JP3550587B2 - Method for manufacturing fine diamond sintered body - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention has excellent wear resistance and heat resistance, for example, when applied to finish cutting tools of difficult-to-cut materials such as high Si-Al alloys, ultra-precision machining tools of metal, and drawing dies, etc. The present invention relates to a method for producing a diamond sintered body expected to exhibit cutting performance and wire drawing performance.
[0002]
[Prior art]
Conventionally, it is well known that a fine-grained diamond sintered body using a metal such as Co as a sintering aid is manufactured by sintering with a normal ultra-high pressure synthesis apparatus. Also, without using any metal sintering aid, by using alkaline earth metal carbonate as a sintering aid, and sintering under higher pressure and temperature conditions than before, excellent heat resistance A method of synthesizing a high-hardness diamond sintered body is known (Diamond and Related Mater., Vol. 5, pp. 34-37, 1996).
[0003]
[Problems to be solved by the invention]
However, in the case of the above-mentioned metal-based fine-grained diamond sintered body, in order to manufacture a sintered body composed of fine particles while suppressing abnormal grain growth of diamond, it is necessary to limit the sintering temperature low (J. Am. Ceram. Soc., Vol. 74, pp. 5-10, 1990), the hardness of the sintered body is far from the original properties of diamond.
[0004]
Also, conventional fine-grained diamond sintered bodies contain a large amount of metal sintering aids, so that under high temperature conditions, graphitization and cracking can easily occur due to thermal stress caused by the difference in the coefficient of thermal expansion between metal and diamond. Since the sintered body is deteriorated due to the introduction and the like, it is difficult to use it for a cutting tool of a difficult-to-cut material.
[0005]
Since the diamond sintered body having excellent heat resistance using carbonate as an auxiliary is limited to a relatively large particle diameter of about 5 μm, the sharpness required for ultra-precision machining tools and the like is required. There was a problem in manufacturing a cutting tool having a cutting edge shape and in the surface roughness of a wire when used in a drawing die.
In order to solve these problems, an object of the present invention is to develop a method for manufacturing a fine-grained diamond sintered body having the original characteristics of diamond having excellent heat resistance.
[0006]
[Means for Solving the Problems]
In the production of a diamond sintered body using a carbonate as an aid, the limitation on the particle size of the obtained sintered body is closely related to the viscosity of the molten carbonate used for the sintering aid. Even if natural diamond powder (for example, a commercially available product having an indicated particle size of 2 to 4 μm) is laminated on magnesium carbonate and sintered under the conditions of 7.7 GPa and 2300 ° C., only about 0.1 mm of molten carbonate forms the diamond layer. Therefore, a diamond sintered body cannot be synthesized.
[0007]
In order to synthesize a fine diamond sintered body, the viscosity of the molten carbonate is reduced, the molten salt easily infiltrates the diamond layer, and the molten salt infiltrated between the diamond particles functions as a diamond sintering aid. You have to do it.
It is well known that the melting point of the carbonate can be easily reduced by adding a volatile component such as water or carbon dioxide to the carbonate. In this case, a capsule for sealing these volatile components under high pressure and high temperature conditions is required.
[0008]
As a result of intensive studies on the capsule shape, material, sample configuration, and the like, it has been clarified that the fluid phase can be sealed with a single capsule made of a high melting point metal such as Ta or Mo. Our recent study also revealed that the C—O—H fluid phase mainly composed of the volatile component functions as a diamond synthesis catalyst (J. Crystal Growth, 209, 999-1003, 2000). Year).
[0009]
The present inventor has improved the above-mentioned method and found a means capable of realizing the synthesis of a high-hardness and high-toughness fine-grained sintered diamond material having a submicron particle size and excellent heat resistance.
That is, the present invention uses a mixture of a carbonate and an organic substance that forms a supercritical fluid phase as a sintering aid, and in a state where diamond is thermodynamically stable at 2000 ° C. or higher in a state of being laminated on a diamond powder layer. This is a method for producing a fine-grained diamond sintered body, characterized by producing a fine-grained diamond sintered body having a submicron particle diameter by sintering under high pressure and high temperature conditions.
Further, the present invention is the above-mentioned method for producing a fine-grained diamond sintered body, characterized in that a supercritical fluid phase is sealed and sintered with a Ta or Mo capsule.
