Diamond polycrystal and tool having diamond polycrystal

Abstract

A diamond polycrystal including diamond particles, wherein a content rate of the diamond particles with respect to the diamond polycrystal is more than 99 vol%, a median particle diameter d50 of the diamond particles is 10 nm or more and 200 nm or less, and a dislocation density of the diamond particles is 2.0 x 10 15 m ‑2 or more and 4.0 x 10 16 m ‑2 or less.

Description

Technical Field

[0001] This disclosure relates to polycrystalline diamond and tools incorporating polycrystalline diamond. Background Technology

[0002] Polycrystalline diamond has excellent hardness and lacks hardness directionality and cleavage, so it is widely used in cutting tools, dressing tools, die heads, and drilling bits.

[0003] Traditionally, polycrystalline diamond is obtained by sintering diamond powder (as raw material) with sintering aids or binders under thermodynamically stable high pressure and high temperature conditions (generally around 5–8 GPa and 1300–2200 °C). Sintering aids can include iron group metals such as Fe, Co, and Ni, and carbonates such as CaCO3. Binders can include ceramics such as SiC.

[0004] The diamond polycrystals obtained by the above method contain sintering aids or bonding materials. These sintering aids and bonding materials may contribute to a decrease in the hardness, strength, or heat resistance of the diamond polycrystals.

[0005] Diamond polycrystals with sintering aids removed through acid treatment are also known, as well as diamond polycrystals with excellent heat resistance using heat-resistant SiC as a bonding material. However, these diamond polycrystals have low hardness or strength, and their mechanical properties as tool materials are insufficient.

[0006] On the other hand, it is possible to directly transform non-diamond-like carbon materials such as graphite, glassy carbon, amorphous carbon, and onion carbon into diamond under ultra-high pressure and high temperature without the use of sintering aids. Diamond polycrystalline materials are obtained by sintering while directly transforming from a non-diamond phase to a diamond phase (International Publication No. 2005 / 065809 (Patent Document 1), H. Sumiya et al., Japanese Journal of Applied Physics 48(2009)120206 (Non-Patent Document 1)).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2005 / 065809

[0010] Non-patent literature

[0011] Non-patent literature 1: H. Sumiya et al., Japanese Journal of Applied Physics 48(2009)120206 Summary of the Invention

[0012] The diamond polycrystal disclosed herein is a diamond polycrystal containing diamond particles, wherein,

[0013] The content of the diamond particles is greater than 99% by volume relative to the diamond polycrystal.

[0014] The median particle size d50 of the diamond particles is greater than 10 nm and less than 200 nm.

[0015] The dislocation density of the diamond particles is 2.0 × 10⁻⁶. 15 m -2 Above and 4.0×10 16 m -2 the following.

[0016] The tool disclosed herein comprises the aforementioned diamond polycrystal. Attached Figure Description

[0017] Figure 1 This is a phase equilibrium diagram for carbon. Detailed Implementation

[0018] [The problem this disclosure aims to solve]

[0019] In recent years, there has been a demand for more efficient cutting processes (e.g., high feed rates), leading to expectations for further improvements in the properties of polycrystalline diamond (e.g., increased thermal conductivity, increased hardness, increased toughness, etc.).

[0020] This disclosure was made in view of the above circumstances, and its purpose is to provide a diamond polycrystal with excellent toughness and excellent hardness, and tools incorporating the diamond polycrystal.

[0021] [The Effects of This Disclosure]

[0022] According to this disclosure, it is possible to provide a diamond polycrystal with excellent toughness and excellent hardness, as well as a tool containing a diamond polycrystal.

[0023] [Description of embodiments of this disclosure]

[0024] The embodiments of this disclosure are first described by listing them.

[0025] [1] One aspect of this disclosure relates to a diamond polycrystal that comprises diamond particles, wherein,

[0026] The content of the aforementioned diamond particles is greater than 99% by volume relative to the aforementioned diamond polycrystalline material.

[0027] The median particle size d50 of the aforementioned diamond particles is greater than 10 nm and less than 200 nm.

[0028] The dislocation density of the aforementioned diamond particles is 2.0 × 10⁻⁶. 15 m -2 Above and 4.0×10 16 m -2 the following.

[0029] The aforementioned polycrystalline diamond exhibits improved toughness and hardness due to the moderately low dislocation density of its diamond particles. In other words, this polycrystalline diamond possesses both excellent toughness and excellent hardness.

[0030] [2] Preferably, the dislocation density of the diamond particles is 4.0 × 10⁻⁶. 15 m -2 Above and 1.0×10 16 m -2 The following is a description of how diamond polycrystalline materials are formed, resulting in superior toughness and hardness.

[0031] [3] Preferably, the median particle size d50 of the diamond particles is 10 nm or more and 100 nm or less. By specifying this, a diamond polycrystalline material with superior hardness is formed.

[0032] [4] Preferably, the diamond polycrystal further comprises boron, and the boron content is 0.01% by mass or more and 1% by mass or less relative to the diamond polycrystal. By specifying it in this way, a diamond polycrystal with sliding properties and electrical conductivity is formed.

[0033] [5] Preferably, the Knoop hardness at room temperature is 80 GPa or higher. By specifying this, diamond polycrystals with better wear resistance are formed.

[0034] [6] Preferably, in the diamond polycrystal of this disclosure, the content of at least one metallic element selected from the group consisting of Group IV, Group V, Group VI elements, iron, aluminum, silicon, cobalt and nickel of the periodic table is less than 1% by volume. By specifying this, a diamond polycrystal with superior hardness is formed.

