KR20050088415A - Heat-resistant composite diamond sintered product and method for production thereof - Google Patents

Abstract

A heat-resistant composite diamond sintered product which comprises a sintered product from a superfine synthetic diamond powder, characterized in that said sintered product is produced with no sintering auxiliary and is a composite sintered product comprising diamond crystals and a trace amount of non-diamond carbon formed and has a Visckers hardness of 85 GPa or more; and a method for producing the above heat-resistant composite diamond sintered product which comprises encapsulating a synthetic diamond powder having an average particle diameter of 200 nm or less by the use of a Ta or Mo capsule, and heating and pressuring said capsule using a super high pressure synthesis apparatus under a condition wherein diamond is thermodynamically stable, that is, of a temperature of 2100°C or higher and a pressure of 7.7 GPa or more, to thereby sinter the diamond powder.

Description

Heat-resistant composite diamond sintered product and method for production

The present invention relates to a heat resistant diamond composite sintered body and a method of manufacturing the same.

Conventionally, it is known that the diamond sintered compact which uses metals, such as Co, as a sintering aid, and the diamond sintered compact which uses carbonate as a sintering aid, are manufactured by the usual ultrahigh pressure synthesis apparatus (patent document 1, 2). In addition, a synthetic method is obtained in which a high hardness diamond sintered body having excellent heat resistance is known by sintering under alkaline pressure metal temperature carbonate as a sintering aid without using any metal sintering aid at all. Patent document 1). However, since such a sintered compact has high viscosity of molten carbonate, its particle size is limited to a relatively large particle size of about 5 µm even though it is small.

The present inventors produced a mixed powder in which oxalic acid dihydrate, which is a source of CO ₂ -H ₂ O fluid phase, was added to carbonate, and the mixed powder had a natural particle diameter of 0 to 1 탆. Although the method of laminating | stacking diamond powder and manufacturing a fine diamond sintered compact was reported (patent document 3, nonpatent literature 2,3), the manufacture requires high temperature of 2200 degreeC or more.

The present inventors reported the example which sintered the fine diamond powder, for example, the diamond powder of 0-0.1 micrometer of particle diameter widths by the same method (nonpatent literature 4). However, abnormal grain growth of diamond occurred, and a high hardness diamond sintered body could not be produced.

Recently, a method of synthesizing a diamond sintered body without a sintering aid under conditions of 12 to 25 GPa, 2000 to 2500 ° C by a direct conversion reaction from graphite to diamond road has been announced, and it is reported that it becomes a translucent sintered body (Non Patent Literature 5). .

Patent Document 1 Special Publication No. 52-12126

Patent Document 2 Special Publication No. 4-50270

Patent Document 3 Publication No. 2002-187775

Non Patent Literature 1 Diamond and Related Mater., Vol. 5, pages 34-37, Elsevier Science S.A, 1996

Non-Patent Literature 2 The 41st High-Pressure Discussion Lecture Summaries Collection, 108 pages, Japan High Pressure Society, 2000

Non-Patent Document 3 Proceedings of the 8th NIRIM International Symposium on Advanced Materials, pages 33-34, Institute of Inorganic Materials, 2001

Non-Patent Document 4 Collection of Lectures on the 42nd High Pressure Discussion Forum, p. 89, Japan High Pressure Society, 2001

[Non-Patent Document 5] T.Irifune et al., `` Characterization of polycrystalline diamonds synthesized by direct conversion of graphite using multi anvil apparatus '', 6th High Pressure Mineral Physics Seminar, 28 August, 2002, Verbania, Italy

1 is a cross-sectional view conceptually illustrating an example of a state in which a diamond powder is filled in a capsule for sintered body synthesis for sintering diamond powder in the production method of the present invention.

2 is an X-ray diffraction figure of the sintered body obtained in Example 1 ((a) before heat treatment and (b) after heat treatment).

3 is a photographic electron microscope structure photograph of the wavefront of the sintered compact obtained in Example 1. FIG.

(The best mode for carrying out the invention)

In the method for producing a diamond sintered body of the present invention, synthetic ultrafine diamond powder is used as a starting material. BRIEF DESCRIPTION OF THE DRAWINGS In the manufacturing method of this invention, sectional drawing which shows an example of the state in which the diamond powder was filled in the capsule for sintered compact synthesis for sintering diamond powder.

