JP2792136B2 - High toughness polycrystalline diamond and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-toughness polycrystalline diamond which is suitable for use as a cutting tool, a wear-resistant tool or the like and has remarkably improved strength, heat resistance and wear resistance.

[Conventional technology]

As a diamond for a tool, a diamond sintered body obtained by sintering a fine powder of diamond under an ultra-high pressure is used for a cutting tool, a drill bit, a drawing die and the like made of nonferrous metal.

For example, Japanese Patent Publication No. 52-12126 discloses that diamond powder is brought into contact with a powder compact or sintered body of a WC-Co cemented carbide and sintered, and a part of Co is used as a bonding metal in the diamond powder. About 10 to 15% by volume of Co
A technique for producing a diamond sintered body containing the same is disclosed.

Although this diamond sintered body has practical performance for cutting tools made of non-ferrous metal, it has a drawback of poor heat resistance. For example, when heated to 700 ° C. or higher, wear resistance and strength are reduced, and at a temperature higher than 900 ° C., the sintered body is broken. It is considered that such a defect in heat resistance is caused by graphitization of diamond at an interface between diamond particles and Co as a binder and thermal stress based on a difference in coefficient of thermal expansion when both are heated.

As an attempt to improve the heat resistance of the above-mentioned diamond sintered body, for example, JP-A-53-114589 discloses a method in which the sintered body is subjected to an acid treatment to dissolve and remove Co as a binder,
JP-A-61-33865 discloses that Si and / or S
One using iC is disclosed. Although the heat resistance of each of these sintered bodies is improved to about 1100 to 1200 ° C,
The former has the disadvantage that the strength is lower than that of the conventional sintered body using Co binder because the former is due to the pores formed by removing Co and the latter is because the bonding between diamond particles is less. was there.

Therefore, it was considered that a tool material excellent in strength, wear resistance and heat resistance, containing no binder and only diamond particles sintered, was ideal. From this idea, attempts have been made to sinter only diamond powder under ultra-high pressure. However, since diamond particles are not easily deformed, pressure is not transmitted to the gaps between the particles, and as a result, graphitization occurs. The fact is that only a complex of

On the other hand, in recent years, the technology for producing a polycrystalline body substantially consisting of diamond only by the low-pressure gas phase method has been developed, and it has become possible to synthesize an ideal tool material that cannot be produced by the ultra-high pressure method as described above. Is coming. For example, Japanese Patent Application No. 1-51
No. 485 has a thickness of 50 µm or more and an average crystal grain size of 50 µm or less, and the peak ratio (Y / X) of diamond carbon (X) and non-diamond carbon (Y) by Raman spectroscopy is used as an index of purity. A polycrystalline diamond for tools characterized by being 0.2 or less is disclosed.

[Problems to be solved by the invention]

Although these polycrystalline diamonds have the above-mentioned required characteristics, they also have improved strength and wear resistance when cutting hard-to-cut materials such as hard ceramics and Al alloys containing more than 20% Si. Need to be done.

In the present invention, the polycrystalline body of the prior application is further improved to provide an excellent tool material.

[Means for solving the problem]

In order to achieve the above object, in the present invention, substantially only diamond synthesized by the low-pressure gas phase method, and the 30
It has been found that a high toughness polycrystalline diamond characterized in that 〜100% is directly bonded without having a clear grain boundary is effective.

[Action]

Upon reaching the present invention, the present inventors first observed the microstructure of a polycrystalline diamond of the prior application in order to find a method for further improving the strength and wear resistance thereof. FIG. 2 shows a TEM of a thin polycrystalline diamond obtained by ion thinning with a thickness of 100 μm and a particle size of about 5 μm.
It is the photograph observed with (transmission electron microscope). From this photograph, it can be seen that the polycrystal is mainly composed of twin crystals, and has high purity with almost no defects such as defects inside the diamond particles and amorphous carbon in the grains and at the grain boundaries. However, when this is compared with the microstructure of the sintered diamond shown in FIG. 3, it can be seen that there is a clearly different point. That is, in the sintered diamond of FIG. 3, there is no clear grain boundary, and diamond particles are directly bonded to each other, whereas in the polycrystal of FIG. 2, a clear grain boundary exists between diamond grains. Exists.

These grain boundaries are a kind of defect, and the bonding strength between particles is not only due to covalent bonds, but also partly due to van der Waals bonds. It was considered that the material did not exhibit much better properties than the sintered diamond.

From the above observations, the present inventors have conducted intensive studies and as a result, substantially consisted only of diamond synthesized by the low-pressure gas phase method, and formed a boundary portion between diamond particles.
It has been found that a high toughness polycrystalline diamond characterized in that 30 to 100% does not have a clear grain boundary and is directly bonded exhibits excellent performance.

As a method for producing the same, in the synthesis of diamond by the low-pressure gas phase method, it is effective to select the synthesis conditions so that the initial nucleation density of diamond on the substrate is 10 ⁸ to 10 ¹² cm ^-2. It is.