[0035] [7] Preferably, in the diamond polycrystal of this disclosure, the content of at least one unavoidable impurity selected from the group consisting of hydrogen, oxygen, nitrogen, alkali metal elements and alkaline earth metal elements is less than 0.1% by volume. By specifying this, a diamond polycrystal with superior hardness is formed.

[0036] [8] One aspect of the present disclosure relates to a tool having the aforementioned diamond polycrystal.

[0037] The aforementioned tools possess excellent toughness and hardness due to their high-toughness and hardness, thus exhibiting superior wear resistance and chip resistance in high-speed machining of various materials. Here, "wear resistance" refers to the material's resistance to tool wear during machining. "Chip resistance" refers to the material's resistance to tool chipping during machining.

[0038] [Details of the embodiments disclosed herein]

[0039] The following describes in detail the embodiments of this disclosure. However, this disclosure is not limited to these examples. Here, in this specification, expressions such as "A to Z" refer to the upper and lower limits of a range (i.e., above A and below Z). When no unit is specified in A, but only in Z, the unit of A is the same as the unit of Z.

[0040] Polycrystalline Diamond

[0041] The diamond polycrystalline material involved in this embodiment is a diamond polycrystalline material containing diamond particles, wherein,

[0042] The content of the aforementioned diamond particles is greater than 99% by volume relative to the aforementioned diamond polycrystalline material.

[0043] The median particle size d50 of the aforementioned diamond particles is greater than 10 nm and less than 200 nm.

[0044] The dislocation density of the aforementioned diamond particles is 2.0 × 10⁻⁶. 15 m -2 Above and 4.0×10 16 m -2 the following.

[0045] The aforementioned polycrystalline diamond comprises diamond particles. That is, the polycrystalline diamond is based on diamond particles and substantially does not contain a binding phase (binder) formed by one or both of the sintering aid and the binding material. Therefore, the aforementioned polycrystalline diamond exhibits very high hardness and strength. Furthermore, even under high-temperature conditions, the aforementioned polycrystalline diamond does not experience deterioration of its mechanical properties or granulation due to differences in thermal expansion coefficients with the binding material or the catalytic effect of the binding material. Additionally, in one aspect of this embodiment, diamond particles can also be understood as diamond grains.

[0046] The aforementioned polycrystalline diamond is a polycrystalline material composed of multiple diamond particles. Therefore, the polycrystalline diamond does not have the directionality (anisotropy) and cleavage of a single crystal, and has isotropic hardness and wear resistance in all directions.

[0047] Diamond polycrystals may contain unavoidable impurities within a range that demonstrates the effects of this embodiment. Examples of unavoidable impurities include, for instance, hydrogen, oxygen, nitrogen, alkali metals (lithium (Li), sodium (Na), potassium (K), etc.), and alkaline earth metals (calcium (Ca), magnesium (Mg), etc.). Specifically, in this embodiment, the content of at least one unavoidable impurity selected from the group consisting of hydrogen, oxygen, nitrogen, alkali metals, and alkaline earth metals in the aforementioned diamond polycrystal is preferably less than 0.1% by volume. The lower limit for the content of the aforementioned unavoidable impurities can, for example, be 0% by volume or more. Furthermore, when the aforementioned unavoidable impurities include two or more elements, the total content of each element is considered the content of the aforementioned unavoidable impurities.

[0048] The concentrations of hydrogen, oxygen, nitrogen, etc., in polycrystalline diamond can be determined using secondary ion mass spectrometry (SIMS). For example, a "CAMECA IMS-7f" (manufactured by AMETEK) can be used in this method, with the primary ion species set to Cs. + Set the primary acceleration voltage to 15.0kV and the detection area to... To determine the concentration of impurities.

[0049] The diamond polycrystalline material in this embodiment is a sintered body, but sintered bodies are usually intended to contain a binder, so the term "polycrystalline" is used in this embodiment.

[0050] <Diamond particles>

[0051] (Diamond particle content)

[0052] In this embodiment, the content of the diamond particles is greater than 99% by volume relative to the diamond polycrystalline material, preferably greater than 99% by volume and less than 100% by volume.

[0053] The diamond particle content (volume %) in a diamond polycrystal can be determined by combining an energy-dispersive X-ray diffraction (EDX) apparatus (e.g., the X-MAX80 EDS system manufactured by OXFORD) with a scanning electron microscope (SEM) (e.g., the JSM-7800F (trade name) manufactured by Nippon Electron Ltd.) (hereinafter also referred to as "SEM-EDX") and X-ray diffraction. The specific determination method is described below.

[0054] First, a sample containing a cross-section of the diamond polycrystal is prepared by cutting it at any point. The cross-section can be prepared using a focused ion beam apparatus, a cross-section polishing machine, or similar equipment. Next, the cross-section is observed using a SEM (Self-Electron Microscopy) to obtain a reflected electron image. In the reflected electron image, areas containing diamond particles and non-diamond-like carbon are black areas, while other areas (e.g., elements derived from the binding material) are gray or white areas. The magnification used when observing the cross-section using the SEM is appropriately adjusted so that at least 100 diamond particles are observed in the field of view. For example, the magnification used when observing the cross-section using the SEM can be 10,000x.

[0055] Next, the aforementioned reflected electron images were binarized using image analysis software (such as "Win ROOF ver. 7.4.5" and "Win ROOF 2018" from Mitani Corporation). This image analysis software automatically sets an appropriate binarization threshold based on the image information (the measurer does not arbitrarily set the threshold). Furthermore, the inventors confirmed that the measurement results did not change significantly even when the image brightness was altered. Based on the binarized image, the area ratio of pixels originating from the dark field (pixels originating from diamond particles and non-diamond carbon) within the area of ​​the measurement field was calculated. By treating the calculated area ratio as a volume percentage, the total content of diamond particles and non-diamond carbon (volume %) could be determined.

