JP6863076B2 - Polycrystalline diamond and its manufacturing method, scribing tool, scribing wheel, dresser, rotary tool, wire drawing die, cutting tool, electrode and processing method using polycrystalline diamond - Google Patents

Description

The present invention relates to polycrystalline diamond and a method for producing the same. The polycrystalline diamond according to the present invention is suitably used for a scribing tool, a scribing wheel, a dresser, a rotary tool, a wire drawing die, a cutting tool, an electrode and the like. Furthermore, the present invention relates to a processing method using polycrystalline diamond.

In recent years, it has become clear that nano-polycrystalline diamond has an isotropic hardness that exceeds that of natural single crystal diamond. Nanopolycrystalline diamonds having been imparted with conductivity by adding a boron compound to such a material have been developed. Further, by incorporating boron in diamond crystal grains in an atomic substitution type, nanopolycrystalline diamond exhibiting semiconductor characteristics based on a diamond structure has been developed.

For example, Japanese Patent Application Laid-Open No. 2012-106925 (Patent Document 1) is a polycrystal composed substantially only of diamond, in which the maximum particle size of diamond is 100 nm or less, the average particle size is 50 nm or less, and the inside of the diamond particles. Discloses a high-hardness conductive diamond polycrystal containing 10 ppm or more and 1000 ppm or less of boron.

Further, Japanese Patent Application Laid-Open No. 2013-28500 (Patent Document 2) is composed of carbon, a Group III element added so as to be dispersed in carbon at the atomic level, and unavoidable impurities, and has a crystal grain size of 500 nm or less. The polycrystalline diamond is disclosed.

Japanese Unexamined Patent Publication No. 2012-106925 Japanese Unexamined Patent Publication No. 2013-028500

In the high-hardness conductive diamond polycrystal disclosed in Japanese Patent Application Laid-Open No. 2012-106925 (Patent Document 1), boron oxide is formed on the surface of diamond because boron is contained in the diamond crystal as a boron compound. , Higher oxidation resistance. However, since such a boron compound does not have a high hardness like diamond instead of a diamond structure and has a coefficient of thermal expansion different from that of diamond, there are problems such as deterioration of wear resistance and generation of cracks at high temperature. ..

In the polycrystalline diamond disclosed in Japanese Patent Application Laid-Open No. 2013-28500 (Patent Document 2), since boron is dispersed at the atomic level and does not contain a boron compound, the occurrence of cracks and the like is suppressed, but the surface of the diamond is covered. Since a protective oxide is not formed and the oxidation resistance is not high, there is a problem such as a decrease in wear resistance.

Therefore, a protective film for protecting the surface can be formed, the above-mentioned problems are solved, and a polycrystalline diamond having high wear resistance, a method for producing the same, and a scribing tool formed by using the above-mentioned polycrystalline diamond. , A scribing wheel, a dresser, a rotary tool, a wire drawing die, a cutting tool and an electrode, and a processing method using the above-mentioned polycrystalline diamond.

The polycrystalline diamond according to an aspect of the present invention is a polycrystalline diamond having a diamond single phase as a basic composition, the polycrystalline diamond is composed of a plurality of crystal grains, and the polycrystalline diamond is boron and boron. It contains a compound, hydrogen, and oxygen, the balance is carbon and trace impurities, and the above-mentioned boron is dispersed in the above-mentioned crystal grains at the atomic level, and 90 atomic% or more of the above is present as an isolated substitution type. The above-mentioned boron compound, the above-mentioned hydrogen and the above-mentioned oxygen are present in the above-mentioned crystal grains as an isolated substitution type or the above-mentioned penetrating type, the above-mentioned boron compound contains an oxygen-containing boron compound, and the above-mentioned crystal grains have a particle size of 500 nm. The surface of the polycrystalline diamond is coated with a protective film.

A method for producing a polycrystalline diamond according to another aspect of the present invention comprises carbon, boron dispersed in the crystal grains of the carbon at the atomic level, and 90 atomic% or more of the carbon present as an isolated substitution type, and a boron compound. The first step of preparing graphite containing hydrogen and oxygen, the second step of filling the container with the graphite in an inert gas atmosphere, and the diamond in the container by pressure heat treatment. The above-mentioned boron compound includes an oxygen-containing boron compound.

According to the above, a protective film for protecting the surface can be formed, and a polycrystalline diamond having high wear resistance and a method for producing the same, a scribing tool, a scribing wheel, and a dresser formed by using the above-mentioned polycrystalline diamond. , Rotating tools, wire drawing dies, cutting tools and electrodes, and machining methods using the above polycrystalline diamond.

FIG. 1 is a graph showing an example of the results of SIMS of polycrystalline diamond according to an aspect of the present invention. FIG. 2 is a graph showing the results of TOF-SIMS on the surface of polycrystalline diamond according to an aspect of the present invention. FIG. 3 is a graph showing an example of a mass change of a polycrystalline diamond according to an embodiment of the present invention when heated in the atmosphere. FIG. 4 is a graph showing an example of the results of dynamic friction coefficient measurement in a pin-on-disc sliding test of polycrystalline diamond according to an embodiment of the present invention. FIG. 5 is a graph showing an example of the result of Knoop hardness measurement of polycrystalline diamond according to an aspect of the present invention. FIG. 6 is a graph showing an example of the result of measurement of the wear rate of polycrystalline diamond according to an aspect of the present invention with respect to silicon dioxide. FIG. 7 is a flowchart showing a process of a method for producing polycrystalline diamond according to another aspect of the present invention.

[Explanation of Embodiments of the Present Invention]
First, embodiments of the present invention will be listed and described.

[1] The polycrystalline diamond according to an embodiment of the present invention is a polycrystalline diamond having a diamond single phase as a basic composition, the polycrystalline diamond is composed of a plurality of crystal grains, and the polycrystalline diamond is composed of a plurality of crystal grains. , Boron, boron compound, hydrogen, oxygen, and the balance is carbon and trace impurities. The boron is dispersed in the crystal grains at the atomic level, and 90 atomic% or more of the boron is isolated and substituted. It exists as a type, and the above boron compound, the above hydrogen and the above oxygen enter into the crystal grains as an isolated substitution type or an invasion type (in the case of a boron compound, a cluster substitution type or a cluster that partially replaces a lattice as a cluster). The boron compound contains an oxygen-containing boron compound, the crystal grains have a particle size of 500 nm or less, and the surface of the polycrystalline diamond is protected. It is covered with a film. The polycrystalline diamond according to the present embodiment maintains a high-hardness diamond structure inside thereof, and can form an oxide film as a protective film for protecting the surface, resulting in high wear resistance.

[2] 99 atomic% or more of the above-mentioned boron may be present in the above-mentioned crystal grains as an isolated substitution type. Such polycrystalline diamond is more likely to maintain the high hardness diamond structure inside the polycrystalline diamond.

[3] The total atomic concentration of boron in the boron and the boron compound can be 1 × 10 ¹⁴ cm ^-3 or more and 1 × 10 ²² cm ^-3 or less. Such polycrystalline diamond can form a suitable protective film on its surface.

[4] The atomic concentration of the hydrogen can be 1 × 10 ¹⁷ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less. Such polycrystalline diamond can stably contain oxygen in the crystal and can suppress a decrease in hardness.

[5] In the polycrystalline diamond according to the present embodiment, the atomic concentration of the oxygen can be 1 × 10 ¹⁷ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less. In such polycrystalline diamond, the formation of a protective film which is an oxide film on the surface is promoted, the oxidation resistance is improved, the friction coefficient is lowered, and the decrease in hardness can be suppressed.

[6] the polycrystalline diamond in the Raman spectrum measurement, half-width of the peak area half width is 20 cm ^-1 or less about the 1575 cm ^-1 ± 30 cm ^-1, around the 1300 cm ^-1 ± 30 cm ^-1 Can be less than 1% of the peak area where is 60 cm ^{-1 or less.} Such polycrystalline diamond can maintain an isotropic hardness that exceeds that of natural diamond.

[7] The surface of the polycrystalline diamond (the surface coated with the protective film) can have a coefficient of dynamic friction of 0.06 or less. Such polycrystalline diamond has high sliding characteristics and wear resistance.

[8] The surface of the polycrystalline diamond (the surface coated with the protective film) can have a coefficient of dynamic friction of 0.05 or less. Such polycrystalline diamond has high sliding characteristics and wear resistance.

[9] The protective film can contain BO _x clusters and at least one of O and OH that are oxygen-terminated carbons. BO _x clusters are considered to be formed by the reaction of B (boron) exposed on the surface and B (boron) in the boron compound, and O and OH, which are the oxygen terminations of carbon, are formed by the reaction of carbon exposed on the surface. It is considered that they are formed, and all of them have high slidability and a small coefficient of friction, so that wear resistance is high.

[10] The protective film can contain precipitates precipitated from the crystal grains. Such polycrystalline diamond has high wear resistance because the protective film contains precipitates having high slidability and a low coefficient of friction.

[11] The average film thickness of the protective film can be 1 nm or more and 1000 mm or less. Such polycrystalline diamond can satisfactorily reduce the coefficient of friction.

[12] That is, the polycrystalline diamond of the present embodiment is a polycrystalline diamond having a diamond single phase as a basic composition, the polycrystalline diamond is composed of a plurality of crystal grains, and the polycrystalline diamond is boron. , Boron compound, hydrogen, oxygen, and the balance is carbon and trace impurities. The boron is dispersed in the crystallites at the atomic level, and 99 atomic% or more of the boron is isolated and substituted. The above-mentioned boron compound, the above-mentioned hydrogen and the above-mentioned oxygen exist as an isolated substitution type or the above-mentioned invading type in the above-mentioned crystal grains, the above-mentioned boron compound contains a boron compound containing oxygen, and the above-mentioned crystal grains are the grains thereof. The surface of the polycrystalline diamond having a diameter of 500 nm or less is coated with a protective film, and the total atomic concentration of the boron and the boron in the boron compound is 1 × 10 ¹⁴ cm ^-3 or more 1 ×. and the 10 ²² cm ^-3 or less, the hydrogen, the atom concentration is 1 × 10 ²⁰ cm ^-3 or less than 1 × 10 ¹⁷ cm ^-3, the oxygen, the atomic concentration of 1 × 10 ¹⁷ cm ^{- 3} or more 1 × 10 ²⁰ cm ^-3 or less, the polycrystalline diamond in the Raman spectrum measurement, the area of the peak half width is 20 cm ^-1 or less around the 1575cm ^-1 ± 30cm ^-1, 1300cm ^- It is less than 1% of the peak area where the half-price width is 60 cm ^{-1 or less centered on 1} ± 30 cm ^-1 , the polycrystalline diamond has a dynamic friction coefficient of 0.05 or less on its surface, and the protective film has a dynamic friction coefficient of 0.05 or less. , BO _x clusters and at least one of O and OH that are oxygen-terminated of the carbon, and the protective film contains precipitates precipitated from the crystal grains. Such a polycrystalline diamond maintains a high-hardness diamond structure inside thereof and forms an oxide film as a protective film for protecting the surface, thereby increasing the oxidation resistance and reducing the coefficient of kinetic friction. The sliding characteristics are high and the abrasion resistance is high.

