μm or less. (Appendix 2) A vitrified bond superabrasive wheel according to Appendix 1, wherein the standard deviation of the inter-pore distances of the large pores is half or less of the average inter-pore distances of the large pores. (Appendix 3) A vitrified bond superabrasive wheel according to Appendix 1 or 2, wherein the average diameter of the small pores is 1.0 μm or more and 2.0 μm or less. (Appendix 4) A vitrified bond superabrasive wheel according to any one of Appendixes 1 to 3, wherein the large pores are spherical and the ratio of the minor axis a to the major axis b (a / b) of the large pores is 0.5 or more and 1.0 or less. (Appendix 5) A vitrified bond superabrasive wheel according to any one of Appendixes 1 to 4, wherein the proportion of the large pores in the superabrasive layer is 15 volume % or more and 50 volume % or less. (Appendix 6) The vitrified bond superabrasive wheel according to any one of Appendices 1 to 5, wherein the superabrasive layer contains a filler, the filler comprising at least one selected from the group consisting of silicon carbide, hBN, and alumina, and the content of the filler in the superabrasive layer is 2% by volume or more and 40% by volume or less. (Appendix 7) The vitrified bond superabrasive wheel according to any one of Appendices 1 to 6, wherein the softening temperature of the vitrified bond is 600°C or more and 900°C or less. (Appendix 8) SiC, GaN, LiTaO ３(lithium tantalate), or LiNbO ３ 8. The vitrified bond superabrasive wheel according to any one of claims 1 to 7, which is used for processing a compound semiconductor wafer of (lithium niobate).

[0063] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0064] 2 Vitrified bond, 3 Superabrasive grain, 4 Filler, 5 Small pores, 6 Superabrasive grain layer, 7 Large pores, 7A Straight line, 7G Center of gravity, 7T Delaunay triangle, 9 Base metal, 10 Superabrasive grain wheel, 11 Workpiece (SiC wafer), 12 Chips, 100 Grinding method, 110 Table.

Claims

1. A vitrified-bond superabrasive wheel having a vitrified-bond superabrasive layer fixed to a base metal, wherein the superabrasive layer has superabrasive grains, a vitrified bond, and pores, the average grain size of the superabrasive grains is 0.02 μm or more and 1.0 μm or less, the pores include small pores with diameters of 0.10 μm or more and less than 10 μm, the average diameter of the small pores is 0.3 μm or more and 3.0 μm or less, the pores include large pores with diameters of 20 μm or more and 500 μm or less, the average diameter of the large pores is 20 μm or more and 120 μm or less, and the average distance between the large pores is 40 μm or more and 300 μm or less.

2. A vitrified bond superabrasive wheel according to claim 1, wherein the standard deviation of the distance between the large pores is not more than half the average value of the distance between the large pores.

3. A vitrified bond superabrasive wheel according to claim 1 or 2, wherein the average diameter of the small pores is 1.0 μm or more and 2.0 μm or less.

4. A vitrified bond superabrasive wheel according to claim 1 or 2, wherein the proportion of the small pores in the superabrasive layer is 5.0 volume % or more and 40.0 volume % or less.

5. A vitrified bond superabrasive wheel according to claim 1 or 2, wherein the large pores are spherical and the ratio of the minor axis a to the major axis b (a / b) of the large pores is 0.5 or more and 1.0 or less.

6. A vitrified bond superabrasive wheel according to claim 1 or 2, wherein the large pores account for 5.0% by volume or more and 40.0% by volume or less of the superabrasive layer.

7. A vitrified bond superabrasive wheel according to claim 1 or 2, wherein the superabrasive layer contains a filler, the filler comprising at least one type selected from the group consisting of silicon carbide, hBN, and alumina, and the content of the filler in the superabrasive layer is 2% by volume or more and 40% by volume or less.

8. A vitrified bond superabrasive wheel according to claim 1 or 2, wherein the softening temperature of the vitrified bond is 600°C or higher and 900°C or lower.

9. SiC, GaN, LiTaO ３ (lithium tantalate), or LiNbO ３ 3. The vitrified bonded superabrasive wheel according to claim 1, which is used for processing a compound semiconductor wafer of (lithium niobate).

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