COATED SUPER-ABRASIVE GRAINS, ABRASIVE GRAINS AND WHEEL

Abstract

A coated superabrasive grain comprises: a body composed of cubic boron nitride; and a coating film covering at least a portion of a surface of the body, the body having a dislocation density of 9 x 1014 / m2 or less, the coating film including one or more types of compounds formed from at least one type of element selected from the group consisting of an element from group 4, an element from group 5 and an element from group 6 of the periodic table, aluminum and silicon, and at least one type of element selected from the group consisting of oxygen, nitrogen, carbon, and boron.

Description

COATED SUPER-ABRASIVE GRAINS, ABRASIVE GRAINS AND WHEEL Field of Invention This description relates to coated superabrasive grains, abrasive grains, and a wheel. This application claims priority based on Japanese Patent Application No. 2019-144242 filed on August 6, 2019. The entire content of the description in that Japanese patent application is incorporated herein by reference. Background of the Invention A superabrasive tool (a wheel) from PTL 1 (Japanese Open Patent No. 2002-137168) is known as a tool used for precision machining. This superabrasive tool comprises a disc-shaped substrate and an abrasive grain layer formed on an outer peripheral portion of the substrate. The abrasive grain layer includes superabrasive grains (primarily cubic boron nitride abrasive grains) and an adhesive material that bonds the superabrasive grains together and also fixes the superabrasive grains to the outer peripheral portion of the substrate. APPOINTMENT LIST PATENT LITERATURE [PTL 1] Japanese Open Patent No. 2002-137168 cocí nn / zznz / E / YiAi Ref. 330654 Brief Description of the Invention According to the present description, a coated superabrasive grain comprises: a body composed of cubic boron nitride; and a coating film covering at least a portion of a surface of the body, and a body having a dislocation density of 9 x 10⁻¹² / m² or less, the coating film including one or more types of compounds formed from at least one type of element selected from the group consisting of an element of group 4, a group 5 or a group 6 element of the periodic table, aluminum and silicon, and at least one type of element selected from the group consisting of oxygen, nitrogen, carbon and boron. According to the present description, an abrasive grain is composed of cubic boron nitride and has a dislocation density of 9 * io” / m2o less. According to the present description, a grinding wheel comprises: a disc-shaped substrate; and a superabrasive layer has one or both of the superabrasive grains coated and the previous abrasive grain. Brief Description of the Figures Fig. 1 is a schematic cross-section of a superabrasive grain coated according to a first modality. Fig. 2 is an enlarged cross-section of a portion of the coated superabrasive grain shown in Fig. 1, which is surrounded by a circle drawn with a dashed line. Fig. 3 is a schematic perspective view of a wheel according to a third modality. Fig. 4 is a cross-section of the wheel shown in Fig. 3 as a cut along a plane that includes a line (IV)-(IV). Fig. 5 is an enlarged cross-section of a part of the wheel shown in Fig. 4 that is surrounded by a circle drawn with a dashed line. Detailed Description of the Invention Problem to be solved by the present description The coated superabrasive grains included in the PTL 1 abrasive grain layer are, by definition, uncoated abrasive grains (i.e., their bodies are not coated). A portion of the abrasive grain layer that comes into contact with a workpiece during grinding is locally exposed to high temperatures. Thus, when the PTL 1 tool is used to grind the workpiece, it is exposed to high temperatures. This causes the workpiece to adhere to the abrasive grain layer, and the layer itself to wear down chemically, resulting in a reduced grinding ratio. Accordingly, one object of the present description is to provide coated superabrasive grains that can be used for a tool to allow the tool to have a high grinding ratio, abrasive grains, and a wheel that has a high grinding ratio. Advantageous effect of the present description According to the present description, coated superabrasive grains can be provided that can be used for a tool to allow the tool to have a high grinding ratio, abrasive grains and a wheel that has a high grinding ratio. Description of the modalities of the present description First, the modalities of the present description will be specified and described. (1) A coated superabrasive grain in a form described herein comprises: a body composed of cubic boron nitride; and a coating film covering at least a portion of a surface of the body, COCI ηη / 77P7 / E / YILI the body having a dislocation density of 9 x io” / m2o less, the coating film includes one or more types of compounds formed from at least one type of element selected from the group consisting of an element from group 4, an element from group 5 or an element from group 6 of the periodic table, aluminum and silicon, and at least one type of element selected from the group consisting of oxygen, nitrogen, carbon and boron. A tool using the coated superabrasive grains described herein may have a high grinding ratio. In this description, a grinding ratio is defined as the volume of a ground workpiece divided by the total volume of superabrasive grains worn away. (2) Preferably, the body of the abrasive grain has a single crystal structure. This makes it easier to improve the strength of the abrasive grain body. (3) Preferably, the body of the abrasive grain has a polycrystalline structure. This helps the tool that uses superabrasive grains to have a better grinding ratio. (4) Preferably, the abrasive grain body has a dislocation density of 2 χ ioi« / m2o or less. The lower COCI ηη / 77Π7 / E / YILI dislocation density improves the abrasive grain body in terms of strength. In addition, it also improves the adhesion of the interface between the coating film and the abrasive grain body and suppresses film detachment. Preferably, the abrasive grain body has a dislocation density of 5 * 10¹³ / m² or less. The lower dislocation density further improves the hardness of the abrasive grain body. In addition, it also further improves the adhesion of the interface between the coating film and the abrasive grain body and further suppresses film detachment. (6) Preferably, the coating film includes aluminum and oxygen. When the coating film includes aluminum and oxygen, its heat stability and wear resistance are improved. As a result, damage such as wear and destruction of the coating film and the abrasive grain body are suppressed. (7) Preferably, the coating film includes y-AbOs. This allows the coating film to be composed of a plurality of crystal grains having a reduced average grain size, thus giving the coating film greater strength and improving the adhesive force between the coating film and the abrasive grain body. This, in turn, suppresses the destruction and detachment of the film due to the impact caused when the film comes into contact with a workpiece. Therefore, the coating film can maintain satisfactory wear resistance for a long period of time. (8) Preferably, the coating film includes a plurality of crystal grains, and the plurality of crystal grains has an average grain size of 500 nm or less. This further improves the strength of the coating film. (9) Preferably, in the coating film, the aluminum and oxygen have an Al / O atomic ratio of 0.2 or more and 0.9 or less. This further improves the wear resistance of the coating film and also increases the bond strength between the coating film and the abrasive grain body. (10) Preferably, the Al / O ratio is equal to or greater than 0.4 and 0.7 or less. This further improves the wear resistance of the coating film and also improves the adhesion strength between the coating film and the abrasive grain body. (11) Preferably, the coating film has a thickness of 50 nm or more and 1000 nm or less. When the coating film has a thickness of 50 nm or more, it facilitates the improvement of the coating film itself in wear resistance and thus the suppression of damage to the coating film and the abrasive grain body. When the coating film has a thickness of 1000 nm or less, the coating film is not excessively thick and therefore does not detach easily, and a state with the coating film formed on an external surface of the abrasive grain body is easily maintained. (12) Preferably, the coating film has a multilayer structure composed of two or more types of unit layers. When the coating film has a multilayer structure, the residual stress of each layer increases. This increases the hardness of the coating film and thus suppresses damage to the coating film. (13) Preferably, the coated superabrasive grain has a grain size of 30 pm or more and 600 pm or less. Coated superabrasive grit with a grain size of 30 µm or larger is not excessively small, so it adheres easily to a substrate and thus facilitates the grinding of a workpiece. It is also easily manageable, thus facilitating the construction of the grinding wheel. Coated superabrasive grit with a grain size of 600 µm or smaller is not excessively large and therefore does not easily fracture or similarly damage itself due to an impact force acting on the abrasive grit body upon contact with a workpiece. (14) An abrasive grain in one embodiment of the present description is composed of cubic boron nitride and has a dislocation density of 9 * io>« / m2o less. The abrasive grain of the present description is of high hardness, and a tool that uses such abrasive grains can have a high grinding ratio. (15) Preferably, the abrasive grain has a monocrystalline structure. This facilitates the improvement of the abrasive grain in terms of its strength. (16) Preferably, the abrasive grain has a polycrystalline structure. This helps a tool using such abrasive grains to have a better grinding ratio. (17) Preferably, the dislocation density is 6.5 x 10⁻⁶ / m² or less. The lower dislocation density improves the hardness of the abrasive grain. (18) Preferably, the dislocation density is 2 x io>« / m2o less. The lower dislocation density improves the hardness of the abrasive grain. I cooked ηη / ζζηζ / E / γίΛΐ (19) Preferably, the dislocation density is 5 x 1013 / m2 or less. The lower dislocation density further improves the abrasive grain body in hardness. (20) Preferably, the abrasive grain is composed of crystallites that are 250 nm or larger in size. This helps a tool using such abrasive grains to have a better grinding ratio. (21) Preferably, the crystallite has a size of 450 nm or larger. This helps a tool using such abrasive grains to have a better grinding ratio. (22) Preferably, the crystallite has a size of 600 nm or larger. This helps a tool using such abrasive grains to achieve a better grinding ratio. (23) Preferably, the abrasive grain has a grain size of 30 µm or larger and 600 µm or smaller. Abrasive grain with a grain size of 30 µm or larger is not excessively small and therefore facilitates the grinding of a workpiece and is also easily manageable, thus facilitating the construction of a wheel. Abrasive grain with a grain size of 600 µm or smaller is not excessively large and therefore does not easily fracture or similarly become damaged due to an impact force acting on the body of the abrasive grain when it comes into contact with a workpiece. (24) A wheel in a modality of the present description comprises: a disc-shaped substrate; and a superabrasive grain layer covering at least one outer peripheral surface of the substrate, the superabrasive layer having one or both of the above-mentioned superabrasive grains and the above-mentioned abrasive grains. The wheel of the present description may have a high grinding ratio. The details of the features described herein are set out below with reference to the figures. In the figures, the same reference numbers designate identical or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, depth, and the like are modified as appropriate for clarity and simplicity in the figures and do not necessarily represent actual dimensional relationships. In the present description, an expression in the form of A to B means the upper and lower limits of an interval (i.e., A or more and B or less), and when A is not accompanied by any unit and B is accompanied by only one unit, A has the same unit as B. In this description, when a compound or similar is represented by a chemical formula without specifying any specific atomic ratio, it shall include any conventionally known atomic ratio and need not necessarily be limited to what falls within a stoichiometric range. For example, for TiAlN, the ratio of the number of atoms that constitute TiAlN includes any conventionally known atomic ratio. This also applies to descriptions for compounds other than TiAlN. First type: coated superabrasive grains A coated superabrasive grain according to one embodiment of the present description will now be described with reference to Figs. 1 and 2. Fig. 1 is a schematic cross-section of a coated superabrasive grain according to a first embodiment. Fig. 2 is an enlarged cross-section of a portion of the coated superabrasive grain shown in Fig. 1, which is enclosed in a circle drawn with a dashed line. According to the present invention, a coated superabrasive grain 1 of the present description comprises: an abrasive grain body 2 composed of cubic boron nitride; and a coating film including aluminum and one or both of oxygen and nitrogen, and coating at least a portion of a surface of the abrasive grain body 2, the body 2 having a dislocation density of 9 * 10⁻⁶” / m² or less. The coating film includes one or more types of compounds formed from at least one type of element selected from the group consisting of an element of group 4, an element of group 5, and an element of group 6 of the periodic table, aluminum and silicon, and at least one type of element selected from oxygen, nitrogen, carbon, and boron. A tool using such coated superabrasive grains of the present description can have a high grinding ratio.One reason for this is inferred as indicated in points (i) to (iv) below:. (i) The coated superabrasive grain described herein has a body composed of cubic boron nitride. Cubic boron nitride has a high hardness. Therefore, the coated superabrasive grain using cubic boron nitride as its body exhibits excellent wear resistance. Consequently, a tool using the coated superabrasive grain described herein can have a high grinding ratio. (ii) The coated superabrasive grain of the present description has its body with a surface at least partially coated with a film. The coated superabrasive grain thus having the film can suppress a chemical reaction caused by the body of the abrasive grain and a component of a workpiece during grinding. In addition, it can prevent the atoms that constitute the body of the abrasive grain from diffusing