JP2018087118A - Polycrystalline diamond and manufacturing method therefor, processing method using scribe tool, scribe wheel, dresser, rotation tool, orifice for water jet, wire drawing die, cutting tool, electrode and polycrystalline diamond - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide polycrystalline diamond covered with a water insoluble protective film and capable of suppressing tribo-plasma.SOLUTION: The polycrystalline diamond is polycrystalline diamond having a diamond single phase as a basic composition, constituted by a plurality of crystal particles, contains boron, nitrogen, silicon and the balance carbon and a trace amount of impurities, in which the boron is dispersed in the crystal particles at atom level, 90 atom% or more thereof exists as an isolated substituted type, the nitrogen and the silicon exist as the isolated substituted type or an immersion type in the crystal particles and the crystal particles have particle diameter of 500 nm or less.SELECTED DRAWING: None

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 scribe tools, scribe wheels, dressers, rotary tools, water jet orifices, wire drawing dies, cutting tools, electrodes, and the like. The present invention further relates to a processing method using polycrystalline diamond.

  In recent years, it has become clear that nanopolycrystalline diamond (hereinafter sometimes referred to as “NPD”) has an isotropic hardness that exceeds that of natural single crystal diamond. Nanopolycrystalline diamond imparted with conductivity by adding a boron compound to such a material has been developed. Furthermore, nano-polycrystalline diamond having semiconductor characteristics based on a diamond structure has been developed by incorporating boron into the diamond crystal grains in an atomic substitution type.

  For example, in Japanese Patent Application Laid-Open No. 2012-106925 (Patent Document 1), a polycrystalline diamond containing a boron compound as an impurity and having a boron oxide protective film formed on the surface by heating in the atmosphere to improve oxidation resistance. The body has been proposed. In JP2013-028500A (Patent Document 2), the Group 3 element of the Periodic Table is atom-substituted and contained in diamond crystal grains, thereby having p-type conductivity without containing a boron compound. Nanopolycrystalline diamonds have been proposed.

JP 2012-106925 A JP 2013-028500 A

  However, the diamond polycrystal disclosed in Patent Document 1 has low hardness because the boron compound is not included in the crystal lattice of diamond, and the thermal expansion coefficient of the boron compound and diamond is different, so cracks occur at high temperatures. There was room for improvement in these respects. Since the nano-polycrystalline diamond disclosed in Patent Document 2 is oxidized when a work material such as ceramic or resin containing oxygen is processed, there is room for improvement in oxidation resistance.

  Furthermore, in the conventional nano-polycrystalline diamond, when processing an insulating work material, tripoplasma is generated between the work material and NPD and the work material tend to be worn out together. . Furthermore, since the protective film of boron oxide is water-soluble, the protective effect cannot be exhibited when an aqueous cutting fluid is used. Therefore, there is a demand for nanopolycrystalline diamond that can suppress the generation of triboplasm while suppressing the decrease in hardness and the generation of cracks, and that forms a water-insoluble protective film.

  The present invention has been proposed in view of the above circumstances, and is formed using polycrystalline diamond capable of forming a water-insoluble protective film while suppressing generation of triboplasma, a method for producing the same, and polycrystalline diamond. An object is to provide a scribe tool, a scribe wheel, a dresser, a rotating tool, a water jet orifice, a wire drawing die, a cutting tool and an electrode, and a processing method using the polycrystalline diamond.

The polycrystalline diamond according to one embodiment of the present invention is polycrystalline diamond having a basic composition of a single phase of diamond, the polycrystalline diamond is composed of a plurality of crystal grains, and the polycrystalline diamond includes boron, Ni and silicon are included, the balance is carbon and trace impurities, the boron is dispersed at the atomic level in the crystal grains, and 90 atomic% or more thereof is present as an isolated substitution type, the nitrogen and The silicon is present as an isolated substitution type or an interstitial type in the crystal grains, and the trace impurities include BC ₅ and B ₄ C, and the BC ₅ has a diffraction angle 2θ of 0 in X-ray diffraction measurement. in the range of up to 90 ° °, relative to the total area of all the diffraction peaks derived from diamond, the total area of all the diffraction peaks derived from the BC ₅ is less than 1%, Serial B ₄ C is in a range from the diffraction angle 2θ is 0 ° in the X-ray diffraction measurement to 90 °, relative to the total area of all the diffraction peaks derived from the diamond, all of the diffraction peaks of the B ₄ C-derived The total area of the crystal grains is less than 0.5%, and the crystal grains have a grain size of 500 nm or less.

The method for producing polycrystalline diamond according to one aspect of the present invention includes a first step of preparing graphite containing carbon, boron, nitrogen, silicon, and BC ₅ and B ₄ C as trace impurities, A second step of filling the container in an inert gas atmosphere, and a third step of converting the graphite into diamond by pressure heat treatment in the container, wherein the boron is contained in the crystal grains of the graphite. Dispersed at the atomic level, and 90 atomic% or more of them exist as isolated substitution types.

  According to the above, it is possible to provide a polycrystalline diamond capable of forming a water-insoluble protective film while suppressing triboplasma and a method for producing the same.

FIG. 1 is a graph showing an example of the distribution of additive elements inside the polycrystalline diamond according to the present embodiment. FIG. 2 is a graph showing changes in the amount of tool wear of a polycrystalline diamond cutting tool with respect to the cutting distance when high-purity alumina (purity: 99.9% by mass) is used as a work material. FIG. 3 is a flowchart showing the steps of the method for producing polycrystalline diamond according to the present embodiment. FIG. 4 is a flowchart for explaining a first step in the polycrystalline diamond manufacturing method according to the present embodiment.

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

[1] The polycrystalline diamond according to one aspect of the present invention is a polycrystalline diamond having a basic composition of a diamond single phase, wherein the polycrystalline diamond is composed of a plurality of crystal grains, It contains boron, nitrogen, and silicon, and the balance is carbon and trace impurities, and boron is dispersed at the atomic level in the crystal grains, and 90 atomic% or more thereof exists as an isolated substitution type, The nitrogen and silicon are present as isolated substitution type or interstitial type in the crystal grains, and the trace impurities include BC ₅ and B ₄ C, and BC ₅ is a diffraction angle in X-ray diffraction measurement. in the range of 2θ is from 0 ° to 90 °, relative to the total area of all the diffraction peaks derived from diamond, the total area of all the diffraction peaks derived from the BC ₅ is less than 1% Ri, the B ₄ C is in the range of diffraction angles 2θ in the X-ray diffraction measurement from 0 ° to 90 °, relative to the total area of all the diffraction peaks derived from the diamond, all derived from the B ₄ C The total area of the diffraction peaks is less than 0.5%, and the crystal grains have a particle size of 500 nm or less. With such a configuration, it is possible to form a water-insoluble protective film on the surface of polycrystalline diamond while suppressing triboplasma.

  [2] It is preferable that the surface of the polycrystalline diamond is covered with a protective film. Since this protective film is a water-insoluble protective film, when it is used for a tool or the like, a protective effect can be exerted against an aqueous cutting fluid.

  [3] The protective film preferably contains at least one selected from the group consisting of silicon oxide, silicon nitride, and boron nitride. Since these protective films are water-insoluble protective films, they can exhibit a protective effect against an aqueous cutting fluid when used in a tool or the like.

  [4] It is preferable that the protective film includes precipitates precipitated from the crystal grains. Since these protective films are also water-insoluble protective films, they can exert a protective effect against an aqueous cutting fluid when used in a tool or the like.

  [5] The protective film preferably has an average film thickness of 1 nm to 1000 nm. Thereby, a friction coefficient can be reduced favorably.

  [6] It is preferable that 99 atomic% or more of the boron is present in the crystal grains as an isolated substitution type. Thereby, triboplasma can be suppressed more.

[7] The boron preferably has an atomic concentration of 1 × 10 ¹⁴ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less. Thereby, triboplasma can be further suppressed.

[8] The nitrogen preferably has an atomic concentration of 1 × 10 ¹⁸ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less. Thereby, a water-insoluble protective film can be formed.

[9] The silicon preferably has an atomic concentration of 1 × 10 ¹⁸ cm ⁻³ or more and 2 × 10 ²⁰ cm ⁻³ or less. Thereby, a water-insoluble protective film can be further formed.

[10] the polycrystalline diamond 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% of the peak area of 60 cm ⁻¹ or less. Thereby, the isotropic hardness exceeding a natural single crystal diamond can be maintained.

  [11] The polycrystalline diamond preferably has a dynamic friction coefficient of 0.2 or less. Thereby, it becomes suitable when processing insulating work materials, such as ceramics and resin.

  [12] The polycrystalline diamond preferably has a dynamic friction coefficient of 0.1 or less. Thereby, it becomes more suitable when processing insulating work materials, such as ceramics and resin.

[13] A method for producing polycrystalline diamond according to one embodiment of the present invention includes a first step of preparing graphite containing carbon, boron, nitrogen, silicon, and BC ₅ and B ₄ C as trace impurities. A second step of filling the graphite into a container under an inert gas atmosphere, and a third step of converting the graphite into diamond by pressure heat treatment in the container, wherein the boron is a crystal of the graphite. It is dispersed at the atomic level in the grains, and 90 atomic% or more thereof exists as an isolated substitution type. With such a configuration, it is possible to produce polycrystalline diamond in which a water-insoluble protective film is formed on the surface while suppressing triboplasma.

  [14] The first step includes a step A, a step B, and a step C. The step A includes carbon-containing first particles having a maximum particle size of 1 μm or less and carbonization having a maximum particle size of 100 nm or less. A step of mixing boron particles, boron nitride particles having a maximum particle size of 100 nm or less, and at least one of silicon nitride particles and silicon carbide particles having a maximum particle size of 100 nm or less, and forming the mixture into a first molded body, In step B, the first molded body is heated and sintered at 2000 ° C. to 2500 ° C. to obtain the first sintered body, and then the first sintered body is pulverized into a powder having a maximum particle size of 50 μm or less. The step C is a step of preparing the graphite by pulverizing and shaping the powder until the maximum particle size is less than 1 μm, and heating and sintering at 2000 ° C. or higher and 2500 ° C. or lower. And the carbon-containing first particles include the charcoal It is preferably a carbon-containing particles, except for the boron particles and the silicon carbide particles. As a result, it is possible to efficiently produce polycrystalline diamond capable of forming a water-insoluble protective film on the surface while suppressing triboplasma.

  [15] The first step further includes a step D performed after the step B and before the step C, and the step D alternately includes the steps D1, D2, and D3 alternately. The D1 step is a step of forming the powder into a second molded body, and the D2 step is to heat-sinter the second molded body at 2000 ° C. or higher and 2500 ° C. or lower to form a second sintered body. Preferably, the step D3 is a step of pulverizing the second sintered body again into the powder having a maximum particle size of 50 μm or less. Thereby, polycrystalline diamond capable of forming a water-insoluble protective film on its surface while suppressing triboplasma can be produced more efficiently.

  [16] The step D preferably includes the step D1, the step D2, and the step D3 alternately five times or more. As a result, polycrystalline diamond capable of forming a water-insoluble protective film on the surface thereof while suppressing triboplasma can be more efficiently produced.

  [17] The step D preferably includes the step D1, the step D2, and the step D3 alternately 10 times or more. This makes it possible to most efficiently produce polycrystalline diamond capable of forming a water-insoluble protective film on the surface while suppressing triboplasma.