As shown in the microstructure of FIG. 1, the polycrystalline body of the present invention has no clear grain boundary at the boundary between the grains as in the case of sintered diamond, and diamond grains are directly bonded. . 30-100% of grain boundaries are directly bonded
The reason is that if the amount is less than that, a dramatic improvement in strength and wear resistance cannot be expected. Preferably 70-
Ideally, 100% is directly bonded. Also,
The reason for setting the average crystal grain size to 0.5 to 15 μm is mainly to improve the strength, and the range of 1 to 10 μm is more preferable. If it is larger than this range, the strength will gradually decrease, and if it is smaller than this range, the wear resistance will be reduced.
Such control of the crystal grain size is described in Japanese Patent Application No.
63-139143 and Japanese Patent Application No. 63-148631.

The reason why the thickness of the polycrystalline diamond is set to 0.05 to 3 mm is that the flank wear width during the service life of the cutting tool is 0.
This is because the thickness is often not less than 05 mm, and if the thickness is less than 0.05 mm, the strength is reduced and the material is easily broken. The upper limit of 3 mm indicates a standard of the maximum thickness generally used, and it is possible to produce a thicker one according to the application.

In producing the polycrystal of the present invention, diamond can be synthesized by any known low-pressure gas phase method. That is, a method of decomposing and exciting the source gas using thermionic emission plasma discharge, a film forming method using a combustion flame, and the like are effective. As the raw material gas, for example, it is common to use a mixed gas containing, as main components, hydrocarbons such as methane, ethane, and propane; alcohols such as methanol and ethanol; organic carbon compounds such as esters; and hydrogen as main components. However, other than these, an inert gas such as argon, oxygen, carbon monoxide, water and the like may be contained in the raw material as long as the carbon synthesis reaction and its characteristics are not impaired.

However, as disclosed in Japanese Patent Application No. 1-51485,
It is necessary to select synthesis conditions under which defects and impurities do not enter the inside and the grain boundaries of the generated diamond.

Furthermore, the most important point in the present invention is to select the synthesis conditions so that the initial nucleation density of diamond on the substrate is 10 ⁸ to 10 ¹² cm ⁻² . The reason is that if the initial nucleation density is less than 10 ⁸ cm ^-2 , the initial nucleus grows and starts to contact the adjacent nucleus, and the size of each diamond particle becomes 1 μm or more. This is because a direct connection between them becomes difficult to occur. That is, in order for diamond particles to directly bond with each other, it is necessary to increase the surface energy thereof. One of the methods is to increase the initial nucleation density to 10 ⁸ cm ^-2 or more. is there.

Also, the reason for setting the upper limit to 10 ¹² cm ^-2 is that in the current technology, when starting to synthesize at a higher nucleation density, the initial diamond particles bond remarkably, and when it is larger than 15 μm, it becomes coarse. This is because the possibility is high.

After the growth and bonding of these nuclei progress and cover the surface of the base material, if the synthesis is continued under the conditions disclosed in Japanese Patent Application No. 1-51485, the state in which the interparticle bonding occurs. Continue in the thickness direction.

The polycrystalline diamond of the present invention synthesized by such a method is separated from the substrate and supported in the same manner as the present inventors' previously filed Japanese Patent Application Nos. 63-34033 and 63-34034. The member can be brazed to a tool, or a thick one can be used as a single tool.

〔Example〕

Example 1 By microwave plasma CVD, H ₂ was used as a source gas.
With _{250cc / min, CH 4 5cc /} min, and Ar 80 cc / min, it was attempted production of polycrystalline tire Monde on the Mo base pressure 200 torr. Initial nucleation densities of the (A) mirror-polished surface of the substrate Mo and the (B) diamond-treated particles having a particle size of 1 μm were examined. Result (A)
Was 10 ³ cm ^-2 , whereas (B) was 10 ⁹ cm ^-2 . After the investigation, synthesis was continued under the same conditions until the thickness became 120 μm.

After completion of the synthesis, the Mo base was dissolved in aqua regia and only polycrystalline diamond was recovered. First, the purity of each polycrystalline diamond was evaluated by Raman spectroscopy.

As a result, in both (A) and (B), the results as shown in FIG. 4 were obtained, and it was found that non-diamond carbon was hardly contained.

When the microstructure of each polycrystal was observed by TEM, (A) had an average particle size of 25 μm and no direct bonding of particles was observed, while (B) had an average particle size of 5 μm.
Direct bonding was observed at about 60% of the grain boundary.

Next, in order to evaluate tool performance, each polycrystalline diamond was brazed to a cemented carbide base metal to produce a cutting tip. As a comparative material, a cutting tip was similarly manufactured using ultrahigh-pressure sintered diamond containing 10% by volume of a binder Co and having an average particle diameter of 10 μm. Using a round bar of AC9B alloy (Al-20Si) with four grooves extending in the axial direction on the outer peripheral surface as a work material, cutting speed 300m / min, depth of cut 0.2mm, feed 0.1mm / r
ev, dry cutting was performed, and the tool performance was evaluated.