into the film and the workpiece. This can suppress the progression of wear of the abrasive grain body and the adhesion of the workpiece component, and, consequently, the grinding force is low and stable over a long period of time. As a result, the fracture of the abrasive grain body due to adhesion and exfoliation is also reduced, along with the increased grinding force and other similar effects.A tool that uses such coated superabrasive grains of the present description can therefore have a high grinding ratio. (iii) The coated superabrasive grain of the present description comprises one or more types of compounds formed from at least one type of element selected from the group consisting of an element from group 4, an element from group 5, and an element from group 6 of the periodic table, aluminum and silicon, and at least one type of element selected from the group consisting of oxygen, nitrogen, carbon, and boron. This increases the stability of the coating film against heat and improves wear resistance in the grinding of a workpiece. As a result, damage such as wear and destruction of the coating film and the abrasive grain body is eliminated. A tool using super-abrasive coated grains of the type described herein can therefore have a high grinding ratio. (iv) The coated superabrasive grain described herein has a body with a dislocation density of 9 χ io» / m2o or less. When the abrasive grain has a body with a dislocation density of 9 χ iok / m2o or less, it exhibits excellent hardness. Furthermore, there are few lattice defects in the abrasive grain body, which can reduce defects caused during grinding. Additionally, it also reduces lattice defects at the interface between the abrasive grain body and the coating film, which are attributed to lattice defects in the abrasive grain body itself. Therefore, it improves the adhesive strength between the coating film and the abrasive grain body and suppresses film detachment. As a result, damage such as wear and destruction of the coating film and the abrasive grain body is suppressed.A tool that uses the coated superabrasive grains of the present description can therefore have a high grinding ratio. Grain size of coated superabrasive grains Coated superabrasive grains preferably have a grain size of 30 µm or more and 600 µm or less. For coated superabrasive grain of the first type, the grain size of the coated superabrasive grain means the grain size of a single coated superabrasive grain. Coated superabrasive grit with a grain size of 30 µm or larger is not excessively small and therefore easily attaches to a wheel, facilitating workpiece grinding and making wheel construction easier. Coated superabrasive grit with a grain size of 600 µm or smaller is not excessively large and therefore is not easily fractured or similarly damaged by impact forces when it comes into contact with a workpiece. The coated superabrasive grit has a grit size with a lower limit preferably of 30 µm or more, more preferably 50 µm or more, and even more preferably 60 µm or more. The coated superabrasive grit has a grit size with an upper limit preferably of 600 µm or more, more preferably 300 µm or less, and even more preferably 150 µm or less. The coated superabrasive grit has a grit size of 50 µm or more and 300 µm or less, more preferably 60 µm or more and 150 µm or less. The grain size of the coated superabrasive grain is measured with a laser diffraction type particle size distribution analyzer (the SALD series manufactured by Shimadzu Corporation). Abrasive grain body Composition The abrasive grain body is composed of cubic boron nitride (hereafter also referred to as cBN). Cubic boron nitride has excellent hardness. Therefore, coated superabrasive grains using cubic boron nitride exhibit excellent wear resistance. A tool using the coated superabrasive grains described herein can thus have a high grinding ratio. The abrasive grain body inevitably includes impurities that may have an effect described herein. Examples of unavoidable impurities include carbon (C), aluminum (Al), silica (Si), lithium (Li), calcium (Ca), and magnesium (Mg). The abrasive grain body contains unavoidable impurities in an amount, for example, by mass, of 0.001% or more and 0.5% or less. The composition of the abrasive grain body can be identified using an energy dispersive X-ray analyzer (EDX) (Octane Elect EDS system) (registered trademark) accompanying a scanning electron microscope (SEM) (JSM-7800F (registered trademark) manufactured by JEOL Ltd.). Dislocation density The abrasive grain body has a dislocation density of 9 * io» / m2o less. When the abrasive grain body has a dislocation density of 9 * io» / m2o less, it exhibits excellent hardness. Furthermore, there are few lattice defects in the abrasive grain body, which can reduce defects caused during grinding. Additionally, lattice defects at the interface between the abrasive grain body and the coating film are also reduced, thus improving the adhesive strength between the coating film and the abrasive grain body and suppressing film detachment. As a result, damage such as wear and destruction of the coating film and the abrasive grain body is suppressed.A tool that uses superabrasive grains coated as described herein can thus have a high grinding ratio. The abrasive grain body has a dislocation density with a lower limit preferably of 1 x 10⁸ / m² or more, more preferably 1 x 10¹⁰ / m² or more, more preferably 5 x 10¹⁰ / m² or more. The abrasive grain body has a dislocation density with an upper limit preferably of 9 x 10⁻⁹ / m² or less, more preferably 6.5 x 10⁻⁵ / m² or less, more preferably 2 x 10⁻⁵ / m² or less, more preferably 5 x 10¹³ / m² or less. The abrasive grain body has a dislocation density preferably of 1 × 10⁸ / m²o more and 9 × ioi« / m²o less, more preferably 1 × 10⁸ / m²o more and 6.5 × io“ / m²o less, more preferably 1 × 10¹⁰ / m²o more and 2 × iok / m²o less, even more preferably 5 × 10¹⁰ / m²o more and 5 × 10¹³ / m²o less. The dislocation density of the abrasive grain body is measured at SPring-8, a large-scale synchrotron radiation facility (located in Hyogo Prefecture). Specifically, it is measured using the following method. Cubic boron nitride powder was prepared. The powder to be measured was introduced into a 0.3 mmcp capillary tube manufactured by TOHO for X-ray crystallography (Mark Tube (registered trademark) manufactured by TOHO), and thus prepared as a sealed sample. The specimen was subjected to an X-ray diffraction measurement under the following conditions, and a line profile of a diffraction peak from each orientation plane of the principal orientations of cubic boron nitride is obtained, which are (111), (200), (220), (311), (400) and (531). Conditions for X-ray diffraction measurement X-ray source: synchrotron radiation. Equipment condition: MYTHEN detector COCI ηη / 77Π7 / E / YILI Energy: 18 keV (wavelength: 0.6888 angstrom) Camera length: 573 mm Measurement peaks: six cubic boron nitride peaks (111), (200), (220), (311), (400) and (531). When it is difficult to obtain a profile based on texture and orientation, the peak corresponding to that Miller index is excluded. Measurement condition: There are 9 or more measurement points fixed across the width at half the maximum corresponding to each measurement peak. The intensity of the upper peak is set to 2000 counts or more. The peak tail is also used in the analysis, and consequently, the measurement interval is set to approximately 10 times the total width at half the maximum. A line profile obtained from the above X-ray diffraction measurement will include both true broadening attributed to a physical quantity such as non-homogeneous deformation of the sample and broadening attributed to the equipment. To determine non-homogeneous deformation and crystallite size, the equipment-attributed component is removed from the measured line profile to obtain a true line profile. The true line profile is obtained by fitting the measured line profile and the equipment-attributed line profile using a pseudo-Voigt function, and subtracting the equipment-attributed line profile. LaB6 was used as a standard sample to remove the equipment-attributed broadening of a diffracted peak. When using significantly collimated radiation, the equipment-attributed broadening of a diffracted peak can be considered zero. The resulting true line profile is analyzed using the modified Williamson-Hall method and the modified Warren-Averbach method to calculate the dislocation density. The modified Williamson-Hall method and the modified Warren-Averbach method are well-known line profile analysis methods used to determine dislocation density. The expression of the modified Williamson-Hall method is represented by the following expression (I): 0.9 T~ ... Δ.Α. - i- ................. £>'Ai U) D s 2 J where ΔK represents a mean width of a line profile, D represents a crystallite size, M represents a dislocation arrangement parameter, b represents a Burgers vector, p represents the dislocation density, K represents a scattering vector, O(K2C) represents a higher-order term of K2C, and C represents a mean contrast factor. C in expression (I) is represented by the following expression (II): C = Choo [I - q(h2k2+ h2l2+ k2l2) / (h2+ k2+12)2] ... (II). In the above expression (II), a contrast factor Choo has been introduced for screw dislocation and another for edge dislocation, and a coefficient q for each contrast factor is obtained using the ANIZC calculation code, with a slip system of <110> {111}, and elastic stiffness Cu, C12, and C44 of 8.44 GPa, 1.9 GPa, and 4.83 GPa, respectively. The Choo contrast factor is 0.203 for screw dislocation and 0.212 for edge dislocation. Note that the screw dislocation ratio is fixed at 0.5 and the edge dislocation ratio is fixed at 0.5. Furthermore, a relationship is established between dislocation and non-homogeneous deformation, represented by expression (III) using the contrast factor C, as indicated below: <c(L)2> = (pCb2 / 4n)In(RelL) ... (III), where Re represents the effective radius of the dislocation. From the relationship of the previous expression (III) and the Warren-Averbach expression, the following expression (IV) can be presented, and as the modified Warren-Averbach method, the panda crystallite size of the cocí nn / zznz / E / YiAi dislocation density can be determined. InA(L) = InAs (L) - (nL2pb2 / 2) ln(RelL)( K2C) + O(K2C)2(IV) , where A(L) represents a Fourier series, As(L) represents a Fourier series for a crystallite size, and L represents a Fourier length. For details of the modified Williamson-Hall method and the modified Warren-Averbach method, see T. Ungar and A Borbely, The effect of dislocation contrast on *-ray line broadening: A new approach to line profile analysis, Appl. Phys. Lett., vol.69, no.21, p.3173, 1996, and T. Ungar, S. Ott, P. Sanders, A Borbely, J. Weertman, Dislocations, grain size and planar faults in nanostructured copper determined by high resolution X-ray diffraction and a new procedure of peak profile analysis, Act Mater, vol. 10, pp.3693- 3699, 1998. Crystal Structure The abrasive grain body can have a monocrystalline or polycrystalline structure. A monocrystalline structure readily enhances the abrasive grain's strength. A polycrystalline structure, on the other hand, allows for a better grinding ratio in tools using such grains. Crystalline structure The crystalline structure of the abrasive grain body can be identified by a composite analysis of X-ray diffraction (XRD) analysis (which measures the intensity of a peak) (device: MiniFlex 600 (registered trademark) manufactured by JOEL Ltd.) and information on the composition of the abrasive grain body, or by observation with a scanning transmission electron microscope (STEM) JEM-2100F / Cs (registered trademark) manufactured by JEOL Ltd. and energy-dispersive X-ray spectroscopy (EDX) accompanying the STEM. Size of the crystal grain that makes up the body of the abrasive grain When the abrasive grain body 2 has a monocrystalline structure, the abrasive grain body has a grain size corresponding to the grain size of a single crystal. When the abrasive grain body has a single-crystal structure, a lower limit for the grain size of the single crystal (corresponding to the grain size of the abrasive grain body) can be 30 µm or more, 50 µm or more, or 60 µm or more. An upper limit for the grain size of the single crystal can be 600 µm or less, 300 µm or less, or 150 µm or less. The single crystal can have a grain size of 30 µm or more and 600 µm or less, 50 µm or more and 300 µm or less, or 60 µm or more and 150 µm or less. When the abrasive grain body 2 has a single-crystal structure, the single-crystal grain size is measured using a laser diffraction type particle size distribution analyzer (the SALD series manufactured by Shimadzu Corporation). When the abrasive grain body 2 has a polycrystalline structure, the abrasive grain body is composed of a plurality of crystal grains having an average grain size preferably of 100 nm or more and 6000 nm or less, more preferably 200 nm or more and 4000 nm or less, particularly preferably 300 nm or more and 2000 nm or less. When the abrasive grain body 2 has a polycrystalline structure, the average grain size of the plurality of crystal grains that constitute the abrasive grain body is determined from a cross-section of the abrasive grain body exposed by a FIB (focused ion beam), and observed in a HAADF (high-angle annular dark field)-STEM image obtained through a STEM (JEMARM200F Dual-X (registered trademark) produced by JEOL Ltd.). From the contrast difference of each crystal grain in the HAADF-STEM image, a cross-sectional area of ​​each crystal grain is derived using image analysis software (WinROOF ver. 7.4.1 (registered trademark) manufactured by Mitani Corporation), and the diameter of a circle with an area equal to that cross-sectional area (or an equivalent circle diameter) is determined.An average value of the equivalent circle diameters of ten crystal grains is taken as the average grain size of the plurality of crystal grains making up the body of the abrasive grain. The crystallite constitutes the body of the abrasive grain, and the size of the crystallite In this description, a crystallite, which is a constituent of the abrasive grain body, is defined as a region within a single crystal that has the same crystal orientation. A crystallite size is defined as the size of a region within a single crystal that has the same crystal orientation, and is defined as the length of a region with the same crystal orientation when the abrasive grain is viewed in cross-section. In this description, a crystallite size corresponds to the diameter of the equivalent circle of a crystallite. Ideally, the crystallite size is 250 nm or larger. This helps a tool using such abrasive grains achieve a better grinding ratio. Although the reason is unknown, it is deduced that a larger crystallite size suppresses crack propagation during