JP5534181B2 - Diamond polycrystal - Google Patents

Description

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

In cutting the material, a cutting tool and a cutting method suitable for the work material are selected.
In order to achieve a long life in the cutting process, it is important how the cutting edge temperature can be suppressed during cutting, and a tool material excellent in thermal conductivity is used heavily. In general, even in cutting using ultra-high pressure sintered tools such as diamond sintered bodies and cBN sintered bodies with excellent thermal conductivity, the cutting edge is used under high-efficiency conditions with high speed conditions, large cutting depths, and high feed conditions. As the temperature rises, chemical wear such as diffusion with the work material and oxidation occurs. Therefore, as measures for suppressing tool wear, changing to a low speed condition, cutting resistance suppression by reducing the wedge angle of the tool blade edge, or cooling of the cutting point by discharging coolant to the cutting point, and the like are performed.

  For example, as a measure for further prolonging the life in cutting difficult-to-cut materials, Patent Document 1 discloses ultra-high pressure sintering that has a heat conductivity of at least 100 W / m · K or more at a portion related to cutting of the cutting edge. An invention has been disclosed in which the cutting edge temperature of the cutting tool to which the body material is applied is suppressed by cooling with a high-pressure coolant, thereby suppressing the temperature rise of the cutting edge due to cutting heat.

  On the other hand, for cutting of brittle difficult-to-cut materials such as glass, ceramics, carbide, and sintered alloy difficult-to-cut materials, cutting is performed under high-speed conditions and the temperature at the cutting point of the workpiece is increased by laser assist. It has been proposed to soften the work material or change the chip generation mechanism from brittle mode to ductile mode to achieve a good machined surface, but in principle, the tool edge is exposed to high temperatures. In addition, since the tool is rapidly cooled, the cutting tool is likely to be deteriorated, and chipping and sudden loss are likely to occur. In addition, the machine tool also has problems such as restrictions on the number of rotations of the spindle and the need to install an expensive laser device.

  Thus, in difficult-to-cut material cutting in which it is indispensable to keep the cutting point at a high temperature, the fracture resistance, heat resistance, and thermal conductivity of the blade material are important. For the cutting tool, an ultra-high pressure sintered body tool such as a diamond sintered body or a cBN sintered body, which is superior in high-temperature hardness and strength, is more suitable than conventional cemented carbide or cermet.

Generally, a polycrystalline diamond called sintered diamond has a hardness that is at least twice as high as that of a cBN sintered body tool, and excels in cutting performance under a cutting edge temperature condition of 600 ° C. or lower. Due to the reverse conversion action from diamond to graphite by the sintering aid as the main component and deterioration due to oxidation, the cutting performance at high temperatures is inferior.
That is, diamond polycrystals which are widely used industrially as sintered diamond include diamond polycrystals using iron group elements such as Co and Ni as sintering aids, such as cutting tools, dressers, dies, etc. Used for tools and drill bits. However, since this diamond polycrystal has an iron group element metal such as Co between the diamond particles, mechanical properties such as hardness and strength of the diamond polycrystal are lowered by the graphitization and oxidation of diamond. .

  Also known are those using carbonates as sintering aids (see Patent Literature 2 and Patent Literature 3) and those using SiC. Polycrystalline diamond using carbonates as sintering aids. Is superior in heat resistance as compared with the one using Co as a sintering aid, 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 4 describes a method of synthesizing fine diamond by heating a carbon nanotube to 10 GPa or more and 1600 ° C. or more. 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 grain size of the diamond grains constituting the polycrystal 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.

  As a polycrystalline diamond that does not leave a sintering aid in the sintered body, a dense polycrystalline diamond that is obtained by direct conversion using non-diamond carbon as a raw material has been developed (Patent Documents 5 to 5). (See Patent Document 8). These polycrystals have excellent heat resistance and extremely excellent mechanical properties such as hardness and wear resistance as compared with diamond polycrystals in which the sintering aid remains in the structure.