As shown in FIG. 1, the graphite disk 4A for suppressing the deformation | transformation of a capsule is put in the bottom of the cylindrical Ta capsule 3, and diamond powder is made using Ta or Mo foil 1A. Pressurized charging (2A). Ta or Mo foil is used for the separation of diamond powders to synthesize a sintered body of a desired thickness, separation of graphite and diamond powder, prevention of intrusion of a pressure medium, seal in a fluid phase, and the like. Ta or Mo foil 1B is arrange | positioned on this diamond powder 2A. By the same method, after filling three layers of diamond powder (2B, 2C, 2D) through Ta or Mo foil (1C, 1D), Ta or Mo foil (1E) is arrange | positioned and the deformation suppression of a capsule thereon Distribute the master disk made of graphite (4B).

This capsule is accommodated in a pressure medium, pressurized to 7.7 GPa or more under room temperature conditions using a high pressure device by a static compression method such as a belt type ultrahigh pressure synthesizing apparatus, and a predetermined temperature of 2100 ° C. or higher under the same pressure condition. It heats to and sintering. If the pressure is less than 7.7 GPa, the desired heat resistant sintered compact cannot be obtained even at a temperature of 2100 ° C or higher. If the sintering temperature is lower than 2100 ° C, the desired heat resistant sintered body cannot be obtained even at a pressure of 7.7 GPa or more. Even if the temperature and pressure are higher than necessary, the energy efficiency is only deteriorated. Therefore, it is preferable that the temperature and pressure be minimized in consideration of the corresponding limit of the apparatus.

Synthetic diamond powder having an average particle diameter of 200 nm or less is a powder obtained by classifying after crushing a synthetic diamond powder having a large particle size, and the measuring method is a measured value by a microtrack UPA particle size-measuring apparatus. Such a measuring method is well-known (for example, see Unexamined-Japanese-Patent No. 2002-35636). Such synthetic diamond powder can be obtained as a commercial item (for example, brand name MD200 (average particle diameter 200nm) and MD100 (average particle diameter 100nm) by a same-name diamond company).

(Initiation of invention)

In addition to use as a high performance tool in the field of cutting tools, a diamond sintered body having high heat resistance and high precision machining tools in which single crystals have been used conventionally, and also as precious metal products, is required. In particular, the heat resistance of diamond sintered tools is demanded along with the high speed of cutting oil bits for oil drilling and special parts for automobiles.

Conventionally, high hardness diamond sintered bodies are manufactured by high pressure and high temperature sintering under super high pressure conditions of 5.5Gpa to 7.7Gpa using a sintering aid, regardless of metals and nonmetals. In the method for producing a diamond sintered body using such a sintering aid, since the material used for the sintering aid remains as a solid in the sintered body after high pressure and high temperature sintering, the ratio of the bonds between the diamond particles is reduced.

Compared with the ideal diamond sintered body which does not contain the sintering aid at all, the hardness of such a sintered body is lowered or the sintering aid remaining in the sintered body is chemically reacted with diamond, which causes deterioration of the characteristics of the sintered body. Moreover, the synthesis | combination of the sintered compact which does not contain the sintering aid at all requires very high pressure and temperature.

When sintering natural diamond powder having a particle size width of 0 to 0.1 µm using a sintering aid that becomes a carbonate-COH fluid phase, a high-hardness fine diamond sintered body in which carbonates are homogeneously distributed among diamond particles is easily formed under conditions of 7.7 GPa and 1700 ° C. or more. It is possible to synthesize (JP-A 2002-030863 = JP-A 2003-226578).

Therefore, the present inventors use a sintering aid in which a hydrogen-terminated synthetic diamond powder having an average particle diameter of 100 nm is converted into a carbonate-COH fluid for the purpose of reducing the synthesis cost of the high-hardness fine diamond sintered body using the carbonate as the sintering aid. It was laminated on the phase and treated under high pressure and high temperature conditions to try to synthesize a diamond sintered body. The recovered sample was divided into layers and the carbonate was infiltrated to the middle, but the homogeneous infiltration of the sintering aid in the carbonate-COH fluid phase in the diamond powder could not be realized. This plastic deformation is easy, and thus the voids between the diamond powder particles are partially broken, so that the melt sintering aid is not homogeneously infiltrated.