grinding, thus improving the abrasive grain's hardness and minimizing abrasive grain defects during the grinding process. For crystallite size, a lower limit of 250 nm or more, 450 nm or more, or 600 nm or more can be set. For crystallite size, an upper limit of 2000 nm or less, 1500 nm or less, or 1000 nm or less can be set. The crystallite size can be 250 nm or more and 2000 nm or less, 450 nm or more and 1500 nm or less, or 600 nm or more and 1000 nm or less. The crystallite size is calculated similarly to how the dislocation density of the abrasive grain body is calculated. In the expression above (I), the crystallite size is represented by D. Abrasive grain body grain size The body of the abrasive grain may have a grain size of 30 gm or more and 600 gm or less, 50 gm or more and 300 gm or less, or 60 gm or more and 150 gm or less. As mentioned herein, the grain size of the body of the abrasive grains means the grain size of the body of a single coated superabrasive grain. When the abrasive grain body 2 has a monocrystalline structure, the grain size of the abrasive grain body, which corresponds to the grain size of a single crystal, is measured with a laser diffraction type particle size distribution analyzer (the SALD series manufactured by Shimadzu Corporation). When the abrasive grain body (body 2) has a polycrystalline structure, the grain size is determined from a cross-section of the abrasive grain body exposed by a focused ion beam (FIB) and observed on a high-angle annular dark field (HAADF) STEM image obtained using a JEM ARM200F Dual-X (registered trademark) manufactured by JEOL Ltd. Based on the contrast difference of each crystal grain in the HAADF-STEM image, a cross-section of the abrasive grain body is obtained using image analysis software (WinROOF version 7.4.1 (registered trademark) manufactured by Mitani Corporation), and the diameter of a circle with an area equal to that cross-sectional area (or an equivalent circle diameter) is determined. The equivalent circle diameter corresponds to the abrasive grain body size.An average value of the bodies of ten abrasive grains is taken as the average grain size of the abrasive grain body. Coating film The coating film 3 covers at least a portion of the surface of the abrasive gram body 2. The fact that the coating film covers at least a portion of the surface of the abrasive gram body 2 can be confirmed by the following method. A molded body is produced in which coated superabrasive grains are embedded in epoxy resin. The content of coated superabrasive grains in the molded body is 50% or more by volume relative to the resin. The molded body has a rectangular or cube-shaped form. The molded body undergoes a CP (cross-section polishing) process. This process is performed in two stages. In the first stage, the molded body's surface is processed until a cross-section of at least one coated superabrasive grain is visible. Subsequently, in the second stage, the processed surface undergoes another CP process to remove a thickness corresponding to a length equivalent to 50% of the grain size of the coated superabrasive grain. Note that the grain size of the coated superabrasive grain is a value measured with a particle size distribution analyzer of the laser diffraction type described earlier. Subsequently, the cross-section of the molded body is observed with a SEM to obtain a backscattered electron image. From the backscattered electron image, it can be confirmed that the coating film covers at least a portion of the surface of body 2 of the abrasive grain. The coating film 3 preferably covers the entire surface of the abrasive grain body 2. The super-abrasive grain, thus coated with this film, can suppress a chemical reaction caused by the abrasive grain body and a workpiece component during grinding. Furthermore, it prevents the atoms constituting the abrasive grain body from diffusing into the coating film, the workpiece, and other materials. This suppresses the progression of wear on the abrasive grain body and adhesion to the workpiece component, resulting in a low and stable grinding force over an extended period. Consequently, abrasive grain body fracture due to adhesion and detachment is reduced, grinding force is increased, and other similar issues are also minimized.A tool that uses the coated superabrasive grains of the present description can therefore have a high grinding ratio. Note that the grinding ratio is the volume of a ground part divided by the total volume of abrasive grains worn. A method for calculating the grinding ratio is described below. The total volume of abraded coated superabrasive grains worn is determined as follows: Before and after a wheel with coated superabrasive grains affixed to it is used in a grinding process, the wheel is used to grind a carbon plate to transfer ripples from the abrasive surface of the wheel to the carbon plate. During the grinding of the carbon plate, the wheel is rotated to cut into the carbon plate without moving the carbon plate. The cross-sectional shape of the waviness on each carbon plate transferred before and after the grinding process is measured using a needle-type surface roughness gauge (SURFCOM (registered trademark) manufactured by TOKYO SEIMITSU CO., LTD.) in a direction perpendicular to the direction of wheel rotation. The two cross-sectional shapes obtained before and after the grinding process are compared to determine the reduced area. Let χ (the reduced area), χ (the diameter of the grinding wheel), and n be the total wear volume of the coated superabrasive grains. The volume of workpiece material removed (hereafter also referred to as volume removal) is determined by the product of the depth of cut and the length and thickness of the workpiece. The volume of material removed is represented by a horizontal axis, and the amount removed is represented by a vertical axis to plot a change. From this, a linear function of the change is determined using the least squares method to calculate a gradient. This is used to calculate the total volume removed from coated superbaked abrasive grains for any given volume removal rate. Composition The coating film 3 includes one or more types of compounds formed by at least one element selected from the group consisting of a Group 4 element (titanium (Ti), zirconium (Zr), hafnium (Hf), and similar elements), a Group 5 element (vanadium (V), niobium (Nb), tantalum (Ta), and similar elements), and a Group 6 element (chromium (Cr), molybdenum (Mo), tungsten (W), and similar elements) of the Periodic Table, aluminum, and silicon, and at least one element selected from the group consisting of oxygen, nitrogen, carbon, and boron. This suppresses damage such as wear and destruction of the coating film and the abrasive grain body. A tool using superabrasive grains coated as described herein can thus have a high grinding ratio. Examples of a compound formed from the first element and nitrogen (i.e., a nitride) include titanium nitride (TIN), zirconium nitride (ZrN), hafnium nitride (HfN), vanadium nitride (VN), niobium nitride (NbN), tantalum nitride (TaN), chromium nitride (Cr2N), molybdenum nitride (MoN), tungsten nitride (WN), titanium zirconium nitride (TiZrN), titanium hafnium nitride (TiHfN), titanium vanadium nitride (TiVN), titanium niobium nitride (TiNbN), titanium tantalum nitride (TiTaN), titanium chromium nitride (TiCrN), titanium molybdenum nitride (TiMoN), and titanium tungsten nitride. (TiWN), zirconium hafnium nitride (ZrHfN), zirconium vanadium nitride (ZrVN), zirconium niobium nitride (ZrNbN), zirconium tantalum nitride (ZrTaN), zirconium chromium nitride (ZrCrN), zirconium molybdenum nitride (ZrMoN), zirconium tungsten nitride (ZrWN),hafnium and vanadium nitride (HfVN), hafnium and niobium nitride (HfNbN), hafnium and tantalum nitride (HffaN), hafnium and chromium nitride (HfCrN), hafnium and molybdenum nitride (HfMoN), hafnium and tungsten nitride (HfVN), va (VNbN), vanadium and tantalum nitride (VTaN), vanadium and chromium nitride (VCrN), vanadium and molybdenum nitride (VMoN), vanadium and tungsten nitride (VWN), niobium and tantalum nitride (NbTaN), niobium and chromium nitride (NbC), (NbMoN), niobium and tungsten nitride (NbWN), tantalum and chromium nitride (TaCrN), tantalum and molybdenum nitride (TaMoN), tantalum and tungsten nitride (TaWN), chromium-molybdenum nitride (CrMoN), chromium-tungsten nitride (CrWN), molybdenum-tungsten (MoWN), aluminum nitride (A1N) and silicon nitride (SÍ3N4) ., Examples of a compound formed by the first element and carbon (i.e., a carbide) may include titanium carbide (Tic), zirconium carbide (ZrC), hafnium carbide (HfC), vanadium carbide (VC), niobium carbide (NbC), tantalum carbide (TaC), chromium carbide (Cr2C), molybdenum carbide (MoC), tungsten carbide (WC), titanium zirconium carbide (TiZrC), titanium hafnium carbide (TiHfC), titanium vanadium carbide (TiVC), titanium niobium carbide (TiNbC), titanium tantalum carbide (TiTaC), titanium chromium carbide (TiCrC), titanium molybdenum carbide (TiMoC), titanium tungsten carbide (TiWC), zirconium hafnium carbide (ZrHfC), zirconium vanadium carbide (ZrVC), and so on. zirconium and niobium (ZrNbC), zirconium tantalum carbide (ZrTaC), zirconium chromium carbide (ZrCrC), zirconium molybdenum carbide (ZrMoC), zirconium tungsten carbide (ZrWC), hafnium vanadium carbide (HfVC), hafnium niobium carbide (HfNbC),hafnium tantalum carbide (HfTaC), hafnium chromium carbide (HfCrC), hafnium molybdenum carbide (HfMoC), hafnium tungsten carbide (HfWC), vanadium niobium carbide (VNbC), vanadium tantalum carbide (VTaC), vanadium chromium carbide (VCrC), vanadium molybdenum carbide (VMoC), vanadium tungsten carbide (VWC), niobium tantalum carbide (NbTaC), niobium chromium carbide (NbCrC), niobium molybdenum carbide (NbMoC), niobium tungsten carbide (NbWC), chromium tantalum carbide (TaCrC), molybdenum tantalum carbide (TaMoC), tungsten tantalum carbide (TaWC), chromium molybdenum carbide (CrMoC) chromium tungsten carbide (CrWC), molybdenum and tungsten carbide (MoWC), aluminum carbide (Al4C3) and silicon carbide (SiC). Examples of a compound formed from the first element, carbon, and nitrogen (i.e., a carbonitride) may include titanium carbonitride (TiCN), zirconium carbonitride (ZrCN), hafnium carbonitride (HfCN), aluminum carbonitride (AlCN), and silicon carbonitride (SiCN). Examples of a compound formed by the first metallic element and boron (i.e., a boride) may include titanium boride (TiB2), zirconium boride (ZrB2), hafnium boride (HfB2), vanadium boride (VB2), niobium boride (NbB2), tantalum boride (TaB2), chromium boride (CrB2), molybdenum boride (MoB2), tungsten boride (WB), aluminum boride (A1B2), and silicon boride (S1B4). Examples of a compound formed from the first metallic element and oxygen (i.e., an oxide) may include titanium oxide (TiO2), zirconium oxide (ZrO2), hafnium oxide (HfO2), vanadium oxide (V2OS), niobium oxide (Nb2Os), tantalum oxide (Ta2Os), chromium oxide (Cr2Os), molybdenum oxide (MoOs), tungsten oxide (WO3), aluminum oxide (A12Os), and silicon oxide (SiO2). Examples of a compound formed from the first metallic element, nitrogen, and oxygen (i.e., an oxynitride) may include titanium oxynitride (TiON), zirconium oxynitride (ZrON), hafnium oxynitride (HfON), vanadium oxynitride (VON), niobium oxynitride (NbON), tantalum oxynitride (TaON), chromium oxynitride (CrON), molybdenum oxynitride (MoON), tungsten oxynitride (WON), aluminum oxynitride (AlON), silicon oxynitride (SiON), and sialon (SiAlON). The above compound can be one type of compound or two or more types of compounds in combination. The coating film may include a derived solid solution. The derived solid solution of the above compound means a state in which two or more types of the above compounds are dissolved in the crystal structure of each other, and means an interstitial solid solution, a substitutional solid solution, or the like. The coating film preferably includes the above compound and the solid solution derived from the above compound in a total amount of 0% by volume or more and 90% by volume or less, more preferably 5% by volume or more and 70% by volume or less, even more preferably 10% by volume or more and 50% by volume or less. Ideally, the coating film includes aluminum and oxygen. This increases the coating film's stability under heat and improves wear resistance. As a result, damage such as wear and destruction of the coating film and the abrasive grain body is suppressed. A compound containing aluminum and oxygen includes Al₂O₃ (alumina). For Al₂O₃, there are crystalline structures such as (X-Al₂O₃, γ-Al₁₂θ₃, δ-Al₁₂θ₃, η-Al₁₂θ₃, Θ-Al₂O₃, K-Al₂O₃, pAl₂O₃, and χ-Al₁₂θ₃). The coating film may include any of these crystalline structures. While Al₂O₃ (alumina) has an Al to O atomic ratio of 2:3, the Al₂O₃ (alumina) in the present invention does not necessarily have an Al to O atomic ratio that exactly matches 2:3, and may fall within a range as will be described later. The coating film preferably includes the compound comprising aluminum and oxygen in a total amount preferably of 10% by volume or more and 100% by volume or less, more preferably 30% by volume or more and 95% by volume or less, even more preferably 50% by volume or more and 90% by volume or less. The coating film 3 preferably includes γ-A12θ3. This allows the coating film to be composed of a plurality of crystal grains having a reduced average grain size, thus enabling the coating film to have greater strength and also improving the adhesion strength between the coating film and the abrasive grain body. This, in turn, suppresses the destruction and detachment of the film due to the impact caused when the film comes into contact with a workpiece. Therefore, the coating film can maintain satisfactory wear resistance over a long period of time. In the coating film, the aluminum and oxygen preferably have an Al / O atomic ratio of 0.2 or higher and 0.9 or lower. This further improves the coating film's wear resistance and also enhances the adhesive strength between the coating film and the abrasive grain body. Aluminum and oxygen have an Al / O atomic ratio, most preferably 0.4 or more and 0.7 or less, and even more preferably 0.45 or more and 0.65 or less. This ratio improves the wear resistance of the coating film and also increases the adhesion strength between the coating film and the abrasive grain body. One method for measuring the atomic ratio of aluminum and oxygen in the coating film is as follows: The coated superabrasive grain is subjected to inductively coupled high-frequency plasma spectroscopy (ICP) and inert gas fusion to measure the Al and oxygen content, respectively. These are then converted to atomic percentages to calculate an atomic ratio. Coating film 3 may include unavoidable impurities, a trace amount of unreacted metallic aluminum remaining from the coating film formation process, an amorphous component of a compound containing aluminum and oxygen, and similar materials. Examples of