JP2011241464A - Super-hard composite material and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diamond-containing super-hard composite material which has a sufficiently high density and uniform structure and is produced without using an ultra-high pressure vessel.SOLUTION: The super-hard composite material having a relative density of ≥85% is obtained by mixing hard powder of a carbide, a nitride or the like, 0-10 wt.% of an iron group metal, and diamond particles having an average particle diameter of 10-1,000 μm, and then sintering the resulting mixture by electrically heating the mixture at a heating speed of 100-10,000 °C/min in the temperature range of ≥900°C and keeping temperature for <30 s at a temperature not higher than 1,900°C, under a pressure within the range of 0-200 MPa.

Description

  The present invention relates to a superhard composite material comprising a sintered body of tungsten carbide (with or without a binder) or the like and diamond particles dispersed therein to form a composite material. The present invention relates to a material and a manufacturing method thereof.

  Diamond has attracted great interest as an element of wear-resistant materials because of its very high hardness. Many techniques have been tried to incorporate tiremonds into the matrix to obtain a dense material. However, a major problem is that the thermal stability of diamond is insufficient at high temperatures and normal pressures. Up to now it has been thought that high pressure methods are necessary to obtain good results. In the methods disclosed in Patent Documents 6, 7, 8, and 10, a high-pressure and high-temperature apparatus is required. Using an ultra-high pressure vessel, artificial diamond was developed under conditions of high temperature and high pressure of 5.5 GPa to 10 GPa at 1400 ° C to 2400 ° C. As a result, a diamond compact with better wear resistance than cemented carbide has been developed as the hardest material on earth. However, in order to manufacture these diamond materials, expensive equipment such as an ultrahigh pressure vessel is required.

  Many patents disclose techniques for sintering diamond materials under pressure and temperature conditions that are thermodynamically unstable for solid phase diamond, thereby producing a diamond composite without employing an ultra-high pressure vessel. ing.

  A number of previous patents have disclosed materials consisting of uncoated diamond in a cemented carbide matrix. For example, Patent Document 2 discloses a material in which one volume fraction of diamond particles is embedded in a tungsten carbide-cobalt 3-4 volume fraction having a Co (cobalt) content of 3% to 25%. Patent Document 4 discloses a method of manufacturing an article by simultaneously heating and pressing a sintered composition, that is, by a hot press method.

  In Patent Document 5, the diamond cemented carbide mixture is subjected to the resistance method, that is, the energization of the mixture is performed simultaneously with the heating of the press die by the high-frequency current, so that the sintering temperature up to 1800 ° C. is 3000 ° C. to 10,000 ° C./min. Heat at a rate. On the other hand, Patent Document 9 discloses a technique for producing a composite member containing diamond or CBN (cubic boron nitride) carbide particles coated with metal in a binder phase by infiltration.

  Furthermore, in Patent Document 11, a diamond / tungsten carbide-cobalt composite is obtained by direct resistance heating and pressure sintering. Here, the sintering is performed in a liquid phase and is produced by heating in a short time, and the cobalt component is more than 10% by volume. Unlike the present invention, the prior art disclosed in Patent Document 11 is not intended for a diamond composite, that is, neither a diamond-tungsten carbide composite without a binder nor a super-hard composite material with a low cobalt content. . Contrary to Patent Document 11 which is the prior art, the present invention does not require any diamond coating to prevent the graphitization of diamond and increase the density of the powder.

  It is an object of the present invention to provide an ultra-hard composite material having a sufficiently dense and uniform structure that can be produced without the use of an ultra-high pressure vessel and a method for producing such a material.

According to one aspect of the present invention, an ultrahard material that includes the following (a) and (a) and satisfies the conditions (c) to (e) is provided.
(A) A hard phase made of a material containing at least one element selected from the group consisting of WC, TiC, TiN, SiC, and Ti (C, N).
(A) A plurality of diamond particles dispersed in a structure containing the hard phase.
(C) The hard phase and the diamond particles are sintered by direct resistance heating and pressure sintering under conditions where diamond is thermodynamically metastable and diamond undergoes no or very little graphitization. The
(D) Diamond has a strong bond with the matrix.
(E) The composite material has a relative density greater than 85%.

  The ultra-hard composite material includes a metal binder phase of 0 wt% to 10 wt% mainly composed of an iron group metal such as Co having an fcc structure as a main crystal system, and the metal binder phase includes the hard phase and the diamond. Sintered with the particles, the structure may further comprise the metal binder phase.

  The diamond particles may have an average particle size ranging from 10 μm to 1000 μm, and the content of the diamond particles may be 5% by volume to 50% by volume.

  The ultra-hard composite material may further include at least one of cubic boron nitride and wurtzite boron nitride.

