JPH0665469B2 - Manufacturing method of fine-grained diamond sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to fine grain diamond firing suitable as a tool material for fine machining of difficult-to-cut materials, a material for wire drawing dies required to have a smooth finished surface, and the like. The present invention relates to a method for producing a tie.

(Prior Art and Problems to be Solved) A diamond single crystal is the most excellent substance among the currently known substances in terms of hardness and wear resistance. However, diamond single crystals have drawbacks such as brittleness and limitation of available size. For the purpose of eliminating these drawbacks, diamond sintered bodies have been developed and are commercially available.

It is known that these sintered bodies exhibit excellent properties as cutting tool materials for difficult-to-cut materials such as Al-Si alloys and ceramics. However, it is very difficult to process these sintered bodies into a sharp cutting edge shape. The reason is that the size of the particles of the diamined sintered body is as large as several microns or more.

In order to solve this problem, conventionally, a fine-grained diamond sintered body has been manufactured as a diamond sintered body that can be processed into a sharp cutting edge shape. The following methods are known as the manufacturing method.

(B) A method of obtaining a fine-grained diamond sintered body by adding a considerable amount of carbide such as WC to diamond powder and sintering it under high temperature and high pressure conditions (Japanese Patent Publication No. 61-58432). According to this method, the complete bonding of the diamond particles to each other is hindered by the carbide such as WC, so that the grain growth of diamond is suppressed and a diamond sintered body composed of fine particles of 1 μm or less can be obtained.

(B) A method of synthesizing a diamond sintered body composed of fine particles with an average particle size of 0.5 μm under a very high pressure of about 90 GPa by the impact compression method using explosives (New Diamond Forum, 10th Regular Study Group ( July 1988), Kenichi Kondo).

However, in the fine grained diamond sintered body according to the former method (a), since direct bonding between diamond particles is inhibited by carbides such as WC, it is possible to form a sharp cutting edge shape, but the bonding between diamonds is Since it does not exist, there is a problem in its hardness and wear resistance.

The latter method (b) is a method for synthesizing fine-grained diamond sinters under very high pressure conditions of about 90 GPa, so it is very difficult to synthesize diamond sinters without cracks. The density of the sintered body is about 98%. From these things, it is considered difficult to process the sintered body into a tool having a sharp cutting edge shape at present.

To solve the above problems, more basic research will be necessary.

The present invention has been made to solve the above-mentioned problems of the prior art, and has a direct bond between diamond particles, has high hardness and excellent wear resistance, and has an average particle size of 0.5 μm or less. It is an object of the present invention to provide a method for producing a diamond sintered body.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present inventor has conducted extensive research on a method for synthesizing a fine-grained diamond sintered body, and as a result, prior to sintering, secondary particles of the starting diamond powder were Is suppressed by heat treatment under the addition of cubic boron nitride powder and a polymer substance, and then by sintering,
There is no abnormal grain growth and diamond particles are directly bonded to each other,
The present invention has been made by finding that it is possible to obtain a diamond sintered body that is homogeneous and has fine particles.

That is, the present invention relates to a diamond powder having a particle size of 0.5 μm or less and a cubic boron nitride powder having a particle size of 0.5 μm or less 2.5 to 10
wt% and organic polymer substance 15 to 30 wt% are mixed, and then heat-treated in a nitrogen stream, and the powder is filled in an alloy container or laminated with an alloy substrate, and is heated to 1350 in a diamond stable region. The gist is a method for producing a fine-grained diamond sintered body, which is characterized by sintering at a temperature of ℃ or more.

The present invention will be described in more detail below.

(Operation) Next, a basic experiment conducted by the present inventor to obtain a fine-grained diamond sintered body will be sequentially described.