  [18] The first carbon-containing particles preferably include at least one selected from the group consisting of pyrolytic graphite, graphene, and an oxide of the graphene. Thereby, it can contribute from the viewpoint of a raw material to efficient manufacture of the polycrystalline diamond provided with the said effect.

  [19] In the third step, it is preferable to perform a pressure heat treatment directly on the graphite in a pressure heating apparatus. Thereby, polycrystalline diamond having a basic composition of a diamond single phase can be produced without including a binder phase (binder) made of cobalt or the like.

  [20] The pressure heat treatment is preferably performed under conditions of 6 GPa or more and 1200 ° C. or more. Thereby, the polycrystalline diamond provided with the said effect can be manufactured efficiently.

  [21] The pressure heat treatment is preferably performed under conditions of 8 GPa to 30 GPa and 1500 ° C. to 2300 ° C. Thereby, a polycrystalline diamond having the above effect can be produced more efficiently.

  [22] One embodiment of the present invention is preferably a scribe tool formed using the polycrystalline diamond. Thereby, a scribe tool can be provided using the polycrystalline diamond which formed the water-insoluble protective film on the surface, suppressing triboplasma.

  [23] One aspect of the present invention is preferably a scribe wheel formed using the polycrystalline diamond. Thereby, a scribe tool can be provided using the polycrystalline diamond which formed the water-insoluble protective film on the surface, suppressing triboplasma.

  [24] One embodiment of the present invention is preferably a dresser formed using the polycrystalline diamond. Thereby, it is possible to provide a dresser using polycrystalline diamond in which a water-soluble protective film is formed on the non-surface while suppressing triboplasma.

  [25] One aspect of the present invention is preferably a rotary tool formed using the polycrystalline diamond. Thereby, a rotary tool can be provided using the polycrystalline diamond which formed the water-insoluble protective film on the surface, suppressing a triboplasma.

  [26] One aspect of the present invention is preferably an orifice for water jet formed using the polycrystalline diamond. Thereby, the orifice for water jets can be provided using the polycrystalline diamond which formed the water-insoluble protective film on the surface, suppressing triboplasma.

  [27] One embodiment of the present invention is preferably a wire drawing die formed using the polycrystalline diamond. Thereby, a wire drawing die can be provided by using polycrystalline diamond having a water-insoluble protective film formed on the surface thereof while suppressing triboplasma.

  [28] One aspect of the present invention is preferably a cutting tool formed using the polycrystalline diamond. Thereby, a cutting tool can be provided using the polycrystalline diamond which formed the water-insoluble protective film on the surface, suppressing triboplasma.

  [29] One embodiment of the present invention is preferably an electrode formed using the polycrystalline diamond. Thereby, an electrode can be provided using polycrystalline diamond in which a water-insoluble protective film is formed on the surface while suppressing triboplasma.

  [30] The processing method according to one aspect of the present invention is preferably a processing method for processing an object using the polycrystalline diamond. Thereby, a target object can be processed using the polycrystalline diamond which formed the water-insoluble protective film on the surface, suppressing a triboplasma.

  [31] The object is preferably an insulator. Thereby, the effect which suppresses the triboplasma with which a polycrystalline diamond is provided can be exhibited suitably.

  [32] The insulator preferably has a resistivity of 100 kΩ · cm or more. Thereby, the effect which suppresses the triboplasma with which a polycrystalline diamond is provided can be exhibited more suitably.

[Details of the embodiment of the present invention]
Hereinafter, embodiments of the present invention will be described in more detail. Here, the notation of the format “A to B” in this specification means the upper and lower limits of the range (that is, A or more and B or less), and there is no unit description in A, and the unit is described only in B. In this case, the unit of A and the unit of B are the same.

  Further, in the present specification, when a compound or the like is represented by a chemical formula, when the atomic ratio is not particularly limited, it should include any conventionally known atomic ratio and should not necessarily be limited to a stoichiometric range. For example, when “SiN” is described, the ratio of the number of atoms constituting SiN is not limited to Si: N = 1: 1 of SiN, for example, and includes any conventionally known atomic ratio. The same applies to the description of compounds other than “SiN”. In this embodiment, metalloid elements such as boron (B) and silicon (Si) and nonmetallic elements such as nitrogen (N) and carbon (C) necessarily constitute a stoichiometric composition. There is no need.

≪Polycrystalline diamond≫
The polycrystalline diamond according to this embodiment has a diamond single phase as a basic composition and is composed of a plurality of crystal grains. Furthermore, polycrystalline diamond contains boron, nitrogen, and silicon, with the balance being carbon and trace impurities. Boron is dispersed at the atomic level in crystal grains, and 90 atomic% or more thereof exists as an isolated substitution type. Nitrogen and silicon exist as isolated substitution type or interstitial type in the crystal grains. Polycrystalline diamond has a particle size of 500 nm or less. Furthermore, it is preferable that the surface of the polycrystalline diamond according to this embodiment is covered with a protective film.

  Since the polycrystalline diamond according to the present embodiment has a diamond single phase as a basic composition, the polycrystalline diamond does not include a binder phase (binder) formed by either or both of a sintering aid and a catalyst, and a high temperature condition. Even underneath, degranulation does not occur due to differences in thermal expansion coefficient. Furthermore, polycrystalline diamond is a polycrystal composed of a plurality of crystal grains, and since the grain size is 500 nm or less, there is no directionality and cleavage as in single crystals, etc. It has a direct hardness and wear resistance. Since polycrystalline diamond contains boron, nitrogen, and silicon in crystal grains, the surface thereof is covered with a water-insoluble protective film. As a result, the oxidation resistance is enhanced, and the sliding characteristics and wear resistance are enhanced by reducing the friction coefficient.

Polycrystalline diamond contains BC ₅ and B ₄ C as trace impurities. BC ₅ has a total area of 1% of all diffraction peaks derived from BC ₅ with respect to the total area of all diffraction peaks derived from diamond in the range of diffraction angle 2θ in the X-ray diffraction measurement from 0 ° to 90 °. Is less than. B ₄ C has a total area of all diffraction peaks derived from B ₄ C relative to a total area of all diffraction peaks derived from diamond in the range of diffraction angle 2θ in X-ray diffraction measurement from 0 ° to 90 °. It is less than 0.5%. Due to such a low concentration of BC ₅ and B ₄ C, the polycrystalline diamond maintains good isotropic hardness and wear resistance in all directions.

  From the viewpoint of polycrystalline diamond having isotropic hardness and wear resistance in all directions, the maximum grain size of polycrystalline diamond (the grain diameter of the largest of the crystals constituting the polycrystal) is 500 nm or less. It is. The maximum grain size of polycrystalline diamond is preferably 200 nm or less. On the other hand, the minimum grain size of polycrystalline diamond may be 1 nm or more.

  When the grain diameter of the polycrystalline diamond is 500 nm or less, an effect having isotropic hardness can be obtained. Furthermore, the effect which has the mechanical strength peculiar to a diamond is acquired by being 1 nm or more. The grain size of the polycrystalline diamond is more preferably 20 nm or more and 200 nm or less. In addition, the aspect ratio of the major axis a and the minor axis b of each particle is more preferably a / b <4.

  The grain size of polycrystalline diamond can be measured by electron microscopy such as SEM and TEM. An arbitrary surface of the observation polishing surface is prepared by polishing an arbitrary surface of the polycrystalline diamond to prepare an observation polishing surface for measuring the grain size, for example, using a SEM at a magnification of 20000 times. Observe (1 field of view). Since about 120 to 200,000 crystal grains of polycrystalline diamond appear in one field of view, ten of these grains are obtained, and all of them are confirmed to be 500 nm or less. By performing this for all the fields 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 diameter of the polycrystalline diamond can also be measured by an X-ray diffraction method (XRD method) based on the following conditions.
Measuring device: Trade name (product number) “X'pert”, X-ray light source manufactured by PANalytical: Cu-Kα ray (wavelength is 1.54185 mm)
Scanning axis: 2θ
Scanning range: 20 ° ~ 120 °
Voltage: 40kV
Current: 30mA
Scan speed: 1 ° / min.
The half width is obtained from the Scherrer equation (D = Kλ / Bcos θ) after peak fitting. Here, D is the crystal grain size of diamond, B is the diffraction line width, λ is the X-ray wavelength, θ is Bragg, and K is a correction coefficient (0.9) determined from the correlation with the SEM image.

<Elements in crystal grains>
Polycrystalline diamond contains boron, nitrogen, and silicon, with the balance being carbon and trace impurities. Boron is dispersed at the atomic level in the crystal grains of polycrystalline diamond, and 90 atomic% or more thereof exists as an isolated substitution type. Nitrogen and silicon exist as isolated substitution type or interstitial type in the crystal grains of polycrystalline diamond. Therefore, a protective film is formed by the reaction of boron exposed on the surface of polycrystalline diamond with at least one of nitrogen and silicon and the reaction of these elements with oxygen in the atmosphere. Then, the surface of the polycrystalline diamond is covered with the protective film. This protective film increases the oxidation resistance of the polycrystalline diamond, and the protective film further reduces the dynamic friction coefficient, so that the sliding characteristics and wear resistance are improved. In the present embodiment, the protective film may include a precipitate formed by depositing on the surface of the polycrystalline diamond.

  In polycrystalline diamond, boron is dispersed at the atomic level, and more than 90 atomic% of the diamond exists as an isolated substitution type. Therefore, the exposed boron is oxidized when the surface is worn, so that only the surface is oxidized. A protective film is formed, and the diamond structure inside, that is, in each crystal grain, is maintained. Boron does not aggregate in the form of clusters in the crystal grains of polycrystalline diamond, nor does it aggregate at the crystal grain boundaries of polycrystalline diamond, so there is no segregation of impurities that can cause cracks due to temperature changes and impacts. Absent. Furthermore, polycrystalline diamond contributes to the suppression of tripoplasma because of its conductivity, its surface energy is lowered by the protective film on its surface, and it is easy to attract electrons inside.

  Here, in this specification, “dispersing at the atomic level” means that different elements such as boron have a finite activation energy (temperature-dependent electrical resistance) in carbon constituting the crystal grains of polycrystalline diamond. It means to disperse without changing the crystal structure of diamond, or such a state of dispersion. That is, such a dispersed state is a state in which a heterogeneous element that precipitates in isolation is not formed, and a heterogeneous compound other than diamond is not formed. “Isolated substitution type” refers to an existence form in which different elements such as boron, nitrogen, and silicon are isolated and replaced with carbon located at lattice points of polycrystalline diamond or graphite. The “interstitial type” refers to a form in which different elements such as nitrogen and silicon have entered a gap between carbons located at lattice points of a crystal lattice of polycrystalline diamond.

  The dispersion state and existence form of boron, nitrogen, and silicon in the polycrystalline diamond according to the present embodiment can be observed by TEM (transmission electron microscope) or HRTEM (high resolution transmission electron microscope). It can be confirmed by TOF-SIMS (time-of-flight type-secondary ion mass spectrometry) that boron is “dispersed at the atomic level” and “isolated substitution type”. It can also be evaluated by TOF-SIMS that nitrogen and silicon are present in an “isolated substitution type” or “interstitial type”.