  However, the polycrystalline diamond obtained by directly converting these non-diamond carbons as a starting material is a dense body and excellent in mechanical strength and heat resistance, but iron such as Co, which is inferior in mechanical strength and heat resistance at high temperatures. Since it does not have a sintering aid mainly composed of a group element, it has a high thermal conductivity of 400 w / m · K or higher, which is the thermal conductivity of a conventional commercially available diamond sintered compact. For this reason, the tool performance was insufficient as a cutting tool for brittle difficult-to-cut materials in which it is important to keep the cutting point at high temperatures such as glass, ceramics, cemented carbide, and sintered alloy difficult-to-cut materials.

JP 2009-45715 A 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 has low heat conductivity, high strength and excellent heat resistance for use in a cutting tool capable of cutting in a state where the cutting point is kept at a high temperature and the material strength of the work material is reduced. An object is to provide a polycrystalline diamond.

As a result of diligent research, the present inventors have optimized the sintering conditions using a non-diamond carbon material as a starting material, so that a thermal conductivity of 300 W / · A diamond polycrystal having an extremely low K or less was obtained.
That is, the present invention relates to a polycrystalline diamond as described below.

(1) more than 95 wt% obtained by converting directly without the addition of non-diamond carbon material a sintering aid or a catalyst in an ultra high pressure and ultra high temperature is polycrystalline body comprising diamond, diamond particles 3 Diamond that is dimensionally bonded and includes fine pores between particles, and the proportion of the fine pores in the polycrystalline diamond is 50 vol% or less, and the thermal conductivity is 300 W / m · K or less. Polycrystal.
(2) The diamond polycrystal according to (1), characterized in that it is composed of diamond particles having an average particle size of 50 nm or less and a D95 particle size of 100 nm or less.
( 3 ) The polycrystalline diamond according to (1) or (2), wherein the thermal conductivity is 100 W / m · K or less.
( 4 ) The polycrystalline diamond according to ( 2 ) or ( 3 ), wherein the polycrystalline diamond is composed of diamond particles having an average particle size of 20 nm or less and a D95 particle size of 30 nm or less.

  Since the polycrystalline diamond of the present invention has a very low thermal conductivity of 300 W / m · K or less, the material strength of the work material is reduced while maintaining the processing point at a high temperature, and the polycrystalline diamond By cutting the cutting edge of the body tool plastically, it is possible to perform cutting that avoids brittle fracture of the work material.

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

The diamond polycrystal of the present invention is a diamond polycrystal obtained by directly converting a raw material carbon material. Unlike a conventional diamond sintered body in which diamond particles are sintered using a sintering aid, 95 Excellent heat resistance because more than mass% is made of diamond. Further, the diamond polycrystalline body disclosed in Patent Documents 5 to 8 is controlled by controlling the average particle diameter of the diamond sintered particles forming the diamond polycrystalline body to 50 nm or less and the D95 particle diameter to 100 nm or less. Compared to the above, a polycrystalline diamond having an extremely low thermal conductivity of 300 W / m · K or less can be obtained.

Even if the average particle size is 50 nm or less, the thermal conductivity increases if the ratio of particles close to 100 nm is high. On the other hand, even if coarse particles exceeding 100 nm are included, if the ratio is as low as 5% or less, the wear resistance of the coarse particles is utilized, but the thermal conductivity is not improved.
Since this diamond polycrystal has extremely fine diamond particles, a cutting edge ridge line with very high accuracy can be created when used as a cutting tool. Depending on how the raw carbon and the sintering conditions are selected, fine pores may be generated between the particles. The ratio (porosity) of the pores in the polycrystalline diamond is up to 50 vol%. However, since the diamond particles are three-dimensionally firmly bonded, they can endure as a tool material. From the viewpoint of mechanical strength, a structure having voids of 30 vol% or less is desirable.

  The high-hardness diamond polycrystal of the present invention is a non-diamond type carbon raw material that is directly converted to diamond without adding a sintering aid or a catalyst under ultrahigh pressure and high temperature. A polycrystalline diamond having an average particle size of 50 nm or less, a D95 particle size of less than 100 nm, and a porosity of 50 vol% or less, wherein the diamond particles are three-dimensionally bonded, It is a polycrystalline diamond characterized by the presence of pores in between, and its thermal conductivity is as low as 300 W / m · K or less. For this reason, it is a high-hardness material suitable for processing that keeps the cutting point at a high temperature and capable of forming a highly accurate cutting edge shape. More preferred is a polycrystalline diamond having an average particle size of 30 nm or less and a D95 particle size of less than 50 nm, and a thermal conductivity of 100 W / m · K or less.