First, for the purpose of synthesizing a fine-grained diamond sintered body, using the sample configuration shown in FIG. 1, commercially available static synthetic diamond powder with a grain size of 1 μm or less was laminated on a WC-16 wt% Co substrate, and 6 GPa, Sintering was performed at 1400 ° C for 30 minutes. When the cross section and the surface of the obtained diamond sintered body layer were observed with an optical microscope, abnormal grain growth of diamond was partially observed in the peripheral portion of the diamond layer and in the vicinity of the WC-Co interface. Further, the central part of the end face of the diamond layer was unsintered. Therefore, in order to synthesize a diamond sintered body without abnormal grain growth by changing the sintering conditions variously, sintering was performed using the same sample structure as that shown in FIG. However, in most cases, the obtained diamond sintered body has an abnormal grain growth portion,
Alternatively, when there was no abnormal grain growth, it was unsintered. Furthermore,
As a result of repeated research to elucidate the reason why fine diamond powder tends to grow abnormally, it is important to suppress the formation of secondary particles in the starting diamond powder and to sinter at the lowest possible temperature. Became clear.

Next, as a result of diligent research to suppress the secondary particles of the fine diamond powder, it was found that it is effective to uniformly add an additive to the surface of the fine diamond powder and suppress the formation of the secondary particles. . That is, regarding the selection criteria of additives, first, non-diamond carbon was added to the surface of fine-grained diamond to try to suppress the formation of secondary particles of diamond. As the non-diamond carbon, fine carbon is desirable from the viewpoint of adding a small amount of carbon, and carbon black was used as fine carbon. However, carbon black is not easily converted into diamond even when it is heat treated, mixed or laminated with a diamond synthesis catalyst, and subjected to high temperature and high pressure treatment in the diamond synthesis region. Since it remains in the diamond sintered body as non-diamond carbon,
It is not preferable because only a low-strength sintered body can be obtained. From this point of view, a method has been found in which an organic polymer substance is uniformly added to the diamond powder surface in place of non-diamond carbon, and the addition is followed by sintering to uniformly add carbon to the diamond powder surface.

Specifically, first, polyethylene glycol (hereinafter abbreviated as “PEG”) in 10 cc of benzene solvent is used.
00) 0.4 g was melted and 2 g of fine diamond powder having a particle size of 1 μm or less was dispersed by ultrasonic waves. As PEG, those having a smaller average molecular weight of about 200 may be used. After dispersion, air dry in the air, and after drying, 500 in a nitrogen stream.
The PEG was carbonized by heating each at 2 ° C and 900 ° C for 2 hours.
As a result of SEM observation of the sample after the heat treatment, fine carbon was homogeneously deposited on the surface of the diamond particles. This PEG
The added diamond powder was crushed in a boron carbide mortar, and the sample structure was the same as that shown in Fig. 1, 6GPa, 1400 ℃ × 30
Sintered under the condition of minutes. Abnormal grain growth was not observed at all in the obtained diamond sintered body, and it was a fine-grained diamond sintered body having a grain size of 1 μm or less. The reason for obtaining such a fine-grained diamond sintered body is that the formation of secondary particles of the starting diamond powder was suppressed, and that Co from the WC-Co layer to the diamond was homogeneously moved by the added carbon in the diamond. Conceivable.

However, when sintering was performed in the same manner as the above-mentioned experiment except that diamond powder having a particle size of 0.5 μm or less was used, it was found that it was only partially sintered and was almost unsintered. Despite the same sintering conditions, it is considered that the reason why the diamond powder having a small grain size is difficult to sinter is because the finer grain powder is more difficult to transfer Co from the WC-Co layer to the diamond layer. Although the sintering temperature was raised to 1430 ° C and the other conditions were exactly the same, a sintered body was synthesized, but many abnormal grain growths were observed in the peripheral portion of the diamond layer and in the vicinity of the WC-Co interface. Sintering temperature,
Attempts were made to synthesize a sintered body by changing the sintering time and the heating rate, but a diamond sintered body without abnormal grain growth could not be synthesized.

From these experimental results, in order to synthesize a fine diamond sintered body of 0.5 μm or less, it is necessary to add a substance that suppresses abnormal grain growth in addition to organic polymer substances such as PEG It has proved very difficult to control growth.