[13] The method for producing polycrystalline diamond according to another embodiment of the present invention is carbon and boron dispersed in the crystal grains of the carbon at the atomic level and 90 atomic% or more of the carbon is present as an isolated substitution type. The first step of preparing graphite containing a boron compound, hydrogen, and oxygen, the second step of filling the container with the graphite in an inert gas atmosphere, and adding the graphite in the container. The boron compound includes an oxygen-containing boron compound, which comprises a third step of converting to diamond by pressure heat treatment. The method for producing polycrystalline diamond according to the present embodiment can maintain a high-hardness diamond structure inside and form a protective film for protecting the surface, so that a polycrystalline diamond having high wear resistance can be obtained. Can be manufactured.

[14] In the first step, at least one of an organic compound containing graphite, graphene, graphene oxide, and a six-membered ring of carbon, a liquid first organic compound containing boron, hydrogen, and oxygen, and hydrogen and oxygen are used. A first α sub-step of obtaining a mixture by mixing with the containing liquid second organic compound can be included. As a result, it is possible to maintain the internal high-hardness diamond structure and form a protective film for protecting the surface, so that polycrystalline diamond having high wear resistance can be produced more efficiently.

[15] In the first step, at least one of a liquid first organic compound containing boron, hydrogen and oxygen and a liquid third organic compound containing boron, and a liquid second organic compound containing hydrogen and oxygen are used. Can include a first β sub-step to obtain a mixture by mixing. As a result, it is possible to maintain the internal high-hardness diamond structure and form a protective film for protecting the surface, so that polycrystalline diamond having high wear resistance can be produced more efficiently.

[16] The first organic compound can be at least one of trimethyl borate and triethyl borate. As a result, it is possible to maintain the internal high-hardness diamond structure and form a protective film for protecting the surface, so that polycrystalline diamond having high wear resistance can be produced more efficiently.

[17] The second organic compound can be alcohols. As a result, it is possible to maintain the internal high-hardness diamond structure and form a protective film for protecting the surface, so that polycrystalline diamond having high wear resistance can be produced more efficiently.

[18] The first step can further include a second sub-step of forming the graphite by thermally decomposing the mixture at 1500 ° C. or higher and 1800 ° C. or lower. As a result, it is possible to maintain the internal high-hardness diamond structure and form a protective film for protecting the surface, so that polycrystalline diamond having high wear resistance can be produced more efficiently.

[19] The method for producing a polycrystalline diamond further includes a fourth step after the first step and before the second step, and the fourth step includes steps A, B and C. A step of repeating the steps a plurality of times in this order, a step A is a step of crushing the graphite into a crushed body, a step B is a step of molding the crushed body into a molded body, and a step C is a step of molding the molded body into a molded body. By thermally decomposing at 1500 to 1800 ° C., the above graphite can be prepared again. This makes it possible to avoid mixing of trace impurities such as _{B 4 C as much as possible.}

[20] In the third step, the graphite can be directly subjected to pressure heat treatment in the pressure heating device. As a result, polycrystalline diamond having a diamond single phase as a basic composition can be produced without containing a bonded phase (binder) made of cobalt or the like.

[21] The pressure heat treatment can be performed under the conditions of 6 GPa or more and 1200 ° C. or more. This makes it possible to efficiently produce polycrystalline diamond having the above effects.

[22] The pressure heat treatment can be performed under the conditions of 8 GPa or more and 30 GPa or less and 1500 ° C. or more and 2300 ° C. or less. This makes it possible to efficiently produce polycrystalline diamond having the above effects.

[23] The scribe tool according to still another embodiment of the present invention can be formed by using the above-mentioned polycrystalline diamond. Since the scribe tool according to this embodiment is formed by using the above-mentioned polycrystalline diamond, it has high wear resistance.

[24] The scribe wheel according to still another embodiment of the present invention can be formed by using the above-mentioned polycrystalline diamond. Since the scribe wheel according to this embodiment is made by using the above-mentioned polycrystalline diamond, it has high wear resistance.

[25] The dresser according to still another embodiment of the present invention can be formed by using the above-mentioned polycrystalline diamond. Since the dresser according to the present embodiment is made by using the above-mentioned polycrystalline diamond, it has high wear resistance.

[26] The rotary tool according to still another embodiment of the present invention can be formed by using the above-mentioned polycrystalline diamond. Since the rotary tool according to this embodiment is made by using the above-mentioned polycrystalline diamond, it has high wear resistance.

[27] The wire drawing die according to still another embodiment of the present invention can be formed by using the above-mentioned polycrystalline diamond. Since the wire drawing die according to the present embodiment is made by using the above-mentioned polycrystalline diamond, it has high wear resistance.

[28] The cutting tool according to still another embodiment of the present invention can be formed by using the above-mentioned polycrystalline diamond. Since the cutting tool according to this embodiment is made by using the above-mentioned polycrystalline diamond, it has high wear resistance.

[29] The electrode according to still another embodiment of the present invention can be formed by using the above-mentioned polycrystalline diamond. Since the electrode according to this embodiment is made by using the above-mentioned polycrystalline diamond, it has high wear resistance.

[30] In the processing method according to still another embodiment of the present invention, the object can be processed using the above-mentioned polycrystalline diamond. Since the processing method according to the present embodiment processes the object using the above-mentioned polycrystalline diamond, the object can be processed efficiently and at low cost.

[31] The object can be an insulator. Even if the object is an insulator, the object can be processed efficiently and at low cost without causing abnormal wear due to triboplasma or the like.

[32] The insulator can have a resistivity of 100 kΩ · cm or more. Even if the object is an insulator having a resistivity of 100 kΩ · cm or more, the object can be processed efficiently and at low cost without causing etching by triboplasma.

[Details of Embodiments of the present invention]
Hereinafter, embodiments of the present invention will be described in more detail. Here, in the present specification, the notation 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 there is no description of the unit in A, and the unit is described only in B. In the case, the unit of A and the unit of B are the same. Further, when a compound or the like is represented by a chemical formula in the present specification, it shall include all conventionally known atomic ratios when the atomic ratio is not particularly limited, and is not necessarily limited to those in the stoichiometric range.

<< Embodiment 1: Polycrystalline diamond >>
The polycrystalline diamond according to the present embodiment has a diamond single phase as a basic composition and is composed of a plurality of crystal grains. In addition, polycrystalline diamond contains boron, boron compounds, hydrogen and oxygen, with the balance being carbon and trace impurities. Boron is dispersed in crystal grains at the atomic level, and 90 atomic% or more of it exists as an isolated substitution type. Boron compounds, hydrogen and oxygen are either isolated-substituted or invasive in the crystal grains (in the case of boron compounds, they include cluster-substituted or cluster-invading clusters that partially replace the lattice as clusters). included. The boron compound includes an oxygen-containing boron compound (hereinafter, also referred to as an oxygen-containing boron compound). The grain size of the crystal grains is 500 nm or less. The surface of polycrystalline diamond is coated with a protective film.

Since the polycrystalline diamond according to the present embodiment has a diamond single phase as a basic composition, it does not contain a bonding phase (binder) formed by a sintering aid and / or a catalyst, and is under high temperature conditions. Even underneath, bleaching does not occur due to the difference in thermal expansion rate. Furthermore, polycrystalline diamond is a polycrystalline diamond composed of a plurality of crystal grains, and since its particle size is 500 nm or less, it does not have the directional and cleavage properties of a single crystal, and is anisotropic to all directions. Has anisotropic hardness and abrasion resistance. Since polycrystalline diamond contains boron, a boron compound, hydrogen, and oxygen in the crystal grains, its surface is coated with a protective film which is an oxide film. As a result, the oxidation resistance becomes high, and the sliding characteristics and the wear resistance become high due to the reduction of the coefficient of kinetic friction.

In the polycrystalline diamond of the present embodiment, the maximum grain size of the crystal grains of the polycrystalline diamond is 500 nm or less, preferably 200 nm or less, from the viewpoint of having isotropic hardness and abrasion resistance in all directions. , 100 nm or less is more preferable. Further, from the viewpoint of suppressing a decrease in altitude due to grain boundary slip of the polycrystalline diamond, the minimum particle size of the crystal grains of the polycrystalline diamond is preferably 1 nm or more, more preferably 20 nm or more.

The particle size of polycrystalline diamond can be measured by electron microscopy such as SEM and TEM. By polishing any surface of polycrystalline diamond, an observation polishing surface for measuring the particle size is prepared, and at any one place of the above observation polishing surface at a magnification of 20000 times using, for example, SEM. Observe (1 field). Since about 120 to 200,000 crystal grains of polycrystalline diamond appear in one field of view, the particle size of 10 of them is obtained, and it is confirmed that all of them are 500 nm or less. By doing this for the entire field of view over the entire size of the sample, it can be confirmed that the grain size of the polycrystalline diamond is 500 nm or less.

The particle size of polycrystalline diamond can also be measured by an X-ray diffraction method (XRD method) based on the following conditions.
Measuring device: Product name (product number) "X'pert", PANalytical X-ray light source: Cu-Kα ray (wavelength 1.54185 Å)
Scanning axis: 2θ
Scanning range: 20 ° to 120 °
Voltage: 40kV
Current: 30mA
Scan speed: 1 ° / min
The full width at half maximum was obtained from the Scherrer equation (D = Kλ / Bcosθ) after peak fitting. Here, D is the particle size of the diamond crystal grain, B is the diffraction line width, λ is the wavelength of the X-ray, θ is the Bragg angle, and K is the correction coefficient (0.9) determined from the correlation with the SEM image.