unavoidable impurities include trace amounts of iron (Fe), nickel (Ni), chromium (Cr), manganese (Mn), and carbon (C) derived from a template (primarily SUS, carbon, and similar materials) used during the manufacturing process. The coating film preferably contains unavoidable impurities in a mass amount of 0.001% or more and 0.5% or less, more preferably 0.001% or more and 0.1% or less. The composition of coating film 3 is analyzed using SEM-EDS and ICP analysis for qualitative and quantitative evaluation, respectively. SEM-EDS analysis is performed under the same measurement conditions as the analysis of the abrasive grain composition, and ICP analysis is performed under the same measurement conditions as the method for analyzing the atomic ratio of aluminum to oxygen in the coating film; therefore, they will not be described repeatedly. Average grain size of a plurality of crystal grains that make up the coating film The coating film 3 can be a polycrystal that includes a plurality of crystal grains. I cooked ηη / ζζηζ / Ε / γίΛΐ In this case, the plurality of crystal grains preferably has an average grain size of 500 nm or less. This further improves the strength of the coating film and thus facilitates suppressing damage to the coating film itself caused by impact (or stress) forces generated when the abrasive grain comes into contact with a workpiece. Furthermore, this facilitates relieving the impact force acting on the abrasive grain body upon contact with the workpiece, making damage to the abrasive grain body less likely. The smaller the average grain size of the coating film, the greater the strength of the coating film itself. An upper limit for the average grain size of the plurality of crystal grains included in the coating film is preferably 500 nm or less, more preferably 100 nm or less, and more preferably 50 nm or less. A lower limit for the average grain size is preferably 1 nm or more, more preferably 5 nm or less, and more preferably 10 nm or more. The average grain size is preferably 1 nm or more and 500 nm or less, more preferably 5 nm or more and 100 nm or less, and more preferably 10 nm or more and 50 nm or less. The average grain size of the plurality of crystal grains included in the coating film is calculated using a HAADF-STEM image obtained by a STEM. Specifically, it is calculated using the following method. Initially, when the coating film is thicker than 100 nm, it is mechanically polished and subjected to Ar ion milling to achieve a thickness of 100 nm or less. This operation is unnecessary when the coating film is already 100 nm thick or less. The STEM has a magnification of 6.5 million times and is used to observe a HAADF-STEM image of the coating film to identify ten or more areas where an atomic arrangement can be observed. An area where the atomic arrangement is observable is taken as a crystal grain. In a HAADF-STEM image, a crystal grain with a different crystal orientation is unobservable, and an area where an atomic arrangement is observable can be considered a crystal grain. The diameter of the equivalent circle of an area where an atomic arrangement is observed is considered a crystal grain. The diameter of the equivalent circle can be calculated using image analysis software (WinROOF ver. 7.4.1 (registered trademark) manufactured by Mitani Corporation). The average grain size of the ten or more crystal grains is taken as the average grain size of the plurality of crystal grains included in the coating film. Crystal Structure of the Coating Film The coating film is subjected to a crystal structure analysis to identify a coating substance using the following method: The crystalline structure of the coating film is analyzed by STEM observation combined with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (using a MiniFlex600 (registered trademark) manufactured by JOEL Ltd. as the instrument). EDS is measured under general conditions. XRD is observed under the following conditions: X-ray diffractometer: MiniFlex600 (registered trademark) manufactured by JOEL Characteristic X-rays: Cu-Ka (wavelength: 1.54 angstroms) Tube voltage: 45 kV Tube current: 40 mA Filter: Multi-layered mirror Optical system: Concentration method X-ray diffractometry: method 8-28 By analyzing the electron diffraction of the coating film, it can be verified whether the coating film contains amorphous particles. Structure The coating film 3 may have a COCI ηη / 77P7 / E / YILI monolayer structure. As shown in Fig. 2, the coating film 3 can have a multilayer structure composed of two or more types of unit layers. When the coating film has a multilayer structure, the residual stress of each unit layer increases. This increases the hardness of the coating film and thus suppresses damage to the coating film. When the coating film has a multilayer structure, the number of layers is not particularly limited. For example, two or three layers can be used. In this case, adjacent unit layers preferably have different compositions. For example, when the coating film 3 has a three-layer structure (Fig. 2), and a first unit layer 31, a second unit layer 32, and a third unit layer 33 are formed sequentially outward from the body side 2 of the abrasive grain, the first unit layer 31 and the third unit layer 33 can have the same composition, and the second unit layer 32 can have a different composition from that of the first unit layer 31 and the third unit layer 33. Furthermore, the first unit layer 31, the second unit layer 32, and the third unit layer 33 can all have different compositions.The structure of the coating film 3 can be analyzed by cross-sectional observation with a STEM. Thickness The coating film 3 preferably has a thickness of 50 nm or more and 1000 nm or less. When the coating film is 50 nm or thicker, it facilitates an improvement in the wear resistance of the coating film itself and thus reduces damage to both the coating film and the abrasive grain body. When the coating film is 1000 nm or less thick, it is not excessively thick and therefore does not detach easily, and a state with the coating film formed on an external surface of the abrasive grain body is easily maintained. When coating film 3 has a multilayer structure, the thickness of coating film 31 is the sum of the thickness of each layer. When coating film 3 has a multilayer structure, each layer can have the same or different thicknesses. A lower limit for the coating film thickness is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 150 nm or more. An upper limit for the coating film thickness is preferably 1000 nm or less, more preferably 500 nm or less, and even more preferably 300 nm or less. The coating film has a thickness more preferably COCI ηη / 77Π7 / E / YILI of 100 nm or more and 500 nm or less, even more preferably of 150 nm or more and 300 nm or less. In this description, coating film thickness means the average thickness of the coating films of 10 randomly selected superabrasive grains. The coating film thickness of each superabrasive grain used to calculate the average value is calculated using the following method. Initially, a molded body is produced in which a plurality of coated superabrasive grains are embedded in epoxy resin. The content of coated superabrasive grains in the molded body is 50% or more by volume relative to the resin. The molded body has a rectangular or cube-shaped form. The molded body undergoes a cross-sectional polishing (CP) process. This process is performed in two stages. In the first stage, the molded body's surface is processed until a cross-section of at least one coated superabrasive grain is visible. Subsequently, in the second stage, the processed surface undergoes another CP process to remove a thickness corresponding to a length equivalent to 50% of the grain size of the coated superabrasive grain. Note that the grain size of the coated superabrasive grain is a value measured using a particle size distribution analyzer of the laser diffraction type described earlier. Subsequently, the cross-section of the molded body is observed using a SEM to obtain a backscattered electron image. In the backscattered electron image, three portions of the coating film of a single-coated superabrasive grain are randomly selected, and their thickness is measured. The average thickness of the three portions is defined as the coating film thickness of the single-coated superabrasive grain. Method for producing coated superabrasive grains A method for producing coated superabrasive grains may comprise the steps of: preparing an abrasive grain body made of cubic boron nitride (hereinafter also referred to as the preparation step), pretreating the abrasive grain body (hereinafter also referred to as the pre-coating treatment step), and forming a coating film on a surface of the abrasive grain body (hereinafter also referred to as the coating step). Preparation stage Cubic boron nitride was prepared as the raw material for the abrasive grain body. The type of cubic boron nitride used is not particularly limited, and any known cubic boron nitride can be used. Pre-coating treatment stage The prepared body of the cubic boron nitride abrasive grain undergoes pretreatment. This can reduce the dislocation density of the abrasive grain body. Examples of pretreatment include heat treatment, electron beam exposure, plasma exposure, and microwave exposure. The heat treatment can be carried out in a vacuum at a temperature of 850 to 1400°C for 15 to 300 minutes, for example. This can sufficiently reduce the dislocation density of the abrasive grain body. The temperature is preferably higher than that of a post-coating heat treatment stage described below. Exposure to the electron beam can be performed with an exposure energy of 10 to 40 MeV for 3 to 20 hours, for example. This can sufficiently reduce the dislocation density of the abrasive grain body. Coating stage Subsequently, a coating film is formed on the surface of the heat-treated abrasive grain. The coating film is formed by: arc ion coating (AIP), high-power magnetron sputtering (HIPIMS), an arc plasma powder or similar physical vapor deposition method; spray pyrolysis, metal-organic chemical vapor deposition (MOCVD), or chemical vapor deposition; or similar methods. Among others, the arc plasma powder method is optimal. The coating is applied under conditions that include a target material of at least one single substance selected from a group 4 element, a group 5 element and a group 6 element of the periodic table, aluminum, silicon and carbon, or an alloy or compound thereof, an atmosphere that includes at least one of the following elements: oxygen, nitrogen and argon, a discharge voltage equal to or greater than 10 V and equal to or less than 200 V, a discharge frequency equal to or greater than 1 Hz and equal to or less than 20 Hz, a capacitor with a capacitance equal to or greater than 360 μR and less than or equal to 1800 μE, and a number of shots of 1,000 or more and 10,000,000 or less.Therefore, a coating film that includes one or more types of compounds formed from at least one type of element selected from the group consisting of an element from group 4, an element from group 5 and an element from group 6 of the periodic table, aluminum and silicon, and at least one type of element selected from the group consisting of oxygen. COCI ηη / 77Π7 / E / YΙΛΙ Nitrogen, carbon and boron can form on a surface of the abrasive grain body. Post-coating heat treatment stage After the coating film forms, a post-coating heat treatment stage is preferably performed. Immediately after coating film formation, the coating film is mainly amorphous, and by applying appropriate heat treatment, the coating film can be structurally controlled, and the adhesive strength between the coating film and the abrasive grain body can also be improved. For example, for aluminum oxide, heat treatment at 700°C or higher begins to generate γ-AlzOs, and at 1200°C or higher it begins to generate α-AlzOs. Such a phase transition of a crystalline structure involves a volume change, and an inconsistency can occur at the interface between the coating film and the abrasive grain body. When the heat treatment is at a high temperature, the coating film tends to be composed of crystal grains with a larger grain size. When the heat treatment is at a low temperature, the coating film tends to be composed of crystal grains with a smaller grain size. For example, when heat treatment is applied at a temperature of 800 to 1000°C for 30 to 240 minutes, the coating film can contain γ-AlgOs and be composed of a plurality of crystal grains with an average grain size of 500 nm or less. This provides high hardness, suppresses inconsistencies at the interface between the abrasive grain body and the coating film, and achieves tight adhesion without gaps through interdiffusion of atoms between the abrasive grain body and the coating film. It also contains a minimal amount of unreacted metallic aluminum, an amorphous aluminum-oxygen component, and similar components. The atomic ratio of aluminum to oxygen (Al / O) in the coating film 3 can be controlled by arc plasma powder, atmospheric oxygen partial pressure during heat treatment, or similar methods. The Al / O ratio increases when the oxygen partial pressure is reduced and decreases when the oxygen partial pressure is increased. An Al / O ratio of 0.2 or higher facilitates the generation of γ-AlgOs, an Al / O ratio of 0.9 or lower allows for maintaining insulation, and an Al / O ratio of 0.4 or higher and 0.7 or lower allows for a significantly improved grinding ratio. I cooked nn / zznz / E / YiAi Application The super-abrasive grain coated according to the first modality is conveniently applicable as an abrasive grain for a grinding tool (whetstone) such as a wheel. Second type: Abrasive grain An abrasive grain in one embodiment of the present description is composed of cubic boron nitride and has a dislocation density of 9 * io>« / m2o or less. A tool using abrasive grains of the present description may have a high grinding ratio. One reason for this is inferred as follows: The abrasive grain described herein has a low dislocation density. This low dislocation density increases the hardness of the abrasive grain. Therefore, the abrasive grain described herein is free from significant defects during a grinding process. A tool using abrasive grains described herein can thus have a high grinding ratio. The abrasive grain of the second modality can have the same configuration as the abrasive grain body included in the coated superabrasive grain of the first modality. That is, the abrasive grain body of the first modality that is only used as an abrasive grain is the abrasive grain of the second modality. I cooked nn / zznz / E / YiAi The abrasive grain of the second modality may be configured to be identical to the body of the abrasive grain included in the coated superabrasive grain of the first modality in: composition; dislocation density; crystal