[0056] Based on the binarized image, the area ratio of pixels originating from the visible field of view (pixels originating from other regions) in the measured field of view is calculated, thereby allowing the determination of the content (volume %) of other regions.

[0057] The inventors of this invention have confirmed that as long as the total (volume %) of the content of diamond particles and the content of non-diamond carbon in the diamond polycrystal is measured in the same sample, the measurement results show almost no deviation even if the selected measurement field of view is changed and multiple calculations are performed. That is, the inventors of this invention believe that even if the measurement field of view is arbitrarily set, the results will not change arbitrarily.

[0058] Furthermore, the fact that pixels originating from dark-field imaging are derived from diamond particles and non-diamond-like carbon can be confirmed by performing SEM-EDX-based elemental analysis on diamond polycrystals.

[0059] Next, X-ray spectra of the aforementioned cross-section of the diamond polycrystalline material were obtained using an X-ray diffraction apparatus (Rigaku's "MiniFlex600" (trade name)). The conditions of the X-ray diffraction apparatus at this time are as follows.

[0060] Characteristic X-rays: Cu-Kα (wavelength) )

[0061] Tube voltage: 45kV

[0062] Tube current: 40mA

[0063] Filter: Multilayer mirror

[0064] Optical system: lumped method

[0065] X-ray diffraction method: θ-2θ method.

[0066] In the obtained X-ray spectrum, the peak intensities A and B were measured.

[0067] Peak intensity A: The peak intensity of non-diamond-like carbon after removing the background from the peak intensity near the diffraction angle 2θ = 28.5°.

[0068] Peak intensity B: The peak intensity of the diamond particle after removing the background from the peak intensity near the diffraction angle 2θ = 43.9°.

[0069] The diamond particle content (volume %) was obtained by calculating {peak intensity B / (peak intensity A + peak intensity B)} × {the sum of the diamond particle content obtained in the above SEM-EDX and the non-diamond carbon content (volume %)}. Since both non-diamond carbon and diamond particles have the same electron weighting, the X-ray peak intensity ratio described above can be considered as the volume ratio in the diamond polycrystalline material. Furthermore, no peaks originating from boron were detected in this method. Therefore, even when the diamond polycrystalline material contains boron, the diamond particle content is sometimes 100% by volume.

[0070] (Median particle size d50 of diamond particles)

[0071] The median particle size d50 of the diamond particles is 10 nm or more and 200 nm or less, preferably 10 nm or more and 100 nm or less. By making the median particle size d50 of the diamond particles 10 nm or more, a diamond polycrystalline material with excellent strength is formed. By making the median particle size d50 of the diamond particles 200 nm or less, a diamond polycrystalline material with excellent hardness is formed.

[0072] In this embodiment, the median particle size d50 of the diamond particles refers to the value obtained by measuring the median particle size d50 of multiple diamond particles in each measurement field of view at five arbitrarily selected locations and calculating their average value. The specific method is described below.

[0073] First, a sample containing a cross-section of the diamond polycrystal is prepared by cutting it at any point. The cross-section can be prepared using a focused ion beam apparatus, a cross-section polishing machine, or similar equipment. Next, the cross-section is observed using a SEM to obtain a reflected electron image. The magnification used for SEM observation of the cross-section is appropriately adjusted to ensure that at least 100 diamond particles are observed in the field of view. For example, the magnification used for SEM observation of the cross-section can be 10,000x.

[0074] For the five SEM images, with the grain boundaries of the diamond particles observed within the measurement field of view separated, the equivalent circle diameter of each diamond particle was calculated using image processing software (such as Mitani Corporation's "Win ROOF ver. 7.4.5" and "Win ROOF 2018"). Diamond particles appearing outside the measurement field of view were not counted.

[0075] The median particle size d50 in each measurement field is calculated from the distribution of the equivalent circular diameter of each diamond particle, and their average value is calculated. This average value corresponds to the median particle size d50 of the diamond particles.

[0076] Furthermore, the inventors of this invention have confirmed that as long as the median particle size d50 of the diamond particles is calculated in the same sample, the measurement results show almost no deviation even if the selected location of the measurement field of view in the diamond polycrystalline material is changed and multiple calculations are performed. That is, the inventors of this invention believe that even if the measurement field of view is arbitrarily set, the results will not change arbitrarily.

[0077] (Diamond particle size d90)

[0078] In this embodiment, the diamond particle size d90 is 15 nm or more and 300 nm or less, preferably 15 nm or more and 150 nm or less. By making the diamond particle size d90 15 nm or more, a diamond polycrystalline material with excellent strength is formed. By making the diamond particle size d90 150 nm or less, a diamond polycrystalline material with excellent hardness is formed.

[0079] In this embodiment, the diamond particle size d90 refers to the value obtained by measuring the particle size d90 of multiple diamond particles in each measurement field of view at five arbitrarily selected locations and calculating their average value. The specific method is the same as the method used to determine the median particle size d50 described above.

[0080] (Dislocation density of diamond particles)

[0081] The dislocation density of the aforementioned diamond particles is 2.0 × 10⁻⁶. 15 m-2 Above and 4.0×10 16 m -2 The preferred value is 4.0 × 10⁻⁶. 15 m -2 Above and 1.0×10 16 m -2 The following is an example of achieving a dislocation density of 2.0 × 10⁻⁶ for diamond particles. 15 m -2 The above results in a polycrystalline diamond with excellent toughness and hardness. This is achieved by setting the dislocation density of the diamond particles to 4.0 × 10⁻⁶. 16 m -2 The following forms a diamond polycrystalline structure with excellent strength.

