Cubic boron nitride sintered body and cutting tool including the same

Abstract

A cubic boron nitride sintered body comprising cubic boron nitride particles in an amount of 70% by volume or more and less than 100% by volume, and a bonding material, wherein the bonding material contains an aluminum compound and contains cobalt as a constituent element, and the cubic boron nitride sintered body has a first region where the distance between adjacent cubic boron nitride particles is 0.1 nm or more and 10 nm or less, and when the first region is analyzed using an energy dispersive X-ray analyzer attached to a transmission electron microscope, the atomic percentage of aluminum in the first region is 0.1 or more.

Description

Technical Field

[0001] The present disclosure relates to a cubic boron nitride sintered body and a cutting tool including the cubic boron nitride sintered body. This application claims priority based on Japanese Patent Application No. 2020-130672 filed on July 31, 2020. All the descriptions recorded in the Japanese patent application are incorporated herein by reference. Background Art

[0002] As a high-hardness material for cutting tools and the like, there is a cubic boron nitride sintered body (hereinafter, also referred to as "cBN sintered body"). The cBN sintered body is usually composed of cubic boron nitride particles (hereinafter, also referred to as "cBN particles") and a binder material, and its properties tend to vary depending on the content ratio of the cBN particles.

[0003] Therefore, in the field of cutting, depending on the material of the workpiece and the required machining accuracy, etc., different types of cBN sintered bodies applied to cutting tools are used. For example, a cBN sintered body with a high content ratio of cubic boron nitride (hereinafter, also referred to as "High-cBN sintered body") is suitable for cutting sintered alloys and the like.

[0004] However, the High-cBN sintered body has a tendency to suddenly break. It is considered that this is caused by the weak binding force between cBN particles, resulting in the detachment of cBN particles. For example, International Publication No. 2005 / 066381 (Patent Document 1) discloses a technique for suppressing the occurrence of sudden breakage in a High-cBN sintered body by appropriately selecting a binder material.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: International Publication No. 2005 / 066381 Summary of the Invention

[0008] The cubic boron nitride sintered body according to one aspect of the present disclosure is a cubic boron nitride sintered body including 70% by volume or more and less than 100% by volume of cubic boron nitride particles and a binder material. The binder material contains an aluminum compound and contains cobalt as a constituent element. The cubic boron nitride sintered body has a first region where the distance between adjacent cubic boron nitride particles is 0.1 nm or more and 10 nm or less. When the first region is analyzed using an energy dispersive X-ray analyzer attached to a transmission electron microscope, the atomic percentage of aluminum in the first region is 0.1 or more.

[0009] One aspect of the present disclosure relates to a cutting tool including the above cubic boron nitride sintered body. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is an example of a second image obtained from the cBN sintered body according to the present embodiment.

[0011] Figure 2 is an example of a chart showing the results of elemental line analysis. DETAILED DESCRIPTION

[0012] [Problems to be Solved by the Present Disclosure]

[0013] In recent years, with the rapid high-functionalization of mechanical components, the workability of the workpieces to be machined, which are mechanical components, has been accelerating. Along with this, the problem of cost increase due to the short life of cutting tools has become significant. Therefore, it is desired to further improve the High-cBN sintered body. In view of this, an object of the present disclosure is to provide a cubic boron nitride sintered body capable of achieving a long life, and a cutting tool including the cubic boron nitride sintered body.

[0014] [Effects of the Present Disclosure]

[0015] According to the present disclosure, it is possible to provide a cubic boron nitride sintered body capable of achieving a long life, and a cutting tool including the cubic boron nitride sintered body.

[0016] [Description of Embodiments of the Present Disclosure]

[0017] In order to solve the above problems, the inventors of the present invention conceived to achieve a long life by increasing the bonding force between cBN particles in the High-cBN sintered body. Subsequently, as a result of in-depth research on the reason why the bonding force between cBN particles in the High-cBN sintered body becomes weak, it was found that the layer of oxygen (oxide film) present on the surface of cBN particles hinders the sintering between cBN particles and between cBN particles and the bonding material.

[0018] Based on the above findings, the inventors of the present invention conceived of sintering cBN particles and a bonding material on the basis of having Al, which has a higher reactivity with cBN particles than oxygen, present around the cBN particles, thereby forming a structure of "cBN particle / Al layer (hereinafter, also referred to as "tight contact layer") / cBN particle" between adjacent cBN particles. Since the above-mentioned tight contact layer has a stronger bonding force than the bonding force between cBN particles covered with the above-mentioned oxidation coating film, by having the above-mentioned structure, it is possible to suppress the detachment of cBN particles during cutting, etc., and thus complete the present disclosure capable of achieving a long service life. Further, it was also found that the above-mentioned tight contact layer has the effect of alleviating thermal shrinkage based on the heat generated during cutting, thereby suppressing thermal cracking, and the stability against defects is greatly improved in the present disclosure. Hereinafter, embodiments of the present disclosure will be described first.

[0019] [1] The cubic boron nitride sintered body according to one embodiment of the present disclosure is a cubic boron nitride sintered body including 70% by volume or more and less than 100% by volume of cubic boron nitride particles and a bonding material, wherein the bonding material contains an aluminum compound and contains cobalt as a constituent element, and the cubic boron nitride sintered body has a first region where the distance between adjacent cubic boron nitride particles is 0.1 nm or more and 10 nm or less. When the first region is analyzed using an energy dispersive X-ray analyzer attached to a transmission electron microscope, the atomic percentage of aluminum in the first region is 0.1 or more. The cubic boron nitride sintered body having such characteristics can achieve a long service life of the cutting tool when applied to a cutting tool.

[0020] [2] Preferably, when the distance between adjacent cubic boron nitride particles in the first region is 0.1 nm or more and 7.0 nm or less, the atomic percentage of aluminum in the first region is 0.5 or more. Thereby, the long service life of the cutting tool can be more fully achieved.

[0021] [3] Preferably, the first region contains at least one first element selected from the group consisting of chromium, titanium, vanadium, cobalt, zirconium, tungsten, niobium, hafnium, tantalum, rhenium, silicon, and molybdenum and aluminum as constituent elements. When the first region is analyzed using the energy dispersive X-ray analyzer attached to the transmission electron microscope, when the atomic percentage of aluminum is set as M and the atomic percentage of the element present in the highest concentration among the first elements is set as M1, the ratio M1 / (M + M1) is 0.50 or less. Thereby, the long service life of the cutting tool can be more fully achieved.

[0022] [4] Preferably, the ratio M1 / (M + M1) is 0.010 or more and 0.30 or less. Thereby, the long service life of the cutting tool can be further fully achieved.

[0023] [5] Preferably, the above cubic boron nitride sintered body contains 80% by volume or more and 95% by volume or less of the above cubic boron nitride particles. Thereby, in a cubic boron nitride sintered body with a very large content of cBN particles, the long life of a cutting tool can be achieved.

[0024] [6] The cutting tool according to one aspect of the present disclosure includes the above cubic boron nitride sintered body. A cutting tool having such a feature can achieve long life.