structure; grain size of the crystal grains that constitute the abrasive grain; a crystallite that is a constituent of the abrasive grain, and crystallite size; average grain size of the crystal grains that constitute the abrasive grain; and application. Dislocation density The abrasive grain has a dislocation density of 9 x 10⁻⁶ / m² or less. When the abrasive grain has a dislocation density of 9 x 10⁻⁶ / m² or less, it exhibits excellent strength. Furthermore, there are few lattice defects in the abrasive grain, which can reduce defects caused during grinding. A tool using abrasive grains of this description can therefore achieve a high grinding ratio. A lower limit for the dislocation density of the abrasive grain is preferably 1 * 10⁸ / m² or more, more preferably 1 * 10¹⁰ / m² or more, and even more preferably 5 * 10¹⁰ / m² or more. An upper limit for the dislocation density of the abrasive grain is 9 * 10⁻⁶ / m² or less, preferably 6.5 * 10⁻⁶ / m² or less, more preferably 2 * 10⁻⁶ / m² or less, and even more preferably 5 * 10¹³ / m² or less. The abrasive grain preferably has a dislocation density of 1 × 10⁸ / m²o more and 9 × io” / m²o less, more preferably 1 × 10⁸ / m²o more and 6.5 × w / m²o less, more preferably 1 × 10¹⁰ / m²o more and 2 × ioi« / m²o less, even more preferably 5 × 10¹⁰ / m²o more and 5 × 10¹³ / m²o less. The method for measuring the dislocation density of the abrasive grain is the same as the method for measuring the dislocation density of the abrasive grain body described in the first modality and, therefore, will not be described repeatedly. Crystalline structure Abrasive grains can have a monocrystalline or polycrystalline structure. Monocrystalline grains are easily strengthened. Polycrystalline grains, on the other hand, contribute to a better grinding ratio in tools using them. Size of the crystallite that constitutes the abrasive grain (crystallite size) The abrasive grain is preferably composed of crystallites with a size (crystallite size) of 250 nm or larger. This helps a tool using such abrasive grains achieve a better grinding ratio. Although the reason for this is unknown, it is deduced that a larger crystallite size suppresses crack propagation during the grinding process, thus increasing the abrasive grain's strength and mitigating a large abrasive grain defect during grinding. For the crystallite size, a lower limit of 250 nm or more, 450 nm or more, or 600 nm or more can be established. For the crystallite size, an upper limit of 2000 nm or less, 1500 nm or less, or 1000 nm or less can be established. The crystallite size can be 250 nm or more and 2000 nm or less, 450 nm or more and 1500 nm or less, or 600 nm or more and 1000 nm or less. The method for measuring the size of the crystallites is the same as the method for measuring the size of the crystallites of the abrasive grain body described in the first modality, and consequently, will not be described repeatedly. Abrasive grain size The abrasive grain preferably has a grain size of 30 µm or more and 600 µm or less. In this case, the grain size of the abrasive grain means the grain size of a single abrasive grain. Abrasive grains with a grain size of 30 µm or larger are not excessively small and therefore adhere easily to a wheel, facilitating the grinding of a workpiece. They are also easy to handle, simplifying wheel construction. Abrasive grains with a grain size of 600 µm or smaller are not excessively large and therefore do not fracture or similarly damage easily due to impact forces acting upon them in contact with a workpiece. The abrasive grain has a grain size with a lower limit preferably of 30 gm or more, more preferably of 50 gm or more, and even more preferably of 60 gm or more. The abrasive grain has a grain size with an upper limit preferably of 600 gm or less, more preferably of 300 gm or less, and even more preferably of 150 gm or less. The abrasive grain may have a grain size of 30 gm or more and 600 gm or less, 50 gm or more and 300 gm or less, or 60 gm or more and 150 gm or less. The abrasive grain size is measured using a laser diffraction type particle size distribution analyzer (the SALD series manufactured by Shimadzu Corporation). The first modality describes other details of the abrasive grain configuration besides those mentioned above and, therefore, will not be described repeatedly. A method for producing the abrasive grain described herein may comprise the steps of: preparing a precursor made of cubic boron nitride for the abrasive grain; and subjecting the precursor to heat treatment, electron beam exposure, plasma exposure, or microwave exposure to obtain the abrasive grain. This may yield an abrasive grain composed of cubic boron nitride and having a reduced dislocation density. The specific conditions under which the heat treatment is performed may be the same as the pre-coating heat treatment step of the first modality and, consequently, will not be described repeatedly. Third modality: wheel A wheel according to one modality of the present description will now be described with reference to Figs. 3 to 5. Fig. 3 is a schematic perspective view of a wheel according to the third modality. Fig. 4 is a cross-section of the wheel shown in Fig. 3 cut along a plane including a line (IV)-(IV). Fig. 5 is an enlarged cross-section of a portion of the wheel shown in Fig. 4 enclosed by a circle drawn with a dashed line. Although Figures 3 to 5 show a case where a wheel has a superabrasive layer that includes the coated superabrasive grain of the first modality, this is not exclusive. The superabrasive layer may include the abrasive grain of the second modality instead of the coated superabrasive grain. The superabrasive layer may include both the coated superabrasive grain and the abrasive grain. While the following description will describe a case where the superabrasive layer includes the coated superabrasive grain, a case will be described where the superabrasive layer includes the coated superabrasive grain and the abrasive grain is also included in the present modality. The wheel 10 includes a disc-shaped substrate 11 and a superabrasive grit layer 12 covering at least one outer peripheral surface of the substrate 11, and the superabrasive grit layer 12 is a wheel having the superabrasive grit 1 coated in the first embodiment or the abrasive grit of the second embodiment. The wheel 10 comprises a damage-resistant coated superabrasive grit 1, and therefore has a high grinding ratio. Substratum The substrate 11 is made of a material that includes aluminum and an aluminum alloy, iron and an iron alloy, carbon tool steel, high-speed tool steel, alloy tool steel, cemented carbide, cermet, and similar materials. The substrate can have a selectable size (inner and outer diameters and thickness) as required, depending, for example, on the size of a machine tool such as a machining center in which the superabrasive wheel 10 is installed, i.e., nn / zznz / E / YiAi, depending on the workpiece size. The substrate 11 can be a substrate for a known superabrasive wheel. Layer of coated superabrasive grains The coated superabrasive grain layer 12 in this example is formed to continuously cover the front and peripheral surfaces of the outer peripheral surface 111 of the substrate 11 (see Figs. 3 and 4). The size (thickness and width) of the coated superabrasive grain layer 12 can be selected as appropriate, depending on the size (thickness and width) of the substrate 11. The thickness refers to a length in the radial direction of the wheel 10, and the width refers to a length in the axial direction of the wheel 10. The coated superabrasive grain layer 12 includes coated superabrasive grains 1 and an adhesive material 13 (see Fig. 5). Coated super-abrasive grains Coated superabrasive grain 1 is the coated superabrasive grain of the first modality. Coated superabrasive grain 1 may be a plurality of such coated superabrasive grains. The layer of coated superabrasive grains 12 on the side of its front surface has coated superabrasive grains 1 partially exposed from the adhesive material 13 to provide a cutting edge portion for grinding a workpiece. Conversely, the layer of coated superabrasive grains 12 on the substrate side 11 has coated superabrasive grains 1, all buried in the adhesive material 13. The buried coated superabrasive grains 1 are partially exposed and therefore grind a workpiece during a process in which, while the workpiece is ground by the wheel 10, the coated superabrasive grains 1 on the front surface side of the layer of coated superabrasive grains 12 wear down and fall off, and the adhesive material 13 also wears down. The plurality of coated superabrasive grains 1 may all have their respective bodies 2 identically configured (i.e., identical in material, equal in size, and similar) and their respective coating films 3 identically configured (i.e., identical in material, equal in thickness, and similar). Some coated superabrasive grains 1 may have a body 2 and coating film 3 that differ in configuration (i.e., material, size, and similar) from other coated superabrasive grains 1. The layer of coated superabrasive grains 12 may have mixed in it known abrasive grains other than the coated superabrasive grain 1. A lower limit for the average grain size (a volume-based average diameter d50) of the plurality The COCI ηη / 77Π7 / E / YILI of coated superabrasive grains included in the coated superabrasive grain layer is preferably 30 pm, preferably 40 pm, preferably 50 pm, preferably 60 pm. An upper limit for the mean grain size (the mean diameter d50 based on volume) of the plurality of coated superabrasive grains is preferably 600 pm, preferably 400 pm, preferably 300 pm, preferably 150 pm. The plurality of coated superabrasive grains has an average grain size (an average diameter d50 based on volume) preferably of 30 pm or more and 600 pm or less, preferably 40 pm or more and 400 pm or less, preferably 50 pm or more and 300 pm or less, preferably 60 pm or more and 150 pm or less. The average grain size of the plurality of coated superabrasive grains is determined by immersing the layer of coated superabrasive grains in an acid (e.g., aqua regia (a liquid of a mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1)), dissolving the adhesive material in the acid, extracting the plurality of coated superabrasive grains alone, and measuring the extracted plurality of coated superabrasive grains with a laser diffraction-type particle size distribution analyzer. When the coated superabrasive grain layer is a large layer, the coated superabrasive grain layer is cut to a predetermined volume (e.g., 0.5 cm3) and the adhesive material is dissolved from the cut portion as described above to extract a plurality of coated superabrasive grains. Adhesive material The adhesive material 13 fixes the coated superabrasive grains 1 to the outer peripheral surface 111 (Fig. 4). The adhesive material 13 includes, in this type, a selected type of resin bond, metal bond, vitreous bond, electroplating bond, and a combination thereof, or metallic wax, for example. These bonds and the metallic wax may be known adhesives and metallic wax. For example, resin bonding includes a thermosetting resin such as phenolic resin, epoxy resin, or polyimide resin as its main component. Metallic bonding includes an alloy containing copper, tin, iron, cobalt, or nickel as its main component. Vitrified bonding includes a vitreous material as its main component. Electroplating includes nickel plating. Metallic wax includes silver (Ag) wax and similar materials. The type of adhesive material 13 can be appropriately selected based on the composition of the coating film 3 of coated super-abrasive grains 1, or similar materials. For example, when the coating film 3 of coated super-abrasive grains 1 is electrically conductive, electroplating is excluded as an adhesive material 13, and resin bonding, metal bonding, vitreous bonding, and metal wax can be used. When the coating film 3 of coated super-abrasive grains 1 has insulating properties, all of the above bonding methods can be used, including electroplating and metal wax. The wheel 10 (see Fig. 3) can be produced as follows: a plurality of coated superabrasive grains 1, each comprising a body 2 with a surface coated, at least partially, with a coating film 3 (see Fig. 1), are prepared and fixed to the outer peripheral surface 111 of the substrate 11 by using adhesive material 13 (see Fig. 5). Alternatively, the wheel 10 can be produced as follows: a plurality of bodies 3 of abrasive grains 2 without coating film are prepared and fixed to the outer peripheral surface 111 of the substrate 11 by means of adhesive material 13, and thereafter the bodies 2 have their surfaces (or a part of the cutting edge) coated with coating film 3. In this case, the coating can be carried out by any of the methods AIP, HIPIMS, CVD and arc plasma powder mentioned above. Application Wheel 10, according to one modality, is suitable for grinding automotive parts, optical glass, magnetic materials, semiconductor materials and the like, grinding to form grooves for milling cutters, drills and reamers and the like, grinding to form a switch for an indexable insert and heavy-duty grinding for various tools. EXAMPLES The modalities will now be described more specifically with reference to the examples. However, the modalities are not limited by these examples. Example 1 Production of coated superabrasive grains and abrasive grain Sample 1 to Sample 6, Sample 9 to Sample 18, Sample 20 to Sample 23 For each sample, single-crystal cubic boron nitride was prepared as the body of an abrasive grain. The prepared abrasive grain body for each sample has an average grain size as indicated in Table 1, with the column "abrasive grain body" and the sub-column "average grain size (pm)." For example, for Sample 1, the abrasive grain body has an average grain size of 75 pm. A vacuum heat treatment furnace was used COCI ηη / 77Π7 / E / YILI (NRF-658-0.7D1.5V produced by Nihon tokusyukikai) was used to apply heat treatment as a pre-coating treatment to cubic boron nitride. The heat treatment was performed under the conditions (for atmosphere, temperature, and time) as indicated in Table 1, in the pre-coating heat treatment column, and in the atmosphere, temperature, and time sub-columns. For example, for Sample 1, the heat treatment was performed under vacuum, meaning 1 * 10~3Pa or less at 900°C for 0.5 hours. After heat treatment for pre-coating, a coating film was formed across the entire surface of the cubic boron nitride using the plasma arc powder coating method. The coating was performed with a coating apparatus set up under the conditions described below. Coating apparatus: APD-P nanoparticle forming apparatus produced by ADVANCE RIKO, Inc. Target: aluminum Gas introduced: O2 Pressure deposition: as indicated in Table 1, the condition for the atmosphere when the coating film column is formed. Discharge voltage: 150 V Discharge frequency: 