JP6232817B2 - Nano-polycrystalline diamond and tool comprising the same - Google Patents

Description

  The present invention relates to a nanopolycrystalline diamond and a tool including the same, and more particularly, to a nanopolycrystalline diamond doped with a different element and a tool including the same.

  Up to now, the development of technology for imparting various characteristics such as conductivity to diamond by adding elements other than carbon (hereinafter also referred to as “foreign elements”) to diamond that is insulating has been advanced. ing. Furthermore, in recent years, it has been clarified that nano-polycrystalline diamond composed of nano-sized single crystals has a hardness exceeding that of single-crystal diamond. Therefore, a technique for adding a different element to nano-polycrystalline diamond is currently being developed.

  For example, Japanese Patent Laying-Open No. 2013-28500 (Patent Document 1) describes a technique for producing nano-polycrystalline diamond containing a group 13 element. Since this nano-polycrystalline diamond has a hardness exceeding that of single-crystal diamond and can be electrically conductive, it is useful for tools used in various machining processes.

JP 2013-28500 A

  However, it is known that diamond is not suitable for processing ferrous materials. When a tool made of diamond is used for cutting ferrous materials, the parts that come into contact with the ferrous materials will be worn out, reducing the tool's life, resulting in stable processing of ferrous materials. There is a problem that can not be.

  The present invention has been made in view of the above situation, and an object of the present invention is to provide nano-polycrystalline diamond having high hardness and high wear resistance against iron-based materials, and a tool including the same. There is to do.

The present invention includes carbon and a heterogeneous element doped in a crystal structure composed of carbon, and the heterogeneous element is a first element selected from the group consisting of group 13 elements, and 15 And a second element which is one kind selected from the group consisting of group elements, and each atom concentration of the first element and the second element is 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ³ or less. It is a nanopolycrystalline diamond having an electrical resistivity of 10 Ω · cm or more.

  Moreover, this invention is a tool provided with the said nano polycrystalline diamond.

  ADVANTAGE OF THE INVENTION According to this invention, the nano polycrystalline diamond which has high hardness and the high abrasion resistance with respect to an iron-type material, and a tool provided with this can be provided.

It is a perspective view which shows an example of the state which formed the graphite on the base material. It is a perspective view which shows an example of the state which converted the graphite on a base material directly and produced the nano polycrystalline diamond.

[Description of Embodiment of Present Invention]
The present invention includes carbon and a heterogeneous element doped in a crystal structure composed of carbon, and the heterogeneous element is a first element selected from the group consisting of group 13 elements, and 15 And a second element which is one kind selected from the group consisting of group elements, and each atom concentration of the first element and the second element is 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ³ or less. It is a nanopolycrystalline diamond having an electrical resistivity of 10 Ω · cm or more. The nano-polycrystalline diamond of the present invention can have high hardness and high wear resistance against iron-based materials.

  The nano-polycrystalline diamond preferably exhibits an X-ray diffraction pattern in which the ratio of the peak intensity derived from another crystal structure to the peak intensity derived from the crystal structure composed of carbon is 0.0001 or less. . Thereby, nano-polycrystalline diamond can have higher hardness and higher wear resistance against iron-based materials.

  In the nano-polycrystalline diamond, the single crystal constituting the nano-polycrystalline diamond preferably has a particle size of 500 nm or less. Thereby, nano-polycrystalline diamond can have higher hardness.

  In the nanopolycrystalline diamond, it is preferable that the first element is boron and the second element is nitrogen. In this case, it can have particularly high hardness and particularly high wear resistance against ferrous materials.

  The nano-polycrystalline diamond is preferably used for a tool for processing an iron-based material. In this case, the characteristics of nano-polycrystalline diamond can be fully utilized.

  Moreover, this invention is a tool provided with the said nano polycrystalline diamond. According to the tool of the present invention, it is possible to provide a tool having high hardness and high wear resistance against ferrous materials.

[Details of the embodiment of the present invention]
Hereinafter, the nano-polycrystalline diamond according to the present invention and a tool including the same will be described in more detail.

<Nanopolycrystalline diamond>
The nano-polycrystalline diamond of the present embodiment includes carbon and a different element doped in the crystal structure composed of carbon, and the different element is one selected from the group consisting of group 13 elements. It consists of a first element and a second element which is one kind selected from the group consisting of group 15 elements, and each atom concentration of the first element and the second element is 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ³ or less, and electrical resistivity is 10 Ω · cm or more.