[0082] Previously, the relationship between the dislocation density of diamond particles in diamond polycrystals without a bonding phase and the physical properties of such polycrystals was not considered. Therefore, the inventors of this invention focused on this relationship and conducted an in-depth study on the relationship between the dislocation density of diamond particles and the toughness and hardness of the diamond polycrystal. As a result, it was discovered for the first time that, compared to previously existing diamond polycrystals, moderately reducing the dislocation density of diamond particles improves toughness and hardness. When such diamond polycrystals with excellent toughness and hardness are used in cutting tools (e.g., micro-end mills, micro-drills), they exhibit excellent wear resistance and chip resistance even during fine machining of hard materials such as cemented carbide or hard and brittle materials such as ceramics, and under demanding intermittent cutting conditions. Furthermore, this investigation revealed that the dislocation density of diamond particles in conventional diamond polycrystals (e.g., the diamond polycrystal described in Patent Document 1) is 5 × 10⁻⁶. 16 m -2 Above and 8×10 16 m -2 Therefore, compared with the diamond polycrystal disclosed herein, conventional diamond polycrystals have excessively high dislocation densities. It is therefore believed that these dislocations become the starting point of cracks, or that cracks propagate along the dislocations, thereby reducing the properties (toughness, hardness, etc.) of the diamond polycrystal.

[0083] In this specification, the dislocation density of the diamond polycrystalline material was measured at a large-scale radiation facility (e.g., the Kyushu Synchrotron Light Research Center (Saga Prefecture)). Specifically, the measurement was performed using the method described below.

[0084] Prepare a test specimen made of polycrystalline diamond. The specimen has an observation surface of 2 mm × 2 mm and a thickness of 1.0 mm. The observation surface of the specimen is mirror-polished using a diamond polishing slurry with an average particle size of 3 μm.

[0085] For this test specimen, X-ray diffraction measurements were performed under the following conditions to obtain the line profiles of the diffraction peaks from each orientation plane (111), (220), (311), (331), (422), (440), (531), which are the main orientations of diamond.

[0086] (X-ray diffraction measurement conditions)

[0087] X-ray source: radiation light

[0088] Device requirements: Detector: NaI (fluorescence cutoff via appropriate ROI).

[0089] Energy: 18keV (wavelength: )

[0090] Spectroscopic crystal: Si(111)

[0091] Entrance slit: 3mm width × 0.5mm height

[0092] Light-receiving slit: Double slit (3mm width × 0.5mm height)

[0093] Mirror: Platinum coated mirror

[0094] Angle of incidence: 2.5 mrad

[0095] Scanning method: 2θ-θscan

[0096] The measured peaks were the seven peaks of diamond: (111), (220), (311), (331), (422), (440), and (531). However, peaks of this surface index were excluded when it was difficult to obtain the profile due to texture, orientation, etc.

[0097] Measurement conditions: At least 9 measurement points are required within the full width at half maximum (FWHM) corresponding to each measurement peak. The peak intensity must be at least 2000 counts. The lower edge of the peak is also used for analysis; therefore, the measurement range is approximately 10 times the full WHM.

[0098] The line profile obtained by the above X-ray diffraction measurements is a shape that includes both the true extension caused by physical quantities such as the non-uniform strain of the test specimen and the extension caused by the device. To determine the non-uniform strain and crystallite size, the device-induced component is removed from the measured line profile to obtain the true line profile. The true line profile is obtained by fitting the obtained line profile and the device-induced line profile using a pseudo-Voigt function, and then subtracting the device-induced line profile. LaB6 is used as the standard sample for removing the device-induced diffraction line extension. Furthermore, when using highly parallel radiometric light, the device-induced diffraction line extension can also be considered zero.

[0099] The obtained true line profiles are analyzed using the modified Williamson-Hall method and the modified Warren-Averbach method, from which the dislocation density is calculated. The modified Williamson-Hall method and the modified Warren-Averbach method are well-known line profile analysis methods for determining dislocation density.

[0100] The modified Williamson-Hall method is represented by the following formula (I).

[0101] [Number 1]

[0102]

[0103] In equation (I) above, ΔK represents the half-width of the line profile. D represents the crystallite size. M represents the configuration parameter. b represents the Burgers vector. ρ represents the dislocation density. K represents the scattering vector. O(K 2 C) represents K 2 The higher-order term of C. C represents the average value of the contrast factor.

[0104] The C in the above formula (I) is represented by the following formula (II).

[0105] C = C h00 [1-q(h 2 k 2 +h 2 l 2 +k 2 l 2 ) / (h 2 +k 2 +l 2 ) 2 (II)

[0106] In equation (II) above, the contrast factor C for screw dislocations and edge dislocations is... h00 The coefficient q related to the contrast factor is calculated using the ANIZC code, with the slip system as the reference. <110> {111}, Elastic stiffness C 11 1076 GPa, C 12 125 GPa, C 44 The value is calculated to be 576 GPa. In equation (II) above, h, k, and l correspond to the Miller indices (hkl) of diamond, respectively. Contrast factor C h00 The coefficient q is 0.183 for screw dislocations and 0.204 for edge dislocations. The coefficient q related to the contrast factor is 1.35 for screw dislocations and 0.30 for edge dislocations. Furthermore, the ratio of screw dislocations is fixed at 0.5, and the ratio of edge dislocations is fixed at 0.5.