  The TEM used for confirmation of the dispersion state and the existence form is an arbitrary 10 locations on the observation polishing surface at a magnification of 20000 to 100,000 times with respect to the observation polishing surface for measuring the grain size of the polycrystalline diamond described above. This can be confirmed by observing (10 fields of view).

In TOF-SIMS, for example, by analyzing under the following conditions, it is possible to confirm that each element is “dispersed at the atomic level” and that each element is “isolated substitution type” or “interstitial type”. it can.
Measuring device: Tof-SIMS mass spectrometer (time-of-flight secondary ion mass spectrometer)
Primary ion source: Bismuth (Bi)
Primary acceleration voltage: 25 kV.

  Boron is present in the crystal grains of polycrystalline diamond in an amount of 90 atomic% or more in an isolated substitution form, and preferably in an amount of 95 atomic% or more in an isolated substitution type. More preferably, in the crystal grains of polycrystalline diamond, 99 atomic percent or more thereof is present in isolated substitution type, and most preferably 100 atomic percent is present in isolated substitution type. The ratio of the isolated substitutional boron to the total boron in the polycrystalline diamond crystal grains can be measured by electric conductivity characteristics and CV measurement. Boron is higher than cubic boron nitride having a Mohs hardness of about 50 GPa and Ib type diamond single crystal of about 90 GPa because 90 atomic% or more of the polycrystalline diamond crystal grains are present in the form of isolated substitution. Has hardness. For this reason, polycrystalline diamond is sufficiently useful in applications that make use of wear resistance (for example, for dies and scribing tools). When the ratio of the isolated substitutional boron to the whole boron in the polycrystalline diamond crystal grains is less than 90 atomic%, the aggregated boron does not have a diamond structure and tends to break, and cracks and cracks tend to occur. is there.

(Atom concentration of boron)
Boron has an atomic concentration of 1 × 10 ¹⁴ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less from the viewpoint of forming a suitable protective film on the surface of polycrystalline diamond and setting the particle diameter to 500 nm or less. It is preferably 1 × 10 ¹⁴ cm ⁻³ or more and 1 × 10 ²¹ cm ⁻³ or less. When the atomic concentration of boron is more preferable, the defective rate of the protective film is drastically reduced, and the yield is improved from 30% or more to 90% or more than when the atomic concentration of boron is preferable. The atomic concentration of boron is preferably 1 × 10 ¹⁴ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less from the viewpoint of imparting conductivity for suppressing triboplasma.

Polycrystalline diamond is the atomic concentration of boron is less than 1 × 10 ¹⁹ cm ^-3 shows the electrical characteristics of the p-type semiconductor, showing the electrical characteristics of the metallic conductors in 1 × 10 ¹⁹ cm ^-3 or more. Therefore, the atomic concentration of boron is more preferably 1 × 10 ¹⁸ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less.

When the atomic concentration of boron is 1 × 10 ¹⁴ cm ⁻³ or more, an effect of suppressing triboplasma is obtained, and when it is 1 × 10 ²² cm ⁻³ or less, an effect of suppressing dropout of crystal grains is obtained. can get.

(Atomic concentration of nitrogen)
From the viewpoint of stably containing nitrogen in the crystal grains and suitably forming a water-insoluble protective film on the surface, and reducing the hardness and increasing the grain size, nitrogen has an atomic concentration of 1 ×. It is preferably 10 ¹⁸ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, and more preferably 1 × 10 ¹⁸ cm ⁻³ or more and 1 × 10 ¹⁹ cm ⁻³ or less.

When the atomic concentration of nitrogen is 1 × 10 ¹⁸ cm ⁻³ or more, an effect that a protective film of BN and SiN can be formed on the surface is obtained, and by being 1 × 10 ²⁰ cm ⁻³ or less, The effect that the hardness can be maintained without agglomeration is obtained.

(Atomic concentration of silicon)
Silicon has an atomic concentration of 1 × from the viewpoint that silicon is stably contained in crystal grains and a water-insoluble protective film is suitably formed on the surface, and a decrease in hardness and an increase in particle diameter can be suppressed. It is preferably 10 ¹⁸ cm ⁻³ or more and 2 × 10 ²⁰ cm ⁻³ or less, and more preferably 1 × 10 ¹⁸ cm ⁻³ or more and 1 × 10 ¹⁹ cm ⁻³ or less.

When the atomic concentration of silicon is 1 × 10 ¹⁸ cm ⁻³ or more, an effect of forming a protective film of SiN is obtained, and when it is 2 × 10 ²⁰ cm ⁻³ or less, no aggregation occurs. The effect that the hardness can be maintained is obtained.

(Concentration of trace impurities)
The trace impurities contained in polycrystalline diamond are generic names of elements or compounds that cannot be avoided in the production of polycrystalline diamond, and elements or compounds that may be contained in trace amounts. Polycrystalline diamond contains BC ₅ and B ₄ C as trace impurities. The trace impurities other than BC ₅ and B ₄ C include metal elements classified as transition metals. The content (atomic concentration) of each element such as this metal element is 0 cm ⁻³ or more and 1 × 10 ¹⁸ cm ⁻³ or less, and the total of each element (that is, the inclusion of trace impurities other than BC ₅ and B ₄ C) The amount (atomic concentration) is from 0 cm ^{−3 to} 1 × 10 ²² cm ⁻³ . Therefore, these metal elements may or may not be contained in polycrystalline diamond.

BC ₅ has a total area of 1% of all diffraction peaks derived from BC ₅ with respect to the total area of all diffraction peaks derived from diamond in the range of diffraction angle 2θ in the X-ray diffraction measurement from 0 ° to 90 °. Is less than. B ₄ C has a total area of all diffraction peaks derived from B ₄ C relative to a total area of all diffraction peaks derived from diamond in the range of diffraction angle 2θ in X-ray diffraction measurement from 0 ° to 90 °. It is less than 0.5%. As the sum of BC ₅ and B ₄ C, the total area of all diffraction peaks derived from BC ₅ and B ₄ C is preferably 1% or less with respect to the total area of all diffraction peaks derived from diamond.

BC ₅ has a total area of all diffraction peaks derived from BC _{5 of} 0 relative to the total area of all diffraction peaks derived from diamond in the range of diffraction angle 2θ in X-ray diffraction measurement from 0 ° to 90 °. It is preferably less than 1%, most preferably 0%. Further, the concentration of B ₄ C is such that all diffractions derived from B ₄ C with respect to the total area of all diffraction peaks derived from diamond in the range of diffraction angle 2θ in X-ray diffraction measurement from 0 ° to 90 °. The total area of the peaks is preferably less than 0.1%, most preferably 0%.

The concentration measurement of BC ₅ and B ₄ C as described above can be performed by analysis using an X-ray diffractometer. For example, the measurement can be performed under the following conditions using an X-ray diffractometer (trade name (product number) “X'pert”, manufactured by PANalytical).

Characteristic X-ray: Cu-Kα ray Tube voltage: 30 kV
Tube current: 20mA
X-ray diffraction method: θ-2θ method X-ray irradiation range: A pinhole collimator is used to irradiate X-rays.

  The atomic concentrations of boron, nitrogen, and silicon are determined by SIMS (secondary ion mass spectrometry) inside the polycrystalline diamond, and the vicinity of the polycrystalline diamond (for example, the protective film and the polycrystalline diamond in the vicinity thereof). And from the surface to a depth of 1000 nm can be measured by TOF-SIMS under the conditions described above. The concentration of trace impurities formed with elements other than carbon, boron, nitrogen and silicon can also be measured by ICP-MS (inductively coupled plasma mass spectrometry).

SIMS can measure, for example, the atomic concentration of boron, nitrogen and silicon and the atomic concentration of trace impurities other than BC ₅ and B ₄ C in the polycrystalline diamond by analyzing under the following conditions.
Measuring device: Product name (product number): “IMS-7f”, AMETEK's primary ion species: Cesium (Cs ⁺ )
Primary acceleration voltage: 15kV
Detection area: 30 (μmφ)
Measurement accuracy: ± 40% (2σ).

  FIG. 1 is a graph showing an example of the distribution of additive elements inside the polycrystalline diamond according to the present embodiment. This additive element distribution is measured using SIMS. The polycrystalline diamond shown in FIG. 1 includes carbon-containing first particles having a maximum particle size of 1 μm or less (excluding boron carbide particles and silicon carbide particles), boron carbide particles having a maximum particle size of 100 nm or less, Boron nitride particles having a diameter of 100 nm or less, and both silicon nitride particles and silicon carbide particles having a maximum particle size of 100 nm or less are mixed and formed into a molded body, and the molded body is heated and fired at 2000 ° C. or higher and 2500 ° C. or lower. By forming, graphite is formed, and this is converted directly to diamond by pressure heat treatment under conditions of 16 GPa and 2100 ° C. From FIG. 1, it is understood that the polycrystalline diamond according to the present embodiment contains boron, nitrogen, and silicon at a uniform concentration from the surface to the inside.

<Identification of polycrystalline diamond in Raman spectrum measurement>
Polycrystalline diamond according to 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 half around the 1300 ^-1 ± 30 cm ^-1 The value width is preferably less than 1% of the area of the peak at which the value width is 60 cm ⁻¹ or less. The area ratio is more preferably less than 0.1%, and most preferably 0%. Thereby, it can be seen that the graphite carbon is almost completely converted into diamond carbon, specifically, 99.9 atomic% or more. When the area ratio is 1% or more, the hardness of the polycrystalline diamond tends to decrease. In the Raman spectrum measurement, the peak at which the half width around 1575 cm ⁻¹ ± 30 cm ⁻¹ is 20 cm ⁻¹ or less is derived from amorphous carbon, graphite carbon, or sp2 carbon. A peak having a half-value width of 60 cm ⁻¹ or less centered on 1300 ⁻¹ ± 30 cm ⁻¹ is a peak derived from diamond carbon.

<Dynamic friction coefficient>
The surface of the polycrystalline diamond according to this embodiment preferably has a dynamic friction coefficient of 0.2 or less, more preferably 0.1 or less, further preferably 0.05 or less, and 0.02 Most preferably: Thereby, the polycrystalline diamond can have high sliding characteristics and high wear resistance. If the dynamic friction coefficient of the surface of the polycrystalline diamond exceeds 0.2, the polycrystalline diamond tends not to have the desired sliding characteristics and wear resistance.

The dynamic friction coefficient of the surface of the polycrystalline diamond can be measured by a pin-on-disk sliding test performed under the following conditions.
Ball material: SUS
Load: 10N
Rotation speed: 400rpm
Sliding radius: 1.25mm
Test time: 100 minutes Temperature: Room temperature Atmosphere: Air, Ar or mineral oil.

When the dynamic friction coefficient of the surface of the polycrystalline diamond is 0.2 or less, for example, 0.25 times the dynamic friction coefficient of the surface of the additive-free polycrystalline diamond in a dry atmosphere (for example, at 25 ° C. and a relative humidity of 40% or less). Reduced to: The dynamic friction coefficient of the surface of the polycrystalline diamond according to this embodiment is preferably 0.2 times or less of the dynamic friction coefficient of the surface of the additive-free polycrystalline diamond. As used herein, “non-added polycrystalline diamond” is polycrystalline diamond in which boron, nitrogen, and silicon are not present in isolated substitution in the crystal grains, and these additive elements are grains. Even when it is deposited on the boundary, the atomic concentration does not exceed 1 × 10 ¹⁸ cm ⁻³ .

