Cubic boron nitride sintered body and cutting tool comprising the same

Abstract

The cubic boron nitride sintered body includes cubic boron nitride particles in an amount of 70% by volume or more and less than 100% by volume and a binder material. The binder material contains, as constituent elements, at least one first metal element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten, cobalt, and aluminum. The cubic boron nitride sintered body has a first interface region, which is constituted by a region sandwiched between the interface between the cubic boron nitride particles and the binder material and a first imaginary line at a location 10 nm away from the interface toward the binder material side. When the element present in the highest concentration among the first metal elements in the first interface region is taken as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the binder material outside the first interface region.

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. 2020-130673 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 to be cut, the required machining accuracy, etc., different types of cBN sintered bodies applied to cutting tools are selectively 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 embodiment of the present disclosure includes cubic boron nitride particles in an amount of 70% by volume or more and less than 100% by volume and a binder material. The binder material contains, as constituent elements, at least one first metal element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten, cobalt, and aluminum. The cubic boron nitride sintered body has a first interface region, which is composed of a region sandwiched between the interface of the cubic boron nitride particles and the binder material and a first imaginary line at a location 10 nm away from the interface toward the binder material side. When the element present in the highest concentration among the first metal elements in the first interface region is taken as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the binder material outside the first interface region.

[0009] A cutting tool according to one embodiment of the present disclosure includes the above-described cubic boron nitride sintered body. Detailed Description

[0010] [Problems to be Solved by the Present Disclosure]

[0011] In recent years, with the rapid high-functionalization of mechanical components, the difficulty of machining workpieces, 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 High-cBN sintered bodies. 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.

[0012] [Effects of the Present Disclosure]

[0013] 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.

[0014] [Description of Embodiments of the Present Disclosure]

[0015] In order to solve the above problems, the inventors of the present invention conducted in-depth research on the reasons for the short lifespan of the High-cBN sintered body. As a result, it was found that due to the low affinity between cBN particles and cobalt (Co) in the binder material, the bonding strength at the interface between the cBN particles and the binder material weakened, resulting in the detachment of cBN particles during cutting. Based on the above insights, the inventors of the present invention conceived that at the interface between the cBN particles and the binder material, a metal element with high affinity for cBN particles is present at a high concentration around the cBN particles. On this basis, the cBN particles and the binder material are sintered, thereby improving the bonding strength between the cBN particles and the binder material. As a result, the detachment of cBN particles during cutting can be suppressed, and thus the present disclosure that can achieve long lifespan is completed. Further, it was also found that when a metal element with high affinity for cBN particles is present at a high concentration at the interface between the cBN particles and the binder material, the thermal shrinkage caused by the heat generated during cutting is alleviated, thereby suppressing thermal cracking. Therefore, in the present disclosure, the stability against defects is significantly improved. Hereinafter, the embodiments of the present disclosure will be described first.

[0016] [1] The cubic boron nitride sintered body according to one embodiment of the present disclosure includes cubic boron nitride particles and a binder material in an amount of 70% by volume or more and less than 100% by volume. Among them, the binder material contains, as constituent elements, at least one first metal element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten, cobalt, and aluminum. The cubic boron nitride sintered body has a first interface region, which is constituted by a region sandwiched between the interface between the cubic boron nitride particles and the binder material and a first imaginary line at a location 10 nm away from the interface toward the binder material side. When the element with the highest concentration among the first metal elements in the first interface region is regarded as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the binder material outside the first interface region. The cubic boron nitride sintered body having such a feature can achieve the long lifespan of the cutting tool when applied to the cutting tool.

[0017] [2] Preferably, the cubic boron nitride sintered body has a second interface region, which is constituted by a region sandwiched between the interface and a second imaginary line at a location 2 nm away from the interface toward the binder material side. In the second interface region, the atomic concentration of the first element is 0.7 atomic% or more and 10 atomic% or less. Thereby, the long lifespan of the above-mentioned cutting tool can be more fully achieved.

[0018] [3]Preferably, the cubic boron nitride sintered body contains 85 vol% or more and 95 vol% or less of the cubic boron nitride particles. Thereby, in the cubic boron nitride sintered body in which the content of cBN particles is extremely large, the long life of the cutting tool can be achieved.

[0019] [4]Preferably, the first metal element is at least one selected from the group consisting of zirconium, niobium, chromium, molybdenum, and tungsten. Thereby, the long life of the cutting tool can be more fully achieved.

[0020] [5]Preferably, the first metal element is zirconium. Thereby, the long life of the cutting tool can be further fully achieved.

[0021] [6]The cutting tool according to one aspect of the present disclosure includes the above cubic boron nitride sintered body. The cutting tool having such a feature can achieve a long life.

[0022] [Details of Embodiments of the Present Invention]

[0023] 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, the 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 atomic ratios known in the past, and is not necessarily limited to the atomic ratio within the stoichiometric range.

[0024] [Cubic Boron Nitride Sintered Body (cBN Sintered Body)]

[0025] The cubic boron nitride sintered body (cBN sintered body) according to this embodiment is a cBN sintered body including cubic boron nitride particles (cBN particles) in an amount of 70% by volume or more and less than 100% by volume and a bonding material. The above bonding material contains, as constituent elements, at least one first metal element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten, cobalt, and aluminum. The above cBN sintered body has a first interface region, and the above first interface region is composed of a region sandwiched between the interface between the above cBN particles and the above bonding material and a first imaginary line at a location 10 nm away from the above interface toward the above bonding material side. When the element present in the highest concentration among the above first metal elements in the above first interface region is defined as the first element, the atomic concentration of the above first element in the above first interface region is higher than the atomic concentration of the above first element in the above bonding material outside the above first interface region. A cBN sintered body having such characteristics can achieve a long service life of a cutting tool when applied to the cutting tool.

[0026] <Cubic boron nitride particles (cBN particles)>

[0027] 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. The above cBN sintered body more preferably contains the above cBN particles in an amount of 85% 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 used in the mixed powder described later. In addition, the substance inserted into the capsule of the above mixed powder may melt during ultrahigh-pressure sintering, but since the amount of the melt is extremely 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 raw material powder in the mixed powder. In this way, by controlling the content of the cBN raw material powder used in the mixed powder, the content of the cBN particles in the cBN sintered body can be prepared within a desired range.