[0010]
Further, in the present invention, the sintering aid comprises a mixed powder of an organic substance in an amount of 0.1 mol or more and less than 0.3 mol per 1 mol of a carbonate, and the organic substance in the mixed powder is subjected to high pressure and high temperature conditions. Decomposes to form a supercritical fluid phase comprising CO ₂ and H ₂ O to form a carbonate-CO ₂ -H ₂ O-based sintering aid. It is a manufacturing method.
[0011]
Further, the present invention is the above-described method for producing a fine-grained diamond sintered body, wherein a natural diamond powder having a particle size of 1 μm or less is used as the diamond powder layer.
[0012]
In order to form a supercritical fluid phase using a sintering aid, an organic substance is mixed with a carbonate, this mixture is laminated with diamond powder, and the mixed organic substance is decomposed under high pressure and high temperature conditions to form a supercritical fluid phase. H ₂ O and CO ₂ in a state are generated. The generated supercritical fluid phase lowers the melting point of the carbonate, and the carbonate easily infiltrates into the diamond. The carbonate containing the infiltrated supercritical fluid phase efficiently dissolves a part of the diamond particles, deposits diamond from the molten carbonate supersaturated with carbon, and forms a direct bond between the diamond particles Let it. As a result, a diamond sintered body can be synthesized. It is difficult to synthesize a high-quality sintered body by a method such as mixing diamond powder with a sintering aid.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1A is a sectional view of a Ta or Mo capsule filled with the diamond powder and the sintering aid. FIG. 1B is a cross-sectional view showing a state where the Ta or Mo capsule of FIG. 1A filled with the raw material is incorporated in a belt-type ultra-high pressure synthesizer or the like.
[0014]
Capsules are used because the leakage of the supercritical fluid phase does not lower the melting point of the carbonate. As the material of the capsule, Ta or Mo is preferable among the high melting point metals, and it is not practical with other metals. The case where a Ta capsule is used will be described below, but the same applies to a Mo capsule. As shown in FIG. 1 (a), a sintering aid comprising a mixture of a carbonate and an organic substance forming a supercritical fluid phase is laminated on the diamond powder layer from the bottom of the Ta capsule. Ta foil 5, graphite plate 4, Ta foil 5, diamond powder 1, carbonate-organic mixed powder 2, diamond powder 1, Ta foil 5, diamond powder 1, carbonate-organic mixed powder 2, diamond powder 1, Ta foil 5, a graphite plate 4, and a Ta foil 5 are laminated in this order, filled with a pressure of 200 MPa, and covered.
[0015]
As shown in FIG. 1B, the Ta-made capsule 8 filled with the raw material is inserted into a capsule 12 made of Ta foil, and a NaCl-20 wt% ZrO ₂ molded body is vertically placed through the Ta foil 13. Using a NaCl-10 wt% ZrO ₂ molded body as a pressure medium on the side surface, the periphery is fixed with a steel ring 7, covered with pyrophyllite 6, and heated with a graphite heater 9.
[0016]
As the carbonate, magnesium carbonate or calcium carbonate is suitable. Further, as the organic substance to be added to the carbonate, oxalic acid dihydrate composed of C, O and H or malonic acid which functions as a diamond synthesis catalyst is suitable. For example, oxalic acid dihydrate decomposes to form H ₂ O, CO ₂ and C as shown in the following formula. _{(COOH) 2 · 2H 2 O} → 3 / 2CO 2 + 3H 2 O + 1 / 2C
The mixing ratio is preferably a ratio of 0.1 mol or more to less than 0.3 mol of the organic substance per 1 mol of the carbonate. If it is added in an amount of 0.3 mol or more, the amount of carbonate decreases, and a good sintered body cannot be obtained. In order to synthesize a diamond sintered body having a submicron particle size, it is desirable to use a diamond powder having a particle size of 1 μm or less, for example, a commercially available natural diamond powder having a display particle size of 0 to 1 μm.
[0017]
If the treatment is performed at a pressure of 7.7 GPa or more and a sintering temperature of 2000 ° C. or more for 10 to 30 minutes, fine diamond can be synthesized with good reproducibility. The upper limit of the pressure is about 8 GPa. Above this, the sample space is limited, which is not preferable for industrial production. The upper limit of the sintering temperature is set to about 2500 ° C. because it is defined by the thermodynamic stability conditions of diamond.
[0018]
【Example】
Next, a method for producing a fine-grained diamond sintered body of the present invention will be specifically described with reference to examples.