<Protective film>
In the polycrystalline diamond according to this embodiment, the protective film preferably contains at least one selected from the group consisting of silicon oxide, silicon nitride, and boron nitride. It is considered that silicon oxide is generated when silicon exposed on the surface of the crystal grains due to wear reacts with oxygen in the atmosphere and forms an oxide film as a protective film on the exposed surface. Silicon nitride is considered to be formed when nitrogen exposed on the surface of the crystal grains due to wear reacts with silicon exposed on the surface of the crystal grains, and forms a protective film on the exposed surface. It is done. Boron nitride is also considered to be formed when nitrogen exposed on the surface of the crystal grain due to wear reacts with boron exposed on the surface from the inside of the crystal grain, and forms a protective film on the exposed surface. It is done. Since any protective film has a lubricating action and a small dynamic friction coefficient, the sliding characteristics and wear resistance of polycrystalline diamond can be improved. In particular, since silicon oxide, silicon nitride, and boron nitride are all water-insoluble, a protective effect can be exhibited even when a water-soluble cutting fluid is used.

  The protective film can include precipitates precipitated from the crystal grains. The deposit includes compounds such as boron, nitrogen, and silicon. Compounds such as boron, nitrogen, and silicon exist as interstitial types in the crystal grains of polycrystalline diamond, and are considered to be deposited on the surface exposed to the surface due to wear or the like and become precipitates. Since these precipitates also have a lubricating action, they contribute to the reduction of the dynamic friction coefficient. Furthermore, silicon oxide and boron nitride generated near the surface of polycrystalline diamond may become precipitates.

  The protective film may have an average film thickness of 1 nm or more and 1000 nm or less from the viewpoint of having a volume that fills the space formed by the degranulation even if particles having the maximum particle diameter are degranulated due to mechanical damage. preferable. The average film thickness of the protective film is more preferably 20 nm or more and 500 nm or less. When the average film thickness of the protective film is 1 nm or more, the minute surface roughness is flattened and the solid lubricant effect is exhibited, so that the sliding characteristics are improved. By being 1000 nm or less, an effect that the mechanical cutting of the object to be cut by the underlying diamond works advantageously can be obtained.

Whether or not a protective film is formed on the surface of the polycrystalline diamond can be confirmed by using AES (Auger Electron Spectroscopy). For example, polycrystalline diamond (boron concentration 3.5 × 10 ²⁰ cm ⁻³ , nitrogen concentration 5 × 10 ¹⁸ cm ⁻³ , silicon concentration 1 × 10 ¹⁸ cm ⁻³ ) is analyzed from the surface by chemical analysis using AES. By examining the presence or absence of oxygen in the surface layer up to a depth of about 0.5 nm, the presence or absence of a protective film at room temperature can be confirmed.

  Furthermore, the average film thickness of the protective film on the surface of the polycrystalline diamond can be measured by a nano surface measuring instrument (trade name: “Dektak XT”, manufactured by Brucker) or TEM. For example, the observation polishing surface for measuring the grain diameter of the polycrystalline diamond described above is observed at any five locations (5 fields of view) on the observation polishing surface with a magnification of 20000 times using TEM. Measure with However, in the above five locations, each visual field includes a portion that becomes the surface of polycrystalline diamond. The thickness of the protective film portion of the observation polishing surface appearing in each field of view can be determined for each field of view, and the average value can be used as the average film thickness of the protective film.

  A method for evaluating the physical properties (hardness, wear resistance, and resistivity) of the polycrystalline diamond according to the present embodiment is as follows.

(Evaluation of hardness)
Polycrystalline diamond can be evaluated for hardness by measuring Knoop hardness according to JIS Z 2251: 2009. For example, Knoop hardness is measured with a load of 4.9N. In the polycrystalline diamond according to the present embodiment, boron, nitrogen, silicon, etc. present in the crystal grains become the starting point of plastic deformation, and it is conceivable that the hardness is somewhat lower than that of the additive-free polycrystalline diamond. However, as shown in Table 1 described later, polycrystalline diamond according to this embodiment (for example, B-NPD-III, boron concentration 1 × 10 ¹⁹ cm ⁻³ , nitrogen concentration 1 × 10 ¹⁹ cm ⁻³ , silicon concentration) The Knoop hardness of 1 × 10 ¹⁸ cm ⁻³ ) is equal to or higher than that of synthetic single crystal diamond (Ib type SCD).

(Evaluation of wear resistance)
Furthermore, the wear resistance of polycrystalline diamond can be evaluated by the following method. That is, polycrystalline diamond is processed into a 1 mm × 1 mm × 2 mm cylindrical processed body, and the number # 800 (number (#) means the fineness of the screen) with respect to this processed body, and the larger the number, A wear test (load: 2.5 kgf / mm ² , sliding speed: 200 mm / min) is performed using a metal bond diamond wheel with fine particles passing through the sieve. At this time, the polycrystalline diamond is evaluated to have a wear rate of 0.01 μm / min.

  Furthermore, in the above wear test, mechanical wear and thermochemical wear proceed synergistically, so it is desirable to evaluate the mechanical wear property and the thermochemical wear property as shown below.

As an evaluation of the mechanical wear characteristics of polycrystalline diamond, a low-speed and long-time sliding test is performed on aluminum oxide (Al ₂ O ₃ ) in which mechanical wear proceeds. For example, using a polycrystalline diamond, a test piece having a truncated cone shape with a test surface of a diameter of 0.3 mm is prepared. Next, this test piece is pressed against an Al ₂ O ₃ sintered body (purity: 99.9% by mass) with a constant load of 0.3 MPa by a machining center and slid at a distance of 10 km at a low speed of 5 m / min. Thus, the wear amount is calculated from the spread of the tip diameter, and the mechanical wear characteristics of the polycrystalline diamond are evaluated. The amount of wear of the polycrystalline diamond according to this embodiment is about 20 times that of the additive-free polycrystalline diamond, and the wear resistance is greatly improved. Due to the wear of polycrystalline diamond, the protective film formed on the surface is updated one after another, and it is considered that the sliding characteristics are greatly improved by the lubrication effect each time, and the mechanical wear is remarkably suppressed.

As an evaluation of the thermochemical wear characteristics of polycrystalline diamond, a sliding test is performed on silicon dioxide (SiO ₂ ) where thermochemical wear proceeds. For example, using a polycrystalline diamond, a test piece having a truncated cone shape with a test surface of a diameter of 0.3 mm is prepared. Next, this test piece is fixed and pressed against the test surface at 0.1 MPa while rotating at 6000 rpm (sliding speed of 260 to 340 m / min) using a synthetic quartz (SiO ₂ ) having a diameter of 20 mm as a polishing plate. Thus, the thermochemical wear characteristics of the polycrystalline diamond are evaluated by sliding the test piece and measuring the speed at which the wear progresses (wear speed). Polycrystalline diamond has a lower wear rate and improved wear resistance than additive-free polycrystalline diamond. Due to the wear of polycrystalline diamond, the protective film formed on the surface is updated one after another, and it is considered that the sliding characteristics are greatly improved by the lubrication effect each time, and the mechanical wear is remarkably suppressed.

  The conductivity of polycrystalline diamond can be evaluated by measuring the resistivity by the following method. That is, the surface of the polycrystalline diamond is mirror-finished, and the resistivity is measured by a four-terminal method using electrodes on the processed body. This electrode is formed by annealing a laminated film of Ti / Pt / Au in Ar at 320 ° C. In this embodiment, it is preferable that five processed bodies are prepared, an average value is calculated from the resistivity of these processed bodies, and this average value is used as the resistivity of the polycrystalline diamond.

  From the above, the polycrystalline diamond according to the present embodiment has a water-insoluble protective film formed on the surface thereof, and this protective film can improve oxidation resistance, wear resistance and sliding characteristics. Furthermore, since it has electrical conductivity, abnormal wear due to triboplasma observed in additive-free polycrystalline diamond, single crystal diamond, and the like is also suppressed. Therefore, it is suitable for processing difficult-to-cut materials such as cemented carbide and aluminum alloy, and can exhibit high performance for processing insulating objects such as ceramics, plastics, glass, and quartz. . In particular, since silicon oxide and boron nitride constituting the protective film are both water-insoluble, the protective effect can be exhibited even when a water-soluble cutting fluid is used.

≪Method for producing polycrystalline diamond≫
As shown in FIG. 3, the polycrystalline diamond manufacturing method according to the present embodiment is a first method of preparing graphite containing carbon, boron, nitrogen, silicon, and BC ₅ and B ₄ C as trace impurities. Step S10, a second step S20 in which the graphite is filled into the container under an inert gas atmosphere, and a third step S30 in which the graphite is converted into diamond by pressure heat treatment in the container. Particularly, the boron is dispersed at the atomic level in the crystal grains of the graphite, and 90 atomic% or more thereof exists as an isolated substitution type. With the above configuration, it is possible to produce polycrystalline diamond having high oxidation resistance, sliding characteristics and wear resistance, and a low dynamic friction coefficient.

  The dispersion state and the existence form of boron in the graphite base material and the boron, nitrogen, and silicon in the graphite can be confirmed by the same method as the confirmation method of the dispersion state and the existence form of these elements in the polycrystalline diamond. “Dispersion at the atomic level”, “isolated substitution” or “interstitial”, the concentration of boron, nitrogen and silicon, and the concentration of trace impurities are the same as the confirmation method for polycrystalline diamond. Each can be confirmed.

<First step>
1st process S10 contains A process, B process, and C process. It is preferable that 1st process S10 further includes D process performed after B process and before C process.

Step A includes carbon-containing first particles (for example, high-purity graphene) having a maximum particle size of 1 μm or less, boron carbide particles (for example, B ₄ C particles) having a maximum particle size of 100 nm or less, and a maximum particle size of Boron nitride particles of 100 nm or less (for example, BN particles) and at least one of silicon nitride particles and silicon carbide particles having a maximum particle size of 100 nm or less (for example, SiN particles) are mixed and molded into a first molded body. It is a process. In step B, the first molded body is heated and sintered at 2000 ° C. or higher and 2500 ° C. or lower (eg, 2200 ° C.) to obtain the first sintered body, and then the first sintered body has a maximum particle size of 50 μm. This is a step of pulverizing into the following powders. Step C is a step of preparing graphite by pulverizing and shaping the powder until the maximum particle size is less than 1 μm, and heating and sintering at 2000 ° C. to 2500 ° C. (for example, 2200 ° C.). .

  Furthermore, the D process includes a D1 process, a D2 process, and a D3 process alternately several times. The D step preferably includes the D1 step, the D2 step, and the D3 step alternately 5 times or more, and preferably includes 10 times or more.

  Specifically, step D1 is a step of forming the powder into a second molded body. Step D2 is a step of obtaining the second sintered body by heating and sintering the second molded body at 2000 ° C. or higher and 2500 ° C. or lower (for example, 2200 ° C.). The step D3 is a step of pulverizing the second sintered body again into a powder having a maximum particle size of 50 μm or less. Here, the first carbon-containing particles are carbon-containing particles excluding boron carbide particles and silicon carbide particles, and are selected from the group consisting of pyrolytic graphite having a maximum particle size of 1 μm or less, graphene, and oxides of the graphene. It is preferable to include at least one kind. Thereby, it can contribute to manufacture of an efficient polycrystalline diamond from a viewpoint of a raw material. Hereinafter, the first step in the method for producing polycrystalline diamond according to the present embodiment will be described in detail with reference to FIG. Since the first step shown in FIG. 4 is an example, the first step in the method for producing polycrystalline diamond according to the present embodiment should not be limited to this.