(Non-diamond carbon material)
The diamond polycrystal of the present invention can be obtained by using non-diamond carbon as a raw material and directly converting the raw material into diamond without adding a sintering aid or a catalyst.
As the non-diamond type carbon material, graphite, fullerene, carbon nanotube, amorphous carbon, glassy carbon and the like can be applied, but are not limited thereto. Graphite can be extremely finely controlled in particle size by using powder pulverized into ultrafine particles by a ball mill or a planetary ball mill. It is necessary to arrange and sinter the raw carbon as densely as possible, and powder graphite, carbon nanotubes, amorphous carbon, etc. are used in the form of pellets or rods by cold isostatic pressing, etc. instead of powder. However, the present invention is not limited to these forms.
In order to set the average particle diameter of diamond particles constituting the polycrystalline diamond to 50 nm or less and the D95 particle diameter to 100 nm, it is necessary to make the particle diameter of the non-diamond carbon raw material fine, preferably 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)
Non-diamond carbon is directly converted to diamond by filling the non-diamond carbon raw material into a refractory 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.
Indirect heating is preferable as the heating method for converting the non-diamond carbon material into diamond. This is because direct current heating to the raw material carbon or laser heating that locally applies heat power makes it difficult to keep the entire raw material at a constant temperature, and unconverted portions to diamond are likely to occur.

  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. When using graphitic carbon as a raw material, it is preferable to heat to 1900 ° C. or higher. If the sintering temperature is too high, diamond particles will grow and the thermal conductivity will increase. For this reason, it is desirable to sinter at less than 2200 degreeC. 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 fracture surface was observed for the bulk material, and the powder for the powder material was observed with a scanning electron microscope, and the particle size distribution was measured.
<Average particle diameter of diamond particles and D95 particle diameter>
The average particle size of diamond particles in the polycrystalline diamond was observed 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 the average particle size was 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.
<Porosity>
Extract the void from the high-resolution scanning electron microscope observation image of the sample surfaced, and use image analysis software (for example, ScionImage, manufactured by Scion Corporation) to determine the area of the void. Obtained by comparing with.
<Thermal conductivity>
It was measured by a pulse heating method using a xenon flash lamp.
<Polished surface roughness>
Using a stylus type surface roughness meter, the surface roughness of the sample surfaced with high precision was measured using a diamond stylus.

[Example]
As raw materials, carbon nanotube powder, fullerene powder, glassy carbon powder, graphite powder having an average particle diameter of 0.5 to 1 μm and a purity of 99.95% or more, and pellets of this graphite powder by cold isostatic pressing A bulk sample molded into a shape was used. These mixtures were filled into Mo capsules, sealed, and treated for 10 minutes under various pressure and temperature conditions using a belt-type ultrahigh pressure generator to obtain polycrystalline diamond.
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 porosity and thermal conductivity were 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)

A polycrystal least 95 mass% obtained by converting directly without the addition of sintering aid or a catalyst a non-diamond carbon material under ultra-high pressure and ultra high temperature is made of diamond, diamond particles 3-dimensionally A diamond polycrystalline body characterized by being bonded and containing fine pores between particles, wherein the proportion of the fine pores in the diamond polycrystalline body is 50 vol% or less, and the thermal conductivity is 300 W / m · K or less . 2. The polycrystalline diamond according to claim 1, wherein the polycrystalline diamond is composed of diamond particles having an average particle size of 50 nm or less and a D95 particle size of 100 nm or less. The polycrystalline diamond according to claim 1 or 2 , wherein the thermal conductivity is 100 W / m · K or less. 4. The polycrystalline diamond according to claim 2, wherein the polycrystalline diamond is composed of diamond particles having an average particle size of 20 nm or less and a D95 particle size of 30 nm or less.

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