According to the other aspect of this invention, the manufacturing method of a super-hard composite material provided with the following steps (a) to (c) is provided.
(A) A mixture of diamond particles and a hard alloy matrix material is filled into a press die so that the diamond particles are uniformly dispersed throughout the hard alloy matrix material.
(A) The mixture is heated at a heating rate of 100 to 10000 ° C./min, starting from 900 to 1200 ° C., while simultaneously applying a pressure of 0 to 200 MPa while passing a current through the mixture.
(C) The mixture is kept under a pressure of 0 to 200 MPa at a sintering temperature not exceeding 1900 ° C. for less than 30 seconds.

  The press die may be heated by a heat source around the press die.

  According to the present invention described above, a novel ultra-hard composite material having a sufficiently high density and a uniform structure can be obtained. Furthermore, this ultra-hard composite material can be obtained by a novel process that can be produced in a very short time and without the use of ultra-high pressure vessels.

FIG. 3 is a voltage / temperature / displacement profile of a sintering process according to an embodiment of the present invention. The SEM image obtained by the low magnification (a) and the high magnification (b) of the fracture surface of the sintered composite by the Example of this invention. The low magnification SEM image of the surface of the sintered compact by the Example of the composite_body | complex of this invention after rotating a SiC ball | bowl 3 * 10 ⁴ times. The high magnification SEM image of the sintered compact surface by the Example of the composite_body | complex of this invention after rotating a SiC ball | bowl 3 * 10 ⁴ times. The optical image of the surface without a WC binder after rotating a SiC ball 3 × 10 ⁴ times.

In accordance with the present invention, a method of making a dense, abrasive-resistant molded material includes the following steps.
(A) providing a conductive mixture of binder powder and diamond particles;
(B) Compress this conductive mixture.
(C) The compacted conductive mixture is subjected to discharge sintering to form a compact.

  The composite includes at least one hard phase selected from WC, TiC, TiN, and Ti (C, N) and diamond particles. The composite may also include an iron group metal binder phase. In other words, the composite of the present invention is a sintered body that retains diamond particles in a tungsten carbide matrix with or without a binder, the sintered body being a direct resistance heating and sintering. and reduced)). The binder phase is preferably made from an iron group metal such as Co, Ni, Cr or Fe.

  Direct resistance heating and pressure sintering can be completed in a short time within 10 minutes. This is because resistance heating can rapidly heat, pressurize and cool the material being sintered. Therefore, the time for exposing the material to be sintered to a high temperature can be reduced, and as a result, the sintering can be completed without causing the conversion from diamond to graphite.

In addition to the conditions described above, the composite member of the present invention preferably satisfies the following additional conditions independently or in combination.
(1) Resistance heating and pressure sintering is performed under the condition that diamond is thermodynamically metastable, which may or may not appear as a liquid phase.
(2) The binder phase contains Co, and the main crystal system of Co is fcc.
(3) In the case of a matrix containing cemented carbide, a liquid phase may or may not appear during sintering. The direct resistance heating and pressure sintering according to the present invention enables rapid temperature increase and short-time sintering, thereby making it possible to manufacture an excellent composite member while suppressing the conversion of diamond into graphite.
(4) Each diamond particle has no outer coating.
(5) The average particle size of WC is 0.05 to 100 μm.
(6) The average particle size of the diamond particles is 10 to 1000 μm.
(7) The content of diamond particles is 5 to 50% by volume.
(8) The binder phase content is 0 to 50% by volume.
(9) At least a part of the diamond particles is replaced with cubic boron nitride or wurtzite boron nitride.
(10) At least a part of the WC powder is replaced with one of TiC, TiN, and Ti (C, N).

  Commercially available WC having a particle size of less than 0.1 μm was mixed with diamond particles having a particle size of about 60 μm. A mixture of 22% by volume diamond and WC powder was dry mixed in a horizontal mill for 24 hours. The powder mixture was filled into a cylindrical and hollow graphite mold. The experiment was performed with a 100 kN SPS-1050 apparatus (SPS Syntex Corporation) operated in current control mode (CCm). The current was stopped when the mold surface temperature was 1575 ° C. The sintering process was performed in two steps. In the first step, a current of 1000 A was applied, and then when the temperature reached 900 ° C., the current was suddenly raised to 4000 A and kept constant for 30 seconds. A constant pressure of 120 MPa was applied throughout the sintering process. The sintering conditions are shown in FIG.

  The relative density of the sintered body reached 94%. The polished surface analyzed by X-ray diffraction (XRD) and micro-Raman spectrometer showed no signs of graphite. FIG. 2 shows SEM images of the sintered composite fracture surface at a small magnification (a) and a large magnification (b). Diamond particles are strongly bonded to the matrix. This is because none of the diamond particles have peeled off the matrix, but all of the particles have been cut across the crystal on the fracture surface.