  In the present specification, “nanopolycrystalline diamond” refers to polycrystalline diamond in which the grain size of single-crystal diamond constituting polycrystalline diamond, that is, the grain size of crystal units constituting polycrystalline diamond is nano-sized. The nano-sized single crystal diamond is a single crystal diamond particle having a particle size of less than 1 μm. The “particle diameter” of the single crystal diamond means the longest diameter (major diameter) of the particle. In this specification, the value measured using a scanning electron microscope (SEM) is “ It is described as “particle size”.

  In addition, in this specification, “a heterogeneous element doped in a crystal structure” means that a heterogeneous element is substituted with a part of carbon in a diamond crystal structure formed by covalently bonding carbons to each other. The state, in other words, the state that exists in a state of being covalently bonded to carbon constituting the crystal structure and is dispersed in the crystal structure at the atomic level. The different elements in such a state are different from the different elements clustered in the crystal structure.

  That is, the “heterogeneous elements clustered in the crystal structure” exists in the crystal structure in a form in which a plurality of atoms that are different elements are aggregated. Therefore, for example, when a heterogeneous element clustered in the crystal structure of diamond is included, the heterogeneous element exists non-uniformly in the crystal structure, reducing the homogeneity of nano-polycrystalline diamond and improving the crystal structure. This results in large strains and consequently reduces the hardness of the nanopolycrystalline diamond.

  On the other hand, since the “heterogeneous element doped in the crystal structure” is dispersed in the crystal structure at the atomic level as described above, the nano-polycrystalline diamond containing “the heterogeneous element doped in the crystal structure” Is suppressed in homogeneity as compared with nano-polycrystalline diamond containing “heterogeneous elements clustered in the crystal structure”.

  In nano-polycrystalline diamond, whether or not a different element is contained and the content thereof can be measured by inductively coupled plasma (ICP) analysis. In addition, when nano-polycrystalline diamond contains different elements, whether or not the different elements are dispersed in the crystal structure at the atomic level is, for example, (1) the presence of a crystalline phase of the different elements in nano-polycrystalline diamond By observing whether or not to do so, it can be confirmed by (2) measuring the atomic concentration distribution of different elements in nano-polycrystalline diamond, and appropriately combining (1) and (2) above.

  Regarding (1) above, since the different elements dispersed in the crystal structure at the atomic level do not form a crystal phase different from diamond, the crystal phases of the different elements, that is, the crystal phase of the first element and the second element. The crystal phase and the crystal phase of the compound composed of the first element and the second element are not observed. On the other hand, since the different elements present in a cluster form a crystal phase different from diamond, the crystal phase derived from the different elements is observed. The presence or absence of such a crystal phase can be observed by, for example, X-ray diffraction, and can also be visually observed depending on the size of the crystal phase.

  Regarding (2) above, when the different elements are dispersed in the crystal structure at the atomic level, the atomic concentration distribution of the different elements is uniform as compared to the case where the different elements exist in a clustered state. Such an atomic concentration distribution can be measured by, for example, secondary ion mass spectrometry (SIMS). When the difference in atomic concentration of different elements measured at two arbitrary points in the crystal structure is less than or equal to a predetermined value, the atomic concentration distribution of the different elements can be considered to be uniform. It can be considered that it is in a state dispersed in the crystal structure and not in a clustered state.

  The nanopolycrystalline diamond of this embodiment has a high hardness. The reason why the nano-polycrystalline diamond of this embodiment has high hardness is not clear, but the present inventors infer from the results of various studies as follows.

  That is, the nano-polycrystalline diamond of the present embodiment includes a doped different element, which is different from a clustered different element. As described above, the heterogeneous elements in a clustered state reduce the homogeneity of the nanopolycrystalline diamond and cause a large distortion in the crystal structure, resulting in a decrease in the hardness of the nanopolycrystalline diamond. In contrast, a doped heterogeneous element can exist uniformly in the crystal structure compared to a heterogeneous element in a clustered state, so that a decrease in homogeneity of nano-polycrystalline diamond can be suppressed. As a result, the high hardness of the nano-polycrystalline diamond can be maintained.