[0107] Furthermore, by using a contrast factor C between dislocations and inhomogeneous strain, the following relationship (III) holds. In the following equation (III), R e The effective radius of the dislocation is represented by ε(L). ε(L) represents the non-uniform strain.

[0108] <ε(L) 2 >=(ρCb 2 / 4π)ln(R e / L)(III)

[0109] Based on the relationship in equation (III) above and the Warren-Averbach formula, the dislocation density ρ and crystallite size can be determined as shown in equation (IV) below, as a modified Warren-Averbach method. In equation (IV) below, A(L) represents the Fourier series. S (L) represents the Fourier series related to the crystallite size. L represents the Fourier length.

[0110] lnA(L)=lnA S (L)-(πL 2 ρb 2 / 2)ln(R e / L)(K 2 C)+O(K 2 C) 2 (IV)

[0111] Detailed descriptions of the modified Williamson-Hall method and the modified Warren-Averbach method are found in "T. Ungar and A. Borbely, 'The effect of dislocation contrast on x-ray linebroadening: A new approach to line profile analysis' Appl. Phys. Lett., vol. 69, no. 21, p. 3173, 1996" and "T. Ungar, S. Ott, P. Sanders, A. Borbely, J. Weertman, 'Dislocations, grain size and planar faults in nanostructured copper determined by high resolution X-ray diffraction and a new procedure of peak profile analysis' Acta Mater., vol. 46, no. 10, pp. 3693-3699, 1998."

[0112] The inventors of this invention have confirmed that, as long as the dislocation density of diamond particles is measured in the same sample, even if the selected measurement range is changed and multiple calculations are performed, the measurement results show almost no deviation. That is, the inventors believe that even if the measurement field of view is arbitrarily set, the results will not change arbitrarily.

[0113] Boron

[0114] In this embodiment, the aforementioned diamond polycrystal further comprises boron, and the boron content relative to the diamond polycrystal is preferably 0.01% by mass or more and 1% by mass or less, more preferably 0.05% by mass or more and 0.6% by mass or less. Thus, a diamond polycrystal possessing both sliding and conductive properties is formed. The boron content can be determined by the aforementioned secondary ion mass spectrometry (SIMS) method.

[0115] In one aspect of this embodiment, in the aforementioned diamond polycrystalline material, the content of at least one metallic element selected from the group consisting of Group IV, Group V, Group VI elements, iron, aluminum, silicon, cobalt, and nickel of the periodic table is preferably less than 1 volume%, more preferably 0 volume% or more and 0.1 volume% or less. Here, when two or more metallic elements are included, the aforementioned "content of metallic elements" refers to the total content of the two or more metallic elements. The content of the aforementioned metallic elements can be confirmed by performing microstructural observation and elemental analysis of the diamond polycrystalline material using EDX with SEM.

[0116] Group 4 elements of the periodic table include, for example, titanium (Ti), zirconium (Zr), and hafnium (Hf). Group 5 elements include, for example, vanadium (V), niobium (Nb), and tantalum (Ta). Group 6 elements include, for example, chromium (Cr), molybdenum (Mo), and tungsten (W).

[0117] Knoop Hardness

[0118] The Knoop hardness of the diamond polycrystalline material in this embodiment is preferably 80 GPa or higher at room temperature, more preferably 100 GPa or higher. No specific upper limit is set for the above-mentioned Knoop hardness; from a manufacturing point of view, 150 GPa or lower is preferred. The above-mentioned Knoop hardness is determined by a Knoop hardness test performed under the conditions specified in JIS Z2251:2009.

[0119] The Knoop hardness test, as specified in JIS Z 2251:2009, is a well-known method for determining the hardness of industrial materials. The Knoop hardness test determines the hardness of a material by pressing a Knoop indenter against it under a predetermined temperature and a predetermined load (test load). In this embodiment, the predetermined temperature is room temperature (23°C ± 5°C), and the predetermined load is 4.9 N. The Knoop indenter is a diamond indenter with a diamond-shaped, pyramidal base.

[0120] "tool"

[0121] The polycrystalline diamond of this embodiment possesses excellent hardness and toughness, making it suitable for use in cutting tools, wear-resistant tools, grinding tools, friction stir bonding tools, styluses, etc. In other words, the tool of this embodiment incorporates the aforementioned polycrystalline diamond. This tool exhibits excellent wear resistance and chip resistance in high-speed machining of various materials. When the tool is a cutting tool, it is particularly suitable for the fine machining of materials such as cemented carbide, ceramics, resins, and carbon.

[0122] The aforementioned tools may be made entirely of polycrystalline diamond, or only a portion thereof (e.g., the tip portion in the case of a cutting tool) may be made of polycrystalline diamond.

[0123] Cutting tools can include drill bits, end mills, indexable cutting inserts for drill bits, indexable cutting inserts for end mills, indexable cutting inserts for milling, indexable cutting inserts for turning, metalworking saws, gear cutting tools, reamers, taps, and cutting tools.

[0124] As wear-resistant tools, examples include die heads, scribing tools, scribing wheels, and dressing tools.

[0125] Grinding tools can include grinding stones, etc.

[0126] Manufacturing Methods of Polycrystalline Diamond

[0127] The method for manufacturing polycrystalline diamond involved in this embodiment includes:

[0128] The process of preparing non-diamond-like carbon materials as starting materials (first process);

[0129] The process of increasing pressure (second process) involves moving from the graphite stable region to the diamond region while maintaining a temperature below 300°C from the initial pressure and initial temperature.

[0130] The process of moving from the diamond region to the graphite-stabilized region by increasing the temperature, and maintaining the pressure and temperature in the graphite-stabilized region for a period of 10 minutes to 60 minutes (third process); and

[0131] Further, the pressure and temperature are increased to the sintering pressure and sintering temperature, and the non-diamond carbon material is transformed into diamond particles and sintered at the sintering pressure and sintering temperature (fourth step).