<Elements in polycrystalline diamond>
In the polycrystalline diamond of the present embodiment, boron is dispersed at the atomic level and 90 atomic% or more of the whole is present in the isolated substitution type, and the boron compound, hydrogen and oxygen are present in the isolated substitution type or the penetrating type. Here, in the case of a boron compound, it includes a case where it exists as a cluster substitution type in which the lattice is partially replaced as a cluster or a cluster invasion type invading as a cluster. From these facts, by reaction with at least one of boron, boron compound, hydrogen and oxygen exposed from the inside of polycrystalline diamond on its surface, or reaction with at least one of these elements and compounds with oxygen in the atmosphere, etc. An oxide film is formed, and the oxide film covers the surface of polycrystalline diamond as a protective film. With such a protective film, the oxidation resistance of polycrystalline diamond is increased, and the coefficient of friction is reduced, so that the sliding characteristics and wear resistance are enhanced. In the polycrystalline diamond of the present embodiment, the protective film may contain a precipitate formed by depositing on the surface of the polycrystalline diamond from the inside.

That is, in the polycrystalline diamond of the present embodiment, when the surface is damaged by abrasion and / or breakage, a protective film which is an oxide film is formed only on the surface, and the diamond structure is maintained inside and the hardness is maintained. .. In addition, boron is dispersed at the atomic level and 90 atomic% or more of the whole is contained in an isolated substitution type, so that it does not aggregate in a cluster shape inside and does not aggregate at the grain boundaries of diamond crystals. , There is no impurity segregation that causes cracks due to temperature changes and / or impact. Further, since boron is dispersed at the atomic level and 90 atomic% or more of the whole is contained in an isolated substitution type, a protective film which is an oxide film localized on a desired exposed surface is formed over the entire polycrystalline diamond. Since the charge is in a state of excess holes, it is easier to attract oxygen only to the surface.

In the polycrystalline diamond of the present embodiment, "dispersed at the atomic level" means in the carbon forming the crystal of the polycrystalline diamond when carbon and boron are mixed in a vapor phase state to prepare the polycrystalline diamond. It refers to a dispersed state at a level at which different elements such as boron each have a finite activation energy and are dispersed without changing the diamond crystal structure. That is, such a dispersed state means a state in which a dissimilar element and a dissimilar compound other than diamond that are isolated and precipitated are not formed. The "isolated substitution type" refers to a form in which dissimilar elements such as boron, boron compounds, hydrogen and oxygen are isolated and replaced with carbon located at the lattice point of the crystal lattice of polycrystalline diamond or graphite. Say. Further, the "penetrating type" refers to a form in which dissimilar elements such as boron compounds, hydrogen and oxygen invade the gaps between carbons located at the lattice points of the crystal lattice of polycrystalline diamond. In the case of a boron compound, it includes a cluster substitution type in which the lattice is partially replaced as a cluster or a cluster invasion type invading as a cluster.

The dispersed state and existing form of boron, boron compound, hydrogen and oxygen in the polycrystalline diamond of the present embodiment are observed by a TEM (transmission electron microscope). In addition, being "dispersed at the atomic level" and "isolated substitution type" with boron can be determined by temperature dependence of electrical resistance, detection of activation energy, or TOF-SIMS (time-of-flight type-secondary ion mass spectrometry). Confirm. The presence of "isolated substitution type" or "invasion type" is also evaluated by TOF-SIMS. Atomic concentrations of boron, hydrogen and oxygen in boron and boron compounds are determined by SIMS (Secondary Ion Mass Spectrometry) inside the polycrystalline diamond on and near the surface of the polycrystalline diamond (eg, oxidation as a protective film). Polycrystalline diamond in and around the membrane, up to a depth of 100 nm from the surface) is measured by TOF-SIMS. Here, the distinction between boron and the boron compound can be made by the type of cluster in TOF-SIMS. Therefore, by using SIMS that measures only atoms and TOF-SIMS that measures clusters in combination, the atomic concentration of boron in each of boron and a boron compound can be measured. The dispersed state and the existing state can also be evaluated by XRD (X-ray diffraction), Raman spectroscopy, and the like. Further, the atomic concentration of trace impurities other than carbon, boron compound, boron, hydrogen and oxygen in the polycrystalline diamond of the present embodiment is measured by SIMS or ICP-MS (inductively coupled plasma-mass spectrometry).

In the polycrystalline diamond of the present embodiment, from the viewpoint that the high-hardness diamond structure inside the polycrystalline diamond can be easily maintained, 90 atomic% or more of boron is an isolated substitution type, preferably 95 atomic% of the total. The above is the isolated substitution type, and more preferably 99 atomic% or more of the whole is the isolated substitution type. The ratio of isolated substituted boron to the total boron is measured by TOF-SIMS. Boron is higher than cubic boron nitride, which has a Knoop hardness of about 50 GPa, and Ib-type diamond single crystal, which has a Knoop hardness of about 90 GPa, because 90 atomic% or more of it is present as an isolated substitution type in polycrystalline diamond grains. Has hardness.

In the polycrystalline diamond of the present embodiment, the boron compound contains an oxygen-containing boron compound. When such an oxygen-containing boron compound is exposed from the inside of polycrystalline diamond to its surface, an oxide film is formed by reaction with at least one of boron, hydrogen and oxygen, or reaction with oxygen in the atmosphere like these elements. Once formed, the oxide film coats the surface of polycrystalline diamond as a protective film. Therefore, the oxidation resistance of the polycrystalline diamond is increased, and the friction coefficient is reduced, so that the sliding characteristics and the wear resistance are improved. Here, the oxygen-containing boron compound is not particularly limited, but typical examples thereof include boron oxide and boric acid. Boron oxide has no limitation on the ratio of the number of atoms of boron and oxygen, and includes B ₂ O ₃ , BO _{3, and the} like. _{Further, boric acid also includes H 3} BO ₃ (orthoboric acid), HBO ₂ (metaboric acid), etc., with no limitation on the ratio of the number of atoms of boron, hydrogen, and oxygen.

(Atomic concentration of boron)
In the polycrystalline diamond of the present embodiment, from the viewpoint of forming an oxide film as a suitable protective film on the surface thereof, boron (boron dispersed at the atomic level, the same applies hereinafter) and the total atom of boron in the boron compound concentration, 1 × 10 ¹⁴ cm ^-3 or more 1 × 10 ²² cm ^-3 or less are preferred, 1 × 10 ¹⁴ cm ^-3 or higher than 1 × 10 ²¹ cm ^-3 is preferable. In the more preferable range of the atomic concentration of boron, the defective rate of the protective film is drastically reduced and the yield is improved from 30% or more to 90% or more as compared with the preferable range. Here, from the viewpoint of forming an oxide film as a more suitable protective film on the surface of polycrystalline diamond, the ratio of the atomic concentration of boron to the atomic concentration of boron in the boron compound is in the range of 100: 1 to 100:10. Is preferable.

In addition, polycrystalline diamond exhibits electrical characteristics as a p-type semiconductor in the range of less than ^{1 × 10 19} cm ^-3 within the total atomic concentration range of boron and boron in the boron compound, and is 1 × 10. ^In the range of 19 cm ^-3 or more, it exhibits electrical characteristics as a metallic conductor.

(Atomic concentration of hydrogen)
In polycrystalline diamond of the present embodiment, the oxygen may comprise stably in the crystal, from the viewpoint of suppressing reduction and increase of the crystal grain size of the hardness, the atomic concentration of hydrogen, 1 × 10 ¹⁷ cm ^{- 3} or more and 1 × 10 ²⁰ cm ^-3 or less are preferable, and 1 × 10 ¹⁷ cm ^-3 or more and 1 × 10 ¹⁹ cm ^-3 or less are more preferable. However, even if the hardness is lowered, it has a hardness higher than that of cubic boron nitride having a Knoop hardness of about 50 GPa and an industrial Ib type diamond single crystal having a Knoop hardness of about 90 GPa. It is sufficiently useful for drawing dies, sliding parts, etc.). When there is no hydrogen in the crystal, oxygen reacts with carbon in the polycrystalline diamond to become a carbon oxide (CO _x ) -based gas, which is easily released at a high temperature and it is difficult to add oxygen into the crystal of the polycrystalline diamond.

(Atomic concentration of oxygen)
In the polycrystalline diamond of the present embodiment, from the viewpoint that the formation of a protective film which is an oxide film on the surface is promoted, the oxidation resistance is improved, the friction coefficient is lowered, and the decrease in hardness and the increase in crystal grain size can be suppressed. atomic concentration of oxygen, 1 × 10 ¹⁷ cm ^-3 to 1 × preferably 10 ²⁰ cm ^-3 or less, 1 × 10 ¹⁷ cm ^-3 or more 1 × 10 ¹⁹ cm ^-3 or less is more preferable.

(Concentration of trace impurities)
The trace impurities contained in polycrystalline diamond are a general term for compounds that may be contained in trace amounts in the production of polycrystalline diamond. The content (atomic concentration) of each compound contained as trace impurities is 0 cm ^-3 or more and 1 × 10 ¹⁶ cm ^-3 or less, respectively, and the total of each compound (that is, the content of trace impurities (atomic concentration)) is 0 cm. ^-3 or more and 1 x 10 ¹⁷ cm ^-3 or less. Therefore, trace impurities may or may not be contained in polycrystalline diamond. Trace impurities include B ₄ C and the like. Examples of trace impurities other than these include compounds containing metal elements classified as transition metal elements.

(SIMS measurement)
FIG. 1 is a graph showing an example of the results of SIMS of the polycrystalline diamond of the present embodiment. The polycrystalline diamond shown in FIG. 1 is obtained by directly converting graphite containing boron, a boron compound, hydrogen and oxygen formed by the liquid phase method described later into diamond at 16 GPa and 2100 ° C. The SIMS measurement conditions are as follows.
Measuring device: Product name (product number): "IMS-7f", AMETEK primary ion species: Cesium (Cs +)
Primary acceleration voltage: 15kV
Detection area: 30 (μmφ)
Measurement accuracy: ± 40% (2σ).

With reference to FIG. 1, the polycrystalline diamond of the present embodiment contains boron, hydrogen, and oxygen in uniform concentrations (atomic concentrations) from the surface to the inside.

(TOF-SIMS measurement)
FIG. 2 is a graph showing an example of the results of TOF-SIMS on the surface of the polycrystalline diamond of the present embodiment. The polycrystalline diamond shown in FIG. 2 is the polycrystalline diamond used for SIMS shown in FIG. The measurement conditions for TOF-SIMS are as follows.
Measuring device: TOF-SIMS mass spectrometer (flying time secondary ion mass spectrometer)
Primary ion source: Bismuth (Bi)
Primary acceleration voltage: 25 kV.

With reference to FIG. 2, three types of chemical species _{, BO 2} , O, and O ₂ , have been detected as oxygen-containing species contained in the oxide film as a protective film covering the surface of polycrystalline diamond. Here, since boron is _{detected as BO 2 in the} oxide film, it is considered that boron is dispersed at the atomic level and is mostly contained in the isolated substitution type in the crystals inside the polycrystalline diamond. Be done.

