JP5432610B2 - Diamond polycrystal - Google Patents

Description

  The present invention relates to a polycrystalline diamond material, and more particularly to a polycrystalline diamond having high hardness, high strength and excellent heat resistance used for a cutting tool or the like.

  In cutting the material, a cutting tool and a cutting method suitable for the work material are selected. Grinding using a diamond grindstone is performed for shape processing of hard ceramics and optical glass. However, a grindstone in which diamond abrasive grains are hardened with a general-purpose resin bond or ceramic binder that has a high self-generating effect can be cut well and give shape accuracy, but the surface roughness of the machined surface may be impaired due to falling off of the abrasive grains. . On the other hand, a grindstone using a metal hard binder may become clogged, resulting in increased grinding resistance, which may cause microcracks, surface accuracy deterioration, or damage to the workpiece.

Further, among difficult-to-cut materials, there is a method in which cutting is performed while plastically deforming the tool blade edge in a state where the temperature of the processed portion is kept high and the material strength of the work material is reduced.
Hardened steel is a cBN sintered body tool that is cut by utilizing the softening of the work material by the temperature rise due to friction at the cutting point without using a cutting fluid. Cutting of hard ceramics such as silicon nitride and alumina is extremely difficult, and the method of cutting with a tool with high heat resistance while actively heating and softening the sample using laser irradiation or plasma radiation is used. It has been.

  Thus, the heat resistance and thermal conductivity of the blade material are important for cutting where it is essential to keep the cutting point at a high temperature. In addition to cemented carbide, a cBN sintered body using a ceramic with high heat resistance as a binder is used for the cutting blade. In the case of cemented carbide, the material such as Co starts to melt from about 600 ° C. There was a problem that the heat resistance itself was low.

Compared to cBN sintered body tools, polycrystalline diamond sintered bodies have higher abrasive hardness and excellent cutting performance at low temperatures, but most of them are cutting performance at high temperatures due to the sintering aid contained in the structure. Inferior to
In other words, one that is widely used industrially as a polycrystalline diamond sintered body is a diamond sintered body using Co as a binder, which is used for tools such as cutting tools, dressers and dies, and drill bits. It has been broken. However, in this diamond sintered body, a metal such as Co exists as a continuous layer between the diamond particles, so that the mechanical properties such as hardness and strength of the polycrystalline body are lowered, and the sintering aid used is Since it is contained in the polycrystal and acts as a catalyst for promoting the graphitization of diamond, it is inferior in heat resistance such as the graphitization of diamond is observed from about C700 ° C.

  Also known are those using carbonates as sintering aids (see Patent Literature 1 and Patent Literature 2) and those using SiC. Polycrystalline diamond using carbonates as sintering aids. Is superior in heat resistance to those using Co as a binder, but the mechanical properties are not sufficient due to the presence of a carbonate substance at the grain boundaries. In addition, the polycrystalline diamond using SiC as a sintering aid has high heat resistance, but the material strength is weak because the bonding force between diamond particles is weak.

  Furthermore, for example, Patent Document 3 describes a method of synthesizing fine diamond by heating a carbon nanotube to 10 GPa or more and 1600 ° C. or more (Patent Document 3). However, since the disclosed method pressurizes carbon nanotubes with a diamond anvil and collects and heats them with a carbon dioxide laser, it is impossible to produce a homogenous diamond polycrystal having a size applicable to a cutting tool or the like. .

In order to increase the heat resistance of the diamond polycrystalline body, there is a method of obtaining a structure consisting only of diamond particles by acid-treating the diamond sintered body and dissolving and removing the metal sintering aid in the grain boundary. The formation process of diamond particle bonds is very sensitive to the sintering conditions and the local concentration of the metal catalyst and is difficult to control. For this reason, many sites where the sintering aid is sealed by the diamond particles are generated. At such sites, it is difficult to completely remove the metal sintering aid inside the sintered body by acid treatment, and the heat resistance is inferior to that of polycrystalline diamond containing no sintering aid obtained by direct conversion. It is enough.
Further, the average particle size of the diamond grains constituting the sintered body is approximately 1 μm or more, and the size of the void formed by eluting the sintering aid by acid treatment is about 0.03 to 3 μm. When used as a tool, there are problems such that sufficient shape accuracy of the cutting edge cannot be obtained, the gap size is large, and the material strength is significantly reduced.