Further, in the nanopolycrystalline diamond of the present embodiment, the first element and the second element, which are different elements, each exist in an atomic concentration of 1 × 10 ²² / cm ³ or less in the nanopolycrystalline diamond. If the atomic concentration of the different element becomes too high, the hardness of the nanopolycrystalline diamond may decrease. However, the presence of the different element at such a concentration may maintain the high hardness of the nanopolycrystalline diamond. it can. In the nanopolycrystalline diamond of the present embodiment, the different elements are uniformly dispersed regardless of the content rate, so that it is possible to suppress local variations in characteristics in the nanopolycrystalline diamond.

  Further, in the nanopolycrystalline diamond of the present embodiment, the electrical resistivity is 10 Ω · cm or more, so that it is understood that the atomic concentration of the first element and the atomic concentration of the second element are close to each other. The Since the atomic concentrations of the first element that can be an acceptor of carbon and the second element that can be a donor of carbon are close to each other, the homogeneity of the nanopolycrystalline diamond is maintained. Hardness can be maintained. In this specification, the electrical resistivity is a value measured according to JIS C2141.

In addition to the high hardness, the nano-polycrystalline diamond of the present embodiment has a high wear resistance against iron-based materials. The reason why the nano-polycrystalline diamond of the present embodiment has high wear resistance with respect to the iron-based material is not clear, but based on various examination results, at least the first element or not only the second element but also the first element. And the second element are doped at an atomic concentration of 1 × 10 ¹⁴ / cm ³ or more and the electrical resistivity is 10 Ω · cm or more, in other words, the atomic concentrations of the first element and the second element are It is inferred that the approximation is important.

In the nano-polycrystalline diamond of the present embodiment, the atomic concentrations of the first element and the second element are preferably 10 ¹⁶ / cm ³ or more and 10 ²¹ / cm ³ or less. In this case, nano-polycrystalline diamond can more effectively achieve both high hardness and high wear resistance against iron-based materials.

  In addition, the nano-polycrystalline diamond of the present embodiment exhibits an X-ray diffraction pattern in which the ratio of the peak intensity derived from another crystal structure to the peak intensity derived from the crystal structure composed of carbon is 0.0001 or less. It is preferable. In this case, the ratio of the crystal phase other than diamond, for example, the crystal phase of the first element, the crystal phase of the second element, and the crystal phase of the compound of the first element and the second element in the nano-polycrystalline diamond. Is sufficiently reduced, it can have higher hardness and higher wear resistance against ferrous materials. In addition, the nano-polycrystalline diamond of this embodiment preferably does not contain clustered heterogeneous elements.

  Moreover, it is preferable that the particle diameter of the single crystal which comprises the nano polycrystal diamond of this embodiment is 10 nm or more and 500 nm or less. In this case, since the variation in the grain size of the single crystal constituting the nanopolycrystalline diamond can be reduced while maintaining high hardness, a more uniform nanopolycrystalline diamond can be provided.

  In the nano-polycrystalline diamond of the present embodiment, the first element is preferably boron and the second element is preferably nitrogen. In this case, it has higher hardness and higher wear resistance against iron-based materials. be able to. The reason for this is not clear, but the present inventors have found that boron and nitrogen doped in nano-polycrystalline diamond are covalently bonded to each other based on various investigation results. I guess that it can also demonstrate.

  In addition, the nanopolycrystalline diamond of the present embodiment can be produced by a nanopolycrystalline diamond production method described later, and according to this production method, particles can be formed without interposing a binder between single crystal particles. They can be firmly bonded to each other. Such nano-polycrystalline diamond can have a high hardness as compared with the case where particles are bonded together by a binder. Therefore, it is preferable that the nano-polycrystalline diamond of this embodiment does not contain a binder.

  Moreover, according to the manufacturing method mentioned later, the nano polycrystalline diamond in which the amount of inevitable impurities is sufficiently low can be manufactured. Specifically, in the nano-polycrystalline diamond of the present embodiment, the content of each element that is an inevitable impurity can be set to 0.01% by mass or less. When the content of each element that is an unavoidable impurity is 0.01% by mass or less, slip at the single crystal grain boundary can be suppressed, and the bond between the single crystal grains can be further strengthened. Therefore, the hardness of nano-polycrystalline diamond can be further increased. Therefore, in the nano-polycrystalline diamond of the present embodiment, the content of each element that is an inevitable impurity is preferably 0.01% by mass or less. The inevitable impurities mean elements other than C and the intended heterogeneous elements, and examples thereof include hydrogen (H), oxygen (O), silicon (Si), and transition metals.