In that case, in order to prevent the hardness and wear resistance of the diamond sintered body from being significantly impaired, it is desirable to add a small amount of a hard substance. As a result, by adding a small amount of fine grained cubic boron nitride (CBN),
They have found that abnormal grain growth of diamond can be suppressed. However, if fine diamond powder is added to fine CB
Even if only N powder is used as a starting material, it is difficult to synthesize a homogenous fine-grained diamond sintered body, and at the same time, an organic polymer substance such as PEG is added to form a fine carbon powder on the diamond powder surface. Is essential. This carbon is a diamond synthesis catalyst, Co, Ni, Fe
It is effective for the homogeneous transfer of the same to the diamond layer.

By the way, according to the above method, 100 mg of CBN powder of 0.5 μm or less and 0.5 g of diamond powder of 0.5 μm or less of 2 g
PEG was added and wet mixed in a benzene solvent using a vibrating mill. As the solvent, besides benzene, toluene or cyclohexane can be used. After mixing, they were naturally dried and heat-treated at 500 ° C. and 900 ° C. for 2 hours each in a nitrogen stream. Then, it was crushed and sintered under the conditions of 6 GPa, 1430 ° C. × 30 minutes, using the same sample constitution as in FIG. The obtained sintered body was a diamond sintered body having no abnormal grain growth and having uniform and fine particles. As shown in the SEM photograph of the fractured surface of this sintered body in FIG. 3, this sintered body is a diamond sintered body composed of fine particles having a grain size of 0.5 μm or less. As a result of measuring the Vickers hardness of the sintered body under the condition of a load of 2 kg, it was found to be a high hardness having a hardness of about 60 GPa. Moreover, as a result of examining the distribution of B and N in the sintered body by scanning Auger electron spectroscopy (SAM), it was revealed that CBN was uniformly dispersed in the diamond sintered body. It is considered that this homogeneously distributed CBN suppresses the abnormal grain growth of diamond.

Although the conditions of the present invention are clear from the description of the results of the basic experiments that have led to the discovery of the present invention, the reasons for limiting the conditions of the present invention will be described below comprehensively.

The starting diamond powder needs to have a particle size of 0.5 μm or less in order to obtain a sintered body made of fine particles of diamond. CBN and an organic polymer are added to and mixed with this.

Similarly, CBN has a particle size of 0.5 μm or less, and is 2.5-10 wt.
% Trace amount is added. If it is less than 2.5 wt%, the effect of suppressing the abnormal grain growth of diamond particles by uniformly dispersing CBN cannot be expected, and if it is added in excess of 10 wt%, the direct bond between diamond particles is significantly hindered. Absent.

The organic polymer substance is preferably polyethylene glycol (PEG), but other organic polymer substances may be used, and those having an average molecular weight of about 200 to 4000 are desirable. The amount added is 15 to 30 wt%. If it is less than 15 wt%, the formation of secondary particles of diamond powder cannot be suppressed, and 30 wt%
If it is added in a large amount over the range, it promotes abnormal grain growth of diamond, which is not preferable.

These mixed powders are heat-treated in a nitrogen stream. The heating temperature is not particularly limited, but a range of 500 to 900 ° C is desirable. As a result, carbon is uniformly distributed on the diamond powder surface,
It becomes possible to add CBN.

Then fill these powders in a suitable alloy container, or
Alternatively, it is laminated with an alloy substrate. As the alloy container and the alloy base, a metal alloy or a carbide dispersion alloy containing 5 wt% or more of one or more of Fe, Ni and Co is desirable. These Fe, Ni, Co, etc. act as a diamond synthesis catalyst, and the carbon is effective for the homogeneous transfer of these catalysts to the diamond layer.

Sintering is performed at a temperature of 1350 ° C or higher in the diamond stable region. Sintering cannot be expected below 1350 ° C. However, since the abnormal grain growth of diamond particles is caused at a high temperature such as 1480 ° C, it is preferably lower than 1480 ° C. The diamond stable region is a condition of pressure and temperature at which diamond is thermodynamically stable as compared with graphite, but it can be sintered under a pressure of about 6 GPa. Other sintering conditions are not particularly limited.