[0025] [Details of Embodiments of the Present Invention]

[0026] Hereinafter, one embodiment of the present invention (hereinafter, also referred to as "this embodiment") will be described. However, this embodiment is not limited thereto. In addition, in this specification, an expression in the form of "A to B" means the upper and lower limits of the range (that is, A or more and B or less), and when there is no unit description in A and only a unit is described in B, the unit of A is the same as the unit of B. Further, in this specification, when a compound or the like is represented by a chemical formula, when the atomic ratio is not particularly limited, it includes all known atomic ratios in the past, and is not necessarily limited to the atomic ratio within the stoichiometric range.

[0027] [Cubic Boron Nitride Sintered Body (cBN Sintered Body)]

[0028] The cubic boron nitride sintered body (cBN sintered body) according to this embodiment is a cBN sintered body including 70% by volume or more and less than 100% by volume of cubic boron nitride particles (cBN particles) and a binder material. The above binder material contains an aluminum compound (Al compound) and contains cobalt (Co) as a constituent element. The cBN sintered body has a first region where the interval between adjacent cBN particles is 0.1 nm or more and 10 nm or less. When the first region is analyzed using an energy dispersive X-ray analyzer attached to a transmission electron microscope (hereinafter, also referred to as "TEM-EDX"), the atomic percentage of aluminum (Al) in the first region is 0.1 or more. A cBN sintered body having such a feature can achieve the long life of a cutting tool when applied to a cutting tool.

[0029] [Cubic Boron Nitride Particles (cBN Particles)]

[0030] As described above, the cBN sintered body according to this embodiment includes cBN particles in an amount of 70% by volume or more and less than 100% by volume. The above cBN sintered body preferably contains the above cBN particles in an amount of 70% by volume or more and 99% by volume or less, and more preferably contains the above cBN particles in an amount of 80% by volume or more and 95% by volume or less. That is, the above cBN sintered body is a so-called High-cBN sintered body. The above cBN particles have high hardness, strength, and toughness and play a role as a skeleton in the cBN sintered body. The content (% by volume) of the cBN particles in the cBN sintered body is substantially the same as the content (% by volume) of the cBN raw material powder (coated cBN powder) used in the mixed powder described later. This is because, although the substance inserted into the capsule of the mixed powder sometimes melts during ultra-high pressure sintering, since the amount of the melt is very small, the content of the cBN particles in the cBN sintered body can be regarded as substantially the same as the content of the cBN particles in the mixed powder. By controlling the content of the cBN raw material powder used in the mixed powder in this way, the content of the cBN particles in the cBN sintered body can be prepared in a desired range.

[0031] The content (% by volume) of the cBN particles in the cBN sintered body can be confirmed by performing quantitative analysis based on inductively coupled high-frequency plasma spectrometry (ICP) on the cBN sintered body, or by performing structure observation and elemental analysis using an energy dispersive X-ray analyzer (EDX) attached to a scanning electron microscope (SEM) or an EDX attached to a transmission electron microscope (TEM).

[0032] For example, in the case of using an SEM, the content (% by volume) of the cBN particles can be obtained as follows. First, any position of the cBN sintered body is cut to produce a specimen of the cBN sintered body including a cross section. The above cross section can be produced using a focused ion beam device, a cross-section polishing device, or the like. Then, the above cross section is observed at 2000 times magnification using an SEM to obtain a backscattered electron image. In the above backscattered electron image, the region where the cBN particles are present appears as a black region, and the region where the bonding material is present appears as a gray region or a white region.

[0033] Next, the above backscattered electron image is binarized using image analysis software (for example, "WinROOF" of Mitani Corporation), and each area ratio is calculated based on the binarized image. Then, by assuming that the above area ratio is also continuous in the depth direction of the above cross section, the above area ratio can be obtained as the content (% by volume) of the cBN particles in the cBN sintered body. In addition, the content (% by volume) of the bonding material described later can be obtained simultaneously by this measurement method.

[0034] The area-based D of the cBN particles 50(Average particle size) is not particularly limited and can be set to, for example, 0.1 to 10 μm. Generally, there is a tendency that the smaller D 50 is, the higher the hardness of the cBN sintered body becomes, and there is a tendency that the smaller the deviation in particle size is, the more homogeneous the properties of the cBN sintered body become. The D 50 of the cBN particles is preferably set to 0.5 to 4 μm.

[0035] The D 50 of the cBN particles is obtained as follows. First, according to the above-described method for measuring the content of the cBN particles, a specimen including a cross-section of the cBN sintered body is produced, and a reflected electron image is thereby obtained. Next, the equivalent circle diameter of each black region in the above-described reflected electron image is calculated using the above-described image analysis software. In this case, it is preferable to calculate the equivalent circle diameters of 100 or more cBN particles by observing five or more fields of view.

[0036] Next, the equivalent circle diameters are arranged in ascending order from the minimum value to the maximum value to obtain a cumulative distribution. The particle size at which the cumulative area is 50% in the cumulative distribution is D 50 . In addition, the equivalent circle diameter refers to the diameter of a circle having the same area as the area of the measured cBN particle.

[0037] <Binder material: Composition other than cBN particles>

[0038] The cBN sintered body according to the present embodiment has a binder material as described above. Further, the cBN sintered body may contain inevitable impurities caused by the raw materials used, manufacturing conditions, etc. In this case, the cBN sintered body is composed of cBN particles, a binder material, and inevitable impurities. As the content (volume %) of the above-described binder material, it is preferably more than 0 volume % and 30 volume % or less, and more preferably 5 to 20 volume %. The binder material functions to sinter cBN particles, which are difficult-to-sinter materials, under industrial-level pressure and temperature.

[0039] The above-described binder material contains an Al compound and contains Co as a constituent element. The above-described "containing Co as a constituent element" means that the above-described binder material contains at least any one of metallic Co, Co alloys, or a substitutional solid solution composed of Co and at least one selected from the group consisting of carbon, nitrogen, and oxygen. Examples of the Al compound include CoAl, Al2O3, AlN, and AlB2, and their composite compounds. It is particularly preferable that the above-described binder material contains two or any one of WC (tungsten carbide), metallic Co monomers and Co alloys, and an Al compound. For the following reasons, it is considered that these components in the binder material are particularly effective for extending the life of the above-described cBN sintered body.

[0040] First, Co and Al have a catalytic function, and thus in the subsequent sintering process, they can promote the bonding of cBN particles to each other. Second, it is speculated that WC is effective in order to make the thermal expansion coefficient of the bonding material close to that of the cBN particles. In addition, the above-mentioned catalytic function refers to the function of promoting the diffusion or precipitation of B (boron) and N (nitrogen) constituting the cBN particles via Co or Al.

[0041] In addition to WC, the Al compound, and Co as a constituent element, the above-mentioned bonding material may further contain other components. As other components of the bonding material, it is preferable to contain at least one element selected from the group consisting of chromium (Cr), titanium (Ti), vanadium (V), zirconium (Zr), tungsten (W), niobium (Nb), hafnium (Hf), tantalum (Ta), rhenium (Re), silicon (Si), and molybdenum (Mo). By dissolving at least one element selected from the above group in the Al compound, it is possible to generate more Al layers (tight layers) that are firmly bonded to the cBN particles between adjacent cBN particles. From the viewpoint of preventing the hindrance of the reaction between Al and cBN, the content of at least one element selected from the above group in the bonding material is preferably 50 atomic% or less, more preferably 30 atomic% or less. In addition, at least one element selected from the above group is a component for obtaining the preferred effects of the present disclosure, and thus the lower limit value can be 0 atomic%. Here, in the present specification, the "Al layer (tight layer)" refers to a layer (region) containing Al as a bonding material component in the bonding material layer occupying between adjacent cBN particles in the above-mentioned cBN sintered body. Further, the "Al layer (tight layer)" sometimes refers to the first region described later. In addition, the content (atomic%) of at least one element selected from the above group in the above-mentioned bonding material is a value obtained by taking all the elements measured by the following XRD and ICP analyses as 100 atomic%.