  Moreover, since the nanopolycrystalline diamond of this embodiment has high hardness and high abrasion resistance with respect to an iron-type material, it can be used for the tool for processing an iron-type material. The iron-based material means a material containing iron, and examples thereof include nickel (Ni), manganese (Mn), cobalt (Co), chromium (Cr), and stainless steel in addition to pure iron.

  Examples of tools include cutting tools, grinding tools, and anti-wear tools. Cutting tools include, for example, drills, end mills, cutting edge exchangeable cutting tips for drills, cutting edge exchangeable cutting tips for end mills, cutting edge exchangeable cutting tips for milling, cutting edge exchangeable cutting tips for turning, metal saws, cutting tools , Reamers, taps, etc.

<Tool>
The tool of this embodiment is a tool provided with the nano-polycrystalline diamond described above. Examples of the tool include a cutting tool, a grinding tool, an anti-wear tool, and the like as described above, and specific examples thereof are the same as described above.

  According to the tool of the present embodiment, since the nano-polycrystalline diamond described above is provided, a long life can be exhibited when used for processing an iron-based material, thereby stably processing an iron-based material. can do. The inventors of the present invention processed the nano-polycrystalline diamond of this embodiment as a lathe tip, and cut pure iron using this to obtain a nano-polycrystalline diamond not doped with a different element. In comparison, it has been confirmed that the wear resistance is three times or more.

<Nanopolycrystalline diamond and method for producing a tool including the same>
The nano-polycrystalline diamond of this embodiment can be manufactured as follows, for example. With respect to the following manufacturing method, each step will be described with reference to FIGS.

(Preparation process)
This step is a step of preparing graphite, whereby, as shown in FIG. 1, carbon and a heterogeneous element composed of a first element and a second element doped in a crystal structure composed of carbon. The graphite 1 containing is produced on the substrate 2. The produced graphite 1 is converted into nano-polycrystalline diamond by a conversion step described later, and the single crystal grain size in graphite 1 and the atomic concentration of different elements in graphite 1 are related to nano-polycrystalline diamond. Accordingly, the graphite 1 has a single crystal grain size of 10 μm or less, more preferably 500 nm or less, and the atomic concentration of different elements in the graphite is 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ^3. Hereinafter, it is more preferably formed so as to be 10 ¹⁸ / cm ³ or more and 10 ²¹ / cm ³ or less. Such graphite 1 can be formed on the base material 2 by using, for example, the following chemical vapor deposition (CVD) method.

(CVD method)
First, the base material 2 for vapor-phase-growing graphite on the main surface is arrange | positioned in a vacuum chamber. As a material of the base material 2, any metal, inorganic ceramic material, and carbon material may be used as long as they can withstand a temperature of about 1500 ° C. to 3000 ° C. However, from the viewpoint of reducing impurities mixed in the graphite that is the raw material of the nanopolycrystalline diamond, it is preferable that at least the main surface of the base material is a carbon material, and it is more preferable that the material is diamond or graphite with very few impurities. .

  Next, the base material 2 disposed in the vacuum chamber is heated at a temperature of about 1500 ° C. to 3000 ° C. As a heating method, a known method can be adopted. For example, a method of installing a heater capable of directly or indirectly heating the base material 2 in a vacuum chamber can be mentioned.

  Next, a hydrocarbon gas and a gas containing a different element are introduced into the vacuum chamber. At this time, the degree of vacuum (pressure) in the vacuum chamber is set to atmospheric pressure or lower. Thereby, hydrocarbon gas and the gas containing a different element can be mixed uniformly in a vacuum chamber.

As the hydrocarbon gas, ethane, butane, methane, or the like can be used, and methane is preferably used from the viewpoint that by-products such as ethylene are hardly generated when pyrolyzed because of its low molecular weight. As the gas containing a different element, it is preferable to use a gas composed of a hydride of a different element, a hydrocarbon gas containing a different element, or a halide gas containing a different element. When a gas composed of a hydride of a different element is used, the gas can be easily decomposed at a high temperature, so that the different element can be efficiently supplied onto the substrate. Further, when a hydrocarbon gas containing a different element is used, the different element already bonded to carbon can be supplied onto the substrate, so that the different element can be more efficiently doped into the graphite. . In addition, when a halide gas containing a different element is used, graphite can be synthesized while removing unintended metal impurities by the action of halogen, so that the concentration of metal impurities in graphite can be reduced more effectively. Can do. For example, when boron (B) is doped as the first element and nitrogen (N) is doped as the second element, boron fluoride (HF) gas or ammonia (NH ₃ ) gas can be used.