Dense and high hardness diamond polycrystals obtained by direct conversion using non-diamond carbon as a raw material without leaving a sintering aid in the sintered body have been developed (see Patent Documents 4 to 7). These polycrystalline bodies are superior in heat resistance and have extremely excellent characteristics such as hardness and wear resistance as compared with a polycrystalline diamond sintered body in which a sintering aid remains in the structure.
However, the polycrystalline diamond obtained by directly converting these graphite-like carbons as a starting material is a dense body and excellent in both mechanical strength and heat resistance, but when used as a grinding tool, this high hardness For this reason, it is difficult to process the minute unevenness that becomes the chip pocket, and the grinding resistance increases. On the other hand, the cutting performance with respect to the work material which has high thermal conductivity and it is important to keep the cutting point at a high temperature is inferior. Thus, it has not yet been sufficient in terms of characteristics for grinding and use as a cutting tool.

Japanese Patent Laid-Open No. 4-74766 JP-A-4-114966 JP 2002-66302 A JP 2003-292397 A JP 2004-131336 A Japanese Patent Laid-Open No. 2007-22888 JP 2007-99559 A

The present invention is a diamond polycrystalline body for use in a cutting tool or the like, which has high strength, excellent heat resistance, low thermal conductivity, high temperature at the cutting point, and high cutting performance in cutting difficult-to-cut materials. The purpose is to provide.

As a result of intensive studies, the present inventors have optimized a sintering condition using a non-diamond type carbon material as a starting material, so that 95% by mass or more of the sintered body is made of diamond, and the diamond particles are three-dimensional. It was found that a high-hardness sintered body that is firmly bonded to each other and has minute voids can be obtained.
That is, the present invention relates to a polycrystalline diamond as described below.

(1) A non-diamond type carbon raw material is a polycrystalline body composed of 95% by mass or more of diamond, which is obtained by directly converting non-diamond type carbon raw material under ultrahigh pressure / high temperature without adding a sintering aid or a catalyst. The particle size is 100 nm or less, the average particle size is 50 nm or less, diamond particles are three-dimensionally bonded to form pores, and the porosity is 0.01 to 30 vol%. Diamond polycrystal.
(2) The diamond polycrystalline body according to (1), wherein the D95 particle diameter of the equivalent circle diameter of the pores is 500 nm or less and the average value of the equivalent circle diameter is 100 nm or less.
(3) The polycrystalline diamond according to (1) or (2), wherein the particle has a D95 particle size of 50 nm or less and an average particle size of 30 nm or less.
(4) The polycrystalline diamond according to any one of (1) to (3), having a hardness of 50 GPa or more.

  The diamond polycrystal of the present invention is a dense diamond polycrystal obtained by directly converting the thermal conductivity because diamond particles are three-dimensionally bonded and have high mechanical strength and is a porous body. Since it is comparatively low, grinding and cutting can be performed while maintaining the processing point at a high temperature.

It is a figure which shows the area | region where a diamond is thermodynamically stable by the relationship between a pressure and temperature.

  The polycrystalline diamond according to the present invention is a sintered body obtained by directly converting a non-diamond type carbon material as a raw material into diamond, and a conventional diamond sintered body obtained by sintering diamond particles using a sintering aid. Unlike the bonded body, the bonds between the diamond particles are formed at the same time as the particles. Therefore, the diamond particles are extremely strongly bonded and integrated, and the diamond particles have a three-dimensional continuous structure.

  The diamond polycrystal of the present invention is a polycrystal comprising 95% by mass or more of non-diamond type carbon raw material, which is directly converted to diamond without adding a sintering aid or a catalyst under ultrahigh pressure and high temperature. The particles are composed of diamond sintered particles (primary particles) having a D95 particle size of 50 nm or less and 100 nm or less and an average particle size of 50 nm or less. The maximum primary particle size is preferably 50 nm or less and the average particle size is preferably 30 nm or less.

In the polycrystalline diamond according to the present invention, diamond particles are three-dimensionally bonded to form fine pores (voids) between the particles. The porosity of the polycrystalline diamond according to the present invention is 0.01 vol% or more and 30 vol% or less.
By setting the porosity to the above numerical range, the thermal conductivity can be lowered without impairing the mechanical strength of the polycrystalline diamond.
The D95 particle diameter of the equivalent circle diameter of the pores is preferably 500 nm or less, and the equivalent circle diameter of voids between the particles is preferably 100 nm or less on average. By setting the equivalent circle diameter within this numerical range, sufficient cutting edge ridge line processing accuracy can be obtained in combination with reducing the particle size of the diamond particles when used as a cutting tool.