6 Hz Capacitor capacity: 1080 μΕ baked ηη / ζζηζ / Ε / γίΛΐ Amount of powder processed: 30 g Dust container rotation speed: 50 rpm After the coating film formed on the surfaces of the cubic boron nitride particles, a vacuum heat treatment furnace was used to perform the heat treatment to obtain coated superabrasive grains. The post-coating heat treatment was carried out under the conditions indicated in Table 1, the post-coating heat treatment column, and the sub-columns for atmosphere, temperature, and time. For example, for Sample 1, the heat treatment was performed in a vacuum (1 * ICu3Pa or less) at 850°C for 30 minutes. Sample 7 The abrasive grain body was prepared from single-crystal cubic boron nitride with an average grain size of 75 µm. In the case of sample 7, no pre-coating heat treatment was performed, and a coating film was formed across the entire surface of the cubic boron nitride using the plasma arc powder method to obtain coated superabrasive grains. Sample 7 was not subjected to post-coating heat treatment. Sample 8 Super-abrasive grains were produced coated in the same way as in Sample 6, except that polycrystalline cubic boron nitride with an average grain size of 75 pm was used as the abrasive grain body. Sample 19 Single-crystal cubic boron nitride with an average grain size of 75 µm was prepared as the abrasive grain body. A vacuum heat treatment furnace was used to apply the pre-coating heat treatment to the cubic boron nitride. The pre-coating heat treatment was carried out under the conditions (for atmosphere, temperature, and time) indicated in Table 1, column "Pre-coating heat treatment", sub-columns "Atmosphere", "Temperature", and "Time". After the pre-coating heat treatment, a coating film was formed on the entire surface of the cubic boron nitride using the plasma arc powder method. The coating was performed with the same coating apparatus as Sample No. 1, under the same conditions as Sample No. 1, except for the target and the introduced gas. The target material was aluminum and aluminum-titanium (50% atomic Ti and 50% atomic Al). The introduced gas was either O2 (oxygen) or N2 (nitrogen). Initially, a first unit layer with an average thickness of 150 nm was formed on the surface of the abrasive grain body in a nitrogen atmosphere (0.88 Pa) while nitrogen gas was introduced using titanium aluminum as the target. Subsequently, a second unit layer with an average thickness of 150 nm was formed in an oxygen atmosphere (0.88 Pa) while oxygen gas was introduced using aluminum as the target. After the coating film formed on the surfaces of the cubic boron nitride particles, the previously mentioned vacuum heat treatment furnace was used to perform the post-coating heat treatment to obtain coated superabrasive grains. The heat treatment was carried out under the conditions indicated in Table 1, in the post-coating heat treatment column, in the atmosphere, temperature, and time sub-columns. Sample 24 Single-crystal cubic boron nitride with an average grain size of 75 µm was prepared as the abrasive grain body. A vacuum heat treatment furnace was used to apply the pre-coating heat treatment to the cubic boron nitride. The pre-coating heat treatment was carried out under the conditions (atmosphere, temperature, and time) indicated in Table 2, in the "Pre-coating heat treatment" column, and in the "Atmosphere, temperature, and time" sub-columns. I cooked nn / zznz / E / YiAi After the pre-coating heat treatment, a coating film was formed on the entire surface of the cubic boron nitride using the plasma arc powder method. The coating was performed with the same coating apparatus as for Sample No. 1, as set up under the same conditions as Sample No. 1, except for the target and the introduced gas. The target material was titanium-aluminum (50 atomic percent Ti and 50 atomic percent Al), and a coating film was formed in a nitrogen atmosphere (0.88 Pa). The gas introduced was N2 (nitrogen). After the coating film formed on the surfaces of the cubic boron nitride particles, the aforementioned vacuum heat treatment furnace was used to perform the post-coating heat treatment and obtain coated superabrasive grains. The heat treatment was carried out under the conditions indicated in Table 2, in the post-coating heat treatment column, in the atmosphere, temperature, and time sub-columns. Sample 25 For sample No. 25, single-crystal cubic boron nitride with an average grain size of 75 µm was used as the abrasive grain. That is, for sample No. 25, no pre-coating heat treatment was performed, no coating film was formed, and no post-coating heat treatment was performed. Sample 26 For Sample 26, coated superabrasive grains were produced under conditions similar to those of Sample 5, except that the coating film was formed in an argon atmosphere with titanium and carbon used as the target. Sample 27 For Sample 27, coated superabrasive grains were produced under conditions similar to those of Sample 5, except that the coating film was formed in a nitrogen atmosphere with titanium and carbon used as the target. Sample 28 For Sample 28, coated superabrasive grains were produced under conditions similar to those of Sample 5, except that the coating film was formed in an atmosphere of a gaseous mixture of nitrogen and oxygen with silicon and aluminum used as the target. Sample 29 For Sample 29, coated superabrasive grains were produced under conditions similar to those of Sample 5, except that the coating film was formed in an argon atmosphere with titanium and boron used as the target. Sample 30 For Sample 30, single-crystal cubic boron nitride with an average grain size of 75 pm was subjected to a pre-coating heat treatment similar to that applied to Sample 1 to produce abrasive grains. No coating film formed on Sample 30, and the post-coating heat treatment was not performed. Extent The coated superabrasive grains and abrasive grains were produced as described above, where they were subjected to measurement to identify the dislocation density of the abrasive grain body (for Samples 25 and 30, the dislocation density of the abrasive grain), the composition of the coating film, the atomic ratio of aluminum to oxygen in the coating film (hereafter referred to as the Al / O ratio), and the average grain size and average thickness of the coating film. The specific method of measurement is the same as that indicated in the first method and, consequently, will not be described repeatedly. The results are shown in Tables 1 and 2, with the column for abrasive grain body / abrasive grain, the sub-column for dislocation density, and the column for coating film composition, Al / O ratio, average grain size (ηη / ζζηζ / E / γ), and average thickness. Wheel production Coated superabrasive grains, or abrasive grains produced as described above, were used to produce wheels having the same configuration as wheel 10 shown in Figures 3 to 5. More specifically, a plurality of coated superabrasive grains were bonded to an outer peripheral surface of a substrate with an adhesive material to produce each wheel. The substrate was made of S45C and had an outer diameter (DD) of 50 mm, a mounting hole diameter (DD) of 20 mm, and a thickness of 8 mm. The adhesive material was an Ag wax material. Evaluation of grinding performance The grinding performance of each sample wheel was evaluated by determining its grinding ratio. The grinding ratio was determined as follows: each sample wheel was placed in the following apparatus, and a workpiece was ground for 180 minutes under the following conditions. The grinding ratio was then calculated as the volume of the workpiece ground divided by the total volume of superabrasive grains removed. In other words, the higher the grinding ratio, the better the grinding performance. The results are shown in Tables 1 and 2. Workpiece: SCM 415 hardened steel (3.5 mm × 60 mm x 100 mm) Equipment: V-55 machining center produced by Makino Milling Machine Co., Ltd. Peripheral speed of the grinding wheel: 2700 mm / min Cut 0.17 mm Feed rate: 150 mm / min Refrigerant: Emulsion type (YUSHIROKEN (registered trademark)) Table 1 Samples abrasive grain body / abrasive grain pre-coating heat treatment atmosphere condition when forming the coating film (type: post-coating heat treatment abrasive grain body / abrasive grain coating film grinding ratio -oo L or E 8 Structure average grain size (pm) atmosphere temperature (°C) time (hours) atmosphere temperature (C) time (hours) dislocation density Cm2) composition A1 / 0 ratio average grain size (nm) average thickness (nm) 1 cBN single crystal 75 vado 900 05 o¿ 0.88 vado 850 30 9.00 X 1014 AKl 0.7 50 300 3000 2 cBN single crystal 75 vado 900 1 o¿ 0.88 vado 850 30 300 X 1014 A¿>3 07 50 300 3060 3 CBN single crystal 75 ford 900 13 o¿ 0.88 ford 850 30 2.00 7.007 50 300 3400 6 CBN single crystal 75 vado 950 3 O¿ 0.88 vado 850 30 1.00 xl 013 AbOs 0.7 50 300 3500 7 CBN single crystal 75 o¿ 0.88 3.00 X 1015 7 AKL 07 50 300 1600 8 CBN polycrystalline 75 vado 950 3 o¿ 0.88 vado 850 30 1.00 X 1013 7 AbOs 0.7 50 300 3400 9 CBN single crystal 75 vado 100 0 3 o¿ 0.88 vado 950 30 8.00 xl o12 AfcOs 0.7 450 300 3120. Samples abrasive grain body / abrasive grain pre-coating heat treatment atmosphere condition when forming the coating film (type: post-coating heat treatment abrasive grain body / abrasive grain coating film grinding ratio composition Structure average grain size (pm) atmosphere temperature (X) time (hours) atmosphere temperature CC) time (hours) dislocation density ( / m2) composition Al / O ratio average grain size (nm) average thickness (nm) 10 CBN single crystal 75 vado 135 0 3 o¿ 0.88 vado 130 0 30 6.00x 1012 T AtOs 0.7 50 300 3450 11 CBN single crystal 75 vado 950 3 o¿ 0.78 vado 950 30 1.00 X 1013 T AbOs 0.5 50 300 3460 12 CBN single crystal 75 vacuum 950 3 Oa: 0.93 ford 950 30 1.00x1 o13 T AtOo 0.85 50 300 2980 13 CBN single crystal 75 ford 950 3 0.65 ford 950 30 1.00x1 o13 ΑΚλ 025 50 300 2970 14 CBN single crystal 75 ford 950 3 Q¿1 ford 950 30 1.00 X 1013 AbOs 1 50 300 2940 15 CBN crystal single 75 vado 950 3 O¿ 0.55 vado 950 30 1.00 X 1013 T AbOs 0.15 50 300 2930 16 CBN crystal single 75 vado 950 3 o¿ 0.88 vado 850 30 1.00x1 o13 AbOs 0.7 50 30 2800 17 CBN crystal single 75 vado 950 3 o¿ 0.88 vado 850 30 1.00 X 1013 a£>3 0.7 50 800 2810 18 CBN crÉtel único 75 I go 950 3 O¿ 0.88 I go 850 30 1.00 1.00 X 1013 TON (1st head) AKi (2nd head) 07 1st. cap 50 2a. cap 50 1st. capa+ 2a. capa: 300 3300 20 cSN cristel único 30 vado 950 3 02: 0.88 vado 850 30 1.00 X 1013 T ΑΚλ 0.7 50 300 2700 21 CBN cristel único 60 0 vado 950 3 02: 0.88 vado 850 30 1.00 X 1013 ΑΚλ 0.7 50 300 2710 22 CBN crÉtel único 20 vado 950 3 02: 0.88 vado 850 30 1.00 X 1013 'Λ Ab3s 0.7 50 300 2680 23 CBN cristel único 80 0 vado 950 3 02: 0.88 vado 850 30 1.00x1 o13 AbOs 0.7 50 300 2670. cocí ηη / ζζηζ / Ε / γ Table 2 Abrasive grain body / abrasive grain pre-coating heat treatment atmosphere condition when forming the coating film (type: Pa) post-coating heat treatment abrasive grain body / abrasive grain coating film grinding ratio composition Structure average grain size (pm) atmosphere temperature (°C) time (hours) atmosphere temperature (°C) time (hours) dislocation density ( / m2) composition Al / O ratio average grain size (nm) average thickness (nm) 24 CBN single crystal 75 total 900 3 N¿ 0.88 total 850 30 1.00 X 1014 TAN 0.7 50 300 3000 26 CBN single crystal 75 - - - - - - 5.00 X 1015 SnpefculadereaiDmniat» 1000 26 CBN single crystal 75 total 900 25 Os 0.88 tado 850 30 5.00 950 25 o¿ 0.88 850 30 5.00 X 1013 SAJO N - 50 300 2780 29 CBN single crystal 75 all 950 25 o¿ 0.88 tado 850 30 5.00 X 1013 TBr - 50 300 2779 30 c£n single crystal 75 Vacuum 900 05 - - - 9.00 X 1014 Sn coating probe 2143. Assessment The coated superabrasive grains from Sample 1 to Sample 6, from Sample 8 to Sample 24, from Sample 26 to Sample 29, and the abrasive grain from Sample 30 are examples. The coated superabrasive grain from Sample 7 has a body with a dislocation density greater than 9 x 10⁻⁶ and is therefore a comparative example. The abrasive grain from Sample 25 has a dislocation density greater than 9 x 10⁻⁶ and is therefore a comparative example. It has been confirmed that the wheels from Sample 1 to Sample 6, from Sample 8 to Sample 24, and from Sample 26 to Sample 30 have a higher grinding ratio than the wheels from Sample 7 and Sample 25. Example 2 Sample 2-1 to sample 2-6 For Samples 2-1 through 2-5, single-crystal cubic boron nitride with a mean grain size of 75 pm was exposed to an electron beam to produce abrasive grains. For Sample 2-6, polycrystalline cubic boron nitride with a mean grain size of 75 pm was exposed to an electron beam to produce abrasive grains. The electron beam was provided under the conditions specified in Table 3, column "Electron Beam Exposure Condition," and sub-columns "Exposure Energy" and "Exposure Time." Sample 2-7 Single-crystal cubic boron nitride with an average grain size of 7.5 pm was prepared, and a vacuum heat treatment furnace (NRF-658-0.7D1.5V produced by Nihon-tokusyukikai) was used to apply the heat treatment as a pre-coating treatment to the cubic boron nitride. The heat treatment was carried out in a vacuum at 900°C for 0.7 hours. After the pre-coating heat treatment, a coating film was formed over the entire surface of the cubic boron nitride using the arc plasma powder coating method. The coating was performed with the same coating apparatus as for sample No. 1, as set up under the same conditions as for sample No. 1 (see Table 3, column "Atmosphere conditions during coating film formation"). After the coating film formed on the surfaces of the cubic boron nitride particles, the same vacuum heat treatment furnace from Example 1 was used to perform the post-coating heat treatment to obtain coated superabrasive grains for Sample 2-7. The heat treatment was performed under the same conditions as for Sample No. 1 (see Table 3, post-coating heat treatment column, temperature and time sub-columns). Sample 2-8 Single-crystal cubic boron nitride with an average grain size of 75 pm was prepared, and a coating film was formed over the entire surface of the cubic boron nitride using the plasma arc powder method. The coating was performed with the same coating apparatus as for Sample No. 1, as set up under the same conditions as Sample No. 1 (see Table 3, column "Atmosphere Conditions During Coating Film Formation"). After the coating film formed on the surfaces of the cubic boron nitride cocin / zznz / E / YiAi particles, the same vacuum heat treatment furnace from Example 1 was used to perform the post-coating heat treatment to obtain coated superabrasive grains for Sample 2-8. The heat treatment was performed under the same conditions as for Sample No. 1 (see Table 3, post-coating heat treatment column, temperature and time sub-columns). Sample 2-9 Single-crystal cubic boron nitride with an average grain size of 75 pm was prepared, and a coating film was formed over the entire surface