[0132] <First Process: Preparation of Non-Diamond Carbon Materials>

[0133] In this process, a non-diamond carbon material is prepared as the starting material. There are no particular restrictions on the non-diamond carbon material as long as it is carbon. Preferably, the non-diamond carbon material includes low-crystallinity graphite, thermally decomposable graphite, or amorphous carbon. They can be used alone or in combination.

[0134] The purity of the non-diamond carbon material is preferably 99% by volume or more, more preferably 99.5% by volume or more, even more preferably 99.9% by volume or more, and most preferably 100% by volume. In other words, from the viewpoint of suppressing grain growth, the non-diamond carbon material preferably does not contain iron group metals as impurities. Examples of iron group metals include, for example, iron (Fe), cobalt (Co), and nickel (Ni).

[0135] From the viewpoint of suppressing grain growth and promoting the direct transformation to diamond, non-diamond carbon materials are preferably non-diamond carbon materials with low concentrations of impurities such as hydrogen, oxygen, and nitrogen. The concentrations of hydrogen, oxygen, and nitrogen in the non-diamond carbon material are preferably 0.1 vol% or less, more preferably 0.01 vol% or less. Furthermore, the total impurity concentration in the non-diamond carbon material is preferably 0.3 vol% or less, more preferably 0.1 vol% or less.

[0136] The concentration of impurities in non-diamond-like carbon materials can be determined using secondary ion mass spectrometry (SIMS). As an example of this method, a "CAMECA IMS-7f" (manufactured by AMETEK) is used in the apparatus, with the primary ion species set to Cs. + Set the primary acceleration voltage to 15.0kV and the detection area to... To determine the concentration of impurities.

[0137] <Second process: A process of increasing pressure while maintaining a low temperature, moving from the graphite stable region to the diamond region>

[0138] In this process, pressure is increased while maintaining a temperature below 300°C, moving the material from the graphite-stable region to the diamond region, starting with the initial pressure and temperature. Here, "graphite-stable region" refers to the phase equilibrium region of carbon. Figure 1The region of graphite in the above-mentioned graphite stable region is thermodynamically stable. The pressure P (unit: GPa) and temperature T (unit: °C) in the above-mentioned graphite stable region are related by the following formula.

[0139] P <T×0.00286+1.4185

[0140] In this embodiment, "diamond region" refers to the phase equilibrium diagram of carbon. Figure 1 The region of diamond that is thermodynamically stable is defined as follows. The pressure P (in GPa) and temperature T (in °C) in this diamond region are related by the following equation.

[0141] P > T × 0.00286 + 1.4185

[0142] By increasing the pressure and temperature from the initial pressure and temperature to move from the graphite stable region to the diamond region, the desired dislocation density can be formed.

[0143] In this embodiment, the starting temperature is room temperature (23±5℃) and the starting pressure is atmospheric pressure (1013.25hPa).

[0144] In this process, when increasing the pressure from the starting pressure and the starting temperature, it is preferable to do so while maintaining a temperature below 300°C, and more preferably while maintaining a temperature above 0°C and below 300°C. In one aspect of this embodiment, when increasing the pressure from the starting pressure and the starting temperature, the temperature may also be increased within a range not exceeding 300°C.

[0145] <Third step: Maintaining pressure and temperature within the graphite-stabilized region>

[0146] In this process, after moving from the diamond region to the graphite-stabilized region by increasing the temperature, the pressure and temperature in the graphite-stabilized region are maintained for a period of 10 to 60 minutes. By moving back from the diamond region to the graphite-stabilized region and maintaining the pressure and temperature there, the dislocation density can be increased.

[0147] The pressure in the graphite stable region is preferably 1.5 GPa or more and 8 GPa or less, more preferably 2 GPa or more and 8 GPa or less.

[0148] The temperature in the graphite stability region is preferably 0°C or higher and 2500°C or lower, more preferably 100°C or higher and 2000°C or lower.

[0149] In one aspect of this embodiment, preferably, the pressure P in the graphite stable region is 3 GPa or more and 5 GPa or less, the temperature T in the graphite stable region is 1000°C or more and 1300°C or less, and the pressure P and the temperature T satisfy the following relationship.

[0150] P <T×0.00286+1.4185

[0151] The time for maintaining pressure and temperature in the graphite-stable region is preferably 10 minutes or more, more preferably 20 minutes or more. From a manufacturing point of view (e.g., from the point of view of production cycle time), the upper limit of the time for maintaining pressure and temperature in the graphite-stable region is preferably 60 minutes or less.

[0152] <Fourth process: The process of transforming diamond particles and sintering them>

[0153] In this process, the pressure and temperature are further increased to the sintering pressure and sintering temperature. At the aforementioned sintering pressure and sintering temperature, the non-diamond-like carbon material is transformed into diamond particles and then sintered. In one aspect of this embodiment, the heating and pressure increases to the sintering pressure and sintering temperature can be performed simultaneously, or the pressure can be increased to the sintering pressure, followed by the heating to the sintering temperature.

[0154] The sintering pressure is preferably 12 GPa or higher, more preferably 15 GPa or higher. From a manufacturing point of view, the upper limit of the sintering pressure is preferably 25 GPa or lower.

[0155] The sintering temperature is preferably above 1800°C and below 2800°C, and more preferably above 2000°C and below 2600°C.

[0156] The sintering pressure and sintering temperature are preferably 1 minute or more and 20 minutes or less, more preferably 5 minutes or more and 20 minutes or less, and even more preferably 10 minutes or more and 20 minutes or less.