  As described above, in the polycrystalline diamond according to the present invention, the maximum particle diameter of diamond particles is 100 nm or less, and the equivalent circle diameter of the interparticle voids is also sufficiently small as an average of 100 nm or less, so when used as a cutting tool. Sufficient cutting edge ridgeline processing accuracy can be obtained. Further, since the gap between diamond particles is 30 vol% at the maximum, a decrease in mechanical strength is not a problem, and it has higher hardness than diamond, which is hard next to diamond, and can be used as a tool.

The diamond polycrystalline body of the present invention has high mechanical strength because diamond particles are firmly bonded three-dimensionally. In addition, since it has a high density of voids, it has a low thermal conductivity, is suitable for machining that keeps the machining point at a high temperature, and is a high-hardness material capable of forming a highly accurate tool shape. This gap exhibits a great effect as a chip pocket for collecting grinding scraps and cutting fluid removed by grinding during grinding.
Below, the manufacturing method of the diamond polycrystal of this invention is described.

(Non-diamond carbon material)
The present invention is a polycrystalline diamond obtained by directly converting and sintering a non-diamond type carbon material. As the non-diamond type carbon material, fullerene, carbon nanotube, amorphous carbon, glassy carbon, graphite and the like are applicable. However, it is not limited to these.
In order to obtain the polycrystalline diamond of the present invention, it is necessary to arrange and sinter the raw material carbon as densely as possible. Carbon nanotubes, amorphous carbon, etc. are not in powder form, but in the form of pellets by cold isostatic pressing, etc. It is desirable to use it after being molded.
In order to set the D95 particle size of the diamond particles constituting the polycrystalline diamond to 100 nm or less and the average particle size to 50 nm or less, it is necessary to make the particle size of the non-diamond carbon raw material fine, preferably Is 1 μm or less. Setting it to 1 μm or less is one of effective means for setting the average particle diameter of diamond particles to 50 nm or less.

(Conversion to diamond)
The non-graphite carbon raw material is directly converted into diamond by filling the non-graphite carbon raw material in a high melting point metal capsule and holding the diamond in a thermally stable pressure environment for a predetermined time using an ultrahigh pressure generator. It becomes a high-hardness diamond polycrystal. In order to obtain a structure having fine voids of the present invention, it is preferable to perform the treatment at a high temperature of 2000 ° C. or higher.

  Indirect heating is preferable as a heating method for converting non-diamond raw material carbon to diamond. In direct current heating to raw carbon and laser heating that gives local heat, it is difficult to keep the whole raw material at a constant temperature, and it is easy to generate unconverted parts to diamond and parts that do not contain fine voids. It is.

The pressure region in which diamond is thermodynamically stable in the process of converting the raw material carbon into diamond varies depending on the temperature, but requires a pressure of 8.5 GPa or more for a sintering temperature of 1500 ° C. or more. In order to obtain a structure having fine voids, a higher pressure of 12 GPa or higher is preferable when heating to 2000 ° C. or higher.
Further, the holding time of the predetermined temperature and the predetermined pressure in the process of converting to diamond is not particularly limited, but is preferably about 10 to 10,000 seconds.

FIG. 1 shows the region where diamond is thermodynamically stable in terms of the relationship between pressure and temperature.
In the present invention, since the conversion process to diamond is performed at 1500 ° C. or higher as described above, it is preferable to appropriately select from the range shown by hatching in FIG. Further, even in the diamond stable region, an unconverted portion is likely to remain if the pressure is low, and therefore, a pressure slightly higher than the equilibrium line (the one-dot chain line in FIG. 1) is preferable, specifically 8.5 GPa or more. preferable. In FIG. 1, the upper portion of the alternate long and short dash line is the diamond stable region, and the lower portion of the alternate long and short dash line is the graphite stable region.

In this way, although it is a diamond polycrystal composed of diamond of 95 mass% or more, a material suitable for cutting brittle hard materials can be obtained with an extremely low thermal conductivity of 300 W / m · K or less.
If the polycrystalline diamond particles are not three-dimensionally firmly bonded, even if the skiff polishing is performed with a cast iron disk in which diamond abrasive grains are dispersed, the particles fall off during the polishing, so Ra 0.1 μm or less No mirror surface can be obtained. On the other hand, when a strong bond is formed between the particles, a good polished surface can be obtained.
Actual cutting is desirably performed in a heat insulating system and in a non-oxidizing atmosphere in order to improve heat insulating properties.