In addition, the inventors sintered the natural diamond powder having a particle size width of 0 to 0.1 µm for 15 minutes under conditions of 7.7 Gpa and 2300 ° C in a system using no sintering aid. As a result, it became clear that it is difficult to synthesize | harden a high hardness diamond sintered compact from the natural diamond powder of particle size width 0-0.1 micrometer.

The present inventors surprisingly suffer from the above problems when high-temperature high-temperature sintering is performed using synthetic diamond powder having an average particle diameter of 200 nm or less as a starting material and a high-temperature and high-temperature condition in which a diamond sintered body is manufactured using a sintering aid such as carbonate. Was found not to occur, and succeeded in synthesizing a heat-resistant diamond sintered body comprising fine particles containing no sintering aid at all.

In addition, the sintered compact obtained by this manufacturing method contains a small amount of non-diamond carbon as a product to form a composite sintered compact of diamond crystals and non-diamond carbon, and electrical conductivity is imparted to the sintered compact. This non-diamond carbon is estimated to be produced by the partial graphitization of the diamond powder of the starting material. As a result, electrical discharge is provided, thereby enabling electrical discharge machining. In addition, it has sparkles and luster that are not at all in the conventional diamond sintered body.

That is, this invention is (1) the sintered compact of the ultra-fine synthetic diamond powder whose average particle diameter is 200 nm or less, The sintered compact is a composite sintered compact which becomes the trace amount non-diamond carbon produced by diamond crystal sintering without a sintering aid, ) A heat resistant diamond composite sintered body having a hardness of 85 GPa or more.

In addition, the present invention (2) a synthetic diamond powder having an average particle diameter of 200 nm or less is encapsulated in a capsule made of Ta or Mo, and the capsule is subjected to a thermodynamic stable condition of diamond at a temperature of 2100 ° C. or higher and a pressure of 7.7 GPa or higher using an ultrahigh pressure synthesizer. It is a manufacturing method of the heat resistant diamond composite sintered compact of said (1) characterized by sintering diamond powder by heating under pressure.

In the case where the particle diameters of the diamond powders are compared almost identically, the synthetic diamond powder is a powder that is easily plastically deformed as compared with the natural diamond powder. It is considered that the powder having a small particle size distribution of the starting diamond powder has a smaller distribution of the pore size between the particles than the powder having a large distribution. Therefore, when the particle diameter of the diamond powder is approximately constant, and at the same time, the synthetic diamond powder having the smallest average particle diameter is used as the starting material, the diamond particles are easily plastically deformed, and the large surface energy inherently possessed by the small diamond particles is driven. It is thought that a heat resistant diamond composite sintered compact is synthesized even when no sintering aid is used.

When a synthetic diamond powder having an average particle diameter of more than 200 nm is used, the surface energy of the particles becomes smaller and the synthesis of the diamond sintered body becomes difficult as the particle diameter of the diamond particles increases.

The heat-resistant diamond composite sintered body synthesized by the manufacturing method of the present invention is not only for industrial use such as high performance tools in cutting tool field, oil bits requiring heat resistance, but also has a high refractive index inherent to diamond, but it is a diamond sintered body without sintering aid. It has a unique sparkle, and it is easy to manufacture a large sintered compact, and thus a new use as a use for a noble metal is expected.

Since the manufacturing method of this invention can manufacture on the pressure and temperature conditions equivalent to the diamond sintered compact which uses a carbonate as a sintering aid, manufacture of a large sized sintered compact is easy.

Hereinafter, the manufacturing method of the diamond sintered compact of this invention is demonstrated concretely based on an Example.

(Example 1)

A synthetic diamond powder having a commercial average particle size of 100 nm was prepared as a starting material.

At the bottom of the cylindrical Ta capsule having a thickness of 0.8 mm and an outer diameter of 11.6 mm, a 2.6 mm thick disk made of graphite for suppressing the deformation of the capsule was placed. Using Ta foil, 250 mg of diamond powder was applied to the layer at a pressure of 100 MPa. Charged. Ta foil was placed on the diamond powder, and a 2.6 mm thick graphite disk was placed on the Ta foil to suppress deformation of the capsule. After the capsules were press molded, the excess graphite at the top was shaved.