(Process A)
The first step starts from the A step SA. First, as Step SA1 of Step A, particles of high-purity graphene (purity: 99.999% or more) having a maximum particle size of 0.5 to 1 μm, B ₄ C particles having a maximum particle size of 100 nm or less, and a maximum particle size BN particles having a particle diameter of 100 nm or less and SiN particles having a maximum particle diameter of 100 nm or less are prepared. As step SA2 of step A, these particles are uniformly mixed using a mixer in an Ar atmosphere to obtain a mixture. In Step SA2 of Step A, a conventionally known mixing method can be used as long as the particles can be mixed uniformly.

  Further, as step SA3 of step A, the mixture (particle group) is placed on a sintering apparatus and sintered under conditions of 2200 ° C. and 0.1 MPa. As for step SA3 of step A, a conventionally known sintering method can be used as long as sintering is performed at 2200 ° C. and 0.1 MPa.

  Next, the particle size of the sintered particle group as Step SA4 of the A process is made uniform using a sieve having a mesh size of 0.5 μm. In Step SA5 of Step A, only those having a particle size of less than 0.5 μm are selected from the above particle group, and those having a particle size of 0.5 μm or more are discarded.

  As Step SA6 of Step A, a group of particles having a particle size of less than 0.5 μm is molded into a pellet shape using a hot press to obtain a first molded body.

(Process B)
In the first step, the B step SB is performed following the A step SA described above. In Step SB1 of the B process, the first molded body obtained from the A process SA is placed on a sintering apparatus and sintered under conditions of 2200 ° C. and 0.1 MPa to obtain a first sintered body. As long as it sinters on the conditions of 2200 degreeC and 0.1 MPa for step SB1 of B process, a conventionally well-known sintering method can be used. Next, as Step SB2 of the B process, an X-ray diffractometer (for example, trade name (product number) “X'pert”, manufactured by PANalytical Co., Ltd.), characteristic X-ray: Cu-Kα, tube voltage: 30 kV, tube current: 20 mA , Filter: multilayer mirror, optical system: concentration method, X-ray diffraction method: measured by θ-2θ method), it is confirmed that no peak derived from B ₄ C is observed in the obtained first sintered body. When a peak derived from B ₄ C is observed, the first sintered body is discarded.

In step SB3 of the B process, the first sintered body, which has been confirmed to have no B ₄ C-derived peak, has a maximum particle size of 50 μm or less (for example, 1 μm or less in FIG. 4) using a grinding mill. Grind into powder. Also for Step SB3 of the B process, a conventionally known pulverization method can be used as long as it is pulverized to a powder having a maximum particle size of 50 μm or less. Whether or not the maximum particle size of the obtained powder is 50 μm or less is confirmed using a general-purpose particle size distribution apparatus or SEM as Step SB4 of the B process. When the maximum particle size of the powder exceeds 50 μm in Step SB4 of the B process, the powder is discarded.

(D process)
In the first step, it is preferable to perform the D step SD after the B step SB. As step SD1 of D process, the powder by which the maximum particle diameter was confirmed to be 50 micrometers or less is shape | molded into a pellet shape using a hot press, and a 2nd molded object is obtained (D1 process). Then, as step SD2 of D process, it mounts on a sintering apparatus with respect to the said 2nd molded object, and sinters on 2200 degreeC and 0.1 Mpa conditions, and obtains a 2nd sintered body (D2 process). As long as the step SD2 of the D process is sintered under the conditions of 2200 ° C. and 0.1 MPa, a conventionally known sintering method can be used.

Further, as Step SD3 of the D process, the second sintered body is pulverized again into a powder having a maximum particle size of 50 μm or less (for example, 1 μm or less in FIG. 4) using a pulverizer (D3 process). Subsequently, an X-ray diffractometer (for example, trade name (product number) “X'pert”, manufactured by PANalytical Co., Ltd.) is used as step SD4 of the D process for this powder, characteristic X-ray: Cu-Kα, tube voltage: 30 kV Tube current: 20 mA, filter: multilayer mirror, optical system: concentrated method, X-ray diffraction method: measured by θ-2θ method), it was confirmed that no B ₄ C-derived peak was observed, and B ₄ was added to the powder. Confirm that there is no precipitation of C. When a peak derived from B ₄ C is observed, the powder is returned to the step SB3 of the B step.

In the D process SD, it is preferable to repeat the steps SD1 to SD4 of the series of D processes a plurality of times as the step SD5 of the D process (indicated by an asterisk (*) in FIG. 4). That is, it is preferable to perform steps SD1 to SD4 of the D process 5 times or more in total, and more preferably 10 times or more in total. By increasing the number of repetitions of the D step, the concentration of BC ₅ and B ₄ C in the polycrystalline diamond can be effectively reduced.

(Process C)
In the first step, the C step SC is finally performed. First, as Step SC1 of Step C, the powder that has been confirmed not to precipitate B ₄ C in Step SD4 of Step D is ground using a grinding mill until the maximum particle size is less than 1 μm. Further, as Step SC2 of the C process, a powder having a maximum particle size of less than 1 μm is molded into a pellet shape using a hot press to obtain a third molded body. Further, as step SC3 of the C process, the third molded body is placed on a sintering apparatus and sintered under conditions of 2200 ° C. and 0.1 MPa, thereby obtaining a cylindrical graphite having a diameter of 10 × 10 t (t: thickness). Get. From the viewpoint of efficient formation of the polycrystalline diamond, it is preferable that the graphite obtained in this manner is a polycrystal including a crystallized portion at least partially.

Further, the above-mentioned graphite has a BC ₅ concentration of a small amount of impurities, and the above-mentioned BC with respect to the total area of all the diffraction peaks derived from diamond in the range of the diffraction angle 2θ in the X-ray diffraction measurement from 0 ° to 90 °. The total area of all diffraction peaks from ₅ is less than 1%. The concentration of BC ₅ is preferably such that the above-mentioned area ratio is less than 0.1%, most preferably 0%. Further, the concentration of B ₄ C is such that all diffractions derived from B ₄ C with respect to the total area of all diffraction peaks derived from diamond in the range of diffraction angle 2θ in X-ray diffraction measurement from 0 ° to 90 °. The total peak area is less than 0.5%. The concentration of B ₄ C is preferably such that the above-mentioned area ratio is less than 0.1%, most preferably 0%. The concentration of BC ₅ and B ₄ C can be measured under the above-described conditions using the above-described X-ray diffractometer.

The concentration of trace impurities (for example, transition metals) contained in graphite is preferably below the detection limit of SIMS and ICP-MS (less than 10 ¹⁵ cm ⁻³ ). Further, the particle diameter of graphite is preferably 10 μm or less, preferably 1 μm or less from the viewpoint of forming polycrystalline diamond having a small particle diameter of 1 to 500 nm and a uniform distribution of boron, nitrogen and silicon. Is more preferable.

The density of graphite, from the viewpoint of increasing the yield by reducing the volume change when converting the polycrystalline diamond from graphite in a third step described below, 0.8 g / cm ³ or more preferably, 1.4 g / cm ³ More preferably, it is 2.0 g / cm ³ or less.

<Second step>
The second step S20 is a step of filling the above-mentioned graphite into a container under an inert gas atmosphere. By filling graphite into a predetermined container (for example, a cell for high-pressure press) in an inert gas atmosphere, it is possible to suppress a trace amount of impurities from being mixed into the graphite and the polycrystalline diamond to be produced. Here, the inert gas may be any gas that can suppress the mixing of trace impurities, and examples thereof include Ar gas, Kr gas, and He gas.

<Third step>
The third step S30 is a step of converting the graphite into diamond by pressure heat treatment in the container. In particular, in the third step S30, it is preferable to perform a pressure heat treatment directly on the graphite in a pressure device from the viewpoint of suppressing the entry of trace impurities into the polycrystalline diamond. Thereby, it is possible to convert graphite directly into polycrystalline diamond, that is, without adding a sintering aid and a catalyst. Pressurized heat treatment refers to heat treatment performed under pressure.

  The pressure heat treatment in the third step S30 is preferably performed under conditions of 6 GPa or more and 1200 ° C. or more. More preferably, the pressure heat treatment is performed under 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 suitably produce polycrystalline diamond in which boron is dispersed at the atomic level in crystal grains and 90 atomic% or more thereof is present in isolated substitution type, and nitrogen and silicon are present in isolated substitution type or interstitial type. Can do. The pressure heat treatment has no upper limit on the pressure, but the upper limit is on the condition that the temperature is 2500 ° C. When the pressure heat treatment is 7 GPa or more, graphite can be directly converted into polycrystalline diamond. Furthermore, by being 1200 degreeC or more, it becomes possible to convert graphite into a polycrystalline diamond directly. By being 2500 degrees C or less, it becomes possible to convert graphite into a polycrystalline diamond directly, without volatilizing each element.

As described 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 dynamic friction coefficient. Polycrystalline diamond is manufactured with an arbitrary shape and thickness of about 15 × 15 t (t: thickness). For example, when the volume density of graphite is about 1.8 g / cm ³ , polycrystalline diamond shrinks to a volume of 70 to 80% of the graphite by pressure heat treatment, but the shape is the same as or almost the same as graphite. .

<Scribe tool>
The scribe tool according to this embodiment can be produced using the polycrystalline diamond.

  The scribe tool according to this embodiment can be produced by a conventionally known method as long as the polycrystalline diamond is used.

<Scribe wheel>
The scribe wheel according to this embodiment can be produced using the polycrystalline diamond.

  The scribe wheel according to the present embodiment can be manufactured by a conventionally known method as long as the polycrystalline diamond is used.

<Dresser>
The dresser according to this embodiment can be manufactured using the polycrystalline diamond.

  The dresser according to the present embodiment can be produced by a conventionally known method as long as the polycrystalline diamond is used.

<Rotating tool>
The rotary tool according to this embodiment can be manufactured using the polycrystalline diamond.

  The rotary tool according to the present embodiment can be produced by a conventionally known method as long as the polycrystalline diamond is used.

<Orifice for water jet>
The water jet orifice according to the present embodiment can be produced using the polycrystalline diamond.

  The water jet orifice according to this embodiment can be produced by a conventionally known method as long as the polycrystalline diamond is used.

<Wire drawing dies>
The wire drawing die according to this embodiment can be produced using the polycrystalline diamond.

  The wire drawing die according to this embodiment can be produced by a conventionally known method as long as the polycrystalline diamond is used.

<Cutting tools>
The cutting tool according to this embodiment can be produced using the polycrystalline diamond.

  The cutting tool according to this embodiment can be produced by a conventionally known method as long as the polycrystalline diamond is used.

<Electrode>
The electrode according to this embodiment can be manufactured using the polycrystalline diamond.

  The electrode according to this embodiment can be produced by a conventionally known method as long as the polycrystalline diamond is used.

<Processing method>
The processing method according to the present embodiment is a method for processing an object using the polycrystalline diamond. Since the processing method according to the present embodiment processes an object using the polycrystalline diamond, the object can be processed efficiently and at low cost.