  Then, by thermally decomposing the mixed gas at a temperature of 1500 ° C. or higher, carbon is formed on the main surface of the base material from the first element and the second element doped in the crystal structure composed of carbon. In other words, the graphite 1 containing the different elements, that is, the graphite 1 in which the group 13 element and the group 15 element are dispersed in the crystal structure at the atomic level is formed.

  In the above CVD method, in order to make the grain size of the single crystal contained in the graphite 1 10 μm or less, the temperature and pressure in the synthesis conditions are set to 1600 ° C. or more and 13 Torr or more respectively. By setting the particle size of the single crystal to 10 μm or less, the particle size of the single crystal in the nanopolycrystalline diamond produced by direct conversion can be suppressed to less than 1 μm. Further, by adjusting the particle size of the single crystal contained in the graphite 1 to 20 nm or more and 500 nm or less, the particle size of the single crystal constituting the nanopolycrystalline diamond can be set to 10 nm or more and 500 nm or less. The structure of graphite 1 may be a structure in which a single crystal is included in a part and the other part is in a state of amorphous, amorphous carbon, carbon nanotube, fullerene, or the like. Also good. In order to obtain nano-polycrystalline diamond having a more uniform particle diameter, it is preferable to form graphite 1 having a structure in which each graphite phase is formed by a single phase.

Further, in the above CVD method, in order to make each atomic concentration of the different element in the graphite 1 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ³ or less, the hydrocarbon gas and each gas containing the different element are used. Prepare mixing ratio. Specifically, by increasing the mixing ratio of the gas containing the first element and the gas containing the second element to the hydrocarbon gas, the atomic concentration of the first element and the atomic concentration of the first element in the graphite 1 are increased. can do. Also, the atomic concentration of the different element can be adjusted by changing the type of each gas containing the different element. By setting each atomic concentration of different elements in graphite 1 to 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ³ or less, each atomic concentration of different elements in nano-polycrystalline diamond is 1 × 10 ¹⁴ / cm ^3. It can be set to 1 × 10 ²² / cm ³ or less.

In this step, by using the above CVD method, graphite 1 containing carbon and different elements (first element and second element) doped in the crystal structure composed of carbon is formed on the base material 2. Thus, the graphite 1 is formed in which the grain size of the single crystal contained in the graphite 1 is 10 μm or less and the atomic concentration of the different elements is 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ³ or less. . In other words, the group 13 element and the group 15 element are dispersed at the atomic level in the crystal structure at an atomic concentration of 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ³ or less, respectively, Graphite 1 having a particle size of 10 μm or less is vapor grown on the substrate 2.

  In addition, regarding the graphite prepared in this step, each of the different elements is uniformly doped in both the thickness direction and the in-plane direction, that is, the atomic concentration distribution of the different elements in the graphite is uniform. Preferably there is. Since the heterogeneous element is uniformly doped in the graphite, the distribution of the heterogeneous element in the nano-polycrystalline diamond produced by the conversion process described later can be made uniform.

  In order to make the atomic concentration distribution of the different elements uniform, it is preferable to introduce the hydrocarbon gas and the gas containing the different elements into the vacuum chamber at the same time. Thereby, each gas can be easily and uniformly mixed, and the graphite in which the first element and the second element are uniformly doped can be efficiently formed on the substrate. Each gas may be supplied from the direction directly above the main surface of the base material toward the main surface of the base material, and supplied from the oblique direction or the horizontal direction to the base material toward the base material. May be. From the viewpoint of more efficiently and more uniformly doping a different element, it is preferable to supply from the direction directly above the main surface of the base material toward the main surface of the base material. In addition, in order to more efficiently and more uniformly dope a different element, a guide member that guides a hydrocarbon gas and a gas containing the different element onto the main surface of the substrate may be provided in the vacuum chamber.