EXAMPLES Although an Example and a comparative example demonstrate this invention in detail, these Examples are illustrative and the scope of the present invention is not limited to these.
The measuring method is as follows.

<Evaluation of particle size of raw material>
The average particle diameter of the carbon raw material was determined by observing the fracture surface for the bulk raw material and the powder for the powder raw material with a scanning electron microscope and measuring the particle size distribution.
<Average particle size of diamond particles>
The average particle diameter of diamond particles in the polycrystalline diamond was obtained by carrying out image analysis based on a photographed image at a magnification of 100 to 500,000 with a scanning electron microscope. Since diamond is an insulator, a coating of a conductive thin film is necessary for SEM observation at a high magnification, and such a minute particle size cannot be observed. With an SEM equipped with a highly sensitive scintillator photomultiplier combination detector, the acceleration voltage is extremely low (0.7 to 1.5 KV), and the probe current is increased to 15 to 16.5 pA, so that the magnification is 2 to 2. The structure can be observed at a magnification of 100,000 times. Image analysis was performed based on this photographed image to obtain an average particle size and a D95 particle size.
The detailed method is shown below.
First, the particle size distribution of the crystal grains constituting the sintered body is measured based on a photographed image taken with a scanning electron microscope. Specifically, individual particles are extracted using image analysis software (for example, ScionImage, manufactured by Scion Corporation), and the extracted particles are binarized to calculate the area (S) of each particle. Then, the particle size (D) of each particle is calculated as the diameter of a circle having the same area (D = 2√ (S / π)).
Next, the particle size distribution obtained above was processed by data analysis software (for example, Origin manufactured by OriginLab, Mathchad manufactured by Parametric Technology, etc.), and average particle size and D95 particle size were calculated.
In Examples and Comparative Examples described below, ULTRA55 manufactured by Carl Zeiss was used as a scanning electron microscope.

<Hardness>
The hardness was measured using a Knoop indenter and the measurement load was 4.9N.
<Pore diameter and porosity>
Extract the void from the high-resolution scanning electron microscope observation image of the sample surfaced with high accuracy, extract the void using an image analysis software (for example, ScionImage, manufactured by Scion Corporation), and Similar to the particle diameter measurement, the equivalent circle diameter was determined and analyzed to determine the average diameter and the D95 particle diameter. Moreover, it calculated | required by calculating | requiring the area of a pore part and comparing with an image surface.
<Thermal conductivity>
It was measured by a pulse heating method using a xenon flash lamp.

[Example]
As raw materials, an average particle size of 0.5 to 1 μm and a purity of 99.95% or more, fullerene powder, carbon nanotube powder, glassy carbon powder, graphite powder, and this graphite powder by cold isostatic pressing, Using a bulk sample shaped into a pellet, it was treated for 10 minutes under various pressure and temperature conditions. A polycrystalline diamond was obtained.
About the obtained sample, the production | generation phase was identified by X-ray diffraction, and the particle size of the constituent particles was examined by TEM observation. Further, the surface of the obtained sample was polished to a mirror surface, and the hardness on the polished surface was measured with a micro Knoop hardness meter, and the thermal conductivity was measured.
The results are shown in Table 1.

  The diamond polycrystalline body of the present invention has a low thermal conductivity and excellent mechanical strength and heat resistance as compared with a diamond sintered body containing a conventional metal binder and sintering aid. It can be used suitably for a use.

Claims (4)

  More than 95% by mass of a non-diamond carbon raw material obtained by directly converting a non-diamond type carbon raw material without adding a sintering aid or a catalyst under ultra high pressure / high temperature is a polycrystalline body. Polycrystalline diamond characterized by having a diameter of 100 nm or less, an average particle diameter of 50 nm or less, diamond particles three-dimensionally bonded to form pores, and a porosity of 0.01 to 30 vol% body.   2. The polycrystalline diamond according to claim 1, wherein the D95 particle diameter of the equivalent circle diameter of the pores is 500 nm or less, and the average value of equivalent circle diameters is 100 nm or less.   The diamond polycrystal according to claim 1 or 2, wherein the particles have a D95 particle size of 50 nm or less and an average particle size of 30 nm or less.   Hardness is 50 GPa or more, The diamond polycrystal in any one of Claims 1-3.

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