  In the processing method according to this embodiment, the object is preferably an insulator. In the processing method according to the present embodiment, since the polycrystalline diamond has conductivity, even if the object is an insulator, the object is efficiently and inexpensively generated without causing abnormal wear due to triboplasma or the like. Can be processed.

  The insulator preferably has a resistivity of 100 kΩ · cm or more. The upper limit of the resistivity of the insulator is infinite (∞). In the present embodiment, 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.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Example 1: Production of polycrystalline diamond>
(Production of 4 types of polycrystalline diamond)
In Example 1, four types of polycrystalline diamond (B-NPD-I, B-NPD-II, B-NPD-III, and B-NPD-IV) used in Examples 2 to 4 described later were produced. These polycrystalline diamonds all correspond to examples.
1. Preparation of graphite containing boron, nitrogen and silicon First, high-purity graphene (purity: 99.999% or more) having a maximum particle size of 500 μm and graphene oxide as carbon-containing first particles, and the sum of these carbon-containing first particles Is 100 parts by mass, B ₄ C particles having a maximum particle size of 100 nm or less with respect to 100 parts by mass, and 0.05 parts by mass with respect to 100 parts by mass. A BN particle having a particle size of 100 nm or less and a SiN particle having a maximum particle size of 100 nm or less, which is 0.05 parts by mass with respect to 100 parts by mass, are mixed as pellets (φ10 × 10 mm (Cylinder shape). Further, the pellet was heat-sintered at 2200 ° C. to obtain a first sintered body, and then the first sintered body was pulverized into a powder having a maximum particle size of 1 μm (step B). Subsequently, this powder was molded, heated and sintered at 2200 ° C. to obtain a second sintered body, and then the second sintered body was pulverized into a powder having a maximum particle size of 1 μm 10 times. Repeated (step D). Thereafter, the powder pulverized at the end of the step D is further pulverized until the maximum particle size is less than 1 μm, and this is molded, heated and sintered at 2200 ° C., and the graphite (φ10 × 10 mm cylindrical shape) is obtained. Obtained (Step C).
2. Storage of graphite in container After processing the above graphite into a tablet shape, it was sealed in a container (high pressure press cell: cylindrical shape of φ10 × 10 t).
3. Conversion from Graphite to Polycrystalline Diamond The graphite was directly converted into polycrystalline diamond by placing the container in which the graphite was enclosed in a pressurized heating apparatus and subjecting it to a pressure heat treatment under conditions of 16 GPa and 2100 ° C. About the obtained 4 types of polycrystalline diamond, it confirmed that it did not contain a binder phase by making a diamond single phase into a basic composition with the X-ray and electron beam diffractometer. Further, for four types of polycrystalline diamond, boron was dispersed at an atomic level and 90 atomic% or more thereof existed as an isolated substitution type, and the atomic concentration was confirmed using TEM, SIMS, and TOF-SIMS. Furthermore, it was confirmed by TOF-SIMS that nitrogen and silicon exist as isolated substitution type or interstitial type, and the atomic concentration thereof.

  Specifically, the dispersion state at the atomic level of boron by TEM was confirmed by a conventionally known method.

Using SIMS, the atomic concentration of boron, nitrogen, and silicon and the atomic concentration of trace impurities were measured inside the polycrystalline diamond under the following conditions.
Measuring device: Product name (product number): “IMS-7f”, AMETEK's primary ion species: Cesium (Cs ⁺ )
Primary acceleration voltage: 15kV
Detection area: 30 (μmφ)
Measurement accuracy: ± 40% (2σ).

Using TOF-SIMS, it was analyzed that each element was “dispersed at the atomic level” and that each element was “isolated substitution type” or “interstitial type” under the following conditions.
Measuring device: Tof-SIMS mass spectrometer (time-of-flight secondary ion mass spectrometer)
Primary ion source: Bismuth (Bi)
Primary acceleration voltage: 25 kV.

In addition, the resistivity and Knoop hardness were measured by the methods described above, and the oxidation start temperature in the atmosphere was measured by a conventionally known method. These measurement results are shown in Table 1. Furthermore, when trace impurities were detected by SIMS in the above four types of polycrystalline diamond, only BC ₅ and B ₄ C were found. These concentrations were measured by the above X-ray diffraction measurement, and the results are shown in Table 1. The crystal grain size (maximum grain size) of polycrystalline diamond of B-NPD-I, B-NPD-II, B-NPD-III, and B-NPD-IV is an X-ray diffractometer (XRD) based on the above conditions. From the measurement of the full width at half maximum of the (111) peak by (), it was confirmed that both were 500 nm or less.

(Manufacturing of NPD and 1b type SCD, PCD)
In Example 1, as a comparative example, non-isolated substitution type (interstitial type) insulator polycrystalline diamond (NPD) doped with less than 4 × 10 ¹⁹ cm ⁻³ , Ib type single crystal diamond (Ib type SCD) And sintered diamond (PCD) having a particle size (maximum particle size) of 3 to 5 μm formed by bonding and sintering diamond particles with a binder containing cobalt. Furthermore, as a polycrystalline diamond (C-NPD-I) of a comparative example, the powder pulverized at the end of the D step in the above-mentioned C step was formed without making the maximum particle size less than 1 μm, and heated at 2200 ° C. What was prepared from the obtained graphite was prepared. As another comparative diamond diamond (C-NPD-II), the powder was not returned to the B process even though the powder had a peak derived from B ₄ C in the D process. Graphite was obtained and prepared from this graphite. For these comparative examples, the concentration of boron, Knoop hardness, resistivity, and the like were measured by the same method as for the four types of polycrystalline diamond. These measurement results are also shown in Table 1.

<Example 2: Evaluation of wear resistance (thermochemical wear characteristics)>
In Example 2, a cutting tool was prepared by a known manufacturing method using the above-mentioned four types of polycrystalline diamond, 1b type SCD and NPD, and the work material was cut quartz glass having a Vickers hardness (Hv) of 9 GPa. The material was cut and evaluated for wear resistance. The shape of the manufactured cutting tool is a shape classified as a general-purpose throw-away tip, and all of them were R tools having a corner R of 0.8 mm, a clearance angle of 7 °, and a rake angle of 0 °.

  In the wear resistance evaluation, the above-described cutting tools are set on an ultra-precision lathe, the cutting speed (Vc) = 100 to 200 m / min (low speed condition: 100 m / min, high speed condition: 200 m / min), and feed (f ) = 0.001 mm / rot, incision (ap) = 0.005, 0.001 mm The flank wear width Vb (unit: mm) was measured when the work material was cut 200 m. The results are shown in Table 2.

  From Table 2, the wear amount of the cutting tool using the 1b type SCD was large under the low speed condition, and the wear amount of the cutting tool using the four types of polycrystalline diamond and the NPD of the comparative example was almost the same. Under high speed conditions, the amount of wear was large with the cutting tool using 1b type SCD and NPD, whereas the amount of wear was large with B-NPD-II in the cutting tool using four types of polycrystalline diamond. In all other cases, the wear amount was extremely small. These effects are presumed to be due to the fact that the protective film formed on the surface of the four types of polycrystalline diamond exhibits lubricity against quartz and suppresses reactive wear between diamond and quartz. It was done.

<Example 3: Evaluation of wear resistance (mechanical wear characteristics)>
In Example 3, B-NPD-I and B-NPD-III are used among four types of polycrystalline diamond, and a cutting tool is prepared by a known manufacturing method using NPD and PCD as comparative examples. Was cut with a high-purity alumina sintered body (purity: 99.9% by mass) having a Vickers hardness (Hv) of 16 GPa as a work material and evaluated for wear resistance. The shape of the manufactured cutting tool is a shape classified as a general-purpose throw-away tip, and all of them were R tools having a corner R of 0.8 mm, a clearance angle of 7 °, and a rake angle of 0 °.

In the wear resistance evaluation, each of the above-described cutting tools was set in an ultra-precision lathe, and the maximum wear amount (VBmax (unit: μm) with respect to the cutting distance (m) was measured under the following conditions. Show.
Work material: KYOCERA A479 φ50 mm sintered body, turning cutting conditions: Cutting speed (Vc): 30, 300 m / min, feed (f): 0.01 mm, depth of cut (ap): 0.01 mm, dry / wet: wet .

  As shown in FIG. 2, the cutting tool using PCD had a maximum wear amount exceeding 100 μm at a cutting distance of about 600 m. On the other hand, in the cutting tool using NPD, even when the cutting distance exceeds 5000 m, the maximum wear amount does not exceed 100 μm. Furthermore, the cutting tool using B-NPD-I shows 1.5 times higher wear resistance than NPD, and the cutting tool using B-NPD-III is 2 to 2.5 times higher than NPD. High wear resistance.

<Example 4: Life evaluation by cutting an insulator>
In Example 4, a cutting tool was prepared by a known manufacturing method using each of the four types of polycrystalline diamond, 1b type SCD, and NPD, and the work material was cut as polycarbonate (resistivity: ∞ kΩ · cm). The life of the cutting edge was evaluated. The shapes of the produced cutting tools were all R bits having a corner R of 0.8 mm, a clearance angle of 7 °, and a rake angle of 7 °.

In the life evaluation of the cutting edge of Example 4, the above-mentioned cutting tools were set on an ultra-precision lathe, cut at 4.5 km under the following conditions, and after finishing cutting, the damage degree of the cutting edge was evaluated, and the damage The lifetime was calculated for each cutting tool based on the degree. Specifically, the life of other cutting tools when the life of a cutting tool using 1b type SCD was set to 1 was relatively evaluated. The results are shown in Table 3.
Work material: Polycarbonate (Takiron PCP1609A).
Cutting conditions:
(1) Cutting 4.5 km: Cutting speed (V): 100 to 400 m / min, Feed (f): 0.04 mm / rot, Cutting (ap): 0.2 mm
(2) Finish cutting: Cutting speed (V): 75 m / min, feed (f): 0.002 mm / rot, cutting (ap): 0.002 mm, dry / wet: dry.

  From Table 3, when the life of a cutting tool using 1b type SCD is 1, the life of a cutting tool using NPD is 1, but it is 2.8 for a cutting tool using four types of polycrystalline diamond. As described above, all showed a good life. By the protective film formed on the surface of the four types of polycrystalline diamond and the conductivity of the four types of polycrystalline diamond, the wear caused by tripoplasma on the insulating work material such as polycarbonate was suppressed. It was speculated that this was due to the effect and the lubricity being exhibited and the wear being suppressed.

<Example 5: Evaluation in various tools>
(Production of polycrystalline diamond)
Polycrystalline diamond (B-NPD-V to IX) used for evaluation in various tools described later is manufactured by the same method as in Example 1, and boron is added in a non-isolated substitution type (aggregation type) by a conventionally known method. Polycrystalline diamonds (NPD-I to III) were produced. Confirmation that the basic composition is a single phase of diamond, boron is dispersed at the atomic level, and 90% or more of the total exists as an isolated substitution type, and nitrogen and silicon exist as an isolated substitution type or an interstitial type. The same method as in Example 1 was used. Further, the atomic concentrations of carbon, boron, nitrogen and silicon, and trace impurities were measured under the same conditions as in Example 1 by SIMS. When trace impurities were detected by SIMS in the above polycrystalline diamond (B-NPD-V to IX), only BC ₅ and B ₄ C were found.