Further, regarding the graphite prepared in this step, the density is preferably 0.8 g / cm ³ or more and 2.2 g / cm ³ or less, more preferably 1.4 g / cm ³ or more and 2.1 g / cm ^3. It is as follows. When the density of graphite is 0.8 g / cm ³ or more, the change in volume when graphite is directly converted into nano-polycrystalline diamond can be sufficiently reduced in the conversion step described later. The probability that cracks occur in polycrystalline diamond can be suppressed, and changes in the environment in the apparatus can be suppressed. As a result, the manufacturing yield can be improved. Further, when the density of graphite is 2.2 g / cm ³ or less, nano-polycrystalline diamond can be synthesized with a high yield of 80% or more.

  The density of the graphite can be adjusted by, for example, the temperature (° C.) when the graphite is grown on the main surface of the substrate and the introduction rate (sccm) of each gas. Specifically, the density of graphite can be increased by increasing the temperature and increasing the introduction rate of hydrocarbons.

  Further, regarding the graphite prepared in this step, the content of inevitable impurities is preferably low, and specifically, the content of each element that is an inevitable impurity is preferably 0.01% by mass or less. . This is because the content of inevitable impurities in the graphite is inherited by the produced nanopolycrystalline diamond. Further, by suppressing the concentration of inevitable impurities to a low level, grain growth caused by the presence of inevitable impurities can be suppressed, so that a single crystal having a more uniform size can be contained in graphite. In addition, since an analysis apparatus used for analysis capable of measuring the content of inevitable impurities in graphite, such as SIMS analysis and ICP (Inductively Coupled Plasma) analysis, generally has a detection limit of 0.01% by mass, Elements with a content of 0.01% by mass or less will not be detected by the analyzer.

  Mixing of inevitable impurities into the graphite can be suppressed by setting the degree of vacuum in the vacuum chamber when the gas is pyrolyzed relatively high. Specifically, the inventors maintain the pressure in the vacuum chamber at 20 Torr or more and 200 Torr or less, more preferably 20 Torr or more and 120 Torr or less, thereby reducing the content of each element that is an inevitable impurity to 0.01 It has been found that it can be controlled to mass% or less.

  In the above CVD method, the method of introducing the mixed gas into the vacuum chamber after heating the base material has been described. However, the method of heating the base material after introducing the mixed gas may be used, and simultaneously performed. May be.

(Conversion process)
This step is a step in which the graphite formed in the preparation step is sintered and directly converted into nano-polycrystalline diamond, whereby the nano-polycrystalline diamond 3 is placed on the substrate 2 as shown in FIG. Make it.

  Specifically, first, the graphite 1 on the substrate 2 shown in FIG. 1 is placed in a high-temperature high-pressure apparatus. The high-temperature and high-pressure apparatus may be any apparatus that can place graphite inside the apparatus and can control the inside of the apparatus under the above-described conditions. For example, a vacuum chamber used for CVD is used. it can.

  Then, the graphite 1 is exposed to high temperature and high pressure conditions of 1700 ° C. to 2500 ° C. and 15 Torr to 25 Torr. As a result, the graphite 1 is instantaneously sintered and converted into nano-polycrystalline diamond 3 as shown in FIG. In this case, the shape of the nano-polycrystalline diamond 3 inherits the shape of the graphite 1 except for a slight volume change. In addition, after removing the base material 2 from the graphite 1, only the graphite 1 may be exposed to high-temperature and high-pressure conditions. In this case as well, the produced nanopolycrystalline diamond basically takes over the shape of the graphite 1. It will be.

  In this step, it is preferable not to use additives such as sintering aids, catalysts, and binders. According to this step, it is possible to produce nano-polycrystalline diamond in which single crystals are firmly bonded without using an additive, and by using no additive, compared to the case where the additive is used. High hardness nano-polycrystalline diamond can be produced.

According to the manufacturing method described in detail above, the nano-polycrystalline diamond having the above-described characteristics, that is, carbon and the heterogeneous element doped in the crystal structure composed of carbon, It consists of a first element that is one kind selected from the group consisting of elements and a second element that is one kind selected from the group consisting of Group 15 elements, and each atomic concentration of the first element and the second element is Nano-polycrystalline diamond having a resistivity of 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ³ or less and an electrical resistivity of 10 Ω · cm or more can be produced.

