JP2013028500A - Polycrystalline diamond and method for producing the same, scribe tool, scribe wheel, dresser, rotating tool, orifice for waterjet, wire drawing die and cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: polycrystalline nanodiamond to which an acceptor element is added; a production method thereof; and various tools using the polycrystalline diamond.SOLUTION: This polycrystalline nanodiamond 1 is composed of carbon, a group III element 3 added to the carbon so as to disperse in the carbon in an atomic level, and inevitable impurities. The crystal grain diameter of the polycrystalline diamond 1 is 500 nm or less. The polycrystalline diamond 1 is produced by preparing graphite to which a group III element is added so as to disperse in carbon in the atomic level, and applying heat treatment to the graphite with a high pressure press machine. The polycrystalline nanodiamond 1 is useful for tools such as scribe tools, scribe wheels, dressers, rotating tools, orifices for waterjet, wire drawing dice and cutting tools.

Description

  The present invention relates to polycrystalline diamond and a production method thereof, a scribe tool, a scribe wheel, a dresser, a rotary tool, a water jet orifice, a wire drawing die, and a cutting tool. The present invention relates to polycrystalline diamond in which elements are uniformly added (hereinafter referred to as “group III element-added nanopolycrystalline diamond”), a method for producing the same, and various tools using the polycrystalline diamond.

  In recent years, it has become clear that nano-polycrystalline diamond has a hardness exceeding that of natural single-crystal diamond and has excellent properties as a tool. The nano-polycrystalline diamond is originally an insulator, but conductivity can be imparted to the diamond by adding an element that serves as an acceptor to the diamond. For example, E.I. A. Ekimov et al, Nature, Vol. 428 (2004), 542 to 545 (Non-patent Document 1) describes a method for synthesizing diamond to which boron is added.

E. A. Ekimov et al, Nature, Vol. 428 (2004), 542-545

In the method described in Non-Patent Document 1, boron is dissolved in graphite by reacting graphite (graphite) and B ₄ C. However, with this method, it is difficult to disperse boron in graphite at an atomic level. For this reason, when graphite in which boron is dissolved is directly converted to diamond, dopant clusters and the like are generated. Further, when boron is dissolved in graphite, boron hydride, oxide, and the like are generated. Due to these catalytic actions, the crystal grain size of the diamond after conversion may become abnormally large locally. As a result, it becomes difficult to produce boron-doped nanopolycrystalline diamond having a uniform crystal grain size.

  Therefore, the next conceivable method is to use graphite powder and an acceptor element powder such as boron as finely as possible and pulverize them carefully and then mix or further heat-react the raw materials. Is mentioned.

  However, even with this method, it is difficult for the acceptor atoms to be mixed with the graphite powder alone, and many of the acceptor atoms are in the form of clusters in which at least two or more atoms are adjacent. Therefore, the acceptor element concentration distribution is likely to occur in diamond. As a result, diamond crystal grains are likely to grow partly rapidly, and it has been difficult to obtain nano-polycrystalline diamond having uniform nano-sized crystal grains.

  The present invention has been made in view of the problems as described above, and nano-polycrystalline diamond in which an acceptor element is uniformly added to diamond at an unprecedented level, a manufacturing method thereof, and a scribe tool using the polycrystalline diamond. An object of the present invention is to provide a scribe wheel, a dresser, a rotating tool, a water jet orifice, a wire drawing die, and a cutting tool.

  The polycrystalline diamond according to the present invention is composed of carbon, a group III element added so as to be dispersed in the carbon at an atomic level, and unavoidable impurities. The crystal grain size (maximum length of crystal grains) of the polycrystalline diamond is about 500 nm or less.

The group III element is preferably dispersed in carbon as a substitutional isolated atom. The concentration of the group III element is, for example, about 1 × 10 ¹⁴ / cm ³ or more and about 1 × 10 ²² / cm ³ or less. The polycrystalline diamond can be produced by sintering graphite obtained by pyrolyzing a mixed gas of a gas containing a group III element and a hydrocarbon gas at a temperature of 1500 ° C. or higher.

  The method for producing polycrystalline diamond according to the present invention includes a step of preparing graphite in which a group III element is dispersed in carbon at an atomic level, and a heat treatment of the graphite in a high-pressure press apparatus. Converting to diamond.

  In the step of converting the graphite into diamond, it is preferable to heat-treat the graphite in a high-pressure press without adding a sintering aid or a catalyst. The step of preparing the graphite is to introduce a mixed gas of a group III element-containing gas and a hydrocarbon gas into a vacuum chamber, and thermally decompose the mixed gas at a temperature of 1500 ° C. or higher to form graphite on the substrate. The process to perform may be included. In the step of converting the graphite into diamond, the graphite formed on the substrate may be subjected to heat treatment at 1500 ° C. or higher under a high pressure of 8 GPa or higher. The mixed gas is preferably flowed toward the surface of the substrate. For example, methane gas can be used as the hydrocarbon gas.

  The polycrystalline diamond can be used for various tools. Specifically, the polycrystalline diamond can be used for a scribe tool, a scribe wheel, a dresser, a rotating tool, a water jet orifice, a wire drawing die, and a cutting tool.

  In the polycrystalline diamond according to the present invention, since the group III element is added so as to be dispersed at an atomic level in the carbon, the group III element can be added to the diamond with an unprecedented level of uniformity. It is possible to impart p-type conductivity to nano-polycrystalline diamond.

  In the method for producing polycrystalline diamond according to the present invention, in the vacuum chamber, the group III element is converted to polycrystalline diamond by performing heat treatment on the graphite added so as to be dispersed at an atomic level in carbon. Nanopolycrystalline diamond in which a group III element is uniformly added at an unprecedented level can be produced, and p-type conductivity can be imparted to the nanopolycrystalline diamond.

  Since the polycrystalline diamond according to the present invention has excellent oxidation resistance, it is useful for tools such as a scribe tool, a scribe wheel, a dresser, a rotating tool, a water jet orifice, a wire drawing die, and a cutting tool.

It is a perspective view which shows the state which produced the polycrystalline diamond in one embodiment of this invention on the base material. It is a figure which shows an example of the impurity distribution in the boron addition nano polycrystalline diamond in one embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
The group III element-added nanopolycrystalline diamond in the present embodiment includes a group III element added so as to be dispersed at the atomic level in carbon constituting the polycrystalline diamond body. The nano-polycrystalline diamond of the present embodiment is a polycrystalline diamond having a nano-sized crystal grain size that does not use a binder.

  A group III element is an element that can form a bond with one electron less than carbon, and is an element that serves as an acceptor in diamond. Examples of the group III element include boron, aluminum, gallium, indium, and thallium. One or more elements selected from these elements can be used, but other elements having the same function may be used. Among group III elements, boron is preferred, but it is also possible to use mixed elements in combination with boron and other elements.