[0042] The composition of the bonding material can be determined by combining XRD (X-ray diffraction measurement) and ICP. Specifically, first, a test piece with a thickness of about 0.45 to 0.5 mm is cut out from the cBN sintered body, and XRD analysis is performed on the test piece to determine compounds, metals, etc. determined by X-ray diffraction peaks. Next, the above test piece is immersed in fluonitric acid (a mixed acid obtained by mixing concentrated nitric acid (60%) : distilled water : concentrated hydrofluoric acid (47%) in a volume ratio of 2 : 2 : 1) in a closed container to obtain an acid treatment solution in which the bonding material is dissolved. Further, ICP analysis is performed on the acid treatment solution for quantitative analysis of each metal element. Finally, by analyzing the results of XRD and ICP analysis, the composition of the bonding material can be determined.

[0043] Examples of inevitable impurities that may be contained in the cBN sintered body according to the present embodiment include iron, magnesium, calcium, sodium, lithium, and the like. Regarding the above-mentioned inevitable impurities, in the cBN sintered body, each individual impurity may be contained in an amount of 0.01% by mass or less, and the total amount of the impurities as a whole may be contained in an amount of 0.1% by mass or less. In the present specification, the "inevitable impurities" that may be contained in the cBN sintered body are treated as a third component other than cBN and the bonding material.

[0044] <First region>

[0045] The cBN sintered body according to the present embodiment has a first region where the distance between adjacent cBN particles is 0.1 nm or more and 10 nm or less. When the above-mentioned first region is analyzed using an energy dispersive X-ray analyzer (TEM-EDX) attached to a transmission electron microscope, the atomic percentage of Al in the above-mentioned first region is 0.1 or more. The first region is a region formed in the cBN sintered body in a region where the bonding material is present.

[0046] (Analysis based on TEM-EDX)

[0047] The first region can be determined by analyzing, using TEM-EDX, a region in the cBN sintered body where a structure of "cBN particle / bonding material layer / cBN particle" (hereinafter, also referred to as "first structure") is formed between adjacent cBN particles. Hereinafter, a method for determining the first region based on TEM-EDX will be described.

[0048] First, samples are collected from the cBN sintered body, and using an argon ion slicer, thin slices with a thickness of 30 to 100 nm are made from the above samples. Next, the slices are photographed by TEM (transmission electron microscope) at a magnification such that 10 or more and 30 or fewer cBN particles are observed in one field of view, thereby obtaining a first image. Further, in the first image, an area where an interface-like structure formed by adjacent cBN particles is arbitrarily selected. At this time, regarding the area where the interface-like structure of the above cBN particles is inclined in the depth direction with respect to the observation field of view, it is excluded from the selection, or by slightly adjusting the above slice, the interface-like structure of the cBN particles inclined in the depth direction is made perpendicular to the observation field of view. This is because, in the state where the interface-like structure of the above cBN particles is inclined in the depth direction with respect to the observation field of view, there is a risk that the measurement of the interparticle distance D and the elemental line analysis described later cannot be appropriately performed. Next, the selected area where the above interface-like structure is formed is positioned so as to pass near the center of the image, and the observation magnification is changed to 2 million times for observation, thereby obtaining a second image with a size of 100 nm × 100 nm. In the above second image, the area where the above interface-like structure is formed exists as an area where the above first structure is formed and extends from one end of the image through near the center of the image to the other end (the other end) opposite to that end.

[0049] Next, by performing elemental line analysis in a direction perpendicular to the area where the interface-like structure confirmed by the second image is formed, the distribution of the HAADF image intensity is obtained. Further, in the above distribution, the difference from the background to the peak is obtained, and then, two points on the distribution where the value is half of the difference are extracted, and the distance between the two points is defined as the interparticle distance D. This interparticle distance D corresponds to the interval between adjacent cBN particles. That is, the area where the above interface-like structure is formed is detected as having a higher (stronger) intensity as the HAADF image intensity than the area where cBN particles exist, and thus can be used for quantifying the interval (interparticle distance D) between adjacent cBN particles. When the above interparticle distance D is 0.1 nm or more and 10 nm or less, this area is determined as the first area.

[0050] In the above method for determining the first area, it is preferable to prepare second images of ten fields of view for the cBN sintered body as the sample. In this specification, the above analysis is repeatedly performed based on the second images of the above ten fields of view. When the interparticle distance D of 0.1 to 10 nm is confirmed in at least six or more second images (that is, when the first area is observed), it is regarded that the cBN sintered body as the sample has the first area.

[0051] Here, Figure 1 is an example of a second image obtained from the cBN sintered body according to the present embodiment. Refer to Figure 1 . The black region corresponds to a region mainly composed of B and N (the region where cBN particles exist), and the white region or the gray region corresponds to a region where a binding material component other than B and N exists. In addition, the whole of the second image corresponds to the "region having an interface-like structure formed with cBN particles" selected from the first image.

[0052] Figure 2 is an example of a chart showing the results of elemental line analysis. In the above chart, the distance (nm) at which elemental line analysis was performed is represented on the horizontal axis, and the HAADF image intensity (a.u.) calculated based on the results of elemental line analysis is represented on the vertical axis. Figure 2 The "distance D" shown in

[0053] (atomic % of aluminum in the first region)

[0054] In the cBN sintered body according to the present embodiment, when the above first region is analyzed using TEM-EDX, the atomic % of Al in the above first region is 0.1 or more. The value of the atomic % of Al can be obtained based on the results of elemental line analysis of the above second image. Specifically, as the value of the atomic % of Al, the maximum value of the Al peak after removing the background value obtained from the results of the above elemental line analysis is adopted. The reason is that when the area of the Al peak obtained by elemental line analysis is used as the atomic % of Al, the analysis error becomes large. In addition, the atomic % of Al in the above first region is a value obtained by taking all the elements measured by the above elemental line analysis as 100 atomic %.

[0055] In this specification, "the atomic % of Al in the first region is 0.1 or more" means that, in the second images of ten fields of view extracted from the cBN sintered body as a sample, the average value of the atomic % of Al in six or more first regions where the above inter-particle distance D is 0.1 nm or more and 10 nm or less is 0.1 or more. The upper limit value of the atomic % of Al in the first region is not particularly limited. Any upper limit value can be taken as long as it can be measured. For example, the atomic % of Al in the first region can be 50 or less, or 30 or less, or 15 or less.

[0056] Here, in the cBN sintered body according to the present embodiment, when the interval between adjacent cubic boron nitride particles in the first region is 0.1 nm or more and 7.0 nm or less, the atomic % of Al is preferably 0.5 or more. When the atomic % of Al in the first region is 0.5 or more, the bonding strength between cBN particles can be further improved. Thus, when the cBN sintered body is applied to a cutting tool, the long life of the cutting tool can be more fully achieved.