  In order to examine the wear resistance of the ultra-hard composite material (hereinafter referred to as WC diamond material) manufactured as described above, the wear resistance of the above-mentioned materials and also the WC binder-free material according to the prior art for the purpose of comparison. A test was conducted.

  Specifically, the tribological behavior of these samples under dry conditions is determined according to JIS R 1613 abrasion test standard by ball on disc configuration tribometer from CSM Instrument SA (Switzerland). ). This test was carried out by sliding a 6 mm SiC ball polished sample at a constant linear velocity of 0.10 m / s while applying a load of 10 N. The radius of the test mark was 3 mm, and this test was performed 30000 revolutions (565 m). All tests were performed at 25 ° C. and approximately 22% relative humidity. After the ball-on-disk experiment, the sliding wear rate of the bulk sample was calculated from the measurement results of the worn track area.

  FIG. 3 shows an SEM image of the surface of the WC diamond material after 30000 rotations, and FIG. 4 is an enlarged image of a region indicated by a white rectangle in FIG. Even in the magnified image of FIG. 4, very few scratches are observed. This is in contrast to an optical image in which a number of sharp tracks of SiC balls are engraved on the surface of a WC diamond material after testing under the same conditions as WC diamond. The numerical results of the above wear test are shown in Tables 1 to 3 below.

Table 1
Specific wear (m ³ (N m) ⁻¹ )
Material without WC binder 7.470 × 10 ⁻¹⁷
WC diamond material cannot be measured (it is too small to be measured)

Table 2
Specific wear amount SiC ball (m ³ (N m) ⁻¹ ) side WC binderless material 1.16 × 10 ⁻¹⁵
WC diamond material 43.73 × 10 ⁻¹⁵

Table 3
Friction coefficient WC binderless material 0.328 ± 0.022
WC diamond material 0.117 ± 0.019

  Due to the very high hardness and wear resistance, the super hard material of the present invention can be used in cutting tools and similar applications as an alternative to existing materials, coupled with relatively relaxed manufacturing requirements There is expected.

U.S. Patent No. 1904049 US Patent No. 1996598 US Patent No. 2074038 U.S. Pat. No. 2,712,988 U.S. Pat. No. 4,097,274 U.S. Pat.No. 4,370,149 U.S. Pat. No. 4,505,746 U.S. Pat. US Pat. No. 5,096,465 US Pat. No. 5,585,175 US Pat. No. 5,889,219 US Published Patent No. 2008/0168718

Moriguchi et al., "Sintering behavior and properties of diamond / cemented carbides", Int, Journal of Refractory Metals & Hard Materials, 25 237-243 (2007). Michalski et al., "Sintering Diamond / Cemented Carbides by the Pulse Plasma Sintering Method", J. Am. Ceram. Soc., 91 3560-3565 (2008). Shi et al., "The effect of tungsten buffer layer on the stability of diamond with tungsten carbide-cobalt nanocomposite powder during spark plasma sintering", Diamond & Related Materials, 15 1643-1649 (2006).

Claims (6)

An ultra-hard material that includes the following (A) and (I) and satisfies the conditions (C) to (E).
(A) A hard phase made of a material containing at least one element selected from the group consisting of WC, TiC, TiN, SiC, and Ti (C, N).
(A) A plurality of diamond particles dispersed in a structure containing the hard phase.
(C) The hard phase and the diamond particles are sintered by direct resistance heating and pressure sintering under conditions where diamond is thermodynamically metastable and diamond undergoes no or very little graphitization. The
(D) Diamond has a strong bond with the matrix.
(E) The composite material has a relative density greater than 85%. Including 0 wt% to 10 wt% of a metal binder phase mainly composed of an iron group metal such as Co having an fcc structure as a main crystal system, the metal binder phase being sintered together with the hard phase and the diamond particles;
The structure further includes the metal binder phase;
The super-hard composite material according to claim 1.   The ultra-hard composite material according to claim 1, wherein the diamond particles have an average particle size in a range of 10 µm to 1000 µm, and a content of the diamond particles is 5 vol% to 50 vol%.   The ultra-hard composite material according to claim 1, further comprising at least one of cubic boron nitride and wurzeite boron nitride. A method for producing an ultra-hard composite material, comprising the following steps (a) to (c).
(A) A mixture of diamond particles and a hard alloy matrix material is filled into a press die so that the diamond particles are uniformly dispersed throughout the hard alloy matrix material.
(A) The mixture is heated at a heating rate of 100 to 10000 ° C./min, starting from 900 to 1200 ° C. by simultaneously passing a current through the mixture while applying a pressure of 0 to 200 MPa.
(C) The mixture is kept under a pressure of 0 to 200 MPa at a sintering temperature not exceeding 1900 ° C. for less than 30 seconds. The method for producing an ultra-hard composite material according to claim 5, wherein the press die is heated by a heat source around the press die.