From FIGS. 1 and 2, it is expected that there are an oxygen-containing boron compound having an oxygen content of about 0.1 times and a B _{4 C having an oxygen content of about 0.01 times the boron content.}

(Raman spectrum)
Polycrystalline diamond of the present embodiment, in the Raman spectrum measurement, the area of the peak half width is 20 cm ^-1 or less about the 1575 cm ^-1 ± 30 cm ^-1 is a half-value width around the 1300 cm ^-1 ± 30 cm ^-1 Is preferably less than 1%, more preferably less than 0.2% of the peak area of 60 cm ^{-1 or less.} The area of such a peak half width around the 1575 cm ^-1 ± 30 cm ^-1 derived from a polycrystalline diamond amorphous carbon or graphite carbon (SP2 carbon atoms) is 20 cm ^-1 or less, from the diamond carbon (SP3 carbon) Since less than 1% of the peak area where the half-price width is 60 cm ^{-1 or less centered on 1300 cm -1} ± 30 cm ^-1 , graphite carbon is almost completely (specifically, 99 atomic% or more) diamond carbon. Since it has been converted to, it has high hardness.

(Dynamic friction coefficient)
The polycrystalline diamond of the present embodiment has a surface dynamic friction coefficient of preferably 0.06 or less, more preferably 0.05 or less, further preferably 0.04 or less, particularly preferably 0.03 or less, and 0.02. The following are the most preferable. Since such polycrystalline diamond has a low coefficient of dynamic friction in the atmosphere of 0.06 or less, it has high sliding characteristics and high wear resistance.

(Protective film)
In the polycrystalline diamond of the present embodiment, the oxide film formed as a protective film for protecting the surface _{thereof preferably contains BO x} clusters and at least one of O and OH which are oxygen terminations of carbon. BO _x clusters are thought to be obtained by the reaction of surface-exposed B (boron) with oxygen in the atmosphere and oxygen in the crystal (oxygen in the crystal in a vacuum or an inert gas). It is considered that O and OH, which are oxygen terminations, were obtained by reacting the carbon exposed on the surface with oxygen in the atmosphere and oxygen in the crystal (oxygen in the crystal in a vacuum or an inert gas). Since all of them have high slidability and a small friction coefficient, wear resistance is high.

With reference to FIG. 2, from an example of the TOF-SIMS results of the surface of the polycrystalline diamond of the present embodiment, there are three types of _{oxygen species contained in the oxide film which is the protective film, BO 2} , O, and O _2. It can be seen that a chemical species exists. BO ₂ is _{derived from BO x} cluster, and it is considered that BO _x cluster exists in the form of _{BO 2} , B ₂ O ₄ , B ₃ O _{6, and the like.} O and O ₂ are considered to be derived from at least one of O and OH, which are the oxygen terminations of carbon.

In the polycrystalline diamond of the present embodiment, the protective film preferably further contains precipitates precipitated from the crystal grains. In such polycrystalline diamond, the protective film has BO _x clusters and at least one of O and OH, which are oxygen terminations of carbon, and precipitates from crystal grains having higher slidability and a lower coefficient of friction. By including it, the abrasion resistance becomes high. The precipitate is not particularly limited, but is mainly composed of a boron oxide such as _{B 2} O _3. B ₂ O ₃ means that B (boron) and BO ₂ off the surface of polycrystalline diamond react with oxygen in the atmosphere and oxygen in the crystal (oxygen in the crystal in a vacuum or an inert gas). It is thought that it is formed by. Such precipitates also remain and accumulate as debris (specifically, deposits composed of polishing scraps) and have a lubricating action, which contributes to the reduction of the friction coefficient.

In the polycrystalline diamond of the present embodiment, even if the surface of the polycrystalline diamond is damaged due to mechanical damage, a smooth surface is maintained by filling the defective portion with a portion of the protective film other than the defective portion. Therefore, the average thickness of the protective film is preferably 1 nm or more and 1000 nm or less, and more preferably 10 nm or more and 500 nm or less. Here, the average film thickness of the protective film is measured by a stylus type surface shape measuring device (for example, a Dektak (registered trademark) stylus profiling system manufactured by Bruker Co., Ltd.) and a TEM.

That is, the polycrystalline diamond of the present embodiment is a polycrystalline diamond having a diamond single phase as a basic composition. Further, the polycrystalline diamond is composed of a plurality of crystal grains, and the polycrystalline diamond contains boron, a boron compound, hydrogen, and oxygen, and the balance is carbon and trace impurities. The boron is dispersed in the crystal grains at the atomic level, and 99 atomic% or more of the boron exists as an isolated substitution type. The boron compound, hydrogen and oxygen are present in the crystal grains as isolated substitution type or invasion type. The boron compound includes an oxygen-containing boron compound. The grain size of the crystal grains is 500 nm or less. The surface of the polycrystalline diamond is coated with a protective film. The total atomic concentration of the above-mentioned boron and the above-mentioned boron compound is 1 × 10 ¹⁴ cm ^-3 or more and 1 × 10 ²² cm ^-3 or less, and the above-mentioned hydrogen has an atomic concentration of 1 × 10 ¹⁷ cm. ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less, the atomic concentration of the oxygen is 1 × 10 ¹⁷ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less, and the polycrystalline diamond is Raman spectrum measurement. in the area of the peak half width is 20 cm ^-1 or less about the 1575 cm ^-1 ± 30 cm ^-1 is the area of the peak half width is 60cm ^-1 or less around the 1300cm ^-1 ± 30cm ^-1 1 %, The surface of the polycrystalline diamond (the surface coated with the protective film) has a dynamic friction coefficient of 0.05 or less, and the protective film has the BO _x cluster and the oxygen termination of the carbon. It is preferable that the protective film contains at least one of O and OH, and the protective film contains a precipitate precipitated from the crystal grains. Such a polycrystalline diamond maintains a high-hardness diamond structure inside thereof and forms an oxide film as a protective film for protecting the surface, thereby increasing the oxidation resistance and reducing the coefficient of friction. The sliding characteristics are high and the wear resistance is high.

The confirmation and evaluation of the physical properties of the polycrystalline diamond of the present embodiment will be described in detail below with specific examples.

(Confirmation of protective film formation)
Polycrystalline diamond of the present embodiment (boron atomic concentration (referring to the total atomic concentration of boron and boron in a boron compound, the same shall apply hereinafter) 6.8 × 10 ²⁰ cm ^-3 , hydrogen atomic concentration 6.0 × 10 ¹⁸ Oxygen is detected in the surface layer from the surface to a depth of about 0.5 nm by chemical analysis by AES (Auger electron spectroscopy) on the surface of cm ^-3 , oxygen atom concentration 3.0 × 10 ¹⁸ cm ^-3). From this, it can be seen that an oxide film as a protective film is formed on the surface even at room temperature (for example, 25 ° C.).

FIG. 3 is a graph showing an example of a mass change of the polycrystalline diamond of the present embodiment when heated in the atmosphere. With reference to FIG. 3, the polycrystalline diamond containing boron, a boron compound, hydrogen and oxygen and the polycrystalline diamond containing only boron and a boron compound slightly increase in mass up to about 800 ° C. This suggests that the formation of a protective film, which is an oxide film, is promoted on the surface at high temperatures. Further, the mass of polycrystalline diamond containing no boron sharply decreases from about 800 ° C., and the mass of polycrystalline diamond containing only boron and a boron compound gradually decreases from about 800 ° C., whereas the mass of boron, The weight of polycrystalline diamond containing boron compound, hydrogen and oxygen does not decrease up to about 1000 ° C. That is, it is considered that a stable oxide film is formed in the polycrystalline diamond containing boron, a boron compound, hydrogen and oxygen, and this serves as a protective film to improve the oxidation resistance of the polycrystalline diamond.

(Evaluation of dynamic friction coefficient)
FIG. 4 is a graph showing an example of the results of dynamic friction coefficient measurement by the pin-on-disc sliding test of the polycrystalline diamond of the present embodiment. The pin-on-disc sliding test is performed under the following conditions.
Ball material: SUS
Load: 10N
Rotation speed: 400 rpm
Sliding radius: 1.25 mm
Test time: 100 minutes Temperature: Room temperature Atmosphere: Atmosphere (25 ° C and 30% relative humidity).

With reference to FIG. 4, in a dry atmosphere (for example, at 25 ° C. and a relative humidity of 30% or less), the kinematic friction coefficient of polycrystalline diamond containing boron and a boron compound is 0 with respect to the kinematic friction coefficient of polycrystalline diamond without additives. It decreases to .25 times or less, and the kinematic friction coefficient of polycrystalline diamond containing boron, boron compounds, hydrogen and oxygen decreases to 0.20 times or less. Since the oxide film as a protective film formed on the surface of the polycrystalline diamond of the present embodiment is water-soluble, the usage environment is preferably a dry atmosphere, and the relative humidity at 25 ° C. is 30 in the air. The water content is preferably 25% or less, the relative humidity at 25 ° C. is more preferably 20% or less, and the water content is 25 in an atmosphere other than the atmosphere (for example, Ar (argon) atmosphere or mineral oil atmosphere). % Or less is preferable, and a water content of 20% or less is more preferable.

(Evaluation of hardness)
FIG. 5 is a graph showing an example of the result of Knoop hardness measurement of the polycrystalline diamond of the present embodiment. The Knoop hardness measurement is based on JIS Z2251: 2009, and the load in the measurement is 4.9N. With reference to FIG. 5, the noup hardness of the polycrystalline diamond containing boron and the boron compound decreased somewhat with increasing the boron atom concentration with respect to the noup hardness of the additive-free polycrystalline diamond, and the boron, the boron compound. The noup hardness of polycrystalline diamond containing hydrogen and oxygen decreases somewhat further with increasing boron atom concentration, hydrogen atom concentration and oxygen atom concentration. It is considered that boron, boron compounds, hydrogen and oxygen contained in polycrystalline diamond serve as the starting points of plastic deformation and reduce the hardness to some extent. However, the Knoop hardness of polycrystalline diamond with a total atomic concentration of boron 4.0 × 10 ²⁰ cm ^-3 , hydrogen atomic concentration 1.0 × 10 ¹⁹ cm ^-3 and oxygen atomic concentration 1.0 × 10 ¹⁹ cm ^-3. Is equal to or higher than the Knoop hardness of ordinary synthetic single crystal diamond (Ib type single crystal diamond, isolated substitution type nitrogen atom concentration 1.7 × 10 ¹⁹ cm ^-3).