[0057] (Other elements in the first region)

[0058] The first region preferably contains, as constituent elements, at least one or more first elements selected from the group consisting of chromium (Cr), titanium (Ti), vanadium (V), cobalt (Co), zirconium (Zr), tungsten (W), niobium (Nb), hafnium (Hf), tantalum (Ta), rhenium (Re), silicon (Si), and molybdenum (Mo), and Al. In this case, when the first region is analyzed using the energy dispersive X-ray analysis device (TEM-EDX) attached to the transmission electron microscope, when the atomic % of Al is set as M and the atomic % of the element present in the highest concentration among the first elements is set as M1, the ratio M1 / (M + M1) is preferably 0.50 or less. The ratio M1 / (M + M1) is more preferably 0.010 or more and 0.30 or less. When the cBN sintered body having such characteristics is applied to a cutting tool, the long life of the cutting tool can be more fully achieved.

[0059] Here, in this specification, "M1" in the ratio M1 / (M + M1) refers to the value of the atomic % of the element present in the highest concentration among the first elements in the first region as described above. Therefore, for the first elements contained in the first region, not only does the relationship that the ratio M1 / (M + M1) is 0.50 or less hold between the atomic % of the element present in the highest concentration among the first elements and the atomic % of aluminum, but also the relationship that "the atomic % of the first element / (the atomic % of the first element + the atomic % of aluminum) is 0.50 or less" holds between each first element and the atomic % of aluminum. Further, for the first elements contained in the first region, it is further preferred that the relationship that the ratio M1 / (M + M1) is 0.010 or more and 0.30 or less holds between the atomic % of the element present in the highest concentration among the first elements in the first region and the atomic % of aluminum. In addition, the first elements contained in the first region may be only one selected from the above group, or may be two or more.

[0060] The value of M1 / (M+M1) in the above-mentioned first region can be obtained by the same method as that for obtaining the atomic % value of Al in the above-mentioned first region. That is, based on the maximum value of the peak of the element with the highest concentration in the first region among the above-mentioned first elements and the maximum value of the above-mentioned Al peak obtained from the result of the above-mentioned elemental line analysis, the atomic % value (M1) of the element with the highest concentration in the first region among the above-mentioned first elements and the atomic % value (M) of the above-mentioned Al are obtained. Then, by dividing the above-mentioned M1 by the sum of the above-mentioned M1 and M (M+M1), the ratio M1 / (M+M1) can be calculated. In addition, in this specification, "the ratio M1 / (M+M1) is 0.50 or less (0.010 or more and 0.30 or less)" means that the average value of the respective values of M1 / (M+M1) in six or more first regions in which the above-mentioned interparticle distance D is 0.1 nm or more and 10 nm or less is 0.50 or less (0.010 or more and 0.30 or less) in ten fields of view of the second image extracted from the cBN sintered body as a sample.

[0061] <Function>

[0062] As described above, the atomic % of Al in the above-mentioned first region of the cBN sintered body according to the present embodiment is 0.1 or more. In this case, the detailed mechanism of the cBN sintered body is unclear, but it is presumed that for the following reasons, the bonding force between cBN particles is improved, and thus long life can be achieved. That is, the atomic % of Al in the above-mentioned first region being 0.1 or more means that a relatively large amount of Al (high concentration) is contained in the above-mentioned first region (between adjacent cBN particles). When Al is present at a high concentration in the above-mentioned first region, Al, which has a high reactivity with cBN particles, can react with cBN particles more during sintering. It is considered that a large amount of "cBN particle / Al layer (close contact layer) / cBN particle" structure can be formed between adjacent cBN particles, thereby improving the bonding force between cBN particles.

[0063] Furthermore, by including each element contained in the group consisting of Cr, Ti, V, Co, Zr, W, Nb, Hf, Ta, Re, Si, and Mo in the above-mentioned first region, when the ratio M1 / (M+M1) satisfies the relationship of being 0.50 or less, the hardness of the above-mentioned close contact layer formed by sintering can be improved, which is therefore preferable. It is presumed that in this case, by improving the physical properties of the above-mentioned close contact layer that joins cBN particles, the bonding force between cBN particles is more sufficiently improved, and the detachment of cBN particles during cutting is suppressed, etc., thereby achieving long life.

[0064] 〔Cutting tool〕

[0065] The cutting tool according to this embodiment includes the above-mentioned cBN sintered body. Specifically, the above-mentioned cutting tool preferably includes the above-mentioned cBN sintered body as a base material. It is also possible to coat a part or all of the surface of the cBN sintered body used as the base material with a coating film.

[0066] The shape and use of the cutting tool according to this embodiment are not particularly limited. For example, regarding the shape and use of the above-mentioned cutting tool, there may be mentioned a drill bit, an end mill, an indexable insert cutting blade for a drill bit, an indexable insert cutting blade for an end mill, an indexable insert cutting blade for milling, an indexable insert cutting blade for turning, a metal saw, a gear cutting tool, a reamer, a tap, a blade for pin milling of a crankshaft, etc.

[0067] Furthermore, the cutting tool according to this embodiment is not limited to a cutting tool in which the whole tool is composed of a cBN sintered body, but also includes a cutting tool in which only a part of the tool (especially the tip part (cutting edge part), etc.) is composed of a cBN sintered body. For example, a cutting tool in which only the tip part of a substrate (support body) made of cemented carbide or the like is composed of a cBN sintered body is also included in the cutting tool according to this embodiment. In this case, literally, the tip part can be regarded as a cutting tool. In other words, even when the cBN sintered body only accounts for a part of the cutting tool, the cBN sintered body is called a cutting tool.

[0068] The cutting tool according to this embodiment can include a coating film that at least covers the above-mentioned tip part. In this case, the coating film can be formed on the above-mentioned tip part in the cBN sintered body by a conventionally known method. Examples of the method for forming the above-mentioned coating film include physical vapor deposition methods such as ion plating method, arc ion plating method, sputtering method, and ion mixing method. Further, the coating film can also be formed by chemical vapor deposition method. The composition of the above-mentioned coating film is not particularly limited, and any conventionally known coating film can be arbitrarily adopted. For example, as the composition of the coating film, there may be exemplified AlTiSiN, AlCrN, TiZrSiN, CrTaN, HfWSiN, CrAlN, TiN, TiBNO, TiCN, TiCNO, TiB2, TiAlN, TiAlCN, TiAlON, TiAlONC, Al2O3, etc.

[0069] The cutting tool according to this embodiment includes the above-mentioned cBN sintered body, so that the shedding of cBN particles and the like can be suppressed during cutting, and thus the long life can be achieved.

[0070] 〔Manufacturing method of cubic boron nitride sintered body〕

[0071] Regarding the method for manufacturing the cBN sintered body according to the present embodiment, there is no particular limitation as long as the above-described cBN sintered body capable of achieving a long service life when applied to a cutting tool can be obtained. However, from the viewpoints of yield and the like, for example, it is preferable to obtain the cBN sintered body by the following manufacturing method. The inventors of the present invention have found that in the process of manufacturing the cBN sintered body, by preparing raw material powders of the binder material with an increased Al content as described later, applying a coating technique different from the conventional one to the surface of the raw material powder of the cBN particles, etc., a cBN sintered body capable of achieving a long service life can be manufactured.