Example 1
Because natural diamond powder often contains significant amounts of silicate, prior to use, natural diamond powder was treated in molten NaOH using a Zr crucible to remove silicate. To prevent Zr from being mixed into the diamond powder after the treatment, the diamond powder was treated in hot aqua regia after the molten NaOH treatment to remove Zr. As a result of measuring the average particle diameter of the above-described desilicate-treated 0 to 1 μm diamond powder, the average particle diameter was 0.68 μm. Further, 0.1 mol of oxalic acid dihydrate was mixed and added to 1 mol of natural Australian magnesium carbonate to prepare a sintering aid.
[0019]
The sintering aid and the diamond powder were treated in a sample configuration as shown in FIG. 1A and FIG. did. The X-ray diffraction pattern of the sintered body revealed that the sintered body was composed of diamond and a small amount of magnesium carbonate.
[0020]
In order to evaluate the heat resistance of the sintered body, the sintered body was treated in a vacuum at 1200 ° C. for 30 minutes. No change in the hardness of the sintered body before and after the treatment and no introduction of cracks due to the heat treatment were observed. From these results, it is clear that the high-hardness fine-grained diamond sintered body is very excellent in heat resistance.
[0021]
The diamond sintered body was ground, and the Vitzkars hardness of the sintered body was measured at a load of 19.6 N. As a result, it was found that the hardness was 70 GPa or more, which was equal to or higher than that of a diamond single crystal. Observation of the indentation used for the hardness measurement clearly shows that no crack is observed at the tip of the indentation, and that the sintered body is very excellent in toughness. It is well known that cracks are introduced at the tips of indentations in the case of existing coarse-grained diamond sintered bodies. In order to clarify the particle size of the sintered body, the fracture surface of the sintered body was examined with a scanning electron microscope.As a result, it was found to have a submicron particle size, which was almost the same as that of the natural diamond powder as the starting material. Was.
[0022]
Comparative Example 1
On a mixed powder obtained by adding 0.1 mol of magnesium carbonate to 1 mol of oxalic acid dihydrate, a diamond powder subjected to desilicate treatment in the same manner as in Example 1 was laminated, and the same sample configuration as in Example 1 was used. Sintering was performed for 20 minutes under a high pressure and high temperature condition of 7.7 GPa and 2200 ° C. As a result of examining the sample after sintering in the same manner as in Example 1, the sintered body was completely unsintered.
[0023]
【The invention's effect】
The fine diamond sintered body synthesized according to the present invention has a particle diameter in which no abnormal grain growth particles are observed by using a sintering aid composed of a mixture of magnesium carbonate and an organic substance forming a supercritical fluid phase. The present invention realizes the synthesis of a high-hardness, high-toughness fine-grained diamond sintered body having excellent heat resistance of 1 μm or less. Since this sintered body has characteristics not found in conventional sintered bodies, it is expected to be used in fields such as tools for ultra-precision machining, machining tools for difficult-to-cut materials, and drawing dies.
[Brief description of the drawings]
FIG. 1 (a) is a sectional view of a Ta or Mo capsule filled with diamond powder and a sintering aid. FIG. 1B is a cross-sectional view showing a state where the Ta or Mo capsule of FIG. 1A filled with the raw material is incorporated in an ultrahigh-pressure synthesis apparatus.

Claims (5)

Using a mixture of carbonate and an organic substance that forms a supercritical fluid phase as a sintering aid, diamond is sintered in a thermodynamically stable high-pressure high-temperature condition of 2000 ° C or higher in a state of being laminated on a diamond powder layer. A method for producing a fine-grained diamond sintered body having a particle diameter of submicron. 2. The method for producing a fine-grained diamond sintered body according to claim 1, wherein the supercritical fluid phase is sealed and sintered with a Ta or Mo capsule. The sintering aid is composed of a mixed powder of an organic substance in an amount of 0.1 mol or more to less than 0.3 mol with respect to 1 mol of a carbonate, and the organic substance in the mixed powder is decomposed under high pressure and high temperature conditions to form CO _2. production and generating of H _{2 O} consisting of supercritical fluid phase, the fine diamond sintered body according to claim 1 or 2, wherein the forming a carbonate -CO 2 _-H 2 _O-based sintering aid Method. 4. The method according to claim 1, wherein the carbonate is magnesium carbonate or calcium carbonate, and the organic substance is oxalic acid dihydrate or malonic acid. . The method for producing a fine-grained diamond sintered body according to any one of claims 1 to 4, wherein a diamond powder having a particle diameter of 1 µm or less is used as the diamond powder layer.

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