(Evaluation of wear resistance)
Polycrystalline diamond is processed into a cylindrical shape with a diameter of φ1 mm and a height of 2 mm, and a wear test of polycrystalline diamond (load is 2.5 kgf /) using a metal bond diamond wheel (manufactured by Allied Material Co., Ltd.) of No. # 800. According to mm ² , sliding speed 200 mm / min), ^{diamond and boron compounds (total atomic concentration of diamond is 2.5 x 10 19} cm ^{-3 to} 4.0 x 10 ²⁰ cm ^-3 ), hydrogen (atom) concentration containing ^{2.2 × 10 18 cm -3 ~3.5 ×} 10 19 cm -3) and oxygen (atomic concentration of ^{2.2 × 10 18 cm -3 ~2.2 ×} 10 19 cm -3) Since polycrystalline diamond has an abrasion rate of 2.5 to ³ mm 3 / h, its abrasion resistance is 3 to 4 times higher than that of additive-free polycrystalline diamond having an abrasion rate of 10 mm ^{3 / h.} improves.

In the wear test using the metal-bonded diamond wheel described above, mechanical wear and thermochemical wear proceed synergistically. Therefore, as shown below, the mechanical wear characteristics and the thermochemical wear characteristics are evaluated.

In order to evaluate the mechanical wear characteristics of polycrystalline diamond, a low-speed long-time sliding test is _{mainly performed on aluminum oxide (Al 2} O _{3) in which mechanical wear progresses.} Boron and boron compounds (total atomic concentration of boron is 0 cm ^{-3 to} 4.0 x 10 ²⁰ cm ^-3 ), hydrogen (atomic concentration is 0 cm ^{-3 to} 4.0 x 10 ¹⁹ cm ^-3 ) and oxygen (atom) A conical test piece with a tip test surface of 0.3 mm diameter prepared using a polycrystalline diamond containing ^{0 cm -3 to} 4.0 x 10 ²⁰ cm ^-3 ) with a concentration of 0 cm -3 to 4.0 x 10 20 cm -3) was used for the machining center. _{It is pressed against an Al 2} O ₃ sintered body (purity 99.9% by mass) with a constant load of 0.3 MPa and slid at a low speed of 5 m / min for a distance of 10 km to wear from the widening of the tip diameter. Calculate the amount. The amount of wear of polycrystalline diamond containing boron, hydrogen, and oxygen is about 0.05 times that of polycrystalline diamond without additives, and the wear resistance is significantly improved. The lubricating effect of the protective film, which is an oxide film formed on the surface that is renewed by the wear of polycrystalline diamond containing boron, hydrogen, and oxygen, greatly improves the sliding characteristics and significantly suppresses mechanical wear. Conceivable.

In order to evaluate the thermochemical wear characteristics of polycrystalline diamond, a sliding test is _{mainly performed on silicon dioxide (SiO 2) in which thermochemical wear progresses.} Boron and boron compounds (total atomic concentration of boron is 0 cm ^{-3 to} 4.0 x 10 ²⁰ cm ^-3 ), hydrogen (atomic concentration is 0 cm ^{-3 to} 4.0 x 10 ¹⁹ cm ^-3 ) and oxygen (atom) A conical test piece with a tip test surface of 0.3 mm diameter prepared using a polycrystalline diamond containing ^{0 cm -3 to} 4.0 × 10 ²⁰ cm ^-3 ) with a concentration of 0 cm -3 to 4.0 × 10 20 cm -3) was fixed to a test piece having a diameter of 20 mm. Using synthetic quartz (SiO ₂ ) as a polishing machine, while rotating at 6000 rpm (sliding speed 260 to 340 m / min), it is pressed against the test surface of the fixed test piece at 0.1 MPa and slid.

FIG. 6 is a graph showing an example of the results of measurement of the wear rate of this polycrystalline diamond with respect to silicon dioxide. As shown in FIG. 6, polycrystalline diamond containing boron, a boron compound, hydrogen, and oxygen has a lower wear rate and improved wear resistance than polycrystalline diamond without additives. In particular, in polycrystalline diamond having a boron atom concentration of 2 × 10 ¹⁹ cm ^-3 to 2 × 10 ²⁰ cm ^-3 , the wear rate is remarkably low and the wear resistance is greatly improved. Damage to silicon dioxide of polycrystalline diamond is caused by abrasion due to a chemical reaction, but is a protective film that is an oxide film formed on the surface that is renewed by abrasion of polycrystalline diamond containing boron, boron compounds, hydrogen, and oxygen. It is considered that the sliding characteristics are greatly improved by the lubricating effect of the above, and thermochemical wear is remarkably suppressed.

Suppression of mechanical wear and thermochemical wear by suppressing heat generation due to friction in polycrystalline diamond containing boron, boron compounds, hydrogen, and oxygen is suitable for processing difficult-to-cut materials such as cemented carbide and aluminum alloys. It shows that it is suitable.

As described above, in the polycrystalline diamond of the present embodiment, boron dispersed in the crystal at the atomic level and 90 atomic% or more of the whole is contained in the isolated substitution type and boron contained in the isolated substitution type or the penetrating type. Oxides are formed on the surface by compounds, hydrogen and oxygen, and the oxidation resistance and lubricity of the protective film, which is such an oxide film, improves oxidation resistance, abrasion resistance and sliding properties.

Further, since the polycrystalline diamond of the present embodiment has conductivity due to the contained boron, abnormal wear due to triboplasma, which is observed in additive-free polycrystalline diamond, ordinary single crystal diamond, and the like, can be suppressed. Therefore, the polycrystalline diamond of the present embodiment can be expected to have high performance for processing insulating objects such as ceramics, plastics, glass, and quartz.

<< Embodiment 2: Method for producing polycrystalline diamond >>
With reference to FIG. 7, in the method for producing polycrystalline diamond according to the present embodiment, carbon and boron dispersed in the crystal grains of the carbon at the atomic level and 90 atomic% or more thereof exists as an isolated substitution type. The first step S10 for preparing graphite containing a boron compound, hydrogen, and oxygen, the second step for filling the container with the graphite in an inert gas atmosphere, and the graphite in the container. The boron compound includes an oxygen-containing boron compound, which comprises a third step of converting to diamond by pressure heat treatment. The method for producing polycrystalline diamond according to the present embodiment has high abrasion resistance because it can maintain a high-hardness diamond structure inside and form an oxide film as a protective film for protecting the surface. Crystalline diamond can be produced.

<First step>
The first step S10 contains carbon, boron dispersed in the crystal grains of the carbon at the atomic level, and 90 atomic% or more of the carbon exists as an isolated substitution type, a boron compound, hydrogen, and oxygen. From the viewpoint of efficiently producing graphite, it is preferable to include a first sub-step and a second sub-step. Further, the first step S10 may further include a third sub-step from the viewpoint that the graphite contains hydrogen and oxygen. Here, in the first sub-step, one of two types of first sub-steps having different methods can be selected.

(1st sub process)
The first α sub-step, which is the first method selected as the first sub-step, is a liquid containing at least one of an organic compound containing graphite, graphene, graphene oxide, and a six-membered ring of carbon, and boron, hydrogen, and oxygen. This is a sub-step of obtaining a mixture by mixing the first organic compound of No. 1 and a liquid second organic compound containing hydrogen and oxygen. The first α sub-step is advantageous in that the yield of the graphite is high.

The first β sub-step, which is the second method selected as the first sub-step, comprises at least one of a liquid first organic compound containing boron, hydrogen and oxygen and a liquid third organic compound containing boron, hydrogen and This is a sub-step of obtaining a mixture by mixing with a liquid second organic compound containing oxygen. The first β sub-step is advantageous in that the mixture is excellent in uniform dispersibility.

At least one of graphite, graphene, graphene oxide, and an organic compound containing a six-membered ring of carbon increases the yield of graphite. Here, the six-membered ring of carbon includes an aromatic ring such as benzene and an aliphatic ring such as hexane.

The first organic compound is preferably at least one of trimethyl borate and triethyl borate. Trimethyl borate (melting point -29 ° C., boiling point 69 ° C.) and triethyl borate (melting point -85 ° C., boiling point 117 ° C.) are easy to handle because they are liquid in a wide temperature range including room temperature (for example, 25 ° C.). Since the content of boron, hydrogen and oxygen in one molecule is high, boron, hydrogen and oxygen can be added efficiently.

Alcohols are preferable as the second organic compound. Alcohols are easy to handle because they are liquid in a wide temperature range including room temperature (for example, 25 ° C.), are also suitable as a solvent, and are efficiently boron because of the high content of hydrogen and oxygen in one molecule. , Hydrogen and oxygen can be added. From this point of view, alcohols include methanol (melting point -97.78 ° C., boiling point 64.65 ° C.), ethanol (melting point -114.5 ° C., boiling point 78.37 ° C.), 1-propanol (melting point -126.5 ° C.). , Boiling point 97.15 ° C.), 2-propanol (melting point −89.5 ° C., boiling point 82.4 ° C.) and the like are preferable.

The third organic compound is preferably trialkylborane typified by triethylborane. Since these are liquid in a wide temperature range including room temperature (for example, 25 ° C.), they are easy to handle, and since the content of boron in one molecule is high, boron can be added efficiently.

(Second sub-process)
The second sub-step is a sub-step of forming the graphite by thermally decomposing the mixture at 1500 ° C. or higher and 1800 ° C. or lower. By such a sub-step, the graphite can be efficiently obtained from the mixture. From the viewpoint of promoting the formation of the graphite and suppressing the escape of hydrogen and oxygen from the graphite, the conditions for thermal decomposition of the mixture are preferably in an inert gas atmosphere, preferably 0.1 atm or more and 2 atm or less. It is preferably 1500 ° C. or higher and 1800 ° C. or lower. Here, the inert gas refers to a gas that does not react with the organic compound and the graphite when forming the graphite and converting the graphite into polycrystalline diamond, for example, Ar (argon) gas, He ( Helium gas, Xe (xenone) gas and the like are suitable.

<4th process>
The method for producing polycrystalline diamond according to the present embodiment preferably further includes a fourth step after the first step and before the second step described later. The fourth step is a step in which the A step, the B step, and the C step are repeated a plurality of times in this order. Step A is a step of crushing the graphite into a crushed body, step B is a step of molding the crushed body into a molded body, and step C is a step of thermally decomposing the molded body at 1500 to 1800 ° C. This is a step of preparing the above graphite again. This makes it possible to avoid mixing of trace impurities such as _{B 4 C as much as possible.} Whether or not B ₄ C is mixed in the graphite can be confirmed by, for example, the presence or absence of a peak derived from _{B 4} C using an X-ray diffractometer.