  As shown in FIG. 1, a nanopolycrystalline diamond 1 of the present embodiment includes a group III element 3 formed on a substrate 2 and uniformly dispersed at an atomic level. In the present specification, “dispersing at the atomic level” means, for example, when solid carbon is produced by mixing and solidifying carbon and a group III element in a gas phase in a vacuum atmosphere. , A state of dispersion where the group III element is dispersed in the solid carbon.

  The nano-polycrystalline diamond 1 can be produced by subjecting graphite (graphite) formed on a base material to heat treatment under high temperature and high pressure. Graphite is an integral solid and includes a crystallized portion. In the example of FIG. 1, the nanopolycrystalline diamond 1 has a flat plate shape, but it can be considered to have an arbitrary shape and thickness. When the nano-polycrystalline diamond 1 is produced by heat-treating the graphite formed on the base material, the nano-polycrystalline diamond 1 and the graphite basically have the same shape.

  The group III element can be added to the graphite at the stage of forming the graphite. Specifically, a mixed gas of a gas containing a group III element and a hydrocarbon gas is pyrolyzed at a temperature of 1500 ° C. or higher to form graphite on the substrate, and at the same time, a group III element is added to the graphite. Can do.

  Examples of the gas containing the group III element include a first gas composed of a hydride of a group III element, and an organometallic second gas composed of one or more gases selected from trimethyl boron, triethyl boron, and trimethyl borate. An organometallic third gas composed of one or more gases selected from trimethylaluminum, triethylaluminum, dimethylaluminum hydride and triisobutylaluminum, an organometallic composed of one or more gases selected from trimethylgallium and triethylgallium A fourth gas of the system, an organometallic fifth gas composed of one or more gases selected from trimethylindium and triethylindium, an organometallic system composed of one or more gases selected from trimethylthallium and triethylthallium Use any of the 6th gas It is a function. It is also conceivable to appropriately mix two or more of the above gases.

  As described above, by adding a group III element to the graphite forming raw material gas in the gas phase and adding the group III element to the graphite, the group III element is uniformly added to the graphite at the atomic level. can do. Further, by appropriately adjusting the addition amount of the gas containing the group III element to the hydrocarbon gas, a desired amount of the group III element can be added to the graphite.

  The thermal decomposition of the mixed gas can be performed in a vacuum chamber. At this time, by setting the degree of vacuum in the vacuum chamber to be relatively high, mixing of impurities into the graphite can be suppressed. In practice, however, unintended inevitable impurities are mixed in the graphite. Examples of the inevitable impurities include nitrogen, hydrogen, oxygen, silicon, transition metals, and the like, and elements other than the above group III elements that are intended to be added.

  In the graphite used for producing the group III element-added nanopolycrystalline diamond of the present embodiment, the amount of each inevitable impurity is about 0.01% by mass or less. That is, the inevitable impurity concentration in the graphite is about the detection limit or less in SIMS (Secondary Ion Mass Spectrometry) analysis. Moreover, about the transition metal, the density | concentration in graphite is below the detection limit in ICP (Inductively Coupled Plasma) analysis or SIMS analysis.

In this way, by reducing the amount of impurities in graphite to the detection limit level in SIMS analysis and ICP analysis, when producing diamond using the graphite, other than the group III element intended to be added Polycrystalline diamond having an extremely small amount of impurities can be produced. Even when graphite containing impurities slightly larger than the detection limit in SIMS analysis or ICP analysis is used, polycrystalline diamond having characteristics that are remarkably superior to conventional ones can be obtained.
FIG. 2 shows an example of boron and impurity distribution in nano-polycrystalline diamond in the present embodiment. The boron-added nanopolycrystalline diamond shown in FIG. 2 was obtained by heat-treating graphite containing boron, which is a group III element, at 2000 ° C. in a vacuum atmosphere of 10 ⁻² Pa. is there. Boron concentration and impurity concentration were measured by SIMS analysis.
As shown in FIG. 2, it can be seen that the variation in the depth direction of the boron concentration and the concentration of each impurity in the diamond is small. It can also be seen that the amount of impurities in the nanopolycrystalline diamond in the present embodiment has a very low value.
In Table 1 below, B ₄ C as a boron source and graphite prepared by a conventional method are mixed and heat-treated at 2000 ° C. in a vacuum atmosphere of 10 ⁻² Pa to fix boron to the graphite. The result of comparing the mixing ratio of B ₄ C between the boron-doped nanopolycrystalline diamond obtained by melting and the boron-doped nanopolycrystalline diamond of the present embodiment is shown.

As shown in Table 1, in the boron-added nanopolycrystalline diamond obtained by dissolving boron in graphite, the B ₄ C mixing rate increases as the concentration of boron added increases. It can be seen that in the form of boron-doped nanopolycrystalline diamond, even when the boron concentration to be added increases, the B ₄ C mixing rate is extremely low, less than 0.01% by mass.

  The nano-polycrystalline diamond of the present embodiment contains the group III element uniformly at the atomic level as described above, but has a very small amount of impurities. In this nano-polycrystalline diamond, atoms of group III elements do not aggregate in a cluster shape in carbon, and are in a state of being almost uniformly dispersed throughout the diamond. Ideally, the atoms of the group III element are present in isolation from each other in the carbon. Group III element atoms are present in carbon (diamond body) in a state of substitution with carbon atoms, and are not simply mixed in carbon, but group III element atoms and carbon atoms are chemically bonded. It becomes the state that did.

  As described above, since the nanopolycrystalline diamond of the present embodiment includes a group III element dispersed at an atomic level in carbon, the nanopolycrystalline diamond in which the group III element is uniformly added at an unprecedented level is provided. can get. Further, since the group III element can be uniformly dispersed at the atomic level in the nanopolycrystalline diamond, desired p-type conductivity can be imparted over the entire diamond.

  In the nano-polycrystalline diamond of the present embodiment to which the group III element is added, the group III element is dispersed in the diamond at the atomic level, so that the group III element mixed in the diamond in an aggregated state as described above Almost does not exist. Further, the added group III element does not aggregate at the crystal grain boundary of diamond, and the impurities in the diamond are extremely small, so that abnormal growth of the diamond crystal can be effectively suppressed. As a result, nano-polycrystalline diamond having a nano-sized crystal grain size (maximum crystal grain length) of 10 to 500 nm and p-type conductivity is obtained.

  Furthermore, in the nano-polycrystalline diamond of the present embodiment, the concentration distribution of group III elements in the diamond is less likely to occur. Also from this, local abnormal growth of diamond crystal grains can be effectively suppressed. As a result, compared with the conventional example, the size of diamond crystal grains can be made uniform.

  The concentration of the group III element in diamond can be arbitrarily set. It is possible to increase or decrease the concentration of the group III element in diamond. In any case, since the group III element can be uniformly dispersed in the diamond, it is possible to effectively suppress the concentration distribution of the group III element in the diamond. Thereby, it is possible to effectively suppress the occurrence of variation in local conductivity of diamond.