of the cubic boron nitride using the plasma arc powder method to obtain coated superabrasive grains for Sample 2-9. The coating was performed using the same coating apparatus as for Sample No. 1, as set up under the same conditions as Sample No. 1 (see Table 3, column "Atmosphere Condition When Forming the Coating Film"). Sample 2-10 For Sample No. 2-10, single-crystal cubic boron nitride with an average grain size of 75 pm was used to serve as the abrasive grain. Sample 2-11 cooked nn / zznz / E / YiAi Single-crystal cubic boron nitride with an average grain size of 75 pm was exposed to an electron beam. The electron beam was provided under the conditions indicated in Table 3, column "electron beam exposure condition", sub-columns "exposure energy" and "exposure time". After exposing the cubic boron nitride to the electron beam, a vacuum heat treatment furnace (NRF-658-0.7D1.5V produced by Nihon-tokusyukikai) was used to apply the heat treatment as a pre-coating treatment to the cubic boron nitride. The heat treatment was performed in a vacuum at 900°C for 0.7 hours. After the pre-coating heat treatment, a coating film was formed over the entire surface of the cubic boron nitride using the plasma arc powder method. The coating was performed with the same coating apparatus as for Sample No. 1, as set up under the same conditions as Sample No. 1 (see Table 3, column "Atmosphere Conditions During Coating Film Formation"). After the coating film formed on the surfaces of the cubic boron nitride particles, the same vacuum heat treatment furnace from Example 1 was used to perform the post-coating heat treatment to obtain coated superabrasive grains for Sample 2-11. The heat treatment was carried out under the same conditions as for Sample No. 1 (see Table 3, post-coating heat treatment column, temperature and time sub-columns). Measurement The coated superabrasive grains and the abrasive grains produced as described above were measured to identify the dislocation density of the abrasive grain body (for Samples 2-1 to 2-6 and Sample 2-10, the dislocation density of the abrasive grain), the composition of the coating film, the atomic ratio of aluminum to oxygen in the coating film (hereafter also referred to as the Al / O ratio), and the average grain size and average thickness of the coating film. The specific method of measurement is the same as that described in the first embodiment and, consequently, will not be described repeatedly. One result is shown in Table 3, with a column for abrasive grain body / abrasive grain, a sub-column for dislocation density, and a column for coating film, with sub-columns for composition, Al / O ratio, average grain size, and average thickness. To produce a wheel Coated superabrasive grains or abrasive grains produced as described above were used in a method similar to that of Example COCI ηη / 77Π7 / E / YILI to produce wheels that had the same shape as that of Example 1. Evaluation of grinding performance The grinding performance of each sample wheel was evaluated by determining its grinding ratio. The grinding ratio was determined as follows: each sample wheel was placed in the following apparatus, and a workpiece was ground for 180 minutes under the following conditions. The grinding ratio was then calculated as the volume of the ground workpiece divided by the total volume of superabrasive grains worn. In other words, the higher the grinding ratio, the better the grinding performance. The results are shown in Table 3. Workpiece: SCM 415 hardened steel (3.5 mm x 60 mm x 100 mm) Apparatus: V-55 machining center produced by Makino Milling Machine Co, Ltd. Peripheral speed of the grinding wheel: 2700 mm / min Cutting depth: 0.5 mm Feed rate: 100 mm / min Coolant: Emulsion type (YUSHIROKEN (registered trademark)) nn / zznz / E / YiAi Table 3 ω E (L ω 3 E abrasive grain body / abrasive grain condition for electron beam exposure pre-coating heat treatment atmosphere condition when forming the coating film (type: Pa) post-coating heat treatment abrasive grain body / abrasive grain coating film Grinding ratio composition structure average grain size (pm) exposure energy (MeV) exposure time temperature (°C) time (hours) temperature (°C) time (hours) dislocation density ( / m2) composition Al / O ratio average grain size (nm) average thickness (nm) 2-1 cBN single crystal 75 25 13 6.0x1014 without coating film 2300 2-2 cBN single crystal 75 30 5 3.0x1014 without coating film 2320 2-3 cBN single crystal 75 30 10 2.0x10'4 without coating film 2350 2-4 cBN single crystal 75 30 15 6.0x10l! without coating film 2370 2-5 cBN single crystal 75 30 24 5.0x10l! without coating film 2400 2-6 cBN polycrystalline 75 30 10 5.0x1014 without coating film 2320 2-7 cBN single crystal 75 900 0.7 O2: 0.88 850 30 6.2x1014 γ-Al2θ3 0.7 50 300 2280 2-8 cBN single crystal 75 O2: 0.88 850 30 6.5x1014 γ-Al2θ3 0.7 50 300 2250 2-9 cBN single crystal 75 O2: 0.88 1.0x1015 γ-Al2θ3 0.7 50 300 1100 2-10 cBN crystal unique 75 5.0x1015 without coating film 700 2-11 cBN single crystal 75 30 24 900 0.7 O2: 0.88 850 30 1.0x10l! γ-AI2θ3 0.7 50 300 3000. Assessment The coated abrasive and superabrasive grains of Samples 2-1 to 2-8 and Sample 2-11 correspond to the Examples. The coated superabrasive grain of Sample 2-9 has a body with a dislocation density greater than 9xioy and therefore corresponds to a comparative example. The abrasive grain of Sample 2-10 has a dislocation density greater than 9xy and therefore corresponds to a comparative example. It has been confirmed that the grinding wheels from Sample 2-1 to Sample 2-8 and Sample 2-11 all have a higher grinding ratio than the grinding wheels from Sample 2-9 and Sample 2-10. When Samples 2-1 to 2-6 and Sample 2-10 were compared, it was confirmed that the dislocation density decreases when cubic boron nitride is exposed to an electron beam. When Sample 2-9 and Sample 2-10 were compared, it was confirmed that the coated superabrasive grain with the coating film (Sample 2-9) has a body with a lower dislocation density than the abrasive grain alone (Sample 2-10) and achieves a grinding ratio approximately 1.5 times that of the abrasive grain alone (Sample 2-10). Although it is not clear why the body of the abrasive grain in Sample 2-9 has a low dislocation density, there is a possibility that, by coating the body, the abrasive grain has a surface exposed to Al and oxygen ions at the atomic level and, therefore, may have relieved lattice defects in the vicinity of the surface, a possibility that the abrasive grain may vary per se in dislocation, or similar. When Sample 2-8 and Sample 2-9 were compared, it was confirmed that Sample 2-8, subjected to post-coating heat treatment, had a grinding ratio approximately twice that of Sample 2-9 without post-coating heat treatment. Although the reason for this is unknown, it is inferred that, in Sample 2-8, the molecular-level particles irradiated during coating film formation diffuse during post-coating heat treatment and thus reduce defects in the vicinity of the coated abrasive grain surface. When Samples 2-7, 2-8 and 2-9 were compared, it was confirmed that exposure to an electron beam and / or the application of a heat treatment further reduces the dislocation density of the abrasive grain body and improves the grinding ratio. Example 3 Sample 3-1 For sample No. 3-1, single-crystal cubic boron nitride with an average grain size of 7.5 pm was used to serve as the abrasive grain. Sample 3-2 Single-crystal cubic boron nitride with an average grain size of 75 pm was exposed to an electron beam to produce abrasive grains for Sample 3-2. The electron beam was provided under the conditions indicated in Table 4, column electron beam exposure condition, sub-columns exposure energy and exposure time. I cooked nn / zznz / E / YiAi Sample 3-3 to Sample 3-10 Single-crystal cubic boron nitride with an average grain size of 7.5 pm was exposed to an electron beam. The electron beam was provided under the conditions indicated in Table 4, column "electron beam exposure condition", sub-columns "exposure energy" and "exposure time". After exposing the cubic boron nitride to the electron beam, a vacuum heat treatment furnace (NRF-658-0.7D1.5V, produced by Nihon-tokusyukikai) was used to apply the heat treatment and obtain abrasive grains for samples 3-3 to 3-10. The heat treatment was performed under vacuum at a specific temperature for a period of time, as indicated in Table 4, under the column "Heat Treatment (Pre-Coating)" and in the sub-columns "Temperature and Time." For example, for sample No. 3-3, the heat treatment was performed under vacuum at 900°C for 1 hour. Sample 3-11 to Sample 3-13 Single-crystal cubic boron nitride with an average grain size of 7.5 pm was exposed to an electron beam. The electron beam was provided under the conditions indicated in Table 4, column "electron beam exposure condition", sub-columns "exposure energy" and "exposure time". After exposing the cubic boron nitride to the electron beam, a vacuum heat treatment furnace (NRF-658-0.7D1.5V, produced by Nihon-tokusyukikai) was used to apply the pre-coating heat treatment. The heat treatment was carried out in a vacuum at a specific temperature for a period of time, as indicated in Table 4, column (pre-coating) heat treatment, sub-columns temperature and time. For example, for sample No. 3-11, the heat treatment was performed in a vacuum at 950°C for 3.5 hours. After the pre-coating heat treatment, a coating film was formed over the entire surface of the cubic boron nitride in the plasma arc powder method to obtain coated superabrasive grains for Samples 3-11 to 3-13. The coating was performed with the same coating apparatus as Sample No. 1, as set up under the same conditions as Sample No. 1 (see Table 4, column condition for atmosphere when forming the coating film). Measurement The coated superabrasive grains and the abrasive grains produced as described above were subjected to measurements to identify the body crystallite size and dislocation density (for Samples 3-1 to 3-10, the crystallite size and dislocation density of the abrasive grain), the composition of the coating film, the atomic ratio of aluminum to oxygen in the coating film (hereafter also referred to as the Al / O ratio), and the average grain size and average thickness of the coating film. The specific manner in which these measurements are taken is the same as that described in the first embodiment and, consequently, will not be described repeatedly.One result is indicated in Table 4, one column abrasive grain body / abrasive grain, the sub-columns crystallite size and dislocation density, and the column coating film, the sub-columns composition, Al / O ratio, average grain size and average thickness. To produce a wheel Coated superabrasive grains or abrasive grains produced as described above were used in a method similar to that of Example 1 to produce wheels that had the same shape as that of Example 1. Evaluation of grinding performance The grinding performance of each sample wheel was evaluated by determining its grinding ratio. The grinding ratio was determined as follows: each sample wheel was placed in the following apparatus and a workpiece was ground for 180 minutes under the following conditions, and the grinding ratio was determined from the volume of the workpiece ground / the total volume worn of the super grains COCI ηη / 77Π7 / E / YILI abrasives. That is, the higher the grinding ratio, the better the grinding performance. A result of this is shown in Table 4. Workpiece: SCM 415 hardened steel (3.5 mm x 60 mm x 100 mm) Apparatus: V-55 Machining Center produced by Makino Milling Machine Co, Ltd. Peripheral speed of the grinding wheel: 2700 mm / min Cut 1.0 mm Feed rate: 100 mm / min Refrigerant: Emulsion type (YUSHIROKEN (registered trademark)) cocí ηη / ζζηζ / E / γίΛΐ Table 4 Samples abrasive grain body / abrasive grain condition for electron beam exposure pre-coating heat treatment atmosphere condition when forming the coating film (type: Pa) Abrasive grain body / abrasive grain coating film grinding ratio composition structure average grain size (pm) exposure energy (MeV) exposure time (hours) temperature (CC) time (hours) Crystallite size (nm) dislocation density ( / m2) composition Al / O ratio average grain size (nm) average thickness (nm) 3-1 CBN single crystal 75 - - - - - 200 5.0x1014 without coating film 1500 3-2 CBN single crystal 75 25 13 - - - 230 6.0x1014 without coating film 4000 3-3 CBN single crystal 75 25 13 900 1 - 260 8.0x1014 without coating film 5000 3-4 CBN single crystal 75 25 14 900 2 - 400 7.5x1014 without coating film 5200 3-5 CBN single crystal 75 25 15 900 2 - 450 7.0x1014 without coating film 5500 3-6 CBN single crystal 75 25 16 900 3 - 550 6.5x1014 without coating film 5700 3-7 cBN single crystal 75 30 5 900 3.5 - 600 2.0x1014 without coating film 6000 3-8 cBN single crystal 75 30 8 900 6 - 1000 5.0x1013 without coating film 6200 3-9 CBN single crystal 75 30 3 900 1.5 - 300 3.0x1014 without coating film 5900. 3-10 CBN single crystal 75 25 14 900 3 - 600 7.0x1014 without coating film 5800 3-11 CBN single crystal 75 30 5 900 3.5 O2: 0.88 600 2.0x1014 y-AbOs 0.7 50 300 9000 3-12 CBN single crystal 75 25 16 900 3 O2: 0.88 550 6.5x1014 y-AbOs 0.7 50 300 8700 3-13 CBN single crystal 75 25 14 900 2 O2: 0.88 400 7.5x1014 y-AbOs 0.7 50 300 8000 I cooked nn / zznz / E / YiAi Assessment The coated abrasive and superabrasive grains in Samples 3-2 through 3-13 are examples. The coated superabrasive grain in Sample 3-1 has a body with a dislocation density greater than 9 x 10¹⁴, and is therefore a comparative example. It has been confirmed that the wheels from Sample 3-2 to Sample 3-13 all have a higher grinding ratio than the wheel from Sample 3-1. From the result of Example 3, it has been confirmed that the cubic boron nitride that constitutes the abrasive grain (or the body of the abrasive grain) can be varied in dislocation density and crystallite size by exposure to an electron beam and a wheel with higher performance can be obtained. Although the modalities and examples in this description have been described as indicated above, it is also intended from the outset that the configurations of the modalities and examples described above will be appropriately combined and modified in various ways. The embodiments and examples currently described are illustrative in every respect and should not be interpreted as restrictive. The scope of the present invention is defined by the scope of the claims, rather than the embodiments and examples described above, and any modifications are intended to include within the scope and meaning equivalent to the scope of the claims. LIST OF REFERENCE SIGNS coated super-abrasive grain, 2 abrasive grain body, 3 coating film, 31 first unit layer, 32 second unit layer, 33 third unit layer, 10 wheel, 11 substrate, 111 outer peripheral surface, 12 super-abrasive grain layer, 13 bonding material. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