Next, the capsules were filled in a pressure medium of NaCl-10% ZrO ₂ , and sintered for 30 minutes under conditions of 7.7 GPa and 2200 ° C. using a belt type ultrahigh pressure synthesizer, and then the capsules were taken out from the synthesizer.

TaC and the like formed on the surface of the sintered compact were treated with a hydrofluoric acid-acetic acid solution and removed, and the upper and lower surfaces of the sintered compact were ground with a diamond wheel. It was a sintered compact with high grinding resistance, and the average value of the Vickers hardness of the sintered compact after grinding was 90 GPa or more.

In order to evaluate the heat resistance of this sintered compact, it processed for 30 minutes at 1200 degreeC in vacuum. Vickers hardness after treatment did not change at all before treatment. The X-ray diffraction figure of the obtained sintered compact is shown in FIG. Figure 2 (a) is before the heat treatment, Figure 2 (b) is 1200 ℃, 30 minutes, after the vacuum heat treatment. As apparent from the results shown in Fig. 2 (a), the diffraction line of non-diamond carbon has a broad diffraction line at a position d = 3.26 to 3.19 on the high angle side of the diffraction line of (002) of graphite. It is observed that the diamond and very little non-diamond carbon (indicated by ● in the figure) are confirmed, but as is clear from the results of FIG. 2 (b), neither the position nor the intensity of this diffraction line is recognized at all. However, the amount of non-diamond carbon does not change at all even after heat treatment. As shown in Fig. 3, as a result of the structure observation by the electron microscope of the wavefront of the sintered body, it became clear that the sintered body was composed of an average particle diameter of 80 nm and fine particles.

(Comparative Example 1)

Others having a sintering temperature of 2000 ° C. were sintered in the same manner as in Example 1. The obtained sintered body had low grinding resistance and an average of Vickers hardness was 50 GPa.

(Example 2)

Using a synthetic diamond powder having an average particle diameter of 200 nm as a starting material, the other one having a sintering temperature of 2300 ° C. was sintered in the same manner as in Example 1. The obtained sintered compact was extremely high in grinding resistance, and the average of Vickers hardness was 85 Gpa or more, and was quite hard.

(Comparative Example 2)

Others having a synthetic diamond powder having an average particle diameter of 300 nm as a starting material were sintered in the same manner as in Example 2. The obtained sintered compact had a layered crack recognized, and the grinding resistance was remarkably low compared with the sintered compact of Example 2. When the average particle diameter is increased, it is difficult to synthesize a high hardness diamond sintered body.

The diamond sintered body of the present invention has excellent heat resistance and abrasion resistance, and has high hardness. For example, when the diamond sintered body is applied to finish cutting of a difficult material such as a high Si-Al alloy, ultra-precision machining of metals or alloys, and drawing dies, etc. Excellent cutting performance and line drawing performance. Furthermore, it has sufficient heat resistance suitable for high speed cutting of oil drilling oil bits or special parts for automobiles. In addition, since a product made of non-diamond carbon is combined to impart electrical conductivity to the sintered body, the electric discharge machining can be applied to the cutting process of the sintered body, and the processing cost can be reduced.

In addition, since it is a sintered body which can be given various shapes by laser processing, grinding and polishing processing in addition to electric discharge machining, it is expected to be used as a black diamond for precious metals having shiny and gloss which is not present in conventional diamond sintered bodies.

Claims (2)

It is a sintered body of ultra-fine synthetic diamond powder having an average particle diameter of 200 nm or less, and the sintered body is a composite sintered body made of a trace amount of non-diamond carbon produced by diamond crystals without sintering aid, and Vickers hardness is 85 GPa or more. Heat-resistant diamond composite sintered compact. Synthetic diamond powder having an average particle diameter of 200 nm or less is enclosed in a capsule made of Ta or Mo, and the capsule is heated and pressurized under a pressure of 7.7 GPa or higher at a temperature of 2100 ° C. or higher under conditions of thermodynamic stability of diamond using an ultrahigh pressure synthesizer. Sintering the manufacturing method of the heat resistant diamond composite sinter of Claim 1 characterized by the above-mentioned.