[0072] Specifically, the method for manufacturing the cBN sintered body according to the present embodiment preferably includes: a step of preparing raw material powders of the binder material with an increased Al content (first step); a step of obtaining coated cBN powder by coating a metal on the surface of the cBN raw material powder (second step); a step of preparing a mixed powder composed of 70% by volume or more and less than 100% by volume of cBN powder and the balance of the raw material powders of the binder material by mixing the above-described raw material powders of the binder material and the above-described coated cBN powder (third step); and a step of obtaining a cBN sintered body by sintering the above-described mixed powder (fourth step). Hereinafter, each step will be described in detail.

[0073] <First Step>

[0074] The first step is a step of preparing raw material powders of the binder material with an increased Al content. The above-described raw material powders of the binder material can be prepared by preparing in the following manner. First, for example, WC powder, Co powder, and Al powder are manufactured by a conventionally known method or obtained from the market for preparation. Further, since the above-described raw material powders of the binder material may contain other elements in addition to WC, Co, and Al, it is preferable to also prepare powders containing at least one or more elements selected from the group consisting of Cr, Ti, V, Zr, Nb, Hf, Ta, Re, Si, and Mo as other elements. Next, the above-described respective powders are mixed so as to have a predetermined ratio, and then pulverized by a wet ball mill, a wet bead mill, etc., whereby the above-described raw material powders of the binder material can be prepared.

[0075] Regarding the content of Al in the raw material powders of the binder material, it is set to 20 to 40% by mass, and as such a binder material, it is preferable to increase the Al content compared to the conventional one. Thereby, it is possible to suppress the diffusion of metals such as Al coated on the surface of the cBN in the second step described later into the binder material during sintering. The mixing method of the respective powders is not particularly limited, and from the viewpoints of efficient and uniform mixing, ball mill mixing, bead mill mixing, planetary mill mixing, or jet mill mixing is preferable. Each mixing method can be wet or dry.

[0076] <Second process>

[0077] The second process is a process of obtaining coated cBN powder by coating the surface of cBN raw material powder with metal. As the cBN raw material powder, commercially available cBN particles can be used, or cBN powder obtained from B and N by a conventionally known ultra-high pressure synthesis method can be used. Here, before coating the surface of the cBN raw material powder with metal, it is preferable to perform heat treatment on the cBN raw material powder as a pretreatment. Specifically, for the purpose of purification, the cBN raw material powder is heated in a nitrogen atmosphere with a low oxygen partial pressure for reduction treatment. At this time, the heat treatment temperature is preferably 900 to 1600 °C. The heat treatment time only needs to continue until the surface of the cBN raw material powder is sufficiently purified, and there is no particular limitation. For example, it can be set to 1 to 20 hours. The oxygen partial pressure during the reduction treatment is preferably a low oxygen partial pressure of 1×10 -29 atm or less. By performing heat treatment under such a low oxygen partial pressure, the purification of the cBN raw material powder can be carried out sufficiently and efficiently. Thereby, the oxidation of the cBN surface, which is the main cause of hindering sintering, can be suppressed, and the surface of clean cBN particles can be exposed. Thereby, the adhesion between the metal coating the surface of the cBN raw material powder and the cBN particles can be improved.

[0078] Next, in the second process, metals such as Al are coated on the surface of the cBN raw material powder by using the arc plasma powder method (APD method). Through the above operations, coated cBN powder can be obtained. By using the above APD method, different from generally known coating methods such as the sputtering method, AIP method, and CVD method, nano-particles can be laminated on the surface of the cBN raw material powder, and thereby the metal can exist on the surface of the cBN raw material powder in a state with a larger surface area. In such coated cBN powder, the bonding reaction between cBN particles and metal is easily promoted during sintering, and the metal coating is not easily peeled off in the subsequent third process. Therefore, metals such as Al can be biased between adjacent cBN particles, and a cBN sintered body with improved bonding strength between cBN particles can be manufactured. As the metal coating the surface of the cBN raw material powder, Al is preferably used. Thereby, it is easy to selectively locate Al between cBN particles. Further, in the second process, it is also preferable to coat at least one or more elements (first elements) selected from the group consisting of Cr, Ti, V, Co, Zr, W, Nb, Hf, Ta, Re, Si, and Mo on the cBN raw material powder by using the same coating method. That is, it is preferable to coat one first element selected from the above group on the cBN raw material powder, and it is also preferable to coat two or more first elements on the cBN raw material powder. By adjusting the coating amounts of Al and the first element, the value of the ratio M1 / (M + M1) can be controlled.

[0079] <Third process>

[0080] The third process is a process of preparing a mixed powder composed of cBN powder of 70% by volume or more and less than 100% by volume and the balance of the combined material raw powder by mixing the above-mentioned combined material raw powder and the above-mentioned coated cBN powder. Specifically, in the third process, it is preferable to prepare the above-mentioned mixed powder by performing wet ball mill mixing using ethanol, acetone, etc. as solvents on the combined material raw powder and the coated cBN powder. After preparing the mixed powder, the solvent is removed by natural drying. Further, performing heat treatment on the mixed powder (for example, 850 °C or higher under vacuum) can remove impurities such as moisture adsorbed on the surface, so it is preferable.

[0081] <Fourth process>

[0082] The fourth process is a process of obtaining a cBN sintered body by sintering the above-mentioned mixed powder. In this process, a cBN sintered body is manufactured by exposing the above-mentioned mixed powder to high temperature and high pressure conditions for sintering. Specifically, in the fourth process, the above-mentioned mixed powder subjected to vacuum sealing is sintered using an ultra-high temperature and high pressure device. The temperature condition for the sintering treatment is preferably 1500 °C or higher and lower than 2000 °C, more preferably 1600 - 1900 °C. The holding time is preferably 10 - 50 minutes. The sintering pressure condition is not particularly limited, and preferably 5.5 - 8 GPa. By the above operations, a cBN sintered body can be manufactured.

[0083] <Function and effect>

[0084] The method for manufacturing a cBN sintered body according to the present embodiment can manufacture a cBN sintered body capable of achieving long life by going through the above-mentioned respective processes.

[0085] Examples

[0086] Hereinafter, examples are given to explain the present invention in more detail, but the present invention is not limited to these examples.

[0087] 〔Production of specimens〕

[0088] cBN sintered bodies of Specimens 1 to 36 were produced according to the following steps.

[0089] <Specimen 1>

[0090] (First process)

[0091] First, prepare commercially available WC powder, Co powder, and Al powder. Next, mix the above-mentioned powders in a mass ratio of WC:Co:Al = 32:38:30. In addition, the average particle size of each powder is 5 μm. Further, the powders mixed in the above mass ratio are pulverized by mixing using a bead mill to prepare a raw material powder for the bonding material.

[0092] (Second process)

[0093] First, as the cBN raw material powder, prepare commercially available cBN powder (average particle size: 2 μm). Heat-treat the above cBN raw material powder. The above heat treatment is carried out under an extremely low oxygen condition of 1×10 -29 atm or less, at a heat treatment temperature of 1200 °C and a heat treatment time of 10 hours.