[0028] 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 spectroscopy (ICP) on the cBN sintered body, or by performing microstructure observation and elemental analysis using an energy dispersive X-ray analysis device (EDX) attached to a scanning electron microscope (SEM) or an EDX attached to a transmission electron microscope (TEM).

[0029] For example, in the case of using an SEM, the content (volume %) of cBN particles can be determined as follows. First, cut an arbitrary position of the cBN sintered body 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 apparatus, a cross-sectional polishing apparatus, etc. Then, observe the above cross section at 2000 times magnification using an SEM to obtain a reflected electron image. In the above reflected electron image, the area where cBN exists appears as a black area, and the area where the bonding material exists appears as a gray area or a white area.

[0030] Next, use image analysis software (for example, "WinROOF" of Mitani Corporation) to perform binarization processing on the above reflected electron image, and calculate each area ratio based on the image after the binarization processing. Then, by assuming that the above area ratio is also continuous in the depth direction of the above cross section, the content (volume %) of cBN in the cBN sintered body can be obtained. In addition, the content (volume %) of the bonding material described later can be obtained simultaneously by this measurement method.

[0031] In addition, the D 50 (average particle size) of the cBN particles is not particularly limited. For example, it can be set to 0.1 to 10 μm. Generally, there is a tendency that the smaller the D 50 , the higher the hardness of the cBN sintered body becomes, and there is a tendency that the smaller the deviation in particle size, 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.

[0032] The D 50 of the cBN particles is determined as follows. First, according to the above method for measuring the content of cBN particles, produce a specimen of the cBN sintered body including a cross section to obtain a reflected electron image. Then, use the above image analysis software to calculate the equivalent circle diameter of each black area in the above reflected electron image. 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.

[0033] Next, arrange the equivalent circle diameters 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.

[0034] <Bonding material: Components other than cBN particles>

[0035] As described above, the cBN sintered body according to the present embodiment includes a binder material. Further, the cBN sintered body may contain inevitable impurities caused by the raw materials used, manufacturing conditions, and the like. In this case, the cBN sintered body may be composed of cBN particles, a binder material, and inevitable impurities. As the content (volume %) of the above binder material, it is preferably more than 0 volume % and 30 volume % or less, more preferably 1 volume % or more and 30 volume % or less, and still more preferably 5 to 15 volume %. The binder material functions to sinter cBN particles, which are difficult-to-sinter materials, under industrial-level pressure and temperature.

[0036] The above binder material contains, as constituent elements, at least one first metal element selected from the group consisting of titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), hafnium (Hf), tantalum (Ta), chromium (Cr), rhenium (Re), molybdenum (Mo), and tungsten (W), cobalt (Co), and aluminum (Al). Al is preferably contained in the binder material as an Al compound. Examples of the Al compound include CoAl, Al2O3, AlN, and AlB2, and their composite compounds. Further, W is preferably contained in the binder material as WC (tungsten carbide). For the following reasons, these components in the binder material are particularly effective for extending the life of the above cBN sintered body.

[0037] First, Co and Al have a catalytic function, so they can promote the bonding between cBN particles in the sintering process described later. Second, it is speculated that WC is effective for making the thermal expansion coefficient of the binder material close to that of cBN particles. In addition, the catalytic function of Al refers to the function of promoting the diffusion or precipitation of B (boron) and N (nitrogen) constituting cBN particles via Al.

[0038] Third, when the binder material contains the above first metal element as a constituent element, the first metal element has a high affinity for cBN particles, so the bonding force at the interface between cBN particles and the binder material can be increased.

[0039] Here, the first metal element is preferably at least one selected from the group consisting of zirconium, niobium, chromium, molybdenum, and tungsten. The first metal element is more preferably zirconium. Thereby, the bonding force at the interface between cBN particles and the binder material can be increased more sufficiently.

[0040] The composition of the bonding material can be determined by combining XRD (X-ray diffraction) 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 this test piece to determine compounds, metals, etc. based on the X-ray diffraction peaks. Then, the above test piece is immersed in a fluoronitric 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 this acid treatment solution to perform 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.

[0041] Examples of inevitable impurities that can be included in the cBN sintered body according to the present embodiment include iron, magnesium, calcium, sodium, lithium, etc. As the above inevitable impurities, sometimes the above inevitable impurities are included in an amount of 0.01% by mass or less as individual impurities in the cBN sintered body, and sometimes the above inevitable impurities are included in an amount of 0.1% by mass or less as the total sum of the impurities as a whole. In this specification, the "inevitable impurities" that can be included in the cBN sintered body are treated as a third component other than cBN and the bonding material.

[0042] <Atomic concentration of the first element in the first interface region>

[0043] The cBN sintered body according to the present embodiment has a first interface region, which is composed of a region sandwiched between the interface of the cBN particles and the bonding material and a first imaginary line that is 10 nm away from the interface toward the bonding material side. In the case where the element with the highest concentration among the first metal elements in the first interface region is regarded as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the bonding material outside the first interface region. Thus, in the cBN sintered body, a metal element with high affinity for cBN particles can exist at a high concentration around the cBN particles, thereby improving the bonding strength between the cBN particles and the bonding material. The atomic concentration of the first element in the first interface region and the atomic concentration of the first element in the bonding material outside the first interface region can be obtained by analysis using an energy-dispersive X-ray analysis device (TEM-EDX) attached to a transmission electron microscope. Hereinafter, the analysis method using TEM-EDX will be described.

[0044] (Analysis based on TEM-EDX)

[0045] <Measurement of the atomic concentration of the first element in the first interface region>

[0046] First, samples are collected from the cBN sintered body, and using an argon ion slicer, sliced samples with a thickness of 30 to 100 nm are produced from the above samples. Then, the sliced samples are photographed by TEM (transmission electron microscope) at a magnification such that 10 or more and 30 or less cBN particles equivalent to the average particle diameter of the cBN particles in the sintered body can be observed in one field of view, thereby obtaining a first image. Further, an area including the interface between the cBN particles and the bonding material (hereinafter, also referred to as the "interface area") is arbitrarily selected from the first image. At this time, when the structure of the arbitrarily selected interface area is inclined in the depth direction with respect to the observation field of view, by excluding the interface area from the selection or slightly adjusting the above sliced sample, the structure of the interface area inclined in the depth direction is made perpendicular to the observation field of view. This is because, in a state where the structure of the above interface area is inclined in the depth direction with respect to the observation field of view, the structure of the interface becomes unclear, and there is a risk that the measurement of the distance from the interface between the cBN particles and the bonding material described later cannot be appropriately performed. Next, the selected interface area is positioned so as to be 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 above interface area exists in such a way that it extends from one end of the image through the vicinity of the center of the image to the other end (the other end) opposite to that end.