[0157] In the diamond polycrystalline manufacturing method of this embodiment, the high-pressure, high-temperature generating apparatus is not particularly limited as long as it can provide the pressure and temperature conditions necessary for the diamond phase to be thermodynamically stable. However, from the viewpoint of improving productivity and workability, a high-pressure, high-temperature generating apparatus or a multi-anvil type high-pressure, high-temperature generating apparatus is preferred. Furthermore, the container for holding the non-diamond-like carbon material used as raw material is not particularly limited as long as it is made of a material resistant to high pressure and high temperature; for example, Ta, Nb, etc., are preferred.

[0158] To prevent impurities from contaminating the diamond polycrystalline material, for example, a non-diamond-like carbon material is first placed into a capsule made of a high-melting-point metal such as Ta or Nb, and then heated and sealed in a vacuum to remove adsorbed gases and air from the non-diamond-like carbon material. Afterward, the second to fourth steps described above are preferably performed.

[0159] In the diamond polycrystalline manufacturing method of this embodiment, the boundary between the graphite stable region and the diamond region is crossed multiple times during the heating and pressurization process from the initial temperature and initial pressure to the sintering temperature and sintering pressure. By heating and pressurizing in this way, the dislocation density of the manufactured diamond polycrystalline material can be increased.

[0160] Example

[0161] This embodiment will be described in more detail through examples. However, this embodiment is not limited to these examples.

[0162] Fabrication of Polycrystalline Diamond

[0163] <First Process: Preparation of Non-Diamond Carbon Materials>

[0164] First, in samples 1 to 12, the following non-diamond-like carbon materials were prepared as raw materials.

[0165] Non-diamond carbon materials

[0166] Samples 1-5 and Samples 8-11: Graphite powder with a particle size of 3 μm

[0167] Samples 6, 7, and 12: Powders containing boron added to graphite powder with a particle size of 3 μm.

[0168] <Second process: A process of increasing pressure while maintaining a low temperature, moving from the graphite stable region to the diamond region>

[0169] Next, the aforementioned non-diamond-like carbon material was placed in a Ta capsule, heated in a vacuum, and then sealed. Afterwards, using a high-pressure, high-temperature generator, the pressure was increased from the starting pressure and temperature shown in Table 1 to the arrival pressure and temperature of the first stage shown in Table 1. The starting pressure in Table 1 is marked "0 GPa," but represents atmospheric pressure. Furthermore, for samples 9 and 10, the temperature and pressure were increased to the arrival pressure and temperature of the second stage (described later) without undergoing the second process (first stage). The arrival pressure and temperature of the first stage correspond to the aforementioned diamond region, and the following relationship holds.

[0170] P > T × 0.00286 + 1.4185

[0171] <Third step: Maintaining pressure and temperature in the graphite stable region>

[0172] The temperature is increased from the first stage to reach the second stage pressure and temperature shown in Table 1, and this state is maintained during the holding time of the second stage shown in Table 1. Here, the second stage pressure and temperature of samples 1 to 9 and samples 10 to 12 correspond to the pressure P (unit: GPa) and temperature T (unit: °C) of the graphite stable region mentioned above, and the following relationship holds.

[0173] P < T × 0.00286 + 1.4185

[0174] <Fourth process: The process of transforming diamond particles and sintering them>

[0175] After the third process, the non-diamond carbon material is subjected to pressurized heating treatment at the arrival pressure and temperature of the third stage as shown in Table 1, and then pressurized to the sintering pressure and temperature of the fourth stage as shown in Table 1, thereby transforming the non-diamond carbon material into diamond particles and sintering them. Here, for sample 9, the temperature and pressure are increased to the sintering pressure and temperature without going through the third stage. Following the above steps, diamond polycrystalline samples 1 to 12 are obtained. In addition, no sintering aid or binder is added to the non-diamond carbon material. In addition, as sample 13, a commercially available diamond sintered body (manufactured by Sumitomo Electric Industries, Ltd., trade name: DA1000) is prepared. Samples 1 to 7 correspond to the examples. Samples 8 to 13 correspond to the comparative examples. The median particle size d50 of the diamond particles in the above diamond sintered body is 0.5 μm, and the diamond particle content is 90-95% by volume.

[0176] In addition, the aforementioned diamond sintered body uses cobalt as a bonding material.

[0177]

[0178] Evaluation of the properties of polycrystalline diamond

[0179] For the obtained diamond polycrystal, the diamond particles and the contents of boron, metal elements, unavoidable impurities, median particle size d50 and particle size d90, dislocation density, resistivity, and Knoop hardness were measured as follows.

[0180] <Diamond particle content and boron content>

[0181] The diamond particle content in the diamond polycrystal was determined by combining EDX with SEM and X-ray diffraction. The boron content in the diamond polycrystal was determined by SIMS. The specific measurement method was the same as that described in the [Detailed Description of Embodiments of this Disclosure] section above, and therefore will not be repeated. The results are shown in Table 2 (refer to the "Diamond Content" and "Boron Content" sections). Furthermore, regarding samples 2 and 3, it was confirmed that the remaining portion was unconverted graphite.

[0182] <Content of metallic elements (content of iron group elements)>

[0183] The content of iron group elements in polycrystalline diamond and sintered diamond was determined by EDX with attached SEM. Specific measurement conditions are described below. The results are shown in Table 2 (refer to the column “Content of Iron Group Elements Fe, Co, and Ni”).