The concentration of the Group III element is preferably in the range of about 10 ¹⁴ to 10 ²² / cm ³ in order to impart p-type conductivity to diamond. In order to impart good metallic conductivity to diamond, the group III element addition concentration is preferably about 10 ¹⁹ / cm ³ or more, and in order to impart semiconductivity to diamond, a group III element The addition concentration of is preferably less than about 10 ¹⁴ to 10 ¹⁹ / cm ³ .

  Although there was a concern that the addition of a group III element as described above would result in a decrease in hardness compared to non-doped nanopolycrystalline diamond, the hardness was equivalent. That is, the group III element-added nanopolycrystalline diamond of the present embodiment has the same hardness as the non-doped nanopolycrystalline diamond and has p-type conductivity.

  When, for example, a cutting tool is manufactured using the nano-polycrystalline diamond of this embodiment, it has been found that it has cutting performance and life (wear resistance) equivalent to or higher than that of non-doped nano-polycrystalline diamond while having conductivity. It was. Further, when the insulating material is cut, the nano-polycrystalline diamond has conductivity, so that there is an advantage that adhesion of shavings due to static electricity is suppressed. The use of the nanopolycrystalline diamond of the present embodiment will be described in detail later.

  Next, a method for producing the group III element-added nanopolycrystalline diamond of the present embodiment will be described.

  First, the substrate is heated to a temperature of about 1500 ° C. or higher and 3000 ° C. or lower in a vacuum chamber. A well-known method can be adopted as the heating method. For example, it is conceivable to install a heater in the vacuum chamber that can directly or indirectly heat the substrate to a temperature of 1500 ° C. or higher.

  As the substrate, any metal, inorganic ceramic material, and carbon material can be used as long as the material can withstand a temperature of about 1500 ° C. to 3000 ° C. However, the base material is preferably made of carbon from the viewpoint of preventing impurities from being mixed into the raw material graphite. More preferably, it is conceivable that the base material is composed of diamond or graphite with very few impurities. In this case, at least the surface of the substrate may be composed of diamond or graphite.

  Next, a hydrocarbon gas and a gas containing a group III element are introduced into the vacuum chamber. At this time, the degree of vacuum in the vacuum chamber is set to about 20 to 100 Torr. Thereby, hydrocarbon gas and the gas containing a group III element can be mixed within a vacuum chamber. By pyrolyzing the mixed gas at a temperature of 1500 ° C. or higher, graphite in which a group III element is taken in at an atomic level can be formed on the substrate. Note that the base material may be heated after introducing the mixed gas to form graphite containing a group III element on the base material.

For example, methane gas can be used as the hydrocarbon gas. As the gas containing a group III element, the various gases described above can be used. A mixed gas of a hydrocarbon gas and a gas containing a group III element can be introduced into the vacuum chamber at a ratio of 10 ⁻⁷ % to 100%, for example.

  During the formation of graphite, it is preferable that a hydrocarbon gas and a gas containing a group III element flow toward the surface of the substrate. Thereby, each gas can be mixed efficiently in the vicinity of the substrate, and graphite containing a group III element can be efficiently generated on the substrate. The hydrocarbon gas and the group III element-containing gas may be supplied from directly above the base material toward the base material, or may be supplied from the oblique direction or the horizontal direction toward the base material. It is also conceivable to install a guide member that guides hydrocarbon gas or group III element-containing gas to the base material in the vacuum chamber.

  Sintering the graphite produced as described above and added with the group III element dispersed in carbon at an atomic level at a high temperature and high pressure using a high-pressure press or the like, a level unprecedented Thus, a group III element-added nanopolycrystalline diamond in which a group III element is uniformly added can be produced.

  In the step of converting graphite to diamond, it is preferable to heat treat graphite under high pressure without adding a sintering aid or catalyst. In the step of converting graphite into diamond, the graphite formed on the substrate may be subjected to heat treatment at a high temperature and high pressure of 8 GPa or more and 1500 ° C. or more.

The graphite that can be used for producing the nano-polycrystalline diamond according to the present embodiment is, for example, crystalline or polycrystalline that partially includes a crystallization portion. Also, the density of graphite is preferably greater than 0.8 g / cm ³ . Thereby, the volume change at the time of sintering graphite can be made small. Also, from the viewpoint of improving the yield by reducing the volume change when graphite is sintered, the density of graphite should be about 1.4 g / cm ³ or more and 2.0 g / cm ³ or less experimentally. Is more preferable.

The reason why the density of the graphite is within the above range is that when the density of the graphite is lower than 1.4 g / cm ³ , the volume change during the high-temperature and high-pressure process is too large, and the temperature control may not be possible. It is possible. Moreover, if the density of graphite is larger than 2.0 g / cm ³ , the probability that diamond will crack may be doubled or more.

Next, application examples of the nano-polycrystalline diamond of the present embodiment will be described.
In p-type diamond to which an acceptor such as boron is added, a trivalent atom occupies a part of tetravalent carbon. In this case, the number of covalently bonded electrons becomes insufficient in the system, but the diamond structure can be maintained by obtaining electrons from the outside.

  On the other hand, in the case of n-type diamond, when the donor is activated and emits electrons, the electrons occupy the conduction state, that is, the energy state created by banding of antibonding orbitals. For this reason, it is considered that the diamond bond tends to be weakened.

  On the other hand, in the case of an acceptor, it is considered that the bondability of diamond increases because the non-bonded covalent bond is completely satisfied by the amount of one electron received. That is, by adding an acceptor to diamond, it can be expected to improve the heat resistance and wear resistance of diamond.

  For example, in the boron-doped nanopolycrystalline diamond of the present embodiment, boron can be dispersed in the diamond at the atomic level. Therefore, even if a large amount of boron, which is a different element, is added to the diamond, the mechanical properties of the diamond are It is not damaged at all. Therefore, the nano-polycrystalline diamond of the present embodiment has a high Knoop hardness equivalent to that of the non-doped binder-less nano-polycrystalline diamond. Such nano-polycrystalline diamond is useful for tools used in various machining processes.

  The inventors of the present invention manufactured a cutting tool using boron-doped nanopolycrystalline diamond prepared by the method of the present embodiment and containing 0.1% by mass, 0.3% by mass, and 0.6% by mass of boron, respectively. However, when the aluminum material was actually cut, the amount of wear on the flank surface was as small as 3 μm or less even when cutting 30 km. On the other hand, when a cutting tool was prepared using non-doped nanopolycrystalline diamond and the same test was performed, the amount of wear on the flank face was more than twice that of the above boron-doped nanopolycrystalline diamond. .