The method for producing polycrystalline diamond according to the present embodiment is either after the first step and / or after the fourth step, and is as follows before the second step described later. Can be included. That is, it is a step of impregnating the graphite prepared in the first step or the fourth step with at least one of hydrogen and oxygen under vacuum conditions. By such a step, at least one of hydrogen and oxygen can be further added to the graphite in a desired amount. The vacuum conditions are not particularly limited, but are preferably 10 Pa or less, and more preferably 1 Pa or less, from the viewpoint of reducing the mixing of trace impurities. The ambient temperature is preferably 600 ° C. or lower, more preferably 300 ° C. or lower, from the viewpoint of suppressing carbon oxidation. The method of incorporating hydrogen and oxygen into the graphite under vacuum conditions is a method capable of introducing at least one of hydrogen and oxygen into the graphite under the vacuum conditions in a single form or a composite form into polycrystalline diamond. There are no particular restrictions.

The dispersed state and existing form of boron, boron compound, hydrogen and oxygen in the graphite can be confirmed by the same method as the method for confirming the dispersed state and existing form of these elements in the polycrystalline diamond. Regarding "dispersion at the atomic level", "isolated substitution type" or "penetration type", atomic concentrations of boron, hydrogen and oxygen in boron and boron compounds, and concentrations of trace impurities, the above-mentioned polycrystalline diamond Each can be confirmed by the same method as the confirmation method in.

Among the trace impurities of graphite, the atomic concentration of the transition metal is preferably not less than ^{the detection limit of SIMS and ICP-MS (less than 1 × 10 15} cm ^-3). Further, the particle size of the graphite is preferably 10 μm or less, preferably 1 μm, from the viewpoint of forming a polycrystalline diamond having a small particle size of 1 to 500 nm and a uniform distribution of boron, boron compound, hydrogen and oxygen. It is more preferable that it is as follows.

_{In the graphite, the concentration of BC 5} among the trace impurities is in the range where the diffraction angle 2θ in the X-ray diffraction measurement is in the range of 0 ° to 90 °, and the BC _{5 is obtained with respect to the total area of all the diffraction peaks derived from diamond.} The total area of all diffraction peaks of origin is less than 1%. The concentration of BC ₅ is preferably such that the above-mentioned area ratio is less than 0.1%, and most preferably 0%. Further, _{the concentration of B 4} C is such that all the diffractions derived from _{B 4} C are compared with the total area of all the diffraction peaks derived from diamond in the range where the diffraction angle 2θ in the X-ray diffraction measurement is in the range of 0 ° to 90 °. The total area of the peak is less than 1%. The concentration of B ₄ C is preferably such that the above-mentioned area ratio is less than 0.1%, and most preferably 0%. The BC ₅ and B ₄ C concentrations can be measured using the above-mentioned X-ray diffractometer under the above-mentioned conditions.

^{The density of the graphite is preferably 0.8 g / cm 3} or more, preferably 1.4 g / cm, from the viewpoint of reducing the volume change when converting graphite to polycrystalline diamond in the third step described later and increasing the yield. ³ to 2.0 g / cm ³ or less is more preferable.

<Second step>
The second step S20 is a step of putting the graphite into the container under an inert gas atmosphere. By putting the graphite in a predetermined container (high-pressure press cell) under an inert gas atmosphere, it is possible to prevent trace impurities from being mixed into the graphite and the polycrystalline diamond formed. Here, the inert gas is not particularly limited as long as it is a gas capable of suppressing the mixing of trace impurities into the graphite and the polycrystalline diamond formed, and is Ar (argon) gas, Kr (krypton) gas, He (helium). ) Gas and the like.

<Third step>
The third step S30 is a step of converting the graphite into diamond by pressure heat treatment in the container. In the third step S30, when the graphite is converted into the polycrystalline diamond, the graphite is directly converted by directly heat-treating the graphite from the viewpoint of suppressing the mixing of trace impurities into the formed polycrystalline diamond. That is, it is preferable to perform conversion without adding a sintering aid and / or a catalyst or the like.

In the pressure heat treatment in the third step S30, boron is dispersed at the atomic level and 90 atomic% or more of the whole is contained in the crystal of polycrystalline diamond in the isolated substitution type, and the boron compound, hydrogen and oxygen are isolated substitution type. Alternatively, from the viewpoint of preferably producing the polycrystalline diamond contained in the penetration type, the conditions of 6 GPa or more and 1200 ° C. or higher are preferable, and the conditions of 8 GPa or more and 30 GPa or less and 1500 ° C. or higher and 2300 ° C. or lower are more preferable. The pressure heat treatment is preferably 6 GPa or more, more preferably 8 GPa, so that graphite can be directly converted into polycrystalline diamond. The pressure heat treatment is preferably 30 GPa or less, so that graphite can be directly converted into polycrystalline diamond without volatilizing each element. Further, preferably, the temperature is 1200 ° C. or higher, so that graphite can be directly converted into polycrystalline diamond. Preferably, the temperature is 2300 ° C. or lower, so that graphite can be directly converted into polycrystalline diamond without volatilizing each element.

From the above, the method for producing polycrystalline diamond according to the present embodiment can produce polycrystalline diamond having high oxidation resistance, sliding characteristics and wear resistance, and a low coefficient of friction. The polycrystalline diamond is manufactured in an arbitrary shape and thickness having a diameter of φ15 mm and a thickness of about 15 mm. For example, when the volume density of graphite ^{is about 1.8 g / cm 3} , the polycrystalline diamond shrinks to 70 to 80% of the volume of the graphite by pressure heat treatment, but the shape becomes the same as or almost the same as that of graphite. ..

<< Embodiment 3: Scribe tool >>
The scribe tool according to the present embodiment can be created using the polycrystalline diamond of the first embodiment. Since the scribe tool of the present embodiment is formed by using the polycrystalline diamond of the first embodiment, it has high wear resistance.

<< Embodiment 4: Scribe wheel >>
The scribe wheel according to the present embodiment can be produced by using the polycrystalline diamond of the first embodiment. Since the scribe wheel of the present embodiment is formed by using the polycrystalline diamond of the first embodiment, it has high wear resistance.

<< Embodiment 5: Dresser >>
The dresser according to the present embodiment can be made using the polycrystalline diamond of the first embodiment. Since the dresser of the present embodiment is formed by using the polycrystalline diamond of the first embodiment, it has high wear resistance.

<< Embodiment 6: Rotating tool >>
The rotary tool according to the present embodiment can be created by using the polycrystalline diamond of the first embodiment. Since the rotary tool of the present embodiment is formed by using the polycrystalline diamond of the first embodiment, it has high wear resistance.

<< Embodiment 7: Wire drawing die >>
The wire drawing die according to the present embodiment can be produced by using the polycrystalline diamond of the first embodiment. Since the wire drawing die of the present embodiment is formed by using the polycrystalline diamond of the first embodiment, it has high wear resistance.

<< Embodiment 8: Cutting tool >>
The cutting tool according to the present embodiment can be created by using the polycrystalline diamond of the first embodiment. Since the cutting tool of the present embodiment is formed by using the polycrystalline diamond of the first embodiment, it has high wear resistance.

<< Embodiment 9: Electrode >>
The electrode according to the present embodiment can be produced by using the polycrystalline diamond of the first embodiment. Since the electrode according to the present embodiment is formed by using the polycrystalline diamond of the first embodiment, it has high wear resistance.

<< Embodiment 10: Processing method >>
In the processing method according to the present embodiment, the object can be processed using the polycrystalline diamond of the first embodiment. In the processing method according to the present embodiment, the object is processed using the polycrystalline diamond of the first embodiment, so that the object can be processed efficiently and at low cost.

In the processing method according to the present embodiment, the object is preferably an insulator. In such a processing method, since the object is processed using the polycrystalline diamond of the first embodiment having conductivity, even if the object is an insulator, it is efficient without causing abnormal wear due to triboplasma or the like. The object can be processed well at low cost.

In the processing method according to the present embodiment, the insulator as an object preferably has a resistivity of 100 kΩ · cm or more. In such a processing method, since the object is processed using the polycrystalline diamond of the first embodiment having conductivity, even if the object is an insulator having a resistivity of 100 kΩ · cm or more, etching by triboplasma is performed. The object can be processed efficiently and at low cost without generating it.

(Example I: Production of polycrystalline diamond)
1. 1. Preparation of Graphite In Examples 1 to 5, graphite containing boron, boron compounds (specifically, boron oxide and boric acid), hydrogen and oxygen was prepared by the following first step. First, a commercially available flask (volume: 100 mL) is degassed and replaced in an argon atmosphere, and then trimethyl borate as a liquid first organic compound and methanol as a liquid second organic compound are each 1: 0.1. , 1: 0.05, 1: 0.01, 1: 0.005 and 1: 0.001 to give the first mixture. High-purity graphite (purity: 99.995% by mass) or graphene oxide of 4N or more was added to the first mixture, and the mixture was kept at 60 ° C. and stirred for 24 hours to obtain a second mixture. Next, the second mixture was recovered from the flask, degassed in vacuum, and thermally decomposed under the conditions of 1800 ° C. and 13 kPa in an argon atmosphere, whereby the maximum particle size of Examples 1 to 5 was 1 μm or less. The above graphite was obtained.

In Comparative Examples 1 to 3, graphite containing boron but substantially free of hydrogen and oxygen was prepared by the following steps. First, high-purity graphite (purity: 99.995% by mass) having a maximum particle size of 500 nm or less and 4N or more and B ₄ C having a maximum particle size of 100 nm or less are subjected to halogenation treatment at 1: 0.1 and 1: respectively. The graphite having a maximum particle size of 1 μm or less is obtained by mixing at a volume ratio of 0.05 and 1: 0.01, and repeating molding, sintering (sintering conditions are 1800 ° C. and 1 kPa) and pulverization 20 times. Got

2. Storage of Graphite in a Container After processing the above graphite into a tablet shape, it was sealed in a container (high-pressure press cell: cylindrical shape with a diameter of φ10 mm and a height of 10 mm) with Ar gas.