[0047] Next, the interface between the cBN particles and the bonding material is determined from the above interface area in the second image, and then a first imaginary line is set at a point 10 nm away from the above interface toward the bonding material side. Thereby, a first interface area sandwiched between the above interface and the above first imaginary line is formed in the second image. Further, for the first interface area in the second image, elemental line analysis based on EDX is performed in a direction substantially perpendicular to the above first imaginary line. In this case, the beam spot diameter is set to 0.3 nm or less, and the scanning interval is set to 0.1 to 0.7 nm.

[0048] Next, based on the above elemental line analysis, the atomic concentration (atomic %) of each element included as the first metal element in the above first interface region is determined. Here, the concentration of each element included as the above first metal element is the average value (average concentration) of the atomic concentrations of each element obtained for each of the above beam spots. In addition, the atomic concentration (atomic %) of each element included as the above first metal element is obtained by setting all the elements measured in the above beam spot, that is, in the measurement field of view, to 100 atomic %. Thus, in the above first interface region, the first element present at the highest concentration in the above first metal element can be determined. For example, in the above first interface region, the first element present at the highest concentration in the first metal element is preferably 0.7 to 10 atomic % or less.

[0049] <Measurement of the atomic concentration of the first element in the bonding material outside the first interface region>

[0050] On the other hand, the atomic concentration of the first element in the bonding material outside the first interface region can be obtained, for example, by the following method. That is, imaginary lines (hereinafter, also respectively denoted as "imaginary line A" and "imaginary line B") are set at positions 15 nm and 30 nm away from the interface determined in the interface region in the second image toward the bonding material side, respectively. Thus, a region sandwiched by the imaginary line A and the imaginary line B (hereinafter, also denoted as "bonding material region outside the first interface region") is formed in the second image. Next, for the bonding material region outside the first interface region, elemental line analysis based on EDX is performed in a direction substantially perpendicular to either the imaginary line A or the imaginary line B. In this case, the beam spot diameter is also set to 0.3 nm or less, and the scanning interval is also set to 0.1 to 0.7 nm. Thus, based on the above elemental line analysis, the concentration (atomic %) of the first element in the bonding material region outside the first interface region can be obtained (in addition, the atomic concentration of the first element in this case is also set to the average value (average concentration) of the concentrations of each element obtained for each of the above beam spots). For example, the first element in the bonding material region outside the first interface region is preferably 0.01 to 0.3 atomic % or less.

[0051] Here, in this specification, from the viewpoint of suppressing measurement errors, the atomic concentration of the first element in the first interface region and the atomic concentration of the first element in the bonding material outside the first interface region are set to the average concentration obtained by averaging the respective atomic concentrations obtained from the second images of six fields of view. That is, six fields of view of the second images are prepared from the cBN sintered body as the sample, and the above TEM-EDX analysis is performed on the second images to obtain the atomic concentrations of the first element in the six first interface regions and the atomic concentrations of the first element in the above bonding material outside the first interface region, respectively, and they are obtained as their average concentrations.

[0052] <Atomic concentration of the first element in the second interface region>

[0053] Preferably, the cBN sintered body according to this embodiment has a second interface region, which is composed of a region sandwiched between the above interface and a second imaginary line at a location 2 nm away from the above interface toward the bonding material side. In the above second interface region, the atomic concentration of the first element is 0.7 atomic % or more and 10 atomic % or less. Thereby, the bonding strength between the cBN particles and the bonding material at the interface between the cBN particles and the bonding material can be more sufficiently improved.

[0054] The atomic concentration of the first element in the above second interface region can be obtained in the same manner as obtaining the atomic concentration of the first element in the above first interface region. That is, in the above second interface region, by performing element line analysis based on the above EDX in a direction substantially perpendicular to the second imaginary line, the atomic concentration (atomic %) of the first element in the above second interface region can be obtained.

[0055] <Function>

[0056] In the cBN sintered body according to the present embodiment, when the element present in the highest concentration among the first metal elements in the first interface region is defined as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the bonding material outside the first interface region. It is speculated that in this case, for the following reasons, the above cBN sintered body can suppress the detachment of cBN particles during cutting and the like by increasing the bonding strength between the cBN particles and the bonding material, thereby achieving a long service life. That is, since the first interface region is the interface between the cBN particles and the bonding material and its adjacent region, it means that in the cBN sintered body according to the present embodiment, among the first metal elements having a high affinity for the cBN particles in this region, especially the atomic concentration of the first element is high around the cBN particles. Therefore, it is considered that a large amount of the first element reacts with the cBN particles during sintering, thereby significantly increasing the bonding strength at the interface between the cBN particles and the bonding material. In particular, when the atomic concentration of the first element in the second interface region is 0.7 atomic % or more and 10 atomic % or less, the first element becomes highly concentrated in the vicinity of the interface between the cBN particles and the bonding material, so the increase in the bonding strength at the interface between the cBN particles and the bonding material becomes significant. Based on the above, it is speculated that the cBN sintered body according to the present embodiment can suppress the detachment of cBN particles during cutting and the like, thereby achieving a long service life.

[0057] [Cutting tool]

[0058] The cutting tool according to the present embodiment includes the above cBN sintered body. Specifically, the above cutting tool preferably includes the above cBN sintered body as a base material. A coating film may be provided on a part or all of the surface of the cBN sintered body as the base material.

[0059] The shape and use of the cutting tool according to the present embodiment are not particularly limited. For example, regarding the shape and use of the above cutting tool, drill bits, end mills, indexable insert cutting blades for drill bits, indexable insert cutting blades for end mills, indexable insert cutting blades for milling, indexable insert cutting blades for turning, hacksaws, gear cutting tools, reamers, taps, blades for pin milling of crankshafts, etc. can be cited.