  Also, boron-doped nanopolycrystalline diamond of the present embodiment, polycrystalline diamond doped with boron by a conventional method, non-doped nanopolycrystalline diamond, and single-crystal diamond are prepared, and a # 1500 grindstone is used. When polishing was performed by applying a load of 2.5 kg for 30 minutes at 250 rpm, it was confirmed that the wear amount of the boron-added nanopolycrystalline diamond of this embodiment was as extremely small as 0.01 to 0.02 μm / min. . The amount of wear of other diamonds including non-doped nanopolycrystalline diamond was more than five times the amount of wear of the boron-doped nanopolycrystalline diamond of the present embodiment.

  From the above, it was confirmed that excellent wear resistance was obtained by producing a tool using the boron-added nanopolycrystalline diamond of the present embodiment.

  Since the nanopolycrystalline diamond of the present embodiment has conductivity, it can also be applied to electric discharge machining. More specifically, the nano-polycrystalline diamond of the present embodiment can be applied to a tool for producing a complicated three-dimensional shape such as a concave curved surface.

For example, when boron is added to polycrystalline diamond, the concentration of boron added to diamond is in the range of about 10 ²⁰ to 10 ²² / cm ^{3 in} order to obtain a good conductor that can be applied to electric discharge machining. It is preferable. Here, when the boron addition concentration is higher than 10 ²² / cm ³ , it is difficult to uniformly disperse boron in diamond, and there is a concern that the mechanical properties of polycrystalline diamond may be impaired. Therefore, as described above, the concentration of boron added to diamond is preferably 10 ²² / cm ³ or less.

  By adding boron to nanopolycrystalline diamond by the method of the present embodiment, the inventors of the present application have higher heat resistance in an aerobic atmosphere than non-doped nanopolycrystalline diamond to which a different element is not added ( It has also been found that the (oxidation resistance) can be improved.

  The inventors of the present application prepared boron-doped nanopolycrystalline diamond containing 0.1% by mass, 0.3% by mass, and 0.6% by mass of boron, respectively, by the method of the present embodiment. Nano-polycrystalline diamond was prepared and the residual amount of each diamond after heat treatment at 500 ° C. to 900 ° C. for 1 hour was measured. The residual amount of boron-added nano-polycrystalline diamond of this embodiment was There were more than four times the remaining amount of non-doped nanopolycrystalline diamond. That is, it was confirmed that the boron-doped nanopolycrystalline diamond of the present embodiment has excellent heat resistance (oxidation resistance) in an aerobic atmosphere.

  When polycrystalline diamond is used for a cutting tool, even if the tool edge is cooled by cutting fluid or mist during cutting, the temperature of the tool edge will be close to 1000 ° C due to sliding with the work material at the cutting point. Reach. Therefore, when using polycrystalline diamond for a cutting tool, it is also required to have excellent oxidation resistance.

  In the case of the boron-doped nanopolycrystalline diamond according to the present embodiment, a boron oxide film is formed on the surface of the nanopolycrystalline diamond when exposed to a high temperature in an aerobic atmosphere. For this reason, the boron-added nanopolycrystalline diamond according to the present embodiment has better oxidation resistance than ordinary polycrystalline diamond. Therefore, the nano-polycrystalline diamond of the present embodiment is also useful for a cutting tool, and complex shapes can be processed by using the nano-polycrystalline diamond. In addition, it is possible to provide a cutting tool capable of extending the tool life and capable of processing while maintaining high shape accuracy.

  Further, in the above boron-added nanopolycrystalline diamond, boron is dispersed at an atomic level in the diamond, so that a boron oxide film is formed almost uniformly over the entire surface of diamond exposed to high temperature in an aerobic atmosphere. be able to. For this reason, oxidation resistance becomes very high and the above-mentioned effect becomes remarkable.

  When insulating nano-polycrystalline diamond is used for a tool, there are limitations on the diamond processing method. More specifically, as a method of precisely finishing the cutting edge to a level usable as a tool, there is no choice but to rely on mechanical polishing. Therefore, the insulating nano-polycrystalline diamond can be applied only to a planar tool. Specifically, the tool shape is limited to a rectangular cutting tool composed of only a flat surface, which is made of single crystal diamond, a V-shaped cutting tool, an R cutting tool composed of a flat surface and one curved surface, or the like. The rotary tool is also limited to a simple shape having a planar configuration, such as a ball-end mill having a cutting edge shape obtained by cutting off a part of a flat R bit arc, or a drill having four corners of a quadrangular pyramid as cutting edges.

  In contrast, the conductive nanopolycrystalline diamond of the present embodiment is excellent in oxidation resistance, and therefore various blade edge polishing methods can be employed. Therefore, it can be applied to a cutting tool or a rotary tool having a more complicated shape than that of insulating nano-polycrystalline diamond.

  On the other hand, due to the increase in the area of the optical element, the size of the mold is increasing, and the demand for a tool with high wear resistance capable of continuous cutting of the large area mold is also increasing. The nano-polycrystalline diamond of the present embodiment is extremely excellent in wear resistance and can be applied to such a tool.

  Conventionally, single crystal diamond has been used as the material for the water jet orifice. However, with single crystal diamond, the amount of wear varies depending on the crystal orientation (uneven wear), so that there is a problem that the desired cutting width cannot be obtained with the passage of time of use.

  For example, although the amount of wear differs greatly between the (111) plane and the (100) plane of single crystal diamond, the orifice made of single crystal diamond has surfaces with various crystal orientations in the circumferential direction of the inner surface of the orifice hole. ing. Therefore, even if the orifice hole inner surface has a cylindrical shape at the beginning of use, the wear of the surface that easily wears in a short time with use of the orifice progresses, the cylindrical shape collapses, and the inner surface shape of the orifice hole changes from the cylindrical shape to 6 It expands to a polygon such as a square. As a result, there arises a problem that the desired cutting width cannot be obtained as described above.

  It is conceivable to use sintered diamond as a countermeasure against the above-mentioned uneven wear. Sintered diamond is produced by sintering diamond particles using a metal binder such as cobalt, and a metal binder exists between the diamond particles. However, since the metal binder portion is softer than the diamond particles, the wear proceeds in a short time. If the binder decreases, diamond particles also drop off, and the orifice hole expands, resulting in a problem that a stable cutting width cannot be obtained for a long time. In particular, in the case of a water jet for the purpose of improving cutting efficiency, since a solution in which hard particles (alumina, etc.) are added to water is injected at a high pressure, wear of the metal binder part softer than diamond particles proceeds in a short time. There is a problem that a stable cutting width cannot be obtained for a long time.

  In addition, there is a method in which a diamond thin film is coated on the inner surface of a metal orifice hole by CVD (chemical vapor deposition) as polycrystalline diamond containing no metal binder. However, there is a problem that wear tends to progress and the life is short because of the thin film and the low bonding force between diamond particles.

  On the other hand, the nano-polycrystalline diamond of the present embodiment is polycrystalline and extremely excellent in wear resistance, so that the uneven wear as described above can be effectively suppressed. Moreover, since the nano-polycrystalline diamond of this Embodiment does not contain a binder, the progress of wear at the binder portion can also be avoided. Therefore, the nano-polycrystalline diamond of the present embodiment is also useful for water jet orifices.