  In addition, according to the above manufacturing method, since different elements are uniformly dispersed in the graphite, when the graphite is directly converted to diamond, it effectively suppresses local abnormal growth of diamond crystal grains. Can do. Thereby, the particle diameter of the single crystal constituting the nano-polycrystalline diamond can be made more uniform, and as a result, a homogeneous nano-polycrystalline diamond having the above-described characteristics can be produced.

  Moreover, the tool provided with this nano polycrystal diamond can be produced by processing the manufactured nano polycrystal diamond into a desired shape.

  In Example 1, as described in detail below, graphite was prepared by the CVD method, and with respect to the obtained graphite, the measurement of the single crystal grain size, the density measurement, and the content of different elements were measured by the following method. Measurements were made. Thereafter, the graphite is directly converted to produce nano-polycrystalline diamond, and the obtained nano-polycrystalline diamond is measured for the single crystal particle size, X-ray diffraction spectrum, Knoop hardness by the following method, The electrical resistivity was measured.

<Measurement of density>
The density of graphite was measured using the Archimedes method.

<Measurement of grain size of single crystal>
The particle size of each single crystal in the SEM image obtained using an electron microscope was measured.

<Measurement of content of different elements>
The content of each element was measured using an ICP-MS analyzer.

<X-ray diffraction measurement>
An X-ray diffraction spectrum was obtained using an X-ray diffractometer.

<Measurement of Knoop hardness>
Knoop hardness was measured with a micro Knoop hardness meter at a measurement load of 4.9N.

<Measurement of electrical resistivity>
The electrical resistivity (volume resistivity) at a temperature of 20 ° C. was measured with a resistivity meter.

<Example 1>
(Preparation process)
First, a substrate made of single crystal diamond was placed in a vacuum chamber. Next, the substrate in the vacuum chamber is heated at 1900 ° C., and the degree of vacuum in the vacuum chamber is 110 Torr, and methane gas is supplied to the vacuum chamber at 120 sccm, boron fluoride gas is supplied at 30 sccm, and ammonia gas is supplied at 30 sccm. This was continued for 1 hour. As a result, graphite doped with boron and nitrogen having a thickness of about 100 μm was formed on the main surface of the substrate.

The formed graphite has a density of 2.1 g / cm ³ , single crystal grain sizes of 100 nm to 10 μm, and nitrogen and boron atomic concentrations of 10 ²¹ / cm ³ (0.6 mass%), respectively. Met.

(Conversion process)
Next, the graphite on the formed substrate was exposed to a high temperature and high pressure environment of 2200 ° C. and 15 GPa to directly convert the graphite to diamond, thereby producing nano-polycrystalline diamond doped with nitrogen and boron.

  The formed nano-polycrystalline diamond has a single crystal particle size of 10 to 100 nm, a crystal phase other than the single crystal of diamond is not observed in the X-ray diffraction spectrum, the Knoop hardness is 65 GPa, and at 25 ° C. The electrical resistivity was 1 kΩ · cm.

  Furthermore, when this nano-polycrystalline diamond is machined into a bite shape and pure iron is cut using it, the tool life is more than three times that of non-doped nano-polycrystalline diamond, resulting in high wear resistance. It was confirmed to have sex. In addition, the tool life at this time is a use time until a tool wears out and it becomes impossible to cut the pure iron which is a to-be-cut object.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Graphite 2 Base material 3 Nano-polycrystalline diamond

Claims (4)

Carbon and a heterogeneous element doped in the crystal structure composed of the carbon,
The heterogeneous element is composed of boron and nitrogen,
The atomic concentrations of boron and nitrogen are 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ³ or less,
Ri Der electrical resistivity of 10Ω · cm or more,
Nano-polycrystalline diamond that does not contain clustered heterogeneous elements ,
The nano-polycrystalline diamond, wherein the single crystal constituting the nano-polycrystalline diamond has a particle size of 500 nm or less.   2. The nano-polycrystalline diamond according to claim 1, which shows an X-ray diffraction pattern in which a ratio of a peak intensity derived from another crystal structure to a peak intensity derived from a crystal structure composed of carbon is 0.0001 or less. .   The nano-polycrystalline diamond according to claim 1 or 2, which is used for a tool for processing an iron-based material.   A tool comprising the nano-polycrystalline diamond according to any one of claims 1 to 3.

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