  These measurement results are shown in Table 4. Furthermore, the crystal grain size of these polycrystalline diamonds was confirmed to be 200 nm or less from the half width of the (111) peak by an X-ray diffractometer (XRD).

(Production and evaluation of scribe tool)
Using NPD-II and B-NPD-VI, scribe tools each having a tip of 4 points (rectangular plane shape) were produced. Using these scribe tools, 200 scribe grooves having a length of 50 mm were formed on a sapphire substrate with a load of 20 gf. Thereafter, the amount of wear at the tip of the scribe tool was observed with an electron microscope. As a result, the wear amount of the scribe tool using B-NPD-VI was extremely small, 0.1 times that of NPD-II. The same effect was confirmed also about the scribe wheel produced using NPD-II and B-NPD-VI, respectively.

(Production and evaluation of dresser)
Using NPD-II and B-NPD-VI, a single-point (conical) dresser was prepared. These dressers were worn under the condition of using a WA (white alumina) grindstone, the peripheral speed of the grindstone being 30 m / sec, the cutting depth being 0.05 mm, and being wet. Thereafter, the wear amount of the dresser was measured with a height gauge. As a result, the wear amount of the dresser using B-NPD-VI was extremely small, 0.1 times that of the dresser using NPD-II.

(Production and evaluation of micro rotary tool (miniature drill))
A miniature drill having a diameter of 1 mm and a blade length of 3 mm was prepared using NPD-II and B-NPD-VI. Using these miniature drills, a 1.0 mm thick cemented carbide (WC-Co) plate material (composition: 12 mass% Co, balance WC) under the conditions of a rotational speed of 4000 rpm and a feed of 2 μm / time. I made a hole. The number of holes that could be drilled before these miniature drills were worn or broken (number of drillings) was evaluated. As a result, the number of drilling of the miniature drill using B-NPD-VI was 10 times higher than that using NPD-II.

<Example 6: Evaluation of cutting tool I>
In Example 6, by using the same method as in Example 1, the bulk density was 2.0 g / cm ³ , and the boron concentration was 1 × 10 ²¹ cm ⁻³ as measured under the above-described conditions by ICP-MS. Graphite was prepared. This graphite was directly converted into polycrystalline diamond by subjecting this graphite to heat treatment under pressure of 15 GPa and 2200 ° C. using an isotropic high pressure generator. The obtained polycrystalline diamond had a particle size of 10 nm to 100 nm. From the X-ray diffraction pattern, no precipitation of B ₄ C or the like was observed. From the measurement under the same conditions as in Example 1 by SIMS, the silicon concentration was 1 × 10 ¹⁸ cm ⁻³ and the nitrogen concentration was 2.5 × 10 ¹⁸ cm ⁻³ . The boron concentration was 1 × 10 ²¹ cm ⁻³ .

  Using this polycrystalline diamond, a cutting tool body was produced by a conventionally known method. An active brazing material is joined to the cutting tool body in an inert atmosphere, and the surface of the polycrystalline diamond is polished, and then the flank face is cut by electric discharge machining to obtain a corner R of 0.4 mm, a flank angle of 11 °, and a rake angle of 0. Cutting tool I (test tool 1) with an R bit of °, cutting tool I (test tool) with an R bit of corner R 0.4 mm, clearance angle 11 ° and rake angle 0 ° by further grinding the flank face by grinding Each tool 2) was produced. As a comparative example, a cutting tool (comparative tool A) is manufactured by a conventionally known method using sintered diamond containing a conventional cobalt (Co) binder, and the same shape as the test tool 1 is obtained by the same electric discharge machining as the test tool 1. R bytes were given. Further, a cutting tool (comparative tool B) and a tool using the Ib type single crystal diamond (comparative tool C) are respectively produced by using a conventionally known method using additive-free polycrystalline diamond, and these flank surfaces are tested as test tools. The same cutting shape as that of the test tool 2 was provided by processing with the same polishing as in No. 2. The edge line accuracy of the cutting edge by electric discharge machining was as good as 0.5 μm or less for the test tool 1 while the comparative tool A was about 2 to 5 μm. The test tool 2 was as good as 0.1 μm with respect to the ridge line accuracy of the cutting edge by polishing. The test tool 1 had a machining time equivalent to that of the comparative tool A.

Next, for each of the test tools 1 and 2 and the comparative tools A to C, an intermittent cutting evaluation test by turning was performed under the following conditions.
Tool shape: Corner R0.4mm, clearance angle 11 °, rake angle 0 °
Work Material: Material-Aluminum Alloy A390 (Shape: Diameter φ100 × 500mm U-shape with 4 grooves)
Machining method: Cylindrical outer peripheral lathe machining (wet process)
Cutting fluid: Water-soluble emulsion Cutting conditions: Cutting speed (Vc) = 800 m / min, cutting depth (ap) = 0.2 mm, feeding speed (f) = 0.1 mm / rotating cutting distance: 10 km.

  After performing the above intermittent cutting evaluation test, each tool edge was observed to confirm the wear state. As a result, the comparative tool A had a large flank wear amount of 45 μm and the cutting edge shape was greatly impaired, whereas the test tool 1 had a good flank wear amount of 2 μm. Furthermore, the wear amount of the test tool 2 was 0.5 μm, which was 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.

<Example 7: Evaluation of cutting tool II>
In Example 7, by using the same method as in Example 1 except that a mixed gas composed of trimethylboron, methane, nitrogen and silicon was introduced, the bulk density was 2.0 g / cm ³ , SIMS Graphite having a boron concentration of 1 × 10 ¹⁹ cm ⁻³ was prepared under the same conditions as in Example 1 according to 1. This graphite was directly converted into polycrystalline diamond by subjecting this graphite to heat treatment under pressure of 15 GPa and 2200 ° C. using an isotropic high pressure generator. The obtained polycrystalline diamond had a particle size of 10 nm to 100 nm. From the X-ray diffraction pattern, no precipitation of B ₄ C or the like was observed. From the measurement under the same conditions as in Example 1 by SIMS, the silicon concentration was 1 × 10 ¹⁸ cm ⁻³ and the nitrogen concentration was 2.5 × 10 ¹⁸ cm ⁻³ . The boron concentration was 1 × 10 ¹⁹ cm ⁻³ .

  Using this polycrystalline diamond, a cutting tool body was produced by a conventionally known method. An active brazing material is joined to the cutting tool body in an inert atmosphere, and after polishing the surface of the polycrystalline diamond, the flank is further polished to have a corner R of 0.4 mm, a flank angle of 11 °, and a rake angle of 0 °. A cutting tool II (test tool 3) provided with the R bit was prepared. As comparative examples, the same comparative tools A to C used in Example 6 were prepared. The ridge line accuracy of the cutting edge of the test tool 3 was as good as 0.1 μm or less.

  In Example 7, an intermittent cutting evaluation test was performed on the test tool 3 under the same conditions as in Example 6. As a result, the wear amount of the test tool 3 was 0.1 μm, which was very good as compared with the wear amounts of the comparative tools A to C.

<Example 8: Evaluation of cutting tool III>
In Example 8, a mixed gas composed of diborane, methane, nitrogen and silicon was introduced into the reaction vessel, and graphite was produced while keeping the degree of vacuum in the chamber constant at 26.7 kPa. Thereafter, the pressure was reduced to 10 ⁻² Pa or lower and the ambient temperature was cooled to 300 ° C., and then a mixed gas containing silicon and nitrogen was further introduced into the graphite at 1 sccm (standard cubic centimeter per minute). Thus, graphite having a bulk density of 1.9 g / cm ³ and a boron concentration of 1 × 10 ²¹ cm ⁻³ measured under the same conditions as in Example 1 by SIMS was prepared. This graphite was directly converted into polycrystalline diamond by subjecting this graphite to heat treatment under pressure of 15 GPa and 2200 ° C. using an isotropic high pressure generator. The obtained polycrystalline diamond had a particle size of 10 nm to 100 nm. Knoop hardness was 120 GPa. When a 3 mm × 1 mm square test piece was cut out from the polycrystalline diamond and the resistivity was measured by the method described above, it was 0.5 mΩ · cm. From the measurement under the same conditions as in Example 1 by SIMS, the silicon concentration was 1 × 10 ¹⁸ cm ⁻³ and the nitrogen concentration was 2.5 × 10 ¹⁸ cm ⁻³ . The boron concentration was 1 × 10 ²¹ cm ⁻³ .

  Using this polycrystalline diamond, a cutting tool body was produced by a conventionally known method. An active brazing material is joined to the main body of the cutting tool in an inert atmosphere, the surface of polycrystalline diamond is polished, and then the flank face is cut by electric discharge machining to thereby obtain a diameter φ0 having two twisted cutting edges. A 5 mm ball end mill (test tool 4) was produced. As a comparative example, a sintered diamond containing a conventional cobalt (Co) binder is used, and a ball end mill (comparative tool A-2) having the same shape as that of the test tool 4 is cut by the same electric discharge machining as that of the test tool 4. It produced by doing. Furthermore, using additive-free polycrystalline diamond, a ball end mill (comparative tool B-2) having the same shape as the test tool 4 is manufactured by cutting the flank face by laser processing, and the cutting edge quality is locally polished. Was finished to a surface roughness Ra of 30 nm.

In Example 8, a cutting evaluation test was performed on each of the test tool 4, the comparative tool A-2, and the comparative tool B-2 under the following conditions.
Tool shape: Diameter φ0.5mm, 2-flute, ball end mill Work material: Material-STAVAX cemented carbide (WC-12% Co)
Cutting fluid: White kerosene Cutting conditions: Tool rotation speed 420,000 rpm, cutting depth (ap) = 0.003 mm, feed speed (f) = 120 mm / min.

  When the above-mentioned cutting evaluation test was performed, the tool life of the test tool 4 was 5 times longer than that of the comparative tool A-2 and 1.5 times longer than that of the comparative tool B-2. there were. Similar effects were obtained with an aqueous cutting fluid.

<Example 9: Evaluation of orifice I for water jet>
In Example 9, by using the same method as in Example 1, the bulk density was 2.0 g / cm ³ , and the boron concentration was 1 × 10 ¹⁹ cm ⁻³ as measured under the above-described conditions by ICP-MS. Graphite was prepared. This graphite was directly converted into polycrystalline diamond by subjecting this graphite to heat treatment under pressure of 15 GPa and 2200 ° C. using an isotropic high pressure generator. The obtained polycrystalline diamond had a maximum particle size of 100 nm. From the X-ray diffraction pattern, no precipitation of B ₄ C or the like was observed. From the measurement under the same conditions as in Example 1 by SIMS, the silicon concentration was 1 × 10 ¹⁸ cm ⁻³ and the nitrogen concentration was 2.5 × 10 ¹⁸ cm ⁻³ . The boron concentration was 1 × 10 ¹⁹ cm ⁻³ .

  Using this polycrystalline diamond, a water jet orifice I having an orifice hole with a diameter of 300 μm was prepared by a conventionally known method. As a comparative example, a 1b type SCD water jet orifice having the same orifice hole as the water jet orifice I was produced using a 1b type SCD produced by a conventionally known method. Further, an additive-free polycrystalline diamond water jet orifice having the same orifice hole as that of the water jet orifice I was prepared using additive-free polycrystalline diamond prepared by a conventionally known method.