3. 3. Conversion of Graphite to Polycrystalline Diamond The graphite was directly converted to polycrystalline diamond by placing the container containing the graphite in a pressurized heat device and performing a pressure heat treatment under the conditions of 16 GPa and 2100 ° C. Regarding the obtained polycrystalline diamonds of Comparative Examples 1 to 3 and Examples 1 to 5, it was determined that boron was dispersed at the atomic level and 90% or more of the total was contained in an isolated substitution type. And confirmed by TOF-SIMS. Further, regarding the obtained polycrystalline diamonds of Examples 1 to 5, TEM, NEXAFS (X-ray absorption fine structure near the absorption edge) and TEM, NEXAFS (X-ray absorption fine structure near the absorption edge) and Confirmed by TOF-SIMS. Further, it was confirmed by TOF-SIMS that an oxide film was formed as a protective film on the surface of the polycrystalline diamonds of Examples 1 to 5. Further, for the polycrystalline diamonds of Comparative Examples 1 to 3 and Examples 1 to 5, their boron atom concentration, hydrogen atom concentration and oxygen atom concentration were measured by SIMS, and their oxygen-containing boron compounds (boron oxide and boric acid) were measured. ), _{The concentrations of BC 5} and B ₄ C were measured by X-ray diffraction measurement, and the results are summarized in Table 1. In Table 1, the detection limit of the atomic concentration of oxygen was ^{less than 1 × 10 16} cm ^-3 , and the detection limit of the atomic concentration of hydrogen was less than ^{1 × 10 17} cm ^-3.

Confirmation of the dispersion state of boron at the atomic level by TEM was carried out under known conditions.
The conditions for confirming the isolated substitution type or the invasion type of the added element by SIMS, and the measurement conditions for the concentration were as follows.
Measuring device: CAMECA IMS-7f
Primary ion species: Cs +
Primary acceleration voltage: 15.0 kV
Detection area: 30 (μmφ)
Measurement accuracy: ± 40% (2σ).

The conditions for confirming the isolated substitution type or the invasion type of the added element by TOF-SIMS and the measurement conditions for the concentration were as follows.
Measuring device: TOF-SIMS mass spectrometer (flying time secondary ion mass spectrometer)
Primary ion source: Bismuth (Bi)
Primary acceleration voltage: 25 kV.

The X-ray diffraction measurement conditions for measuring the concentrations of BC ₅ and B _{4 C were as follows.}
Characteristic X-ray: Cu-Kα wire tube voltage: 30 kV
Tube current: 20mA
X-ray diffraction method: θ-2θ method X-ray irradiation method: Irradiate X-rays using a pinhole collimator.

(Example II: Creation and evaluation of scribe tool)
Using the polycrystalline diamond of Comparative Example 2 of Example I, a scribe tool having a tip of 4 points (square plane shape) was prepared. Using the created scribe tool, 200 scribe grooves having a length of 50 mm were formed on the sapphire substrate with a load of 20 gf. After that, the amount of wear of the polycrystalline diamond at the tip of the scribing tool was 0.2 times less than that of the Ib-type single crystal diamond scribing tool when observed with an electron microscope. Further, when a scribe tool was prepared in the same manner as above using the polycrystalline diamond of Example 2 of Example I and the same experiment was performed, the amount of wear thereof was higher than that of the scribe tool made of Ib type single crystal diamond. It was 0.02 times, which was extremely small, 0.1 times that of the polycrystalline diamond scribing tool of Comparative Example 2. Further, it was confirmed by TOF-SIMS that an oxide film was formed as a protective film on the surface of the scribe tool prepared by using the polycrystalline diamond of Example 2 of Example I. The same effect was confirmed for the scribe wheel including the scribe tool prepared by using the polycrystalline diamonds of Comparative Example 2 and Example 2 of Example I, respectively.

(Example III: Creation and evaluation of dresser)
Using the polycrystalline diamond of Comparative Example 2 of Example I, a dresser having a single point (conical shape) at the tip was prepared. The prepared dresser was worn using a WA (Hofite Alumina) grindstone in a wet manner under the conditions that the peripheral speed of the grindstone was as low as 30 m / sec and the depth of cut was 0.05 mm. After that, the amount of wear of the dresser was measured by a height gauge meter and found to be 0.3 times less than that of the dresser made of Ib type single crystal diamond. Further, when a dresser was prepared in the same manner as above using the polycrystalline diamond of Example 2 of Example I and the same experiment was performed, the amount of wear thereof was 0 as compared with the dresser made of Ib type single crystal diamond. It was 0.03 times, 0.1 times less than that of the polycrystalline diamond dresser of Comparative Example 2. Further, it was confirmed by TOF-SIMS that an oxide film was formed as a protective film on the surface of the dresser prepared by using the polycrystalline diamond of Example 2 of Example I.

(Example IV: Creation and evaluation of rotary tool)
Using the polycrystalline diamond of Comparative Example 2 of Example I, a drill having a diameter of φ1 mm and a blade length of 3 mm was prepared. Using the prepared drill, a hole was made in a cemented carbide (WC-Co) plate having a thickness of 1.0 mm under the conditions of a rotation speed of 4000 rpm and a feed of 2 μm / rotation. The number of holes that could be drilled before the drill was worn or damaged was five times as large as that of an Ib-type single crystal diamond drill. Further, when a drill was prepared in the same manner as above using the polycrystalline diamond of Example 2 of Example I and the same experiment was performed, the holes that could be drilled before the drill was worn or damaged were found. The number was extremely large, 50 times that of the Ib type single crystal diamond drill and 10 times that of the polycrystalline diamond dresser of Comparative Example 2. Further, it was confirmed by TOF-SIMS that an oxide film was formed as a protective film on the surface of the drill, which is a rotary tool prepared by using the polycrystalline diamond of Example 2 of Example I.

(Example V: Creation and evaluation of cutting tool I)
By using the same method as in Examples 1 to 5 of Example I, the bulk density was 2.0 g / cm ³ , the atomic concentration of boric acid measured by ICP-MS was 1 × 10 ²¹ cm ^-3 , and SIMS. A graphite having an atomic concentration of oxygen measured by 1 × 10 ¹⁸ cm ^-3 and an atomic concentration of hydrogen of 2.5 × 10 ¹⁸ cm ^{-3 was prepared.} This graphite was directly converted to polycrystalline diamond by heat treatment under pressure at 15 GPa and 2200 ° C. using an isotropic high pressure generator. The particle size of the obtained polycrystalline diamond was 10 nm to 100 nm, respectively.

Using this polycrystalline diamond, a cutting tool body was produced by a conventionally known method. This cutting tool body is joined in an inert atmosphere using an active brazing material, the surface of polycrystalline diamond is polished, and then the flank surface is cut by electric discharge machining to have a corner R of 0.4 mm and a flank angle of 11 °. A cutting tool (test tool 1) provided with an R bite having a rake angle of 0 ° was created. For comparison, a conventional tool using sintered diamond containing a cobalt (Co) binder (comparative tool A) was similarly prepared by electric discharge machining. The ridgeline accuracy of the cutting edge due to electric discharge machining was about 2 μm to 5 μm in the comparison tool A using sintered diamond, depending on the particle size of the diamond abrasive grains contained in it, whereas the polycrystalline diamond was used. The tool used (test tool 1) was as good as 0.5 μm or less. The machining time was also the same as that of the comparison tool A.

Furthermore, a cutting tool (test tool 2) in which the flank surface is processed by polishing to provide an R bite with a corner R of 0.4 mm, a flank angle of 11 °, and a rake angle of 0 °, and a cutting tool using additive-free polycrystalline diamond (comparison). A cutting tool (comparative tool C) using tool B) and Ib type single crystal diamond was prepared, and the cutting evaluation of the test contents shown in the following paragraph was performed. For both the test tool 2 and the comparison tool B, the cutting edge ridge line accuracy was 0.1 μm or less, and a precise cutting edge accuracy was obtained.

Next, each of the test tools 1 and 2 and the comparison tools A to C was subjected to an intermittent cutting evaluation test by turning under the following conditions.
-Tool shape: Corner R 0.4 mm, clearance angle 11 °, rake angle 0 °
-Work material: Material-Aluminum alloy A390
-Cutting fluid: Water-soluble emulsion-Cutting conditions: Cutting speed Vc = 800 m / min, cutting ap = 0.2 mm, feed rate f = 0.1 mm / rotation-Cutting distance: 10 km.

After performing the above cutting evaluation test, the tool cutting edge was observed and the wear state was confirmed. As a result, the comparative tool A had a large flank wear amount of 45 μm, and the cutting edge shape was impaired. The amount of flank wear was as good as 2 μm. On the other hand, the polished finish test tool 2 has a wear amount of 0.5 μm, which is very good as compared with the wear amount of the comparative tool B of 3.5 μm and the wear amount of the comparative tool C of 3.5 μm. It was found that the wear resistance characteristics were equal to or better than those of the added polycrystalline diamond, and the tool life was excellent. Further, it was confirmed by TOF-SIMS that an oxide film was formed as a protective film on the surfaces of the test tool 1 and the test tool 2, which are cutting tools produced by using the polycrystalline diamond of this example.

(Example VI: Creation and evaluation of cutting tool II)
By using the same method as in Examples 1 to 5 of Example I, the bulk density was 2.0 g / cm ³ , the atomic concentration of boric acid measured by ICP-MS was 1 × 10 ¹⁹ cm ^-3 , and SIMS. A graphite having an atomic concentration of oxygen measured by 1 × 10 ¹⁸ cm ^-3 and an atomic concentration of hydrogen of 2.5 × 10 ¹⁸ cm ^{-3 was prepared.} This graphite was directly converted to polycrystalline diamond by heat treatment under pressure at 15 GPa and 2200 ° C. using an isotropic high pressure generator. The particle size of polycrystalline diamond was 10 nm to 100 nm, respectively.

This polycrystalline diamond was joined to the cutting tool body using an active brazing material in an inert atmosphere, and the surface of the polycrystalline diamond was polished. Further, a tool using a polycrystalline diamond whose flank surface is polished (test tool 3), a tool using an additive-free polycrystalline diamond (comparative tool B), and a tool using an Ib type single crystal diamond (comparative tool C). ) Was created, and a cutting evaluation test having the same contents as in Example V was performed.

After performing the above cutting evaluation test, the tool cutting edge was observed and the wear state was confirmed. As a result, the wear amount of the test tool 3 was 0.1 μm, the wear amount of the comparison tool B was 3.5 μm, and the wear amount of the comparison tool C was 3.5 μm. It was found that it was very small and good as compared with 3.5 μm, showed wear resistance characteristics equal to or higher than those of the conventional additive-free polycrystalline diamond, and had excellent tool life. Further, it was confirmed by TOF-SIMS that an oxide film was formed as a protective film on the surface of the test tool 3 which is a cutting tool prepared by using the polycrystalline diamond of this example.