[0094] Next, for the cBN raw material powder that has undergone the above heat treatment, Al is coated on the surface of the cBN raw material powder by the APD method under the following coating conditions to obtain coated cBN powder.

[0095] 〈Coating conditions〉

[0096] Coating device: Nanoparticle formation device (“APD-P”, manufactured by ADVANCE RIKO CO., LTD.)

[0097] Target: Use two pieces of pure Al (purity: 99.999%)

[0098] Introduced gas: After evacuating to 10 -4 Pa, introduce argon and set the pressure inside the device to 10 -1 Pa

[0099] Discharge voltage: 150 V

[0100] Discharge frequency: 5 Hz

[0101] Capacitor capacity: 1080 μF

[0102] Shot number: 10000

[0103] Processed powder amount: 25 g

[0104] Rotation speed of the powder container: 50 rpm.

[0105] (Third process)

[0106] The above-mentioned coated cBN powder and the above-mentioned raw material powder of the binding material are compounded in such a way that the volume ratio of the coated cBN powder to the raw material powder of the binding material is 60:40, and uniformly mixed by a wet ball mill method using ethanol. After that, the solvent is removed by natural drying, and the above-mentioned mixed powder is heat-treated under vacuum at 900 °C. Through the above operations, a mixed powder is prepared.

[0107] (Fourth process)

[0108] A cBN sintered body is produced by sintering the above-mentioned mixed powder. Specifically, the above-mentioned mixed powder is filled into a container made of Ta (tantalum) and vacuum-sealed. Then, using a belt-type ultra-high pressure and high temperature generating device, it is sintered for 15 minutes under the conditions of 6.5 GPa and 1700 °C. Through the above operations, the cBN sintered body of Specimen 1 is produced.

[0109] <Specimen 2>

[0110] In the third process, the compounding is carried out in such a way that the volume ratio of the coated cBN powder to the raw material powder of the binding material is 70:30. Except for this, the cBN sintered body of Specimen 2 is produced in the same manner as Specimen 1.

[0111] <Specimen 3>

[0112] In the third process, the compounding is carried out in such a way that the volume ratio of the coated cBN powder to the raw material powder of the binding material is 75:25. And in the second process, the above-mentioned heat treatment temperature for the cBN raw material powder is set to 1000 °C, the heat treatment time is set to 12 hours, and the number of shots of the above-mentioned coating conditions is set to 5000. Except for this, the cBN sintered body of Specimen 3 is produced in the same manner as Specimen 1.

[0113] <Specimen 4>

[0114] In the third process, the compounding is carried out in such a way that the volume ratio of the coated cBN powder to the raw material powder of the binding material is 80:20. Except for this, the cBN sintered body of Specimen 4 is produced in the same manner as Specimen 1.

[0115] <Specimen 5>

[0116] In the third process, the compounding is carried out in such a way that the volume ratio of the coated cBN powder to the raw material powder of the binding material is 89:11. Except for this, the cBN sintered body of Specimen 5 is produced in the same manner as Specimen 1.

[0117] <Specimen 6>

[0118] In the third process, the mixture ratio is set such that the volume ratio of coated cBN powder to binder material raw powder is 95:5. Other than this, a cBN sintered body of Specimen 6 is produced in the same manner as Specimen 1.

[0119] <Specimen 7>

[0120] In the third process, the mixture ratio is set such that the volume ratio of coated cBN powder to binder material raw powder is 99:1. Other than this, a cBN sintered body of Specimen 7 is produced in the same manner as Specimen 1.

[0121] <Specimen 8>

[0122] The commercially available cBN powder prepared as the cBN raw material powder in Specimen 1 is heat-treated under the conditions of 1×10 -29 atm or less, 1200 °C, and 10 hours. The cBN raw material powder after this heat treatment is filled in a container made of Ta (tantalum) and vacuum-sealed, and sintered at 6.5 GPa and 1700 °C for 15 minutes using a belt-type ultra-high pressure and high temperature generating device. Through the above operations, a cBN sintered body of Specimen 8 is produced.

[0123] <Specimen 9>

[0124] In the second process, the cBN raw material powder is not heat-treated nor coated with Al. Other than this, a cBN sintered body of Specimen 9 is produced in the same manner as Specimen 2.

[0125] <Specimen 10>

[0126] In the second process, the surface of the heat-treated cBN raw material powder is not coated with Al. Other than this, a cBN sintered body of Specimen 10 is produced in the same manner as Specimen 5.

[0127] <Specimen 11>

[0128] In the second process, the heat treatment conditions for the commercially available cBN powder prepared as the cBN raw material powder are set to 1400 °C and 20 hours, and for the surface of the heat-treated cBN raw material powder, the number of shots for the coating condition is set to 1000 to coat Al. Other than this, a cBN sintered body of Specimen 11 is produced in the same manner as Specimen 6.

[0129] <Specimen 12>

[0130] In the second process, the heat treatment conditions for the commercially available cBN powder prepared as the cBN raw material powder are set to 1200 °C and 10 hours, and for the surface of the heat-treated cBN raw material powder, the number of shots for the coating condition is set to 5000 to coat Al. Except for this, a cBN sintered body of Specimen 12 is produced in the same manner as Specimen 5.

[0131] <Specimen 13>

[0132] In the second process, for the surface of the heat-treated cBN raw material powder, the number of shots for the coating condition is set to 25000 to coat Al. Except for this, a cBN sintered body of Specimen 13 is produced in the same manner as Specimen 12.

[0133] <Specimen 14>

[0134] In the second process, the heat treatment conditions for the commercially available cBN powder prepared as the cBN raw material powder are set to 1400 °C and 20 hours, and for the surface of the heat-treated cBN raw material powder, the number of shots for the coating condition is set to 50000 to coat Al. Except for this, a cBN sintered body of Specimen 14 is produced in the same manner as Specimen 5.

[0135] <Specimen 15>

[0136] In the second process, the heat treatment conditions for the commercially available cBN powder prepared as the cBN raw material powder are set to 1200 °C and 6 hours, and for the surface of the heat-treated cBN raw material powder, the number of shots for the coating condition is set to 20000 to coat Al. Except for this, a cBN sintered body of Specimen 15 is produced in the same manner as Specimen 5.

[0137] <Specimen 16>

[0138] In the second process, for the surface of the heat-treated cBN raw material powder, the number of shots for the coating condition is set to 35000 to coat Al. Except for this, a cBN sintered body of Specimen 16 is produced in the same manner as Specimen 15.

[0139] <Specimen 17>

[0140] In the second process, for the surface of the heat-treated cBN raw material powder, the number of shots for the coating condition is set to 50000 to coat Al. Except for this, a cBN sintered body of Specimen 17 is produced in the same manner as Specimen 15.

[0141] <Specimen 18>

[0142] In the second process, the heat treatment conditions for the commercially available cBN powder prepared as the cBN raw material powder were set to 1100 °C and 9 hours, and for the surface of the heat-treated cBN raw material powder, the number of shots for the coating condition was set to 80000 to coat Al. Other than this, a cBN sintered body of Specimen 18 was produced in the same manner as Specimen 5.