[0060] 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 referred to as a cutting tool.

[0061] The cutting tool according to this embodiment can include a coating covering at least the above-mentioned tip part. In this case, the coating can be formed on the above-mentioned tip part in the cBN sintered body by a conventionally well-known method. Examples of the method for forming the above-mentioned coating include physical vapor deposition methods such as ion plating method, arc ion plating method, sputtering method, and ion mixing method. Furthermore, the coating can also be formed by chemical vapor deposition method. The composition of the above-mentioned coating should not be particularly limited, and any conventionally well-known coating can be arbitrarily adopted. For example, as the composition of the coating, examples can be shown as AlTiSiN, AlCrN, TiZrSiN, CrTaN, HfWSiN, CrAlN, TiN, TiBNO, TiCN, TiCNO, TiB2, TiAlN, TiAlCN, TiAlON, TiAlONC, Al2O3, etc.

[0062] Since the cutting tool according to this embodiment includes the above-mentioned cBN sintered body, it is possible to suppress the peeling off of cBN particles during cutting, etc., and thus long life can be achieved.

[0063] 〔Manufacturing method of cubic boron nitride sintered body〕

[0064] Regarding the manufacturing method of the cBN sintered body according to this embodiment, as long as the above-mentioned cBN sintered body that can achieve long life when applied to a cutting tool can be obtained, it should not be particularly limited. However, from the viewpoint of yield, etc., for example, it is preferable to obtain the cBN sintered body by the following manufacturing method. The inventors of the present invention found that in the process of manufacturing a cBN sintered body, as described later, by preparing a raw material powder of a bonding material containing a first metal element capable of improving the bonding force with cBN particles, removing impurities in the bonding material, and enriching N on the surface of cBN particles, etc., a cBN sintered body in which the above-mentioned first metal element exists at a high concentration around cBN particles can be manufactured, and thus long life can be achieved. Here, in this specification, "enriching N on the surface of cBN particles" means increasing the concentration of nitrogen (N) element on the surface of cBN particles, or imparting a functional group containing N to the surface of cBN particles.

[0065] Specifically, the method for manufacturing a cBN sintered body according to the present embodiment preferably includes the following steps: preparing a binder raw material powder that improves the bonding strength between the binder raw material powder and the cBN particles, and removing impurities by heat treating the binder raw material powder in a low oxygen atmosphere (first step); preparing a cBN raw material powder, and making the surface of the cBN particles in the cBN raw material powder N-rich (second step); preparing a mixed powder consisting of 70% by volume or more and less than 100% by volume of cBN powder and the remaining binder raw material powder by mixing the above-mentioned binder raw material powder and the above-mentioned cBN raw material powder (third step); and obtaining a cBN sintered body by sintering the above-mentioned mixed powder (fourth step). Each step is described in detail below.

[0066] <First step>

[0067] The first step is to prepare a raw powder of a bonding material that improves the bonding force between the bonding material and the cBN particles, and to remove impurities by heat treating the raw powder of the bonding material in a low oxygen atmosphere. The raw powder of the bonding material can be prepared as follows. First, for example, WC powder, Co powder and Al powder are prepared by manufacturing by a conventionally known method or by obtaining from the market. Furthermore, it is preferred that at least one first metal element selected from the group consisting of Ti, Zr, V, Nb, Hf, Ta, Cr, Re, Mo and W is included as a constituent element in the raw powder of the bonding material, and any one of nitrides, carbides, carbonitrides or hydrides of at least one first metal element selected from the group is prepared by manufacturing by a conventionally known method or by obtaining from the market. Next, the above-mentioned powders are mixed in a predetermined ratio under inert atmosphere conditions, and then pulverized by a wet ball mill, a wet bead mill, etc. under inert atmosphere conditions, thereby preparing the raw powder of the bonding material. By mixing and pulverizing the powders under an inert atmosphere, it is possible to prevent the incorporation of oxygen and the oxidation of the elements of the powders.

[0068] Here, the content of Al in the raw powder of the bonding material is set to 20~40% by mass. As such a bonding material, it is preferred to increase the amount of Al compared to the past. Thus, by alloying the Co in the bonding material, the first element is more likely to diffuse near the interface with the cBN particles than Co during sintering. There is no particular restriction on the mixing method of each powder. From the perspective of efficient and homogeneous mixing, it is preferably ball mill mixing, bead mill mixing, planetary mill mixing or jet mill mixing. Each mixing method can be wet or dry.

[0069] Further, in the first step, impurities are removed by heat-treating the above-described bonding material raw powder in a low-oxygen atmosphere. Specifically, it is preferable to perform a reduction treatment on the above-described bonding material raw powder. For example, the above-described bonding material raw powder is heated in an argon atmosphere with a low oxygen partial pressure to perform a reduction treatment. The heating temperature at this time is preferably 700 to 900 °C. Thereby, impurities such as oxygen can be further removed from the above-described bonding material raw powder.

[0070] <Second Step>

[0071] The second step is a step of preparing cBN raw powder and enriching N on the surface of cBN particles in the cBN raw powder. As the cBN raw powder, commercially available cBN powder can be used, or cBN powder obtained from B and N by a conventionally known ultra-high pressure synthesis method can be used. The inventors of the present invention confirmed that oxides exist on the surface of the cBN powder. It is considered that this is because the cBN powder obtained by ultra-high pressure synthesis is subjected to a cleaning treatment, or the above-described cBN powder is exposed to the atmosphere. Therefore, it is preferable to enrich N on the surface of cBN particles in the cBN raw powder to reduce the amount of oxides.

[0072] As a method for enriching N on the surface of cBN particles, a method of performing heat treatment in a gas atmosphere containing ammonia can be cited. Specifically, it is a method of exposing the above-described cBN raw powder to a gas atmosphere containing ammonia. By exposing the cBN raw powder to a gas atmosphere containing ammonia, oxygen can be reduced on the surface of cBN particles, and at the same time, the surface of cBN particles can be enriched with N.

[0073] In the second step, the average particle size of cBN particles is not particularly limited. From the viewpoint of forming a cBN sintered body having high strength and excellent wear resistance and chipping resistance, the average particle size of cBN particles is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm. According to the above, the oxide film formed on the surface of cBN particles can be reliably removed, and cBN raw powder containing N-enriched cBN particles can be obtained.

