JP2011046555A - Sintered compact of diamond fine particles and production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for production of a sintered compact of diamond fine particles, suppressing abnormal growth of diamond in a sintering process of diamond fine particles by liquid phase sintering. <P>SOLUTION: Prior to the sintering of diamond fine particles with a regulated average particle size (D<SB>50</SB>) of at most 1 μm, a coating layer composed of a carbonated product of a transition metal is formed on the surface of constitution particles. The diamond powder is arranged in closely contact with a metal flux composed mainly of cobalt and nickel; the whole is kept at the pressure and the temperature for thermodynamically stable conditions of diamond in order to sinter and unify the diamond powder. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fine diamond particle sintered body, and more particularly, to a sintered body in which fine diamond particles having an average particle size of 1 μm or less are effectively bonded, and a method for producing the same.

  A diamond sintered body obtained by sintering diamond powder particles under ultra-high pressure and high temperature is widely used as a polishing element for various cutting tools, wear-resistant structural materials, etc. by utilizing its hardness. The diamond sintered body used is manufactured using a cobalt-based or nickel-based molten metal as a sintering aid.

  When the so-called infiltration method is used, in which the sintering aid is placed in contact with the diamond particle layer as a metal lump and supplied by infiltration of the molten metal, the sintering aid is only in the amount required for sintering. Is introduced between diamond powder particles, and as a result, it is known that a sintered body having a dense structure with a narrow interval between diamond particles can be obtained. The resulting diamond sintered body takes the form of a composite material in which a lump of sintering aid metal and a diamond-containing sintered body layer are firmly joined.

  However, in the above infiltration method, since it takes time for the sintering aid metal to penetrate into the diamond layer, the diamond powder to be sintered has a very fine particle size or a thick layer of diamond sintered body is required. In such a case, a mixing method is used in which fine powder of a sintering aid metal (for example, cobalt) is mixed in advance with diamond powder. Although this method relaxes the restrictions on the particle size of the diamond powder and the thickness of the sintered diamond layer described above, the portion where the metal powder was present may remain as a void after sintering, and a dense sintered body The quality of the sintered body is not as good as that of the sintered body by the infiltration method.

  When the diamond sintered body is composed of fine-grained diamond, the toughness is improved and the roughness of the finished surface is small when used as a cutting tool, so it is possible to perform from roughing to finishing with a single blade. It is. Furthermore, since it withstands severe cutting conditions, the processing speed can be increased and the productivity of cutting can be expected to be improved. However, when fine diamond particles are sintered by the liquid phase sintering method, diamond fine particles often grow abnormally, and thus the above-mentioned characteristics cannot be exhibited in many cases. In order to avoid this phenomenon, it is considered that strict sintering temperature control and addition of an abnormal growth inhibitor are necessary.

  Accordingly, a main object of the present invention is to provide a method for producing a sound sintered body of fine-grained diamond in which abnormal growth of diamond is effectively suppressed in the sintering process of diamond fine-particle by liquid phase sintering. is there.

The gist of the present invention is to form a coating layer made of transition metal carbide on the surface of the constituent particles prior to sintering of the sized diamond powder or particles having an average particle size (D ₅₀ ) of 1 μm or less. This diamond powder is placed in close contact with a flux metal based on cobalt or nickel, and the diamond powder is sintered and integrated by maintaining the temperature under pressure and temperature conditions where the diamond is thermodynamically stable. There is to do.

  The diamond sintered body obtained in the present invention by the above method is a diamond sintered body in which fine diamond powder or particles are integrated by sintering, and adjacent particles are interposed through a coating layer made of transition metal carbide. It is characterized by being connected.

  The transition metal carbide layer of the present invention functions as a pinning additive for preventing abnormal growth of diamond particles during sintering. This abnormal growth is interpreted to be caused by the dissolution and precipitation of diamond in the surrounding sintering aid metal melt, but in the method of the present invention, a transition metal carbide coating is present on the diamond particle surface prior to sintering. Therefore, it is understood that the rate of the diamond dissolution / precipitation reaction is greatly reduced, and as a result, a sintered body composed of diamond equivalent to the starting material in particle size can be obtained. In other words, it can be said that the transition metal carbide coating is effective as a material for preventing abnormal growth of diamond particles.

  Incidentally, it is known that cobalt and nickel-based sintering aid metals used for diamond sintering generally have better wettability to transition metal carbides than diamond (carbon). Therefore, in the method of the present invention, the transition metal carbide coating is formed on the diamond surface, so that the infiltration of the sintering aid between the molten metal and the diamond particles is facilitated, and the diamond is bonded through the thin coating layer. A sintered body having a dense structure can be obtained. Furthermore, since the rearrangement of particles occurs in the presence of a liquid phase, a function of promoting densification by this can be expected.