[0143] <Specimen 19>

[0144] In the second process, regarding the coating conditions for coating the surface of the heat-treated cBN raw material powder with metal, one of the two targets was changed to Cr (purity 99.999%), and the shot ratio (Al:Cr) of the two targets was changed to 499:1 (number of shots 5000). Thereby, metal was coated on the surface of the cBN raw material powder. Other than this, a cBN sintered body of Specimen 19 was produced in the same manner as Specimen 5.

[0145] <Specimen 20>

[0146] In the second process, the shot ratio (Al:Cr) of the two targets was changed to 99:1 (number of shots 5000). Thereby, metal was coated on the surface of the cBN raw material powder. Other than this, a cBN sintered body of Specimen 20 was produced in the same manner as Specimen 19.

[0147] <Specimen 21>

[0148] In the second process, the shot ratio (Al:Cr) of the two targets was changed to 9:1 (number of shots 5000). Thereby, metal was coated on the surface of the cBN raw material powder. Other than this, a cBN sintered body of Specimen 21 was produced in the same manner as Specimen 19.

[0149] <Specimen 22>

[0150] In the second process, the shot ratio (Al:Cr) of the two targets was changed to 7:3 (number of shots 5000). Thereby, metal was coated on the surface of the cBN raw material powder. Other than this, a cBN sintered body of Specimen 22 was produced in the same manner as Specimen 19.

[0151] <Specimen 23>

[0152] In the second process, the shot ratio (Al:Cr) of the two targets was changed to 6:4 (number of shots 5000). Thereby, metal was coated on the surface of the cBN raw material powder. Other than this, a cBN sintered body of Specimen 23 was produced in the same manner as Specimen 19.

[0153] <Specimen 24>

[0154] In the second process, the shot ratio (Al:Cr) of the above two targets was changed to 5:5 (the number of shots was 5000), whereby a metal was coated on the surface of the cBN raw material powder. Other than that, a cBN sintered body of Sample 24 was produced in the same manner as Sample 19.

[0155] <Sample 25>

[0156] In the second process, the shot ratio (Al:Cr) of the above two targets was changed to 4:6 (the number of shots was 5000), whereby a metal was coated on the surface of the cBN raw material powder. Other than that, a cBN sintered body of Sample 25 was produced in the same manner as Sample 19.

[0157] <Sample 26>

[0158] In the second process, regarding the coating conditions for coating a metal on the surface of the heat-treated cBN raw material powder, one of the two targets was changed from Cr to V (purity 99.999%), and other than that, a cBN sintered body of Sample 26 was produced in the same manner as Sample 21.

[0159] <Sample 27>

[0160] In the second process, regarding the coating conditions for coating a metal on the surface of the heat-treated cBN raw material powder, one of the two targets was changed from Cr to Co (purity 99.999%), and other than that, a cBN sintered body of Sample 27 was produced in the same manner as Sample 21.

[0161] <Sample 28>

[0162] In the second process, regarding the coating conditions for coating a metal on the surface of the heat-treated cBN raw material powder, one of the two targets was changed from Cr to Zr (purity 99.999%), and other than that, a cBN sintered body of Sample 28 was produced in the same manner as Sample 21.

[0163] <Sample 29>

[0164] In the second process, regarding the coating conditions for coating a metal on the surface of the heat-treated cBN raw material powder, one of the two targets was changed from Cr to W (purity 99.999%), and other than that, a cBN sintered body of Sample 29 was produced in the same manner as Sample 21.

[0165] <Sample 30>

[0166] In the second process, regarding the coating conditions for coating the surface of the heat-treated cBN raw material powder with metal, one of the two targets was changed from Cr to Nb (purity: 99.999%), and other than this, a cBN sintered body of Sample 30 was produced in the same manner as Sample 21.

[0167] <Sample 31>

[0168] In the second process, regarding the coating conditions for coating the surface of the heat-treated cBN raw material powder with metal, one of the two targets was changed from Cr to Hf (purity: 99.999%), and other than this, a cBN sintered body of Sample 31 was produced in the same manner as Sample 21.

[0169] <Sample 32>

[0170] In the second process, regarding the coating conditions for coating the surface of the heat-treated cBN raw material powder with metal, one of the two targets was changed from Cr to Ta (purity: 99.999%), and other than this, a cBN sintered body of Sample 32 was produced in the same manner as Sample 21.

[0171] <Sample 33>

[0172] In the second process, regarding the coating conditions for coating the surface of the heat-treated cBN raw material powder with metal, one of the two targets was changed from Cr to Re (purity: 99.999%), and other than this, a cBN sintered body of Sample 33 was produced in the same manner as Sample 21.

[0173] <Sample 34>

[0174] In the second process, regarding the coating conditions for coating the surface of the heat-treated cBN raw material powder with metal, one of the two targets was changed from Cr to Si (purity: 99.999%), and other than this, a cBN sintered body of Sample 34 was produced in the same manner as Sample 21.

[0175] <Sample 35>

[0176] In the second process, regarding the coating conditions for coating the surface of the heat-treated cBN raw material powder with metal, one of the two targets was changed from Cr to Mo (purity: 99.999%), and other than this, a cBN sintered body of Sample 35 was produced in the same manner as Sample 21.

[0177] <Sample 36>

[0178] In the second process, regarding the coating conditions for coating the surface of the heat-treated cBN raw material powder with metal, one of the two targets was changed from Cr to Ti (purity: 99.999%), and except for this, a cBN sintered body of Specimen 36 was produced in the same manner as Specimen 21.

[0179] 〔Evaluation〕

[0180] <Measurement of interparticle distance D, atomic % of Al, and ratio M1 / (M + M1), and determination of presence or absence of the first region>

[0181] Regarding each of the cBN sintered bodies of Specimens 1 to 18 above, after cutting at an arbitrary position, the exposed surface was polished to produce a smooth surface. Then, using an argon ion slicer, it was sliced into a thickness of 50 nm to produce a section. Next, in the same manner as above, elemental line analysis based on TEM-EDX was performed on the second image (100 nm × 100 nm). The beam diameter in TEM-EDX was set to 0.2 nm, and the scanning interval was set to 0.6 nm. Based on the obtained measurement values, the interparticle distance D and the atomic % of Al were determined in the same manner as above, and the presence or absence of the first region was determined. Specifically, in the determination of the presence or absence of the first region, ten arbitrary second images were observed in Specimens 1 to 18 above, and the case where six or more first regions were observed was recorded as "with the first region", and the case where there were five or less was recorded as "without the first region". In addition, in the specimens of "with the first region", the average value of the interparticle distance D obtained from the elemental line analysis targeting the six or more first regions determined to be the first region was calculated. Further, the atomic % of Al was calculated from the average value of the maximum value of the Al peak obtained from the above elemental line analysis. The results are shown in Table 1. Specimens 2 to 7 and Specimens 11 to 18 are examples, and Specimens 1 and 8 to 10 are comparative examples.

[0182] In addition, since there is no bonding material in Specimen 8, a measurable first region could not be detected. In Specimen 9, in the elemental line analysis of an arbitrarily extracted region having the structure of the interface sample formed with cBN particles, all of the interparticle distances D exceeded 10 nm.