An example of sample composition for synthesizing a sintered body is shown in FIG.
This is a sample configuration in which a heat-treated diamond mixed powder 5 is laminated on a WC-Co substrate 4 in a graphite heater 10 and is sintered under high pressure. Of course, it goes without saying that the sample configuration is not limited to this.

(Example) Next, the Example of this invention is shown.

Example 1 To 2 g of diamond powder having a particle size of 0.5 μm or less, 50 mg of CBN powder having a particle size of 0.5 μm or less and 0.4 g of PEG were added, and 8 cc of benzene was added.
Was wet-mixed using a polyacetal-lined pot. After mixing, air dry and in a nitrogen stream
Heat treatment was performed at 500 ° C. and 900 ° C. for 2 hours each. Then, crushed, laminated this powder on a substrate of WC-16wt% Co, 6GPa,
Sintering was performed at 1430 ° C for 30 minutes. The particle size of the obtained diamond sintered body was 0.5 μm. The hardness was 62 GPa in Vickers hardness.

Comparative Example A starting material was prepared in the same manner as in Example 1 by adding 100 mg of CBN powder having a particle size of 0.5 μm or less and 0.4 g of PEG to 2 g of diamond powder having a particle size of 0.5 μm or less. This starting material powder
It was laminated on a WC-16 wt% Co substrate and sintered under the conditions of 6 GPa and 1430 ° C. for 30 minutes. In the obtained diamond sintered body, two abnormal grain growth particles of about 50 μm were observed around the diamond layer. The sintering temperature of 1480 ° C is considered to be too high as the synthesis temperature for the fine-grained diamond sintered body.

Example 2 The starting material used in the comparative example was a Fe-Ni-Co alloy (Fe64wt).
%, Ni31wt%, Co5wt%), laminated with 6GPa, 1380
Sintering was carried out under the condition of ℃ × 30 minutes. The obtained diamond sinter was composed of fine particles having a particle size of 0.5 μm or less, and was a high hardness sinter with a Vickers hardness of 60 GPa. It is considered that the reason why the homogeneous and high hardness diamond sintered body can be obtained despite the low sintering temperature is that the melting point of the Fe-Ni-Co alloy that acts as a sintering aid is lower than that of Co.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to obtain a fine diamond sintered body having direct bonding between diamond particles and having a particle size of 0.5 μm or less, and high hardness. It also has excellent wear resistance. Therefore, this sintered body can be processed into a sharp cutting edge shape, and is suitable as a tool material for fine processing of difficult-to-cut materials, a material for wire drawing dies which requires smoothness of a finished surface, and the like.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing a sample structure for synthesizing a diamond sintered body, FIG. 2 is a secondary electron image photograph showing a particle structure of a diamond-PEG mixture after heat treatment, and FIG. It is a secondary electron image photograph which shows the particle structure of the fracture surface of a body. 1 ... Stainless steel plate, 2 ... Steel ring, 3 ... Sodium chloride, 4 ... WC-Co substrate, 5 ... Diamond powder, 6 ... Current ring, 7 ... ZrO ₂ plate, 8 ... Copper plate, 9 ... Zirconium foil, 10 ... Graphite heater, 11 ... Sodium chloride-10 wt% zirconia.

Claims (3)

[Claims] 1. A diamond powder having a particle size of 0.5 μm or less is mixed with 2.5 to 10 wt% of cubic boron nitride powder having a particle size of 0.5 μm or less and 15 to 30 wt% of an organic polymer substance, followed by heat treatment in a nitrogen stream. Then, in a state where the powder is filled in an alloy container or laminated with an alloy substrate under a diamond stable region, 13
A method for producing a fine-grained diamond sintered body, which comprises sintering at a temperature of 50 ° C or higher. 2. The alloy container and the alloy substrate are 5 wt% or more of F
The method according to claim 1, which is a metal alloy or a carbide dispersion alloy containing one or more of e, Ni and Co. 3. The heat treatment in the nitrogen stream is 500 to 900 ° C.
The method according to claim 1, wherein