JPS6379758A - Manufacture of high strength polycrystal diamond - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Industrial Application Field This invention is made essentially only of diamond, has high strength and heat resistance, and is suitable for use as cutting tools, rock excavation tools, and wear-resistant tools. The present invention relates to a method for producing high-strength polycrystalline diamond.

(2) Prior Art Sintered bodies made by sintering fine diamond powder under ultra-high pressure are already widely used as tools for cutting non-ferrous metals, drill bits, wire drawing dies, and the like.

A method for producing this type of diamond sintered body is described, for example, in Japanese Patent Publication No. 12126/1983. In the manufacturing method described in this prior art, diamond powder is
It is arranged so as to be in contact with a compact or a sintered viscous body of C--Co cemented carbide, and sintering is performed at a temperature higher than the temperature at which a liquid phase of the cemented carbide is produced and under ultra-high pressure.

During sintering, a portion of the CO in the cemented carbide enters the diamond powder layer and acts as a bonding metal.

However, this type of diamond sintered body has a drawback of being inferior in heat resistance. For example, when this diamond sintered body is heated to a temperature of 750° C. or higher, the wear resistance and strength decrease, and at a temperature of 900° C. or higher, the sintered body breaks. This is thought to be due to graphitization of diamond occurring at the interface between the diamond particles and Co as a binder, and thermal stress caused by the difference in thermal expansion coefficients when the two are heated.

Here, there are two reasons why a diamond sintered body is required to have high heat resistance.

(1) As a method of fixing the sintered body to the tool holder, it is necessary to perform brazing in the atmosphere, and heat is generated during this process. Particularly in drill bits for hard rock drilling, the sintered body is attached to the bit body by a metal matrix. The retention strength of the matrix increases as the melting point of the matrix material increases, and such applications require the use of a matrix having a melting point of 900° C. or higher. Therefore, when attaching the diamond sintered body to the bit body or shank in the atmosphere, sufficient strength cannot be obtained.

(2) When using the sintered body as a tool, if the workpiece material has high hardness, the temperature of the cutting edge increases and becomes a high temperature state.

This phenomenon occurs particularly when cutting, instead of grinding, high-hardness materials such as high-strength ceramics and cemented carbide with a small amount of binder, which have recently been actively developed.

In addition, when wire-drawing hard metals such as W and Mo, these metals have high hardness and tensile strength at room temperature, and low elongation reduction, so they are heated to 700 to 800°C.

In such fields, the above-mentioned sintered bodies do not have satisfactory performance because of their poor heat resistance. By improving heat resistance in this way, it is thought that the field of use of diamond sintered bodies will further expand, and improvements are being made.

3. Regarding the method for solving the problem to be solved by the invention, see, for example, Japanese Patent Application Laid-Open No. 53-114589.
Disclosed in the issue. That is, the sintered body using CO as a binder is treated with an acid to remove most of the binder metal phase.

However, the method disclosed in JP-A-53-114589 has the problem that the removed bonded metal phase portion forms pores, resulting in a decrease in strength. As another method for manufacturing heat-resistant sintered diamond, we are also considering using a binder that is inert to diamond and does not cause thermal deterioration even in high-temperature conditions, instead of iron group metal binders such as CO. has been done.

For example, in the diamond bonded body described in Japanese Patent Publication No. 49-40607, a mixture of diamond and hexagonal boron nitride (hBN) is maintained under high pressure and high temperature conditions in which cubic boron nitride (cBN) is stable. Diamond particles are bonded by cBN by inducing non-catalytic phase transition.

; Yapo'c BN has an extremely small difference in thermal expansion from diamond, and has good thermal conductivity and thermal stability. However, in a sintered body made only of diamond and cBN, the bond between diamond and cBH is weak, and c
Since BN tends to have creases and has low strength, when used as a tool, particles tend to fall off, and a tool with excellent wear resistance has not been obtained.

Furthermore, a method using 5ii6 and/or SiC as a binder based on the same idea is disclosed in Japanese Patent Application Laid-open No. 33865/1983. In the method described in this prior art,
Si is used as a binder raw material. That is, this is a method in which molten Si is impregnated into a diamond powder raw material under high temperature and high pressure, and sintered accompanied by a SiC production reaction. However, this method is inferior, and since unreacted Si remains in the bonding material, it is disclosed in No. 161268/1987 that the bonding material exhibits low strength when exposed to a high temperature condition of 1000 DEG C. or higher. The polishing material disclosed herein is characterized in that it contains 10 to 20% of nickel and Si by volume, and that the respective forms are nickel, silicon, silicon carbide, nickel silicide, etc. .