[0184] EDX conditions

[0185] The accelerating voltage is 15kV

[0186] <Content of unavoidable impurities>

[0187] The content of unavoidable impurities in diamond polycrystals was determined by SIMS. The specific measurement method is the same as that described in the [Details of Embodiments of this Disclosure] section above, and therefore will not be repeated. The results are shown in Table 2 (refer to the "Unavoidable Impurity Content" section).

[0188] <Median particle size d50 and particle size d90 of diamond particles>

[0189] The median particle size d50 and particle size d90 of the diamond particles contained in each diamond polycrystal were measured. The specific measurement method is the same as that described in the [Detailed Description of Embodiments of this Disclosure] section above, and therefore will not be repeated. The results are shown in Table 2 (refer to the "Median Particle Size d50" and "Particle Size d90" columns).

[0190] <Dislocation density of diamond particles>

[0191] The dislocation density of diamond particles in a diamond polycrystalline material was measured. The specific measurement method was the same as that described in the [Detailed Description of Embodiments of this Disclosure] section above, and therefore will not be repeated. The results are shown in Table 2 (refer to the "Dislocation Density" section).

[0192] <Resistivity of diamond particles>

[0193] The resistivity of polycrystalline diamond was measured using the four-probe method according to JIS standard JIS K 7194. The sample size was [size missing]. The results are shown in Table 2 (see the "Resistivity" column). In Table 2, the areas marked with "-" indicate that measurements could not be performed because diamond polycrystalline material is an insulator.

[0194] <Knoop Hardness of Diamond Particles>

[0195] The Knoop hardness of polycrystalline diamond and sintered diamond was measured. The specific measurement method is the same as that described in the [Detailed Description of Embodiments of this Disclosure] section above, and therefore will not be repeated. The results are shown in Table 2 (refer to the "Knoop Hardness" section).

[0196] Evaluation of Tools Containing Polycrystalline Diamond

[0197] <Cutting Processing Test>

[0198] To investigate the wear resistance of cutting tools made from diamond polycrystalline materials (samples 1-12) or diamond sintered materials (sample 13), small-diameter end mills (tool shape: same as NPDB1050-020 manufactured by Sumitomo Electric Industries, Ltd., R0.5) were fabricated using the aforementioned diamond polycrystalline or diamond sintered materials. Cutting was performed under the following conditions, and the wear amount at the time point with a cutting distance of 24 m was calculated. The wear amount was then compared to that of sample 1. The results are shown in Table 2. Since cemented carbide is known to be a difficult-to-cut material, it is believed that the tool tip load increases under the following cutting conditions. Therefore, it can be evaluated that the smaller the wear amount ratio, the better the resistance to chipping and wear in fine machining operations.

[0199] (Cutting conditions)

[0200] Workpiece to be machined: VF20 cemented carbide (HRA92.5)

[0201] Rotation speed: 40,000 / minute

[0202] Feed rate: 200 m / min

[0203] Coolant: Oil mist

[0204]

[0205] "result"

[0206] As shown in Table 2, the wear ratio of samples 1 to 7 (Examples) is 0.9 to 1.2, indicating excellent resistance to chipping and wear. On the other hand, the wear ratio of samples 8 to 10 and sample 12 (Comparative Example) is 1.4 to 2.0. For sample 11 (Comparative Example), the cutting tip developed chipping at a cutting distance of 10 m, therefore subsequent cutting tests were discontinued. For sample 13 (Comparative Example), the cutting tip developed chipping at a cutting distance of 7 m, therefore subsequent cutting tests were discontinued. These results demonstrate that the cutting tools described in the Examples exhibit excellent resistance to chipping and wear. Furthermore, it is evident that the diamond polycrystalline material used in the cutting tools described in the Examples possesses excellent hardness and toughness.

[0207] The embodiments and examples of this disclosure have been described above, but it is also intended from the outset that the above-described embodiments and examples may be appropriately combined or modified.

[0208] The embodiments and examples disclosed herein should be considered exemplary in all respects, and not restrictive. The scope of the invention is defined not by the foregoing description, but by the claims, and is intended to include all modifications equivalent to and within the scope of the claims.

Claims

1. A polycrystalline diamond, wherein the polycrystalline diamond comprises diamond particles, wherein, The content of the diamond particles is greater than 99% by volume relative to the diamond polycrystalline material. The median particle size d50 of the diamond particles is greater than 10 nm and less than 200 nm. The dislocation density of the diamond particles is 2.0 × 10⁻⁶. 15 m -2 Above and 4.0×10 16 m -2 the following, The Knoop hardness at room temperature is above 80 GPa.

2. The polycrystalline diamond according to claim 1, wherein, The dislocation density of the diamond particles is 4.0 × 10⁻⁶. 15 m -2 Above and 1.0×10 16 m -2 the following.

3. The diamond polycrystalline material according to claim 1 or 2, wherein, The median particle size d50 of the diamond particles is above 10 nm and below 100 nm.

4. The diamond polycrystalline material according to claim 1 or 2, wherein, The diamond polycrystalline material also contains boron. The boron content is 0.01% by mass or more and 1% by mass or less relative to the diamond polycrystal.

5. The diamond polycrystalline material according to claim 1 or 2, wherein, The content of at least one metallic element selected from the group consisting of Group 4, Group 5, Group 6 elements, iron, aluminum, silicon, cobalt, and nickel of the periodic table is less than 1 volume.

6. The diamond polycrystalline material according to claim 1 or 2, wherein, The content of at least one unavoidable impurity selected from the group consisting of hydrogen, oxygen, nitrogen, alkali metals and alkaline earth metals is less than 0.1% by volume.

7. A tool, wherein, The tool comprises a diamond polycrystal as described in any one of claims 1 to 6.

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