(Example VII: Creation and evaluation of cutting tool III)
By using the same method as in Examples 1 to 5 of Example I, the bulk density was 1.9 g / cm ³ , the atomic concentration of boric acid measured by ICP-MS was 1 × 10 ²¹ cm ^-3 , and SIMS. A graphite having an atomic concentration of oxygen measured by 1 × 10 ¹⁸ cm ^-3 and an atomic concentration of hydrogen of 2.5 × 10 ¹⁸ cm ^{-3 was prepared.} This graphite was directly converted into polycrystalline diamond by heat treatment under pressure at 15 GPa and 2200 ° C. using an isotropic high pressure generator. The particle size of the obtained polycrystalline diamond was 10 nm to 100 nm, respectively. The Knoop hardness of this polycrystalline diamond was 120 GPa. A 3 mm × 1 mm square test piece was cut out from this polycrystalline diamond, and the electrical resistance was measured and found to be 10 Ω.

This conductive polycrystalline diamond is joined to the cutting tool body using an active brazing material in an inert atmosphere, the surface of the polycrystalline diamond is polished, and then the flank surface is cut by electric discharge machining to form a twisted shape. A ball end mill (test tool 4) having a diameter of 0.5 mm and having two cutting tools was prepared. For comparison, a conventional tool using sintered diamond containing a cobalt (Co) binder (comparative tool A-2) was similarly prepared by electric discharge machining. The ridgeline accuracy of the cutting edge due to electric discharge machining was about 2 μm to 5 μm depending on the particle size of the diamond abrasive grains contained in the comparative tool A-2 using sintered diamond, whereas the polycrystal The tool using diamond (test tool 4) was as good as 0.03 μm or less. Further, using additive-free polycrystalline diamond, an end mill shape having the same shape was created by laser machining, and a tool (comparative tool B-2) in which the flank surface was locally polished to finish the cutting edge quality was created.

Next, the test tool 4, the comparison tool A-2, and the comparison tool B-2 were subjected to an intermittent cutting evaluation test under the following conditions.
-Tool shape: Diameter φ0.5 mm, 2-flute, ball end mill-Work material: Material-STAVAX cemented carbide (WC-12% Co)
-Cutting fluid: White kerosene-Cutting conditions: Tool rotation speed 420000 rpm, depth of cut ap = 0.003 mm
Feed rate f = 120 mm / min.

When the cutting evaluation test with the above contents was performed, the tool life of the test tool 4 was 5 times the tool life of the comparative tool AS and 1.5 times the tool life of the comparative tool B-2, which were very high. It was good. Further, it was confirmed by TOF-SIMS that an oxide film was formed as a protective film on the surface of the test tool 4, which is a cutting tool produced by using the polycrystalline diamond of this example.

(Example VIII: Preparation and evaluation of wire drawing die)
Using the polycrystalline diamonds of Comparative Example 2 and Example 2 of Example I, respectively, a wire drawing die having a diameter of φ0.5 mm was prepared. The life was defined as the time until the wire was worn to a diameter of φ0.48 mm when the wire was drawn at a wire drawing speed of 1 km / min. The life of the wire drawing die prepared by using the polycrystalline diamond of Example 2 of Example I was 10 times the life of the wire drawing die prepared by using the polycrystalline diamond of Comparative Example 2 of Example I. ..

(Example IX: Preparation and evaluation of electrode substrate)
Using the polycrystalline diamonds of Comparative Example 2 and Example 2 of Example I, respectively, an electrode substrate having a length of 9 mm, a width of 5 mm, and a thickness of 1.0 mm was prepared. The electrode substrate prepared using the polycrystalline diamond of Example 2 of Example I has a low resistivity of 10 mΩ · cm and shows good conductivity, and the potential window is in the range of 3 V in a 0.1 M KOH solution. It was found that it has high performance as a chemical electrode. It was found that the electrode substrate prepared using the polycrystalline diamond of Comparative Example 1 of Example I had a high resistivity of 10 MΩ · cm and could not be used as an electrode.

The embodiments disclosed this time should be considered to be exemplary in all respects and not restrictive. The scope of the present invention is indicated by the scope of claims rather than the above-described embodiment, and is intended to include the meaning equivalent to the scope of claims and all modifications within the scope.

S10 1st process S20 2nd process S30 3rd process

Claims (29)

It is a polycrystalline diamond whose basic composition is a single-phase diamond.
The polycrystalline diamond is composed of a plurality of crystal grains.
The polycrystalline diamond contains boron, a boron compound, hydrogen, oxygen, and the balance is carbon and trace impurities.
The boron is dispersed in the crystal grains at the atomic level, and 90 atomic% or more of the boron is present as an isolated substitution type.
The boron compound, the hydrogen and the oxygen are present in the crystal grains as isolated substitution type or invasion type.
The boron compound contains an oxygen-containing boron compound.
The crystal grains have a particle size of 500 nm or less and have a particle size of 500 nm or less.
The surface of the polycrystalline diamond is coated with a protective film .
The protective film is a polycrystalline diamond _{containing BO x} clusters and at least one of O and OH that is the oxygen termination of the carbon. The polycrystalline diamond according to claim 1, wherein 99 atomic% or more of the boron is present in the crystal grains as an isolated substitution type. The polycrystalline diamond according to claim 1 or 2, wherein the boron and the boron in the boron compound have a total atomic concentration of 1 × 10 ¹⁴ cm ^-3 or more and 1 × 10 ²² cm ^{-3 or less.} .. The polycrystalline diamond according to any one of claims 1 to 3, wherein the hydrogen has an atomic concentration of 1 × 10 ¹⁷ cm ^-3 or more and 1 × 10 ²⁰ cm ^{-3 or less.} The polycrystalline diamond according to any one of claims 1 to 4, wherein the oxygen has an atomic concentration of 1 × 10 ¹⁷ cm ^-3 or more and 1 × 10 ²⁰ cm ^{-3 or less.} The polycrystalline diamond according to any one of claims 1 to 5 , wherein the polycrystalline diamond has a coefficient of dynamic friction on its surface of 0.06 or less. The polycrystalline diamond according to any one of claims 1 to 6 , wherein the polycrystalline diamond has a coefficient of dynamic friction on its surface of 0.05 or less. The polycrystalline diamond according to any one of claims 1 to 7 , wherein the protective film contains precipitates precipitated from the crystal grains. It is a polycrystalline diamond whose basic composition is a single-phase diamond.
The polycrystalline diamond is composed of a plurality of crystal grains.
The polycrystalline diamond contains boron, a boron compound, hydrogen, oxygen, and the balance is carbon and trace impurities.
The boron is dispersed in the crystal grains at the atomic level, and 99 atomic% or more of the boron is present as an isolated substitution type.
The boron compound, the hydrogen and the oxygen are present in the crystal grains as isolated substitution type or invasion type.
The boron compound contains an oxygen-containing boron compound.
The crystal grains have a particle size of 500 nm or less and have a particle size of 500 nm or less.
The surface of the polycrystalline diamond is coated with a protective film.
The total atomic concentration of boron in the boron and the boron compound is 1 × 10 ¹⁴ cm ^-3 or more and 1 × 10 ²² cm ^-3 or less.
The hydrogen has an atomic concentration of 1 × 10 ¹⁷ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less.
The oxygen has an atomic concentration of 1 × 10 ¹⁷ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less .
Before SL polycrystalline diamond, the dynamic friction coefficient of the surface is 0.05 or less,
The protective film contains a BO _x cluster and at least one of O and OH that is the oxygen termination of the carbon.
The protective film is a polycrystalline diamond containing precipitates precipitated from the crystal grains. First, a graphite containing carbon, boron dispersed in the crystal grains of the carbon at the atomic level and 90 atomic% or more of the carbon is present as an isolated substitution type, a boron compound, hydrogen, and oxygen is prepared. Process and
The second step of filling the container with the graphite in an inert gas atmosphere, and
In the container, the third step of converting the graphite into diamond by pressure heat treatment is included.
The boron compound is a method for producing polycrystalline diamond, which comprises a boron compound containing oxygen. The first step involves at least one of an organic compound containing graphite, graphene, graphene oxide, and a six-membered ring of carbon, a liquid first organic compound containing boron, hydrogen, and oxygen, and a liquid containing hydrogen and oxygen. The method for producing a polycrystalline diamond according to claim 10 , further comprising a first α sub-step of obtaining a mixture by mixing with a second organic compound. In the first step, at least one of a liquid first organic compound containing boron, hydrogen and oxygen and a liquid third organic compound containing boron and a liquid second organic compound containing hydrogen and oxygen are mixed. The method for producing a polycrystalline diamond according to claim 10 , further comprising a first β sub-step of obtaining a mixture. The method for producing polycrystalline diamond according to claim 11 or 12 , wherein the first organic compound is at least one of trimethyl borate and triethyl borate. The method for producing polycrystalline diamond according to any one of claims 11 to 13 , wherein the second organic compound is an alcohol. The first step according to any one of claims 11 to 14 , further comprising a second sub-step of forming the graphite by thermally decomposing the mixture at 1500 ° C. or higher and 1800 ° C. or lower. A method for producing polycrystalline diamond. After the first step and before the second step, the fourth step is further included.
The fourth step is a step of repeating the A step, the B step, and the C step a plurality of times in this order.
The step A is a step of pulverizing the graphite into a pulverized body.
The B step is a step of molding the pulverized body into a molded body.
The production of polycrystalline diamond according to any one of claims 10 to 15 , wherein the step C is a step of preparing the graphite again by thermally decomposing the molded product at 1500 to 1800 ° C. Method. The method for producing polycrystalline diamond according to any one of claims 10 to 16 , wherein in the third step, the graphite is directly subjected to pressure heat treatment in a pressure heating device. The method for producing polycrystalline diamond according to any one of claims 10 to 17 , wherein the pressure heat treatment is performed under the conditions of 6 GPa or more and 1200 ° C. or more. The method for producing polycrystalline diamond according to any one of claims 10 to 18 , wherein the pressure heat treatment is performed under the conditions of 8 GPa or more and 30 GPa or less and 1500 ° C. or more and 2300 ° C. or less. A scribe tool formed by using the polycrystalline diamond according to any one of claims 1 to 9. A scribe wheel formed by using the polycrystalline diamond according to any one of claims 1 to 9. A dresser formed by using the polycrystalline diamond according to any one of claims 1 to 9. A rotary tool formed by using the polycrystalline diamond according to any one of claims 1 to 9. A wire drawing die formed by using the polycrystalline diamond according to any one of claims 1 to 9. A cutting tool formed by using the polycrystalline diamond according to any one of claims 1 to 9. An electrode formed by using the polycrystalline diamond according to any one of claims 1 to 9. A processing method for processing an object using the polycrystalline diamond according to any one of claims 1 to 9. The processing method according to claim 27 , wherein the object is an insulator. 28. The processing method according to claim 28 , wherein the insulator has a resistivity of 100 kΩ · cm or more.

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