In the sintered body manufactured by this manufacturing method, the ratio of bonding between diamond particles is improved due to the effect of Ni. However, since unreacted Ni and Si still remain in the binder, graphite is generated at high temperatures and the strength is reduced, so that it cannot be said to have excellent heat resistance.

On the other hand, attempts have been made to sinter only diamond powder under ultra-high pressure, but since the diamond particles are difficult to deform, pressure is not transmitted to the gaps between the particles, resulting in graphitization and the formation of diamond-graphite composites. The reality is that all that is gained is the body.

The sintered body described in U.S. Pat. No. 3,913,280 discloses a method in which only diamond powder is solid-phase sintered under conditions where graphite is stable to actively generate graphite between the grains and use it as a binding material. However, this sintered body has poor strength and wear resistance.

It is thought that it is a polycrystalline diamond consisting only of diamonds, which are interconnected. This method of producing polycrystalline diamond is described in Japanese Patent Publication No. 46758/1983. That is, in this method, graphite is energized and heated under ultra-high pressure, and the shaded area A in Fig. 1 (carbon phase diagram) is
Exposure to these conditions causes a non-catalytic phase transition of the graphite to diamond. In addition, as an improvement, in Japanese Patent Publication No. 40-26328, graphite containing boron carbide is used as a raw material, and even after the phase transition to diamond, electricity is continuously applied to raise the temperature to above the carbon melting point (shaded area B in Figure 1). Disclosed is a method for melting at least a portion of phase change-produced diamond.

Although it takes a very short time, it is characterized by significantly higher temperatures and pressures than the conventional manufacturing conditions for sintered diamond using cobalt as a binder (hatched area C in the figure). The sintering temperature is a value based on thermodynamic calculations, as there is currently no known means of measuring high temperatures in such a short period of time, but if the amount of energy injected into the sintering raw material is controlled, Increasing temperature reproducibility is considered relatively inexpensive. However, a drawback of these methods is that the sintering pressure is extremely high, requiring the use of special ultra-high pressure equipment such as that disclosed in Japanese Patent Publication No. 51-46758.

This ultra-high pressure device is a modified version of the belt-type device described in Japanese Patent Publication No. 37-8358, and although the generated pressure can be increased, it is inferior in operability, and the sample space is only a few ma+ in size. . Opposed anvil type devices, such as the Bridgman anvil type device, have relatively good operability, but in order to generate the above-mentioned high pressure, even in this device, the size of the sample space must be Similarly, the production of polycrystalline diamond as a tool material is considered difficult.

Furthermore, in the above-mentioned method of melting all the raw material graphite and solidifying it as diamond, it is difficult to control the grain size of the recrystallized diamond, and only a polycrystalline body with a non-uniform grain size distribution is obtained. Since the strength and wear resistance of polycrystalline bodies depend on their grain size, good tool performance cannot be expected from polycrystalline bodies that exhibit a non-uniform structure.

Therefore, an object of the present invention is to improve the heat resistance, which was a drawback of conventional sintered diamond, without impairing its strength and wear resistance. The present invention provides a method for manufacturing high-strength polycrystalline diamond consisting essentially of diamond.

(4) Means for solving the problem The inventors of the present invention aimed to obtain high-strength polycrystalline diamond that has even greater strength, wear resistance, and heat resistance, and is large enough to be used as a tool material. As a result of intensive study, the following invention has been made.

Placed in a pressure generator, graphite is stable on the carbon phase diagram.
After being exposed to a pressure of less than 10K b, the diamond powder is instantaneously heated to a temperature at which it flows plastically and graphite does not form, and then rapidly cooled, thereby causing self-sintering of the diamond powder in a thermodynamically non-equilibrium state. This is based on a method for producing high-strength polycrystalline diamond, which is characterized by carrying out the following steps.

(5) Effect The method for producing high-strength polycrystalline diamond according to the present invention has been achieved by improving the above-mentioned prior art (Japanese Patent Publication No. 40-26328). In the method disclosed in this prior art, graphite containing boron carbide is used as a sintering raw material. Therefore, in order to produce polycrystalline diamond from this, it is necessary to expose the raw material to a temperature at which the entire raw material melts and forms a carbon melt in a pressure range in which diamond is thermodynamically stable.