  In the present invention, the pinning effect by the transition metal carbide coating and the ease of infiltration make it possible to produce a dense diamond sintered body in which grain growth is suppressed while using submicron-sized diamond as a starting material. It became possible to use a fine diamond having an average particle size of 1 μm or less, particularly an average particle size of 50 nm as a starting material.

  Furthermore, the transition metal carbide coating has a function of preventing, for example, diamond particles used as an abrasive from being oxidized or graphitized in a high-temperature oxidizing atmosphere, and these effects have a large specific surface area value. This is particularly noticeable in fine diamond.

  In the present invention, metals of Group IV, V and VI of the periodic table can be used as transition metals for forming the carbide coating, and Ti, Ta, Nb, Zr, Hf, Si, W, Mo, V, and One selected from Cr, particularly Ti, V or Cr, is preferred.

  Methods for forming transition metal carbide coatings on the surface of diamond particles include solid phase diffusion by heating a mixture of diamond powder and metal fine powder, PVD methods such as sputtering and vapor deposition, and decomposition of transition metal compounds in the plasma space. Several known methods can be used, such as a CVD method to be used or a pyrosol method using movement of transition metal ions in a molten salt.

By these methods, a coating made of TiC, TaC, NbC, ZrC, HfC, SiC, WC, Mo ₂ C, VC, Cr ₃ C ₂ is formed on the surface of fine diamond particles. Also, certain alloys such as Ti-Al and Ti-Si can effectively form (Ti-Al) C and (Ti-Si) C coatings, respectively, by using them as sputtering target materials. .

  The transition metal carbide coating formed on the surface of the diamond particles is preferably as thin as possible from the viewpoint of maintaining the hardness as a diamond sintered body, and more preferably 10 nm or less, particularly 1 nm or less. . For example, when 5% (carbonized) titanium is coated on particles having an average particle size of 100 nm, the average coating thickness is estimated to be 0.2 nm or less.

  In this case, the entire surface of the diamond particle is not covered, but there are DD bond portions where the diamond particles are in direct contact with each other, but at least no abnormal growth of the particle is observed from the observation of the structure of the sintered product. It has been confirmed that the pinning effect by the coating agent is secured.

  As described above, fine particles having an average particle size of 50 nm can be used as the particle size of the starting material diamond used for manufacturing the sintered body. Although applicable to coarse-sized diamond that can be sintered by a normal infiltration method, in the method of the present invention, by utilizing the good wettability between the carbide coating and the sintering aid metal, the infiltration method is used. In the case of submicron diamond sintered body, in which the penetration of the sintering aid metal melt is difficult, and the thick sintered body with a diamond sintered layer thickness exceeding 1 mm, particularly remarkable results were obtained. It is done.

As a starting material diamond, from the viewpoint of manufacturing a sintered body with good reproducibility, it is classified by using the Minamata method and has a narrow particle size distribution range, that is, D ₅₀ value in the cumulative particle size distribution display. ₁₀ value of 0.6 or more, D ₉₀ value is preferably used varieties with granulated particle size distribution of 1.6 or less.

  Even when such a diamond having a narrow particle size distribution width is used, it is observed by microscopic observation that a large amount of fine powder not contained in the starting material exists on the polished surface of the actually sintered diamond layer. This is explained as a crushed piece produced by pressing diamond powder particles when the starting material is pressed to an ultrahigh pressure condition prior to sintering.

When it is necessary to increase the apparent packing density at the time of filling the starting material and reduce the pressurization stroke to the ultra-high pressure condition, the particle size blending technique widely used in the ceramics field is different. A mixture of more than one kind of diamond powder can be used. Alternatively, in the production of wear-resistant materials, the particle size distribution width of the constituent diamond particles is such that the D ₁₀ value is 0.2 or more and less than 0.6, the D ₉₀ value is more than 1.6 and less than 3.0 with respect to the D ₅₀ value in the cumulative particle size distribution display. A wide range of raw materials can also be used.

A diamond coat of MD200 (D ₁₀ = 119 nm, D ₅₀ = 209 nm, D ₉₀ = 307 nm) having an average particle size of about 0.2 μm was coated with a titanium coating by a pyrosol method. An equimolar mixture of diamond powder, titanium powder and sodium chloride and potassium chloride was placed in a SUS reaction vessel and heated at 800 ° C. for 2 hours in an argon atmosphere. As a result of fluorescent X-ray analysis of the obtained diamond, a TiC ratio of 10 wt% was obtained, and the average thickness of the coating layer was estimated to be about 0.5 nm.