  As an application example of the diamond material other than the above, an example in which single crystal diamond is used as the material of the wire drawing die can be given.

  However, since the above-mentioned problem of uneven wear occurs in single crystal diamond, the wire diameter die using single crystal diamond cannot obtain the desired wire diameter and roundness with the lapse of use time. There is a problem.

  Also in the case of a single crystal diamond wire drawing die, the inner surface of the die hole has surfaces of various crystal orientations in the circumferential direction, as in the case of the orifice for water jet. Therefore, even when the shape of the inner surface of the die hole is circular at the beginning of use, wear of the surface that is easily worn proceeds in a short time, and the shape of the inner surface of the die hole is changed from a circular shape to a polygonal shape such as a hexagon. It will spread. As a result, there is a problem that the target wire diameter and roundness cannot be obtained.

  As a countermeasure against the above-mentioned uneven wear, it is conceivable to use sintered diamond. However, as in the case of the orifice for water jet, there is a problem that the die hole expands and a stable wire diameter and roundness cannot be obtained for a long time. is there.

  Therefore, it can be considered that the binder is removed using an acid, but the diamond particles fall off due to the low bonding force between the diamond particles, and the desired wire diameter and roundness cannot be obtained. is there.

  Although it is conceivable to use a polycrystalline diamond obtained by CVD, which is a polycrystalline diamond not containing a binder, there is a problem that wear is likely to proceed because the bonding force between diamond particles is small, and the life is short. Similarly, it is also possible to use polycrystalline diamond containing no binder, obtained by direct conversion sintering by indirect heating at an ultrahigh pressure and high temperature of 8 GPa or more and 2200 ° C. or more using high-purity graphite as a starting material. In this case, since the oxidation resistance is poor, there is a problem that wear tends to proceed and the life is short.

  Furthermore, when manufacturing a polygonal drawing die having a hole shape other than a circle, such as a quadrangle, single crystal diamond is processed with a laser, so that high-precision processing is difficult. Diamond containing a metal binder is electrically conductive and can be subjected to electric discharge machining. However, since diamond has a large particle size, high-precision machining is similarly difficult.

  On the other hand, the nano-polycrystalline diamond of the present embodiment can effectively suppress uneven wear, and since the binder is not included, it is possible to avoid the progress of wear at the binder portion. In addition, the nano-polycrystalline diamond of the present embodiment has a large bonding force between diamond particles, has conductivity, and is excellent in oxidation resistance, and thus is useful for a wire drawing die.

  Similarly, the nano-polycrystalline diamond of the present embodiment is useful for tools such as a scribe tool, a scribe wheel, and a dresser.

  Next, examples of the present invention will be described.

Methane gas and trimethyl boron were mixed at a ratio of 1: 1 in a vacuum chamber, and the mixed gas was sprayed onto a diamond substrate heated to 1900 ° C. At this time, the degree of vacuum in the vacuum chamber was set to 20 to 30 Torr. Then, boron-containing graphite was deposited on the substrate. The bulk density of this graphite was 2.0 g / cm ³ . According to ICP elemental analysis, the boron concentration in the graphite was 0.06% by mass.

The graphite was converted to diamond at a synthesis temperature of 2200 ° C. and 15 GPa to obtain nano-polycrystalline diamond to which boron was added. The polycrystalline diamond had a crystal grain size (maximum crystal grain length) of 10 to 100 nm. From the X-ray pattern, no precipitation of B ₄ C was observed. This nanopolycrystalline diamond had a Knoop hardness of 120 GPa. A substrate having a size of 3 mm × 1 mm was cut out from the nano-polycrystalline diamond, and the electric resistance of the substrate was measured.

Methane gas and trimethyl borate were mixed 1: 1 in a vacuum chamber, and the mixed gas was sprayed onto a diamond substrate heated to 1900 ° C. At this time, the degree of vacuum in the vacuum chamber was set to 20 to 30 Torr. Then, boron-containing graphite was deposited on the substrate. The bulk density of this graphite was 2.0 g / cm ³ . According to ICP elemental analysis, the boron concentration in the graphite was 0.5% by mass.

The graphite was converted to diamond at a synthesis temperature of 2200 ° C. and 15 GPa to obtain nano-polycrystalline diamond to which boron was added. Each polycrystalline diamond had a crystal grain size of 10 to 100 nm. From the X-ray pattern, no precipitation of B ₄ C was observed. This nanopolycrystalline diamond had a Knoop hardness of 120 GPa. A substrate having a size of 3 mm × 1 mm was cut out from the nano-polycrystalline diamond, and the electric resistance of the substrate was measured.

Methane gas and trimethyl borate were mixed 1: 1 in a vacuum chamber, and the mixed gas was sprayed onto a diamond substrate heated to 1900 ° C. At this time, the degree of vacuum in the vacuum chamber was set to 20 to 30 Torr. Then, boron-containing graphite was deposited on the substrate. The bulk density of this graphite was 2.0 g / cm ³ . According to ICP elemental analysis, the boron concentration in the graphite was 0.5% by mass.

The graphite was converted to diamond at a synthesis temperature of 2200 ° C. and 8 GPa to obtain nano-polycrystalline diamond to which boron was added. Each polycrystalline diamond had a crystal grain size of 10 to 100 nm. From the X-ray pattern, no precipitation of B ₄ C was observed. This nanopolycrystalline diamond had a Knoop hardness of 120 GPa. A substrate having a size of 3 mm × 1 mm was cut out from the nano-polycrystalline diamond, and the electric resistance of the substrate was measured.

Methane gas and trimethyl borate were mixed 1: 1 in a vacuum chamber, and the mixed gas was sprayed onto a diamond substrate heated to 1900 ° C. At this time, the degree of vacuum in the vacuum chamber was set to 20 to 30 Torr. Then, boron-containing graphite was deposited on the substrate. The bulk density of this graphite was 2.0 g / cm ³ . According to ICP elemental analysis, the boron concentration in the graphite was 0.5% by mass.

The graphite was converted to diamond at a synthesis temperature of 1800 ° C. and 15 GPa to obtain nano-polycrystalline diamond to which boron was added. Each polycrystalline diamond had a crystal grain size of 10 to 100 nm. From the X-ray pattern, no precipitation of B ₄ C was observed. This nanopolycrystalline diamond had a Knoop hardness of 120 GPa. A substrate having a size of 3 mm × 1 mm was cut out from the nano-polycrystalline diamond, and the electric resistance of the substrate was measured.