[0074] Here, in the case of wanting to manufacture a cBN sintered body containing, for example, Zr as a constituent element of the bonding material, i.e., the first metal element, it is preferable to coat the cBN raw material powder with Zr after preparing the above-mentioned cBN raw material powder in the second process. Thereby, it is easy to selectively arrange the Zr component around the cBN particles. This is not limited to Zr, and the same can be said for other first metal elements. That is, after preparing the above-mentioned cBN raw material powder in the second process, by coating the cBN raw material powder with the first metal element, it is possible to easily selectively arrange the first metal element around the cBN particles. As a specific coating method for the first metal element represented by Zr, at least any one of sputtering, the AlP method, the HIPIMS method, the CVD method, and the arc plasma powder method (APD method) can be used.

[0075] <Third Process>

[0076] The third process is a process 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 bonding material raw material powder by mixing the above-mentioned bonding material raw material powder and the above-mentioned cBN raw material powder. Specifically, in the third process, it is preferable to prepare the above-mentioned mixed powder by performing wet ball milling using ethanol, acetone, etc. as solvents on the bonding material raw material powder and the cBN raw material powder. After preparing the mixed powder, the solvent is removed by natural drying. Further, it is preferable to perform heat treatment on the mixed powder (for example, 850 °C or higher under vacuum), which can remove impurities such as moisture adsorbed on the surface.

[0077] <Fourth Process>

[0078] The fourth process is a process of obtaining a cBN sintered body by sintering the above-mentioned mixed powder. In this process, the above-mentioned mixed powder is exposed to high temperature and high pressure conditions for sintering, thereby manufacturing a cBN sintered body. Specifically, in the fourth process, the above-mentioned mixed powder after 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. According to the above content, a cBN sintered body can be manufactured.

[0079] <Function and Effect>

[0080] The manufacturing method of the cBN sintered body according to the present embodiment can manufacture a cBN sintered body capable of achieving a long service life by going through the above respective processes.

[0081] Examples

[0082] Hereinafter, embodiments will be listed to describe the present invention in more detail, but the present invention is not limited to these embodiments.

[0083] 〔Production of Specimens〕

[0084] The cBN sintered compacts of Specimens 1 to 41 were produced according to the following steps.

[0085] <Specimen 1>

[0086] (First Step)

[0087] First, commercially available WC powder, Co powder, Al powder, and Zr carbide powder were prepared. Next, the above-mentioned powders were mixed and compounded in a mass ratio of WC∶Co∶Al∶ZrC = 22∶45∶28∶5 by a ball mill. In addition, the average particle size of each powder was 2 μm. Further, the powders compounded in the above mass ratio were continuously mixed and pulverized by a ball mill to prepare a combined material raw powder. Then, the combined material raw powder was heated in an argon atmosphere with a low oxygen partial pressure to perform a reduction treatment. According to the above operations, the combined material raw powder was prepared. The above reduction treatment (heat treatment) was set to an extremely low oxygen condition of 1×10 -29 atm or less, the holding temperature was set to 800 °C, and the heat treatment holding time was set to 3 hours.

[0088] (Second Step)

[0089] cBN raw powder with an average particle size of 2 μm was prepared by a known ultra-high pressure synthesis method. Further, the cBN raw powder was subjected to a reduction treatment under the following heat treatment conditions in an ammonia atmosphere to enrich N on the surface of the cBN particles.

[0090] <Heat Treatment Conditions>

[0091] Ammonia flow rate: 0.5 L / min

[0092] Nitrogen flow rate: 5 L / min

[0093] Furnace internal pressure: atmospheric pressure

[0094] Furnace internal temperature: 700 °C

[0095] Holding time: 3 hours

[0096] (Third Step)

[0097] The above cBN raw material powder and the above binder material raw powder are mixed in a volume ratio of cBN raw material powder: binder material raw powder = 60:40, and uniformly mixed by a wet ball milling method using ethanol. After that, the solvent is removed by natural drying, and the above mixed powder is heat-treated under vacuum at 900 °C. According to the above operations, a mixed powder is prepared.

[0098] (Fourth process)

[0099] A cBN sintered body is produced by sintering the above mixed powder. Specifically, the above mixed powder is filled into a container made of Ta (tantalum) in a state of being in contact with a disk made of WC-6%Co cemented carbide and vacuum-sealed. Then, using a belt-type ultra-high pressure and high temperature generating device, it is sintered at 6.5 GPa and 1650 °C for 20 minutes. According to the above operations, the cBN sintered body of Specimen 1 is produced.

[0100] <Specimen 2>

[0101] In the third process, the mixture is carried out in a volume ratio of cBN raw material powder: binder material raw powder = 70:30. Except for this, the cBN sintered body of Specimen 2 is produced in the same manner as Specimen 1.

[0102] <Specimen 3>

[0103] In the third process, the mixture is carried out in a volume ratio of cBN raw material powder: binder material raw powder = 80:20. Except for this, the cBN sintered body of Specimen 3 is produced in the same manner as Specimen 1.

[0104] <Specimen 4>

[0105] In the third process, the mixture is carried out in a volume ratio of cBN raw material powder: binder material raw powder = 91:9. Except for this, the cBN sintered body of Specimen 4 is produced in the same manner as Specimen 1.

[0106] <Specimen 5>

[0107] In the third process, the mixture is carried out in a volume ratio of cBN raw material powder: binder material raw powder = 95:5. Except for this, the cBN sintered body of Specimen 5 is produced in the same manner as Specimen 1.

[0108] <Specimen 6>

[0109] In the third process, the mixture is carried out in a volume ratio of cBN raw material powder: binder material raw powder = 99:1. Except for this, the cBN sintered body of Specimen 6 is produced in the same manner as Specimen 1.

[0110] <Specimen 7>

[0111] In the third process, the mixing of the cBN raw material powder and the binder raw material powder is not performed, so that 100% by mass of the cBN raw material powder is sintered in the fourth process. Except for this, the cBN sintered body of Specimen 7 is produced in the same manner as Specimen 1.