As a result, after placing diamond powder as a raw material in an ultra-high pressure generator and exposing it to a pressure of 110 Kb or less, at which graphite is stable on the carbon phase diagram, the temperature at which diamond flows freely and graphite does not form is reached. We discovered that by instantaneous heating and rapid cooling, diamond powder self-sinters in a thermodynamically non-equilibrium state even under pressure where graphite is stable.

In carrying out this invention, the diamond powder used as a raw material may be either natural or synthetic.

In the polycrystalline body of this invention, especially 0.0
When diamond particles with a particle size of 1 to 200 μm are used, both strength and wear resistance are the best.

The above raw material diamond powder is placed in an ultra-high pressure generating device such as a belt type device, which is currently widely used in industrial production, as shown in Fig. 2, and then heated to a pressure of 110 Kb or less, preferably 20 to 60 Kb, at which the graphite is stable. expose to

In this state, electricity is applied to the heater to instantaneously raise the temperature to an extremely high temperature. Here, setting the sintering pressure to 20 to 60 Kb means 2
Below 0 Kb, sintering of diamond in a non-equilibrium state is difficult to occur and graphite is generated, and above 60 Kb, it is difficult to obtain a large polycrystalline body because the sample space in the ultra-high pressure generator is reduced. It depends. The sintering time, that is, the time from the start of energization to the end of energization, depends on the amount of raw materials, but is from several milliJ seconds to several seconds. The lower limit is determined by whether diamond can sufficiently flow under sintering pressure. However, the lower limit of this temperature is the limit at which graphite is converted into diamond in a thermodynamic equilibrium state, that is, it does not exceed the Berman-Simon line. Furthermore, the upper limit of the sintering temperature is the metastable liquidus of diamond.

The sintering conditions according to the method of the present invention are illustrated in the shaded area in FIG. For controlling the heating power source and the amount of energy to be injected, the device disclosed in Japanese Patent Publication No. 51-46758 and the like can be applied.

All polycrystalline bodies obtained according to the above method have high density and high strength, and can withstand heating up to 1200°C like single crystal diamond. It is also possible to use conductive diamond containing 0.01 to 1.0% by weight of boron, and in this case, heat can be generated by directly applying electricity to the raw material as shown in Figure 3. Since the sintered polycrystalline body is electrically conductive, it has the characteristic that electric discharge machining can be used when machining it into a tool shape.

The reason why the boron content is limited to the above range is that if it is 1.0% by weight or more, a large amount of boron will be contained, which will cause defects and reduce the strength of the polycrystalline body.
, 0.01% by weight or less, the electrical discharge machining becomes difficult due to high resistance, and in particular, there is no need to use diamond powder containing boron.

A polycrystalline body sintered using conductive diamond containing boron having a content within the above range as a raw material also has high strength and high heat resistance.

The uses of the polycrystal obtained by the method of the present invention include:
Examples include not only bits and dies for cutting non-ferrous metals, but also bits for high-efficiency cutting of ceramics, hot wire drawing dies, and bits for drilling hard rocks, which cannot be applied with conventional sintered bodies. Further, ultrafine polycrystalline diamond with a particle size of 0.1 μm or less, which is obtained by selecting and sintering the particle size of the raw material, can be used as a cutting tool for ultra-precision machining of ceramics. Furthermore, since it is a polycrystalline material consisting essentially of diamond,
It is also possible to use it as an inexpensive, highly thermally conductive heat dissipating substrate to replace single crystal diamond.

(6) Examples [Example 1] Synthetic diamond powder with a particle size of 60 to 80 μm was used as a raw material and placed in a belt-type high pressure generator with the configuration shown in FIG. First, after pressurizing to 50 Kb, electricity was started, and when 40 KJ of energy was injected, electricity was stopped and rapidly cooled.

The recovered sample was white and translucent, and its specific gravity was measured by the Archimedes method to be 3.52. As a result of X-ray diffraction, this sample was found to be a polycrystalline body consisting only of diamond.

The particle size was about 70 μm, which is almost the same as the particle size of the raw diamond, and no abnormal grain growth was observed.After being exposed to the conditions for 30 minutes, the compressive strength was measured along with the unheated diamond. As a result, 800Kg/am regardless of heating or not.
For comparison, sintered bodies produced by acid-treating sintered diamond using Co as a binder, and Si &
Similar tests were also conducted on sintered bodies using Si(:) as a binder.These sintered bodies had almost the same heat resistance as the polycrystalline body according to the present invention, but the compressive strength was only 400K.
g/aus'', 470Kg/+an''.