<Comparative Example 1>
Pure graphite having a particle diameter of 2 μm or less and B ₄ C were mixed, and the mixture was fired at 2000 ° C. to dissolve boron in carbon. The boron concentration in the graphite was 0.5% by mass. This graphite was directly converted to polycrystalline diamond at a synthesis temperature of 2200 ° C. and 15 GPa. However, the crystal grain size of the polycrystalline diamond was 1 μm to 100 μm, respectively, and the variation in crystal grain size was large. The polycrystalline diamond had a Knoop hardness of 75 GPa. Further, a substrate having a size of 3 mm × 1 mm was cut out from the polycrystalline diamond, and the electric resistance of the substrate was measured.

<Comparative example 2>
Pure graphite having a particle size of 2 μm or less was immersed in a solution containing boron for 12 hours and then taken out, and the graphite was subjected to heat treatment at 2000 ° C. The boron concentration in the graphite after the heat treatment was 0.003% by mass. Regardless of whether the solution was alkaline, acidic, or organic, boron was rarely incorporated into the graphite.

<Comparative Example 3>
When graphite having a bulk density of 0.8 g / cm ³ was used, the volume change was large, so that the frequency of occurrence of a situation in which an abnormality occurred during the synthesis and the apparatus had to be stopped was twice or more.

<Comparative example 4>
When high-purity graphite without doping was used as a raw material and kept at a high pressure of 8 GPa and a high temperature of 2000 ° C., the graphite was not converted to diamond.

  Using the nano-polycrystalline diamond and the non-doped nano-polycrystalline diamond of the above example, scribe tools with 4 points at the tip (tetragonal planar shape) were produced. Using each of the fabricated scribe tools, 200 scribe grooves having a length of 50 mm were formed on a sapphire substrate with a load of 20 g. Thereafter, when the amount of wear of the polycrystalline diamond at the tip portion of each scribe tool was observed with an electron microscope, the amount of wear of the nano-polycrystalline diamond of the above example was 0. 0 compared to the scribing tool made of single crystal diamond. Less than doubled.

  On the other hand, non-doped nanopolycrystalline diamond is inferior in heat-resistant oxidation characteristics as compared to boron-doped nanopolycrystalline diamond of this example, so the amount of wear at the tip of the scribe tool at a high temperature is three times that of this example. . Thus, by using the nano-polycrystalline diamond of the above example for the scribe tool, the nano-polycrystalline diamond is hardly worn, and therefore the change in the tool shape is small, which is remarkable as compared with the non-doped nano-polycrystalline diamond. It was confirmed that it had a long life.

  A dresser having a single point (conical shape) at the tip was manufactured using the nano-polycrystalline diamond of the above example and non-doped nano-polycrystalline diamond. Each of the produced dressers was abraded using a WA (hoofed alumina) grindstone under the conditions of a low stone peripheral speed of 30 m / sec and a cutting depth of 0.05 mm. Then, when the wear amount of the dresser was measured with a height gauge meter, the wear amount of the nano-polycrystalline diamond of the above example was reduced to 0.3 times or less compared to the dresser made of single crystal diamond.

  On the other hand, non-doped nanopolycrystalline diamond is inferior in heat-resistant oxidation characteristics as compared with boron-doped nanopolycrystalline diamond of this example, and therefore, the wear amount at the tip of the dresser at a high temperature is four times that of this example. Thus, by using the nano-polycrystalline diamond of the above-mentioned example as a dresser, the nano-polycrystalline diamond is hardly worn, and therefore the change in the tool shape is small, which is remarkable as compared with the non-doped nano-polycrystalline diamond. It was confirmed that it had a lifetime.

  A drill (rotary tool) having a diameter of 1 mm and a blade length of 3 mm was produced using the nanopolycrystalline diamond of the above example and non-doped nanopolycrystalline diamond. Using each of the produced drills, a hole was made in a cemented carbide (WC-Co) plate having a thickness of 1.0 mm under the conditions of a rotation speed of 4000 rotations / minute and a feed of 2 μm / revolution. The number of holes that could be drilled before the drill was worn or broken was more than five times greater than that of single crystal diamond drills.

  On the other hand, non-doped nano-polycrystalline diamond is inferior in heat-resistant oxidation characteristics as compared with boron-doped nano-polycrystalline diamond of this example, so that the wear amount of the drill tip at a high temperature is four times that of this example. Thus, by using the nano-polycrystalline diamond of the above example for the drill, the nano-polycrystalline diamond is hardly worn, and therefore the change in the tool shape is small, which is remarkable as compared with the non-doped nano-polycrystalline diamond. It was confirmed that it had a lifetime.

As the nano-polycrystalline diamond used for the wire drawing die, boron-added nano-polycrystalline diamond having an additive element of boron, a concentration of 1 × 10 ¹⁸ / cm ³ , and a crystal grain size of 100 nm was used. Using this nano-polycrystalline diamond, a wire drawing die having a pore diameter of φ30 μm was produced.

  The die life was evaluated using the wire drawing die. Specifically, when drawing time until a die having a hole diameter of φ30 μm was expanded to φ32 μm was measured, the drawing time was 5 times that when single crystal diamond was used, and when non-doped nanopolycrystalline diamond was used. It turns out that it is 2 times.

  On the other hand, non-doped nano-polycrystalline diamond is inferior in heat-resistant oxidation characteristics as compared to boron-doped nano-polycrystalline diamond of this example, so that the amount of wear on the drawing friction surface at high temperature is five times that of this example. It was.

  Thus, by using the nano-polycrystalline diamond of the above example for the wire drawing die, the nano-polycrystalline diamond is hardly worn, and therefore the change in the tool shape is small, compared with the non-doped nano-polycrystalline diamond. It was confirmed that the product had a remarkable lifetime.

As the nano-polycrystalline diamond used for the orifice for the abrasive water jet, boron-doped nano-polycrystalline diamond having an additive element of boron, a concentration of 1 × 10 ¹⁹ / cm ³ and a crystal grain size of 200 nm was used. Using this nano-polycrystalline diamond, a polygonal water jet orifice having a rectangular shape with a short side of 150 μm and a long side of 300 μm was produced.

  The cutting ability was evaluated using the orifice for water jet. Specifically, when the cutting time until the long side of the water jet orifice was expanded to 400 μm was measured, the cutting time was 20 in comparison with polycrystalline diamond containing Co as a metal binder and a diamond particle diameter of 5 μm. It turned out to be double.

  On the other hand, non-doped nano-polycrystalline diamond is inferior in heat-resistant oxidation characteristics compared to boron-doped nano-polycrystalline diamond of this example, so the wear amount of the diamond surface of the holes that come into contact with high-temperature abrasive particles (hard particles) However, it was 3.5 times that of the present example. Thus, by using the nano-polycrystalline diamond of the above example for the nozzle, the nano-polycrystalline diamond is hardly worn, and therefore the change in the tool shape is small, which is remarkable as compared with the non-doped nano-polycrystalline diamond. It was confirmed that it had a lifetime.