[0183] Further, for each cBN sintered body of Specimens 19 to 36, a second image (100 nm × 100 nm) was also obtained in the same manner as for each cBN sintered body of Specimens 1 to 18 described above, and elemental line analysis based on TEM-EDX was performed on this second image. From the obtained measured values, the intergranular distance D, the atomic % of Al, and the ratio M1 / (M + M1) were determined according to the above method, and the presence or absence of the first region was judged. The results are shown in Table 2. Specimens 19 to 36 are all examples. In addition, in Table 2, for the purpose of showing the results of the cutting tests described later, the results of Specimens 5 and 10 are also clearly shown.

[0184] <First Cutting Test>

[0185] Cutting tools for each specimen were produced from each cBN sintered body of Specimens 1 to 18 described above (substrate shape: SNGN090308, cutting edge treatment T01225). Using the cutting tools for each specimen, a cutting test (First Cutting Test) was performed under the following cutting conditions.

[0186] 〈Cutting Conditions〉

[0187] Cutting speed: 1500 m / min.

[0188] Feed rate: 0.2 mm / rev.

[0189] Cutting depth: 0.8 mm

[0190] Coolant: WET

[0191] Coolant liquid: Emulsion 96 (diluted 20 times with water)

[0192] Insert: RM3080R (manufactured by Sumitomo Electric Industries, Ltd.)

[0193] Cutting method: Interrupted cutting

[0194] Lathe: NEXUS 530-II HS (manufactured by Yamazaki Mazak Corporation)

[0195] Workpiece: FC250.

[0196] The cutting edge was observed every 0.5 km of cutting distance, and the amount of chipping of the cutting edge was measured. The amount of chipping of the cutting edge was defined as the recession width due to wear from the position of the cutting edge ridge line before cutting. In the case of chipping, the size of the chipping was defined as the amount of chipping. The cutting distance at the time point when the amount of chipping of the cutting edge was 0.1 mm or more was measured. In addition, the above cutting distance was defined as the life of the cutting tool. The results are shown in Table 1. The longer the cutting distance, the more it can be evaluated that the cutting tool has achieved a long life.

[0197] <Second cutting test>

[0198] Cutting tools for each specimen were made from each of the above-mentioned specimens 5 and 10, and cBN sintered compacts of specimens 19 to 36 (substrate shape: TNGA160404, tip treatment T01225). Using the cutting tools for each of these specimens, a cutting test (second cutting test) was conducted under the following cutting conditions.

[0199] 〈Cutting conditions〉

[0200] Cutting speed: 250 m / min.

[0201] Feed rate: 0.15 mm / rev.

[0202] Depth of cut: 0.1 mm

[0203] Coolant: DRY

[0204] Cutting method: continuous cutting

[0205] Lathe: LB400 (manufactured by OKUMA Corporation)

[0206] Workpiece: sintered part (quenched sintered alloy D40 manufactured by Sumitomo Electric Industries, Ltd., hardness of the machined part after quenching: HRB75).

[0207] The tip was observed at every 0.3 km of cutting distance, and the wear amount of the tip was measured. The cutting distance at the time point when the wear amount of the tip was 100 μm or more was measured. In addition, the above-mentioned cutting distance was regarded as the life of the cutting tool. The results are shown in Table 2. The longer the cutting distance, the more it can be evaluated that the cutting tool has achieved a long life.

[0208] Table 1

[0209]

[0210] Table 2

[0211]

[0212] 〔Discussion〕

[0213] It can be understood from Table 1 that, compared with the cutting tools obtained from the cBN sintered compacts of specimen 1 and specimens 8 to 10 as comparative examples, the cutting tools obtained from the cBN sintered compacts of specimens 2 to 7 and specimens 11 to 18 as examples have achieved a long life.

[0214] As can be understood from Table 2, the cutting tools obtained from the cBN sintered compacts of Specimen 5 and Specimens 19 to 36 as the examples achieved longer life compared to the cutting tools obtained from the cBN sintered compact of Specimen 10 as the comparative example.

[0215] As described above, the embodiments and examples of the present disclosure have been described, but it is also contemplated from the beginning to appropriately combine the configurations of the above-described respective embodiments and examples.

[0216] The embodiments and examples disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is represented not by the above-described embodiments and examples but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A cubic boron nitride sintered body comprising cubic boron nitride particles in an amount of 70% by volume or more and less than 100% by volume, and a binder material, wherein the binder material contains an aluminum compound and contains cobalt as a constituent element, the cubic boron nitride sintered body has a first region where the distance between adjacent cubic boron nitride particles is 0.1 nm or more and 10 nm or less, when the first region is analyzed using an energy dispersive X-ray analyzer attached to a transmission electron microscope, the atomic percentage of aluminum in the first region is 0.1 or more, in the cubic boron nitride sintered body, in ten 100 nm × 100 nm images obtained by photographing a region having a structure similar to an interface between adjacent cubic boron nitride particles at a magnification of 2 million times, six or more of the first regions are observed.

2. The cubic boron nitride sintered body according to claim 1, wherein, When the distance between adjacent cubic boron nitride particles in the first region is 0.1 nm or more and 7.0 nm or less, the atomic percentage of aluminum in the first region is 0.5 or more.

3. The cubic boron nitride sintered body according to claim 1 or 2, wherein the first region contains, as constituent elements, at least one first element selected from the group consisting of chromium, titanium, vanadium, cobalt, zirconium, tungsten, niobium, hafnium, tantalum, rhenium, silicon, and molybdenum, and aluminum, when the first region is analyzed using the energy dispersive X-ray analyzer attached to the transmission electron microscope, when the atomic percentage of aluminum is set as M and the atomic percentage of the element present in the highest concentration among the first elements is set as M1, the ratio M1 / (M + M1) is 0.50 or less.

4. The cubic boron nitride sintered body according to claim 3, wherein, The ratio M1 / (M + M1) is 0.010 or more and 0.30 or less.

5. The cubic boron nitride sintered body according to claim 1 or 2, wherein, The cubic boron nitride sintered body contains the cubic boron nitride particles in an amount of 80% by volume or more and 95% by volume or less.

6. The cubic boron nitride sintered body according to claim 1 or 2, wherein, The D based on the area of the cubic boron nitride particles 50 is 0.1 to 10 μm.

7. The cubic boron nitride sintered body according to claim 1 or 2, wherein, The cubic boron nitride sintered body is composed of the cubic boron nitride particles, the binder material, and inevitable impurities.

8. The cubic boron nitride sintered body according to claim 7, wherein, The inevitable impurities include iron, magnesium, calcium, sodium, and lithium.

9. The cubic boron nitride sintered body according to claim 7, wherein, The inevitable impurities in total contain 0.1% by mass or less.

10. The cubic boron nitride sintered body according to claim 1 or 2, wherein, The binder material contains both or either of WC and Co metal and Co alloy, and an aluminum compound.

11. The cubic boron nitride sintered body according to claim 1 or 2, wherein, The aluminum compound is any one of CoAl, Al2O3, AlN, and AlB2, and their composite compounds.

12. The cubic boron nitride sintered body according to claim 1 or 2, wherein, The binder material contains at least one element selected from the group consisting of chromium, titanium, vanadium, cobalt, zirconium, tungsten, niobium, hafnium, tantalum, rhenium, silicon, and molybdenum, and the content of the at least one element in the binder material is 50 atomic% or less.

13. A cutting tool comprising the cubic boron nitride sintered body according to any one of claims 1 to 12.

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