[Example 2] Natural diamond powder with an average particle size of 10 μm and 0 boron
．． Sintering was performed under the same conditions as in Example 1 using synthetic diamond powder containing 5% by weight as the raw material. The collected samples were cut using a laser processing machine and an electric discharge machine, respectively.
After processing into tool shape, Vickers hardness is 1800Kg
/ 1001″ of 5IsN < Cutting speed of sintered body 80m/
min, depth of cut 1 mm, feed 0.1 mm/rotation, dry type 1
Cut for 0 minutes.

For comparison, a sintered body containing 10% by volume of Co as a binder and a heat-resistant diamond sintered body in which most of the Co was extracted by aqua regia treatment and 8% by volume of pores remained were compared with the above. Cutting was performed under the same conditions.

As a result, the flank wear width of both polycrystalline tips according to the present invention was 0.08 mm, whereas C.

For those that were not eluted, it was 0.35 mm. Furthermore, the sintered body from which Co was extracted broke after 30 seconds of cutting, making it impossible to cut it.

[Example 3] Each of the raw materials shown in Table 2 was sintered using a belt-type high pressure generator under each of the conditions shown in the table. As a result, graphite was generated in the polycrystalline bodies of B and D, and they were unsintered. The reason for this is thought to be that the sintering time for B was too long and graphite was produced in an equilibrium state, and for D the sintering pressure was too low.

In addition, although no graphite was observed in sample E, the bonds between the diamond particles were weak and the diamond particles were a brittle polycrystalline body. This is considered to be because the amount of implanted energy was small, and therefore the diamond was not sufficiently plastically deformed. Another polycrystalline material that was well sintered was cut, coated with TiC, and then brazed to a bit body to create a core pit.

For comparison, a surface-set core pit using natural diamond and a core pit using sintered diamond containing 8% by volume of Co as a binder were fabricated.

For each test piece above, -axial compressive strength 1600 to 1700
Kg/+ad andesite was drilled at 500 revolutions/min. Table 3 shows the digging speed and lifespan.

Among the polycrystals manufactured by the manufacturing method of the present invention, good results were obtained except for C, which contained a large amount of boron and had low strength.

Table 3 Note: X and Y respectively indicate a surface-set core pit using natural diamond and a core pit using sintered diamond with a Co binder.

(7) Effects of the Invention As described above, according to the present invention, it is possible to obtain a high-strength polycrystalline diamond consisting essentially of diamond, which has even better heat resistance, excellent strength, toughness, and wear resistance. Can be done. In particular, unlike conventional diamond sintered bodies, the heat resistance has been significantly improved without reducing strength, making it possible to dramatically expand the range of applications as tool materials.

[Brief explanation of the drawing]

Figure 1 is a phase diagram of carbon.
The sintering conditions are as described in No. In addition, the shaded area C in the figure is the sintering conditions for conventional sintered diamond using Co as a binder, and the shaded area is the sintering conditions for polycrystalline diamond according to the method of the present invention. FIGS. 2 and 3 are cross-sectional views showing the state in which the sintering raw material according to the present invention is placed in an ultra-high pressure generator. Figure 2 shows a configuration for indirect heating that supplies electricity to a graphite heater;
The figure shows a configuration in which electricity is applied directly to the conductive diamond raw material. In the figure, 14) is a carbide piston, 2-(2) is a carbide chamber, 3 (3) is pyrophyllite, 4 (4) is a current-carrying ring, 5 (5) is a current-carrying metal plate, and 6 (is a Graphite, 7 is a graphite heater, 8 is a sintering raw material, and 9 is magnesia. -A'1 Figure 2 Figure

Claims (4)

[Claims] (1) After placing diamond powder as a raw material in an ultra-high pressure generator and exposing it to a pressure of 110 Kb or less, at which graphite is stable on the carbon phase diagram, the temperature at which diamond flows plastically and graphite does not form is reached. A method for producing high-strength polycrystalline diamond, which is characterized by self-sintering of diamond powder in a thermodynamically non-equilibrium state by instantaneous heating and rapid cooling. (2) As diamond powder, its particle size is 0.01~
A method for producing high-strength polycrystalline diamond according to claim (1), characterized in that a diamond having a diameter of 200 μm is used. (3) A conductive diamond powder containing 0.01 to 1.0% by weight of boron is used as a raw material, and the raw material is directly energized to generate self-heating. ) A method for producing high-strength polycrystalline diamond as described in item 2. (4) The method for producing high-strength polycrystalline diamond according to claim (1), characterized in that the sintering pressure is 20 to 60 Kb.