In the same manner as in Example 2, graphite was deposited on the substrate. According to ICP elemental analysis, the boron concentration was 0.5 mass%. This corresponds to a boron concentration of 1 × 10 ²¹ / cm ³ . Using this graphite, nanopolycrystalline diamond was obtained directly from graphite in the same manner as in Example 2. A substrate having a size of 3 mm × 1 mm was cut out from the nanopolycrystalline diamond and measured for electric resistance. As a result, the electric resistance value was 10Ω.

  The conductive nano-polycrystalline diamond was joined to the cutting tool body using an active brazing material in an inert atmosphere. After polishing the surface of the polycrystalline diamond, the flank face was cut by electric discharge machining to produce an R bite. For comparison, a tool (Comparative Example A) using a sintered diamond containing a conventional Co binder was similarly produced by electric discharge machining.

  The edge line accuracy of the cutting edge by electric discharge machining was 2 to 5 μm or less depending on the particle diameter of the diamond abrasive grains contained in Comparative Example A made of sintered diamond, whereas boron-doped nanopolycrystalline diamond ( In Invention Example 1), it was as good as 0.5 μm or less. The processing time was also the same as in Comparative Example A.

  Further, a boron-added nano-polycrystalline diamond tool (Invention Example 2), a non-doped nano-polycrystalline diamond tool (Comparative Example B), and a single-crystal diamond tool (Comparative Example C) were prepared. Cutting evaluation was performed. As for Inventive Example 2 and Comparative Example B, a precise cutting edge accuracy of 0.1 μm or less was obtained.

The contents of the evaluation test are as follows.
・ Tool shape: Corner R0.4mm, clearance angle 11 °, rake angle 0 °
Work material: Material-Aluminum alloy A390
Shape-φ110 × 500mm U-shaped with 4 grooves ・ Processing method: Cylindrical peripheral intermittent turning Wet ・ Cutting fluid: Water-soluble emulsion ・ Cutting condition: Cutting speed Vc = 800m / min, Cutting ap = 0.2mm, Feeding speed f = 0.1 mm / rev, cutting distance 10 km
After performing the cutting evaluation under the above conditions, the tool edge was observed and the wear state was confirmed. In Comparative Example A, the flank wear amount was about 45 μm and the edge shape was greatly impaired. In the case of Inventive Example 1, the flank wear amount was 5 μm and good.

  On the other hand, Example 2 of the polished finish has a wear amount of about 2 μm, which is very good compared to the wear amount of Comparative Example B of 3.5 μm and that of Comparative Example C of 3.5 μm. It was found that the wear resistance was equivalent to or better than that of the nano-polycrystalline diamond and the tool life was excellent.

  In addition, when the characteristics of non-doped nano-polycrystalline diamond are compared with the case of using boron-doped nano-polycrystalline diamond, non-doped nano-polycrystalline diamond is high in the atmosphere at a high temperature of 600 ° C. or higher. It burned by the oxygen and gradually decreased in mass. At 950 ° C., the cutting tool was significantly deformed, and 80% of the nanopolycrystalline diamond was burned out.

  On the other hand, in the nano-polycrystalline diamond of the above example, there was almost no decrease in mass even between 600 ° C. and 800 ° C., and the mass loss was only 5 to 8% even at a temperature of 950 ° C. or higher.

  Thus, even when the nano-polycrystalline diamond of the above example is used for a cutting tool, the nano-polycrystalline diamond has excellent wear resistance and does not burn out even at high temperatures, and therefore changes in the tool shape. It was confirmed that the oxidation resistance was smaller than that of non-doped nanopolycrystalline diamond.

To synthesize nanopolycrystalline diamond raw material, first, methane gas and trimethylboron were mixed at a ratio of 4: 1 in a vacuum chamber and sprayed onto a diamond substrate heated to 1900 ° C. to deposit graphite on the substrate. At this time, the degree of vacuum in the chamber was 20 to 30 Torr. The bulk density of the obtained graphite was 2.0 g / cm ³ . The boron concentration was about 50 ppm by SIMS elemental analysis. This corresponds to a boron concentration of 1 × 10 ¹⁹ / cm ³ .

Using the above graphite, nanopolycrystalline diamond was obtained directly from graphite at a synthesis temperature of 2200 ° C. and 15 GPa. The crystal grain size of the nano-polycrystalline diamond was 10 to 100 nm, respectively. From the X-ray pattern, no precipitation of B ₄ C or the like was observed. The Knoop hardness of this polycrystalline diamond was 125 GPa. A substrate having a size of 3 mm × 1 mm was cut out from the nanopolycrystalline diamond and measured for electric resistance. As a result, the electric resistance value was 500Ω.

  The conductive nano-polycrystalline diamond was bonded to the cutting tool body in an inert atmosphere using an active brazing material, and the surface of the polycrystalline diamond was polished. Further, a boron-doped polycrystalline diamond tool (Invention Example 3), a non-doped nano-polycrystalline diamond tool (Comparative Example D), and a single crystal diamond tool (Comparative Example E) were prepared by cutting the flank face by polishing. Evaluation was performed. The inventive example 3 and the comparative tool D both have a precise cutting edge accuracy of 0.1 μm or less.

The contents of the evaluation test are as follows.
・ Tool shape: Corner R0.4mm, clearance angle 11 °, rake angle 0 °
Work material: Material-Aluminum alloy A390
Shape-φ110 × 500mm U-shaped with 4 grooves ・ Processing method: Cylindrical peripheral intermittent turning Wet ・ Cutting fluid: Water-soluble emulsion ・ Cutting condition: Cutting speed Vc = 800m / min, Cutting ap = 0.2mm, Feeding speed f = 0.1 mm / rev, cutting distance 10 km
In Invention Example 3, the wear amount is about 1.0 μm, which is very good as compared with the wear amount of Comparative Example D of 3.5 μm and the wear amount of Comparative Example E of 3.5 μm. As a result, it was found that it exhibits wear resistance equal to or better than that of conventional non-doped nano-polycrystalline diamond and has an excellent tool life.

  The cutting point of the tool edge during cutting becomes extremely hot. Boron-doped nanopolycrystalline diamond, which has superior oxidation resistance compared to non-doped nanopolycrystalline diamond, is extremely less affected by thermal degradation due to frictional heat during cutting and reactive wear at high temperatures. High performance can be obtained compared to single crystal diamond.

  As described above, even when the nano-polycrystalline diamond of the above-described example is used for a cutting tool, the nano-polycrystalline diamond has excellent wear resistance, and therefore the change in the tool shape is small, and the non-doped nano-polycrystalline diamond. It was confirmed that remarkable performance was exhibited compared to.

In the same manner as in Example 2, graphite was deposited on the substrate. According to ICP elemental analysis, the boron concentration was 0.5 mass%. This corresponds to a boron concentration of 1 × 10 ²¹ / cm ³ . Using this graphite, nanopolycrystalline diamond was obtained directly from graphite in the same manner as in Example 2. A substrate having a size of 3 mm × 1 mm was cut out from the nanopolycrystalline diamond and measured for electric resistance. As a result, the electric resistance value was 10Ω.