[0112] <Specimen 8>

[0113] The above-mentioned first process and second process are not performed. In the third process, a binder raw material powder prepared by mixing the above WC powder, Co powder, Al powder, and Zr carbide powder in a mass ratio of WC:Co:Al:ZrC of 22:45:28:5 and cBN powder obtained by the ultra-high pressure synthesis method are prepared, and they are mixed in a volume ratio of cBN powder:binder raw material powder of 91:9 to obtain a mixed powder. Except for this, the cBN sintered body of Specimen 8 is produced in the same manner as Specimen 1. In addition, when the second image obtained in Specimen 8 is analyzed by TEM-EDX, W is not detected in the first interface region and the second interface region. It is speculated that the reason is that in the case of not performing the first process and the second process, the mixed powder is obtained from the above binder raw material powder and the above cBN powder in the third process.

[0114] <Specimen 9>

[0115] In the first process, a binder raw material powder prepared by mixing the above WC powder, Co powder, and Al powder in a mass ratio of WC:Co:Al of 35:45:20 is prepared. In the second process, the cBN raw material powder is coated with Zr under the following coating conditions. Except for this, the cBN sintered body of Specimen 9 is produced in the same manner as Specimen 4.

[0116] <Coating conditions>

[0117] Coating device: Nanoparticle formation device APD-P ADVANCE Co., Ltd. manufacture

[0118] Target: Zirconium

[0119] Introduced gas: After evacuation of 10 -4 argon gas is introduced

[0120] Discharge voltage: 150V

[0121] Discharge frequency: 6Hz

[0122] Capacitor capacity: 1080 μF

[0123] Shot number: 1000

[0124] Amount of powder processed: 25 g

[0125] Rotation speed of powder container: 50 rpm

[0126] <Specimen 10>

[0127] For the cBN raw material powder prepared in the second process, in the coating conditions of coating Zr by the APD method, the number of shots was set to 50,000, and except for this, a cBN sintered body of Specimen 10 was produced in the same manner as Specimen 9.

[0128] <Specimen 11>

[0129] For the cBN raw material powder prepared in the second process, except for setting the number of shots to 80,000, the coating of Zr based on the APD method performed in the production of Specimen 9 was carried out under the same coating conditions as Specimen 9, and except for this, a cBN sintered body of Specimen 11 was produced in the same manner as Specimen 4.

[0130] <Specimen 12>

[0131] For the cBN raw material powder prepared in the second process, in the coating conditions of coating Zr by the APD method, the number of shots was set to 100,000, and except for this, a cBN sintered body of Specimen 12 was produced in the same manner as Specimen 11.

[0132] <Specimen 13>

[0133] For the cBN raw material powder prepared in the second process, in the coating conditions of coating Zr by the APD method, the number of shots was set to 200,000, and except for this, a cBN sintered body of Specimen 13 was produced in the same manner as Specimen 11.

[0134] <Specimen 14>

[0135] In the first process, the above-mentioned WC powder, the above-mentioned Co powder, and the above-mentioned Al powder were prepared, and the above-mentioned respective powders were mixed at a mass ratio of WC:Co:Al = 38:42:20, and except for this, a cBN sintered body of Specimen 14 was produced in the same manner as Specimen 4.

[0136] <Specimen 15>

[0137] In the first process, the above-mentioned WC powder, the above-mentioned Co powder, the above-mentioned Al powder, and a commercially available metal Cr powder were prepared, and the above-mentioned respective powders were mixed at a mass ratio of WC:Co:Al:Cr = 22:44:25:9, and except for this, a cBN sintered body of Specimen 15 was produced in the same manner as Specimen 4.

[0138] <Specimen 16>

[0139] In the first step, the above WC powder, the above Co powder, the above Al powder, and a commercially available Hf carbide powder are prepared, and the above powders are mixed at a mass ratio of WC:Co:Al:HfC = 22:46:25:7. In addition, a cBN sintered body of Specimen 16 is produced in the same manner as Specimen 4.

[0140] <Specimen 17>

[0141] In the first step, the above WC powder, the above Co powder, the above Al powder, and a commercially available Ta carbide powder are prepared, and the above powders are mixed at a mass ratio of WC:Co:Al:TaC = 22:46:26:6. In addition, a cBN sintered body of Specimen 17 is produced in the same manner as Specimen 4.

[0142] <Specimen 18>

[0143] In the first step, the above WC powder, the above Co powder, the above Al powder, and a commercially available Mo carbide powder are prepared, and the above powders are mixed at a mass ratio of WC:Co:Al:MoC = 20:47:25:8. In addition, a cBN sintered body of Specimen 18 is produced in the same manner as Specimen 4.

[0144] <Specimen 19>

[0145] In the first step, the above WC powder, the above Co powder, the above Al powder, and a commercially available Ti carbide powder are prepared, and the above powders are mixed at a mass ratio of WC:Co:Al:TiC = 20:46:25:9. In addition, a cBN sintered body of Specimen 19 is produced in the same manner as Specimen 4.

[0146] <Specimen 20>

[0147] In the first step, the above WC powder, the above Co powder, the above Al powder, and a commercially available V carbide powder are prepared, and the above powders are mixed at a mass ratio of WC:Co:Al:VC = 20:47:25:8. In addition, a cBN sintered body of Specimen 20 is produced in the same manner as Specimen 4.

[0148] <Specimen 21>

[0149] In the first step, the above WC powder, the above Co powder, the above Al powder, and a commercially available Nb carbide powder are prepared, and the above powders are mixed at a mass ratio of WC∶Co∶Al∶NbC = 20∶44∶30∶6. In addition, a cBN sintered body of Specimen 21 is produced in the same manner as Specimen 4.

[0150] <Specimen 22>

[0151] In the first step, the above WC powder, the above Co powder, the above Al powder, and a commercially available Re carbide powder are prepared, and the above powders are mixed at a mass ratio of WC∶Co∶Al∶ReC = 23∶45∶25∶7. In addition, a cBN sintered body of Specimen 22 is produced in the same manner as Specimen 4.

[0152] <Specimen 23>

[0153] Without performing the above first and second steps, in the third step, a combined material raw powder prepared by mixing the above WC powder, Co powder, Al powder, and a commercially available W powder at a mass ratio of WC∶Co∶Al∶W = 22∶45∶28∶5 and cBN powder obtained by the ultra-high pressure synthesis method are prepared, and they are mixed at a volume ratio of cBN powder∶combined material raw powder = 91∶9 to obtain a mixed powder. In addition, a cBN sintered body of Specimen 23 is produced in the same manner as Specimen 1.