  Using these water jet orifices, the cutting performance was evaluated by measuring the cutting time until the orifice hole was expanded to a diameter of 350 μm under a conventionally known condition. As a result, the water jet orifice I of Example 9 had a cutting time five times that of the 1b type SCD water jet orifice. Furthermore, it had a cutting time twice that of the additive-free polycrystalline diamond water jet orifice.

<Example 10: Evaluation of water jet orifice II>
In Example 10, by using the same method as in Example 1, the bulk density was 2.0 g / cm ³ , and the boron concentration was 1 × 10 ¹⁹ cm ⁻³ as measured under the above-described conditions by ICP-MS. Graphite was prepared. This graphite was directly converted into polycrystalline diamond by subjecting this graphite to heat treatment under pressure of 15 GPa and 2200 ° C. using an isotropic high pressure generator. The maximum grain size of the obtained polycrystalline diamond was 200 nm. From the X-ray diffraction pattern, no precipitation of B ₄ C or the like was observed. From the measurement under the same conditions as in Example 1 by SIMS, the silicon concentration was 1 × 10 ¹⁸ cm ⁻³ and the nitrogen concentration was 2.5 × 10 ¹⁸ cm ⁻³ . The boron concentration was 1 × 10 ¹⁹ cm ⁻³ .

  Using this polycrystalline diamond, a rectangular water jet orifice having a short side of 150 μm and a long side of 300 μm was prepared by a conventionally known method. As a comparative example, a PCD water jet orifice having the same shape as the water jet orifice II was produced using a PCD produced by a conventionally known method. Furthermore, an additive-free polycrystalline diamond orifice having the same shape as the water jet orifice II was prepared using additive-free polycrystalline diamond prepared by a conventionally known method.

  Using these water jet orifices, the cutting property was evaluated by measuring the cutting time until the long side was expanded to 400 μm under conventionally known conditions. As a result, the water jet orifice II of Example 10 had a cutting time 40 times that of the PCD water jet orifice. It had a cutting time twice that of an additive-free polycrystalline diamond water jet orifice.

<Example 11: Performance comparison between B-NPD-III and C-NPD-1>
In this example, B-NPD-III and C-NPD-I shown in Table 1 were compared in performance. As a result, the Knoop hardness of B-NPD-III was 120 GPa, while C-NPD-I was 60 GPa. Further, B-NPD-III was stable up to about 900 ° C. in the atmosphere, whereas C-NPD-I was oxidized and cracked at about 400 to 600 ° C.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims, and is intended to include meanings equivalent to the scope of claims and all modifications within the scope.

S10 1st process S20 2nd process S30 3rd process SA A process SA1-SA6 A process step SB B process SB1-SB4 B process step SCC process SC1-SC3 C process step SD D process SD1-SD4 D process Steps.

Claims (33)

A polycrystalline diamond whose basic composition is a single phase of diamond,
The polycrystalline diamond is composed of a plurality of crystal grains,
The polycrystalline diamond contains boron, nitrogen, and silicon, with the balance being carbon and trace impurities,
The boron is dispersed at the atomic level in the crystal grains, and 90 atomic% or more thereof exists as an isolated substitution type,
The nitrogen and silicon are present as isolated substitution type or interstitial type in the crystal grains,
The trace impurities include BC ₅ and B ₄ C,
The BC ₅ has a total area of all diffraction peaks derived from the BC _{5 with} respect to a total area of all diffraction peaks derived from the diamond in a range where the diffraction angle 2θ in the X-ray diffraction measurement is 0 ° to 90 °. Less than 1%,
The B ₄ C represents all the diffraction peaks derived from the B ₄ C with respect to the total area of all the diffraction peaks derived from the diamond within a diffraction angle 2θ of 0 ° to 90 ° in the X-ray diffraction measurement. The total area is less than 0.5%,
The crystal grain is polycrystalline diamond having a grain size of 500 nm or less.   The polycrystalline diamond according to claim 1, wherein a surface of the polycrystalline diamond is coated with a protective film.   The polycrystalline diamond according to claim 2, wherein the protective film includes at least one selected from the group consisting of silicon oxide, silicon nitride, and boron nitride.   The polycrystalline diamond according to claim 2, wherein the protective film includes a precipitate precipitated from the crystal grains.   The polycrystalline diamond according to any one of claims 2 to 4, wherein the protective film has an average film thickness of 1 nm or more and 1000 nm or less.   The polycrystalline diamond according to any one of claims 1 to 5, wherein 99% or more of boron is present in the crystal grains as an isolated substitution type. The polycrystalline diamond according to any one of claims 1 to 6, wherein the boron has an atomic concentration of 1 x 10 ¹⁴ cm ^-3 or more and 1 x 10 ²² cm ^-3 or less. The polycrystalline diamond according to any one of claims 1 to 7, wherein the nitrogen has an atomic concentration of 1 x 10 ¹⁸ cm ^-3 or more and 1 x 10 ²⁰ cm ^-3 or less. 9. The polycrystalline diamond according to claim 1, wherein the silicon has an atomic concentration of 1 × 10 ¹⁸ cm ⁻³ or more and 2 × 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 about the 1575 cm ^-1 ± 30 cm ^-1 is a half width 60cm around the 1300cm ^-1 ± 30cm ^{-1 - The} polycrystalline diamond according to any one of claims 1 to 9, wherein the polycrystalline diamond is less than 1% of a peak area that is 1 or less.   The polycrystalline diamond according to any one of claims 1 to 10, wherein the polycrystalline diamond has a dynamic friction coefficient of 0.2 or less.   The polycrystalline diamond according to any one of claims 1 to 10, wherein the polycrystalline diamond has a dynamic friction coefficient of 0.1 or less. A first step of preparing graphite containing carbon, boron, nitrogen, silicon, and BC ₅ and B ₄ C as trace impurities;
A second step of filling the graphite into a container under an inert gas atmosphere;
A third step of converting the graphite into diamond by pressure heat treatment in the container,
The method for producing polycrystalline diamond, wherein the boron is dispersed at the atomic level in the crystal grains of the graphite, and 90 atomic% or more thereof is present as an isolated substitution type. The first step includes a step A, a step B, and a step C,
The step A includes carbon-containing first particles having a maximum particle size of 1 μm or less, boron carbide particles having a maximum particle size of 100 nm or less, boron nitride particles having a maximum particle size of 100 nm or less, and a maximum particle size of 100 nm or less. It is a step of mixing at least one of silicon nitride particles and silicon carbide particles and forming the first molded body,
In the step B, the first molded body is heated and sintered at 2000 ° C. or higher and 2500 ° C. or lower to obtain the first sintered body, and then the first sintered body is formed into a powder having a maximum particle size of 50 μm or smaller. Crushing process,
The step C is a step of preparing the graphite by pulverizing and forming the powder until the maximum particle size is less than 1 μm, and heating and sintering at 2000 ° C. or higher and 2500 ° C. or lower,
The method for producing polycrystalline diamond according to claim 13, wherein the carbon-containing first particles are carbon-containing particles excluding the boron carbide particles and the silicon carbide particles. The first step further includes a step D performed after the step B and before the step C,
The D process is a process of repeating the D1 process, the D2 process, and the D3 process five times or more in this order.
The step D1 is a step of forming the powder into a second molded body,
The step D2 is a step in which the second molded body is heated and sintered at 2000 ° C. or higher and 2500 ° C. or lower to obtain a second sintered body,
15. The method for producing polycrystalline diamond according to claim 14, wherein the step D3 is a step of re-pulverizing the second sintered body into the powder having a maximum particle size of 50 μm or less.   The method for producing polycrystalline diamond according to claim 15, wherein the step D is a step in which the step D1, the step D2, and the step D3 are repeated five times or more in this order.   The method for producing polycrystalline diamond according to claim 15, wherein the step D is a step in which the step D1, the step D2, and the step D3 are repeated ten times or more in this order.   18. The polycrystalline diamond according to claim 14, wherein the first carbon-containing particles include at least one selected from the group consisting of pyrolytic graphite, graphene, and an oxide of the graphene. Production method.   The method for producing polycrystalline diamond according to any one of claims 13 to 18, wherein in the third step, a pressure heat treatment is directly performed on the graphite in a pressure heating apparatus.   20. The method for producing polycrystalline diamond according to claim 13, wherein the pressure heat treatment is performed under conditions of 6 GPa or more and 1200 ° C. or more.   The method for producing polycrystalline diamond according to any one of claims 13 to 20, wherein the pressure heat treatment is performed under 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 using the polycrystalline diamond according to any one of claims 1 to 12.   A scribe wheel formed using the polycrystalline diamond according to any one of claims 1 to 12.   A dresser formed using the polycrystalline diamond according to any one of claims 1 to 12.   A rotary tool formed using the polycrystalline diamond according to any one of claims 1 to 12.   An orifice for water jet formed using the polycrystalline diamond according to any one of claims 1 to 12.   A wire drawing die formed using the polycrystalline diamond according to any one of claims 1 to 12.   The cutting tool formed using the polycrystalline diamond of any one of Claims 1-12.   An electrode formed using the polycrystalline diamond according to any one of claims 1 to 12.   The processing method of processing a target object using the polycrystalline diamond of any one of Claims 1-12.   The processing method according to claim 30, wherein the object is an insulator.   The processing method according to claim 31, wherein the insulator has a resistivity of 100 kΩ · cm or more. A polycrystalline diamond whose basic composition is a single phase of diamond,
The polycrystalline diamond is composed of a plurality of crystal grains,
The polycrystalline diamond contains boron, nitrogen, and silicon, with the balance being carbon and trace impurities,
The boron is dispersed at the atomic level in the crystal grains, and 99 atomic% or more thereof is present as an isolated substitution type,
The nitrogen and silicon are present as isolated substitution type or interstitial type in the crystal grains,
The trace impurities include BC ₅ and B ₄ C,
The BC ₅ has a total area of all diffraction peaks derived from the BC _{5 with} respect to a total area of all diffraction peaks derived from the diamond in a range where the diffraction angle 2θ in the X-ray diffraction measurement is 0 ° to 90 °. Less than 1%,
The B ₄ C is in the range of diffraction angles 2θ in the X-ray diffraction measurement from 0 ° to 90 °, relative to the total area of all the diffraction peaks derived from diamond, the total of all the diffraction peaks derived from the B ₄ C The area is less than 0.5%,
The crystal grains have a particle size of 500 nm or less,
The polycrystalline diamond has a surface coated with a protective film,
The protective film includes at least one selected from the group consisting of silicon oxide, silicon nitride, and boron nitride, and includes precipitates precipitated from the crystal grains,
The protective film has an average film thickness of 1 nm to 1000 nm.
The boron has an atomic concentration of 1 × 10 ¹⁴ cm ⁻³ or more and 1 × 10 ²² cm ⁻³ or less,
The nitrogen has an atomic concentration of 1 × 10 ¹⁸ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less,
The silicon has an atomic concentration of 1 × 10 ¹⁸ cm ⁻³ or more and 2 × 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 about the 1575 cm ^-1 ± 30 cm ^-1 is a half width 60cm around the 1300cm ^-1 ± 30cm ^{-1 -} less than 1% of the area of the peaks is ¹ or less,
The polycrystalline diamond is polycrystalline diamond having a dynamic friction coefficient of 0.1 or less.

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