This TiC-coated diamond powder is filled in a 0.1 mm thick tantalum plate container onto a WC-13wt% Co composition cemented carbide substrate to a thickness of about 1 mm, and is estimated to be 6.0 GPa at 1400 ° C. Sintering was performed for 15 minutes. In SEM observation of the diamond layer of the obtained sintered body, grain growth was substantially not observed, and the Knoop indentation hardness was 4140 kgf / mm ² .

  IRM 0-2 grade diamond powder (Tomei Diamond product) having an average particle size of 0.9 μm and titanium powder (6 μm) were thoroughly mixed and held at 850 ° C. for 6 hours to form a TiC coating on the diamond surface. Unreacted titanium metal was removed by hydrochloric acid dissolution.

  The obtained diamond was subjected to fluorescent X-ray analysis in the same manner as in the above example, and an average thickness of about 0.2 nm was obtained from the ratio of the carbide coating layer.

These carbide-coated diamond powders were filled in a tantalum plate container similar to the above example to a cemented carbide substrate having a WC-13 wt% Co composition to a thickness of about 1 mm, and an estimated pressure of 6.0 GPa, 1400 Sintering was performed by maintaining the temperature at 15 ° C. for 15 minutes. SEM observation of the obtained sintered diamond showed substantially no grain growth, and the Knoop hardness was 4300 kgf / mm ² .

  Five kinds of diamonds of operation Nos. 1 to 5 in the following Tables 1 and 2 were used as starting materials, and transition metal carbide coatings were formed according to the respective operation numbers. Further, a cemented carbide block of WC-13% Co was placed as an infiltrant adjacent to the coated diamond particles, and sintered under ultra high pressure and high temperature conditions.

In the obtained sintered body, substantially no grain growth was observed in the diamond layer. The Knoop indentation hardness was 4000 kgf / mm ² or more, and it was used as a cutting tool.

By using the method of the present invention, it was difficult to apply the infiltration method, and manufacturing a sintered body using submicron-class diamond as a raw material and a thick diamond sintered body having a diamond layer thickness exceeding 1 mm This opens up the possibility of realizing tough cutting tools and large wear-resistant materials that can be obtained with a fine structure without grain growth.

Claims (12)

  In a fine diamond particle sintered body obtained by integrating diamond powder or particles having a particle size of 1 μm or less by sintering, adjacent particles are bonded together through a coating layer made of transition metal carbide. Diamond particle sintered body. D _{50 In} a fine diamond particle sintered body in which diamond powder or a group of particles having an average particle size of 1 μm or less is integrated by sintering, each diamond particle has a coating layer made of transition metal carbide, and adjacent particles are A fine diamond particle sintered body, which is bonded through a coating layer.   The fine diamond particle sintered body according to claim 2, wherein the average particle size is 500 nm or less.   The fine diamond particle sintered body according to claim 3, wherein the average particle size is 300 nm or less. In the cumulative particle size distribution display of the diamond particle group, the D ₁₀ value and the D ₉₀ value with respect to the D ₅₀ value are a sized powder having a (single peak) particle size distribution of 0.6 or more and 1.6 or less, respectively. 2. Fine diamond particle sintered body according to 2. ₁₀ value and the D ₉₀ value D for D ₅₀ value of said diamond powder is respectively less than 0.2 to 0.6, and a 1.6 than 3.0 following the (single peak) particle size distribution, fine diamond particles sintered according to claim 2 body. The fine diamond particle firing according to claim 1 or 2, wherein the transition metal carbide is one selected from TiC, TaC, NbC, ZrC, HfC, SiC, WC, Mo ₂ C, VC, and Cr ₃ C _2. Union. (1) D ₅₀ average particle size to form a coating layer comprising a carbide of a transition metal in the following sizing surfaces of the diamond powder or particles of constituent particles 1 [mu] m,
(2) The diamond powder is closely placed with a flux metal mainly composed of cobalt or nickel,
(3) A diamond sintered body characterized in that diamond powder coated with carbide of transition metal is sintered and integrated by maintaining the temperature under pressure and temperature conditions where diamond is thermodynamically stable. Production method.   9. The method according to claim 8, wherein the transition metal is one selected from Ti, Ta, Nb, Zr, Hf, Si, W, Mo, V, and Cr.   The method according to claim 9, wherein the transition metal is one selected from Ti, V, or Cr.   The method according to claim 10, wherein the transition metal is a single metal of Ti, or an alloy with Si or Al. The method for producing a diamond sintered body according to claim 9, wherein the carbide formation of (1) is performed by a solid phase diffusion method, sputtering, PVD, CVD or a pyrosol method.