[0154] <Specimen 24>

[0155] Without performing the above first and second steps, in the third step, a combined material raw powder prepared by mixing the above WC powder, Co powder, Al powder, and Cr powder at a mass ratio of WC∶Co∶Al∶Cr = 22∶45∶28∶5 is prepared. In addition, a cBN sintered body of Specimen 24 is produced in the same manner as Specimen 23.

[0156] <Specimen 25>

[0157] Without performing the above first and second steps, in the third step, a combined material raw powder prepared by mixing the above WC powder, Co powder, Al powder, and a commercially available Hf powder at a mass ratio of WC∶Co∶Al∶Hf = 22∶45∶28∶5 is prepared. In addition, a cBN sintered body of Specimen 25 is produced in the same manner as Specimen 23.

[0158] <Specimen 26>

[0159] Without performing the above-described first process and second process, in the third process, a raw material powder of a bonding material is prepared by mixing the above WC powder, Co powder, Al powder, and commercially available Ta powder in a mass ratio of WC:Co:Al:Ta = 22:45:28:5. Other than this, a cBN sintered body of specimen 26 is produced in the same manner as specimen 23.

[0160] <Specimen 27>

[0161] Without performing the above-described first process and second process, in the third process, a raw material powder of a bonding material is prepared by mixing the above WC powder, Co powder, Al powder, and commercially available Mo powder in a mass ratio of WC:Co:Al:Mo = 22:45:28:5. Other than this, a cBN sintered body of specimen 27 is produced in the same manner as specimen 23.

[0162] <Specimen 28>

[0163] Without performing the above-described first process and second process, in the third process, a raw material powder of a bonding material is prepared by mixing the above WC powder, Co powder, Al powder, and commercially available Ti powder in a mass ratio of WC:Co:Al:Ti = 22:45:28:5. Other than this, a cBN sintered body of specimen 28 is produced in the same manner as specimen 23.

[0164] <Specimen 29>

[0165] Without performing the above-described first process and second process, in the third process, a raw material powder of a bonding material is prepared by mixing the above WC powder, Co powder, Al powder, and commercially available V powder in a mass ratio of WC:Co:Al:V = 22:45:28:5. Other than this, a cBN sintered body of specimen 29 is produced in the same manner as specimen 23.

[0166] <Specimen 30>

[0167] Without performing the above-described first process and second process, in the third process, a raw material powder of a bonding material is prepared by mixing the above WC powder, Co powder, Al powder, and commercially available Nb powder in a mass ratio of WC:Co:Al:Nb = 22:45:28:5. Other than this, a cBN sintered body of specimen 30 is produced in the same manner as specimen 23.

[0168] <Specimen 31>

[0169] Without performing the above-mentioned first process and second process, in the third process, a raw material powder of a bonding material is prepared by mixing the above WC powder, Co powder, Al powder, and commercially available Re powder in a mass ratio of WC:Co:Al:Re = 22:45:28:5. Except for this, a cBN sintered body of Specimen 31 is produced in the same manner as Specimen 23.

[0170] <Specimen 32>

[0171] In the first process, each of the above WC powder, Co powder, Al powder, and Zr carbide powder is mixed in a mass ratio of WC:Co:Al:ZrC = 20:43:28:9 to prepare a raw material powder of a bonding material. Except for this, a cBN sintered body of Specimen 32 is produced in the same manner as Specimen 4.

[0172] <Specimen 33>

[0173] In the first process, each of the above WC powder, Co powder, Al powder, and commercially available W powder is mixed in a mass ratio of WC:Co:Al:W = 20:43:28:9 to prepare a raw material powder of a bonding material. Except for this, a cBN sintered body of Specimen 33 is produced in the same manner as Specimen 4.

[0174] <Specimen 34>

[0175] In the first process, each of the above WC powder, Co powder, Al powder, and Cr powder is mixed in a mass ratio of WC:Co:Al:Cr = 20:43:28:9 to prepare a raw material powder of a bonding material. Except for this, a cBN sintered body of Specimen 34 is produced in the same manner as Specimen 4.

[0176] <Specimen 35>

[0177] In the first process, each of the above WC powder, Co powder, Al powder, and commercially available Hf powder is mixed in a mass ratio of WC:Co:Al:Hf = 20:43:28:9 to prepare a raw material powder of a bonding material. Except for this, a cBN sintered body of Specimen 35 is produced in the same manner as Specimen 4.

[0178] <Specimen 36>

[0179] In the first process, each of the above WC powder, Co powder, Al powder, and commercially available Ta powder is mixed in a mass ratio of WC:Co:Al:Ta = 20:43:28:9 to prepare a raw material powder of a bonding material. Except for this, a cBN sintered body of Specimen 36 is produced in the same manner as Specimen 4.

[0180] <Specimen 37>

[0181] In the first step, the above WC powder, Co powder, Al powder, and commercially available Mo powder are mixed at a mass ratio of WC:Co:Al:Mo = 20:43:28:9 to prepare a raw powder for the bonding material. Other than this, a cBN sintered body of Specimen 37 is produced in the same manner as Specimen 4.

[0182] <Specimen 38>

[0183] In the first step, the above WC powder, Co powder, Al powder, and commercially available Ti powder are mixed at a mass ratio of WC:Co:Al:Ti = 20:43:28:9 to prepare a raw powder for the bonding material. Other than this, a cBN sintered body of Specimen 38 is produced in the same manner as Specimen 4.

[0184] <Specimen 39>

[0185] In the first step, the above WC powder, Co powder, Al powder, and commercially available V powder are mixed at a mass ratio of WC:Co:Al:V = 20:43:28:9 to prepare a raw powder for the bonding material. Other than this, a cBN sintered body of Specimen 39 is produced in the same manner as Specimen 4.

[0186] <Specimen 40>

[0187] In the first step, the above WC powder, Co powder, Al powder, and commercially available Nb powder are mixed at a mass ratio of WC:Co:Al:Nb = 20:43:28:9 to prepare a raw powder for the bonding material. Other than this, a cBN sintered body of Specimen 40 is produced in the same manner as Specimen 4.