Having described the invention as above, the following claims are claimed as property:

1. A coated superabrasive grain characterized in that it comprises: a body composed of cubic boron nitride; and a coating film covering at least a portion of a surface of the body, the body having a dislocation density of 9 x 1014 / m2 or less, the coating film including one or more types of compounds formed by at least one type of element selected from the group consisting of an element of group 4, an element of group 5 and an element of group 6 of the periodic table, aluminum and silicon, and at least one type of element selected from the group consisting of oxygen, nitrogen, carbon and boron.

2. The coated superabrasive grain according to claim 1, characterized in that the body has a monocrystalline structure.

3. The coated superabrasive grain according to claim 1, characterized in that the body has a polycrystalline structure.

4. The super-abrasive grain coated with cocin nn / zznz / E / YiAi in accordance with any of claims 1 to 3, characterized in that the body has a dislocation density of 2 x 1014 / m2 or less.

5. The coated superabrasive grain according to any of claims 1 to 4, characterized in that the body has a dislocation density of 5 x 1013 / m2 or less.

6. The coated superabrasive grain in accordance with any of claims 1 to 5, characterized in that the coating film includes aluminum and oxygen.

7. The coated superabrasive grain according to any of claims 1 to 6, characterized in that the coating film includes yA12O3.

8. The coated superabrasive grain according to any of claims 1 to 7, characterized in that the coating film includes a plurality of crystal grains, and the plurality of crystal grains has an average grain size of 500 nm or less.

9. The coated superabrasive grain according to any of claims 1 to 8, characterized in that in the coating film, the aluminum and oxygen have an Al / O atomic ratio of 0.2 or more and 0.9 or less.

10. The coated superabrasive grain according to claim 9, characterized in that the Al / O ratio is 0.4 or more and 0.7 or less.

11. The coated superabrasive grain according to any of claims 1 to 10, characterized in that the coating film has a thickness of 50 nm or more and 1000 nm or less.

12. The coated superabrasive grain according to any of claims 1 to 11, characterized in that the coating film has a multilayer structure composed of two or more types of unit layers.

13. The coated superabrasive grain according to any of claims 1 to 12, characterized in that it has a grain size of 30 pm or more and 600 pm or less.

14. An abrasive grain composed of cubic boron nitride characterized in that it has a dislocation density of 9 x 1014 / m2 or less.

15. The abrasive grain according to claim 14, characterized in that it has a monocrystalline structure.

16. The abrasive grain according to claim 14, characterized in that it has a polycrystalline COCI ηη / 77Π7 / E / YILI structure.

17. The abrasive grain according to any of claims 14 to 16, characterized in that the dislocation density is 6.5 x 1014 / m2 or less.

18. The abrasive grain according to any of claims 14 to 17, characterized in that the dislocation density is 2 x 1014 / m2 or less.

19. The abrasive grain according to any of claims 14 to 18, characterized in that the dislocation density is 5 x 1013 / m2 or less.

20. The abrasive grain according to any of claims 14 to 19, characterized in that it is composed of crystallites having a size of 250 nm or more.

21. The abrasive grain according to claim 20, characterized in that the crystallite has a size of 450 nm or more.

22. The abrasive grain according to claim 21, characterized in that the crystallite has a size of 600 nm or more.

23. The abrasive grain according to any of claims 14 to 22, characterized in that it has a grain size of 30 pm or more and 600 pm or less.

24. A wheel characterized in that it comprises: a disc-shaped substrate; and a superabrasive grain layer covering at least an outer peripheral surface of the substrate, the superabrasive grain layer having one or both of the superabrasive grains coated in accordance with any of claims 1 to 13 and the abrasive grain in accordance with any of claims 14 to 23.

Images