  The conductive nano-polycrystalline diamond was bonded to the tool body in an inert atmosphere using an active brazing material. After polishing the surface of the polycrystalline diamond, the flank face was cut by electric discharge machining to produce a φ0.5 mm ball end mill (product 4 of the present invention) having two twisted cutting edges. For comparison, a tool (Comparative Example F) using sintered diamond containing a conventional Co binder was similarly produced by electric discharge machining.

  The edge line accuracy of the edge by electric discharge machining was about 2 to 5 μm in Comparative Example F made of sintered diamond, depending on the grain size of the diamond abrasive grains contained, whereas boron-doped nanopolycrystalline diamond In (Invention product 4), it was as good as 0.5 μm or less. Furthermore, using an undoped nano-polycrystalline diamond, an end mill having the same shape was manufactured by laser processing, and the flank face was locally polished to finish the cutting edge quality (Comparative Example G).

The contents of the evaluation test are as follows.
・ Tool shape: φ0.5mm, 2-flute ball end mill ・ Work material: Material-STAVAX
Cutting fluid: white kerosene Cutting conditions: tool rotation speed 20000 rpm, cutting ap = 0.005 mm / pitch, feed speed f = 100 mm / min
When cutting evaluation was performed under the above conditions, the tool life of the product 4 of the present invention was 5 times or more that of Comparative Example F and 1.5 times or more that of Comparative Example G, which was very good.
The cutting point of the tool edge during cutting becomes extremely hot. Boron-doped nanopolycrystalline diamond, which has superior oxidation resistance compared to non-doped nanopolycrystalline diamond, is extremely less affected by thermal degradation and reactive wear due to frictional heat during cutting. High performance can be obtained compared to nano-polycrystalline diamond and single-crystal diamond.

  As described above, even when the nano-polycrystalline diamond of the above-described embodiment is used for a rotary tool, the nano-polycrystalline diamond has excellent wear resistance, and therefore the change in the tool shape is small, and the non-doped nano-polycrystalline diamond. It was confirmed that remarkable performance was exhibited compared to.

In the same manner as in Example 2, graphite was deposited on the substrate. According to ICP elemental analysis, the boron concentration was 0.5 mass%. This corresponds to a boron concentration of 1 × 10 ²¹ / cm ³ . Using this graphite, nanopolycrystalline diamond was obtained directly from graphite in the same manner as in Example 2. A substrate having a size of 3 mm × 1 mm was cut out from the nanopolycrystalline diamond and measured for electric resistance. As a result, the electric resistance value was 10Ω. A scribing wheel having a diameter of 3 mm, a thickness of 0.8 mm, and a blade edge opening angle of 120 ° was produced from the obtained polycrystal by electric discharge machining, and the glass substrate was subjected to scribing evaluation. As a result, the tiremond polycrystal of this example could scribe a long distance of about 250 km.

  For comparison, a scribe wheel having the same shape was made from non-doped polycrystalline diamond and single-crystal diamond, and the glass substrate was similarly subjected to scribing evaluation. It was possible to scribe 240 km, which was almost the same as that of single crystal diamond, but could only scribe a distance of 1/3 with single crystal diamond.

  On the other hand, non-doped nanopolycrystalline diamond is inferior in heat-resistant oxidation characteristics compared to boron-doped nanopolycrystalline diamond of this example, so the amount of wear on the outer periphery of the scribe wheel that becomes high is 1.5 times that of this example. became. Thus, by using the nano-polycrystalline diamond of the above example for the scribe wheel, the nano-polycrystalline diamond is hardly worn, and therefore the change in the tool shape is small, which is remarkable as compared with the non-doped nano-polycrystalline diamond. It was confirmed that it had a long life.

  Furthermore, it was confirmed that excellent tool life, wear resistance, oxidation resistance and the like were exhibited by applying the nano-polycrystalline diamond of this example to various tools.

However, even under conditions other than those described above, it is considered that nanopolycrystalline diamond having excellent characteristics can be produced within the scope described in the claims.
Although the embodiments and examples of the present invention have been described above, various modifications can be made to the above-described embodiments and examples. Further, the scope of the present invention is not limited to the above-described embodiments and examples. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 nano-polycrystalline diamond, 2 substrate, 3 group III element.

Claims (17)

Carbon,
A group III element added to be dispersed in the carbon at an atomic level;
Composed of inevitable impurities,
Polycrystalline diamond having a crystal grain size of 500 nm or less.   The polycrystalline diamond according to claim 1, wherein the group III element is dispersed in the carbon as substitutional isolated atoms. ^{3. The} polycrystalline diamond according to claim 1, wherein a concentration of the group III element is 1 × 10 ¹⁴ / cm ³ or more and 1 × 10 ²² / cm ³ or less.   The polycrystalline diamond is produced by sintering graphite obtained by pyrolyzing a mixed gas of a gas containing a group III element and a hydrocarbon gas at a temperature of 1500 ° C. or higher. The polycrystalline diamond according to claim 3. Preparing a graphite in which a group III element is added so as to be dispersed at an atomic level in carbon;
Performing a heat treatment on the graphite in a high-pressure press to convert the graphite to diamond;
A method for producing polycrystalline diamond, comprising:   6. The method for producing polycrystalline diamond according to claim 5, wherein in the step of converting the graphite into diamond, the graphite is heat-treated in the high-pressure press without adding a sintering aid or a catalyst.   In the step of preparing the graphite, a mixed gas of a gas containing a group III element and a hydrocarbon gas is introduced into the vacuum chamber, and the mixed gas is pyrolyzed at a temperature of 1500 ° C. or higher to form a substrate. The method for producing polycrystalline diamond according to claim 5, comprising a step of forming graphite.   The method for producing polycrystalline diamond according to claim 7, wherein in the step of converting the graphite into diamond, the graphite formed on the substrate is subjected to heat treatment at 1500 ° C or higher under a high pressure of 8 GPa or higher.   The method for producing polycrystalline diamond according to claim 7, wherein the mixed gas is caused to flow toward the surface of the base material.   The method for producing polycrystalline diamond according to any one of claims 5 to 9, wherein the hydrocarbon gas is methane gas.   A scribe tool using the polycrystalline diamond according to any one of claims 1 to 4.   A scribing wheel using the polycrystalline diamond according to any one of claims 1 to 4.   A dresser using the polycrystalline diamond according to any one of claims 1 to 4.   A rotary tool using the polycrystalline diamond according to any one of claims 1 to 4.   An orifice for water jet using the polycrystalline diamond according to any one of claims 1 to 4.   A wire drawing die using the polycrystalline diamond according to any one of claims 1 to 4.   The cutting tool using the polycrystalline diamond of any one of Claims 1-4.