As a result, (A) was lost at the time of cutting for 40 minutes,
(B) had no defect, and the average wear width after 90 minutes of cutting was 0.04 mm. The comparative material did not have any defects, but the average wear width after cutting for 90 minutes was 0.09 mm.

Example 2 A linear tungsten filament having a diameter of 0.5 mm and a length of 20 mm was used as a thermionic emitting material, and a raw material gas comprising hydrogen, a carbon source and water vapor was decomposed and excited to form a first material on a Si substrate.
Polycrystalline diamond was synthesized under the conditions shown in the table.

The properties of the polycrystalline diamond in the initial state of film formation and after synthesis for 20 hours were evaluated. Table 2 shows the results.

When each of the polycrystalline diamonds (C) to (H) was brazed to a cemented carbide base metal to produce a cutting tip, C was cracked during brazing. This is presumably because the thickness was as thin as 50 μm or less, and the strength was low due to no direct bonding between diamond particles, and the influence of thermal stress was large. A390 with four grooves extending in the axial direction formed on the outer peripheral surface by five cutting tips D to H is an alloy (A
l-17Si) Using a round bar as a work material, cutting was performed for 90 minutes in a dry system under the conditions of a cutting speed of 500 m / min, a depth of cut of 0.2 mm, and a feed of 0.1 mm / rev. For comparison, a sintered diamond having an average particle size of 3 μm and containing 15% by volume of Co as a binder was also evaluated.
The results are shown in Table 3.

(E), (F) and (G) according to the present invention all showed good tool properties, while (D) and (H) showed that the strength was insufficient. These are presumably because the initial nucleation density is low and the proportion of direct bonding between diamond particles is low.

Example _{3 C 2 H 6: H 2} ( volume ratio 1: 100) 0-20 further O ₂ mixed gas of
Using raw material gas with volume% added, gas flow rate 200cc / min
And adjust the pressure to 180torr, 900W high frequency (13.56M Hz)
To excite the source gas, and a polycrystalline diamond having a thickness of 0.5 to 0.7 mm was formed on Si substrates having various surface states in a reaction time of 20 hours.

The average particle size of the obtained polycrystalline diamond is 7 μm.
m and thickness 650μm, select four kinds of polycrystals with different ratio of direct bonding between diamond particles, braze each to a cemented carbide holder and perform cutting process, cutting performance of hard ceramics Was evaluated. Cutting evaluation of cutting out good offices of the alumina sintered body round bar ^{_{(H V = 2000kg / mm 2}} ), cutting speed 50 m / min, cut 0.2 mm, feed 0.25 mm / rev
For 15 minutes by a wet method under the following conditions. The results are shown in FIG.

From this result, it can be seen that those having a direct bonding ratio of the grain boundary portion within the range of the present invention have excellent wear resistance.

〔The invention's effect〕

According to the present invention, it is possible to provide a high-toughness polycrystalline diamond having improved strength, heat resistance and wear resistance, and particularly excellent strength and wear resistance.

Therefore, a high-performance tool can be manufactured using this polycrystalline diamond, and it is particularly effective for tools such as cutting tools, excavating tools, and dressers.

[Brief description of the drawings]

FIG. 1 is a TEM microstructure diagram of a polycrystalline diamond according to the present invention. FIG. 2 is a TEM microstructure diagram of a conventional polycrystalline diamond. FIG. 3 is a microstructure micrograph of a conventional sintered diamond by TEM. FIG. 4 shows the Raman spectra of the polycrystalline diamonds (A) and (B) synthesized in Example 1. FIG. 5 shows the results of the cutting performance evaluation of Example 3.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Naoji Fujimori 1-1-1, Koyokita, Itami-shi, Itami-shi, Hyogo Sumitomo Electric Industries, Ltd. Itami Works (56) References JP-A-60-1222795 (JP, A JP-A-62-226889 (JP, A) JP-A-63-123898 (JP, A) JP-A-1-212767 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C30B 1/00-35/00

Claims (4)

(57) [Claims] (1) It consists essentially of diamond synthesized by a low-pressure vapor phase method, and 30 to 100% of the boundary portions of diamond particles constituting each other are directly bonded without having a clear grain boundary. High toughness polycrystalline diamond characterized by the following: 2. The high toughness polycrystalline diamond according to claim 1, wherein the grain size is 0.5 to 15 μm. 3. The high toughness polycrystalline diamond according to claim 1, wherein the thickness is 0.05 to 3 mm. 4. In the synthesis of diamond by a low-pressure gas phase method, the initial formation density of diamond on a substrate is 10 ^8.
A method for producing a high-toughness polycrystalline diamond, characterized in that synthesis conditions are selected so as to be 10 ¹² cm ^-2 .