[0188] <Specimen 41>

[0189] In the first step, the above WC powder, Co powder, Al powder, and commercially available Re powder are mixed at a mass ratio of WC:Co:Al:Re = 20:43:28:9 to prepare a raw powder for the bonding material. Other than this, a cBN sintered body of Specimen 41 is produced in the same manner as Specimen 4.

[0190] 〔Evaluation〕

[0191] <Atomic concentration of the first element in the first interface region, the second interface region, and the bonding material other than the first interface region>

[0192] For each of the cBN sintered compacts of Specimens 1 to 13 described above, after cutting at an arbitrary position, the exposed surface was polished to produce a smooth surface. Then, using an argon ion slicer, a slice with a thickness of 50 nm was made. Next, the second image (100 nm × 100 nm) was analyzed by TEM-EDX as described above. 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 atomic concentrations of the first element in the first interface region, the second interface region, and the bonding material outside the first interface region were respectively determined as described above. The results are shown in Table 1. Specimens 2 to 6 and Specimens 9 to 13 are examples, and Specimens 1 and Specimens 7 to 8 are comparative examples.

[0193] Furthermore, for each of the cBN sintered compacts of Specimens 14 to 41, a second image (100 nm × 100 nm) was obtained in the same manner as for each of the cBN sintered compacts of Specimens 1 to 13 described above, and the second image was analyzed by TEM-EDX. Based on the obtained measurement values, the atomic concentrations of the first element in the first interface region, the second interface region, and the bonding material outside the first interface region were respectively determined as described above. The results are shown in Table 2. Specimens 14 to 22 and Specimens 32 to 41 are examples, and Specimens 23 to 31 are comparative examples. In addition, in Table 2, the results of Specimen 4 (example) and Specimen 8 (comparative example) are also shown in order to present the results of the cutting tests described later.

[0194] <First Cutting Test>

[0195] Cutting tools for each of the specimens were made from the cBN sintered compacts of Specimens 1 to 13 described above (substrate shape: SNGN090308, cutting edge treatment T01225). Using these cutting tools, a cutting test (First Cutting Test) was carried out under the following cutting conditions.

[0196] <Cutting Conditions>

[0197] Cutting speed: 1450 m / min.

[0198] Feed rate: 0.2 mm / rev.

[0199] Depth of cut: 0.3 mm

[0200] Coolant: WET

[0201] Cooling liquid: Emulsion 96 (diluted 20 times with water)

[0202] Cutting tool: RM3080R (manufactured by Sumitomo Electric Industries, Ltd.)

[0203] Cutting method: Interrupted cutting

[0204] Lathe: NEXUS 530-II HS (manufactured by Yamazaki Mazak Corporation)

[0205] Workpiece to be machined: FC250.

[0206] The tip of the cutting tool was observed at every 0.5 km of cutting distance, and the amount of tip wear was measured. The amount of tip wear was defined as the recession width due to wear starting from the position of the tip edge before cutting. In the case of chipping, the size of the chip was regarded as the amount of wear. The cutting distance at the time point when the amount of tip wear reached 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.

[0207] <Second Cutting Test>

[0208] Cutting tools for each specimen were made from the cBN sintered compacts of the above Specimen 4, Specimen 8, and Specimens 14 to 41 (substrate shape: TNGA160404, tip treatment T01225). Using this cutting tool, a cutting test (second cutting test) was carried out under the following cutting conditions.

[0209] <Cutting Conditions>

[0210] Cutting speed: 300 m / min.

[0211] Feed rate: 0.2 mm / rev.

[0212] Depth of cut: 0.1 mm

[0213] Coolant: DRY

[0214] Cutting method: continuous cutting

[0215] Lathe: LB400 (manufactured by OKUMA Corporation)

[0216] Workpiece to be machined: sintered part (quenched sintered alloy D40 manufactured by Sumitomo Electric Industries, Ltd., hardness of the machined part after quenching: HRB75).

[0217] The tip of the cutting tool was observed at every 0.1 km of cutting distance, and the amount of tip wear was measured. The cutting distance at the time point when the amount of tip wear reached 100 μm or more was measured. In addition, the above cutting distance was defined as the life of the cutting tool. The results are shown in Tables 2 to 4. The longer the cutting distance, the more it can be evaluated that the cutting tool has achieved a long life.

[0218]

[0219]

[0220]

[0221]

[0222] [Investigation]

[0223] From Table 1, it can be understood that the cutting tools obtained from each cBN sintered body of Specimens 2 to 6 and Specimens 9 to 13 as examples have achieved longer life compared to the cutting tools obtained from the cBN sintered bodies of Specimen 1 and Specimens 7 to 8 as comparative examples.

[0224] From Tables 2 to 4, it can be understood that the cutting tools obtained from each cBN sintered body of Specimen 4, Specimens 14 to 22, and Specimens 32 to 41 as examples have achieved longer life compared to the cutting tools obtained from the cBN sintered bodies of Specimen 8 and Specimens 23 to 31 as comparative examples.

[0225] 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.

[0226] 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 not represented 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, as constituent elements, at least one first metal element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten, cobalt, and aluminum, the cubic boron nitride sintered body has a first interface region, which is constituted by a region sandwiched between the interface of the cubic boron nitride particles and the binder material and a first imaginary line at a location 10 nm away from the interface toward the binder material side, when the element present in the highest concentration among the first metal elements in the first interface region is taken as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the binder material outside the first interface region, the cubic boron nitride sintered body has a second interface region, which is constituted by a region sandwiched between the interface and a second imaginary line at a location 2 nm away from the interface toward the binder material side, in the second interface region, the atomic concentration of the first element is 0.7 atomic % or more and 10 atomic % or less.

2. The cubic boron nitride sintered body according to claim 1, wherein, the cubic boron nitride sintered body contains the cubic boron nitride particles in an amount of 85% by volume or more and 95% by volume or less.

3. The cubic boron nitride sintered body according to claim 1 or 2, wherein, the first metal element is at least one selected from the group consisting of zirconium, niobium, chromium, molybdenum, and tungsten.

4. The cubic boron nitride sintered body according to claim 1 or 2, wherein, the first metal element is zirconium.

5. A cutting tool, wherein, The cutting tool includes the cubic boron nitride sintered body according to any one of claims 1 to 4.

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