Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
2000-12-21
2004-03-23
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S325000, C428S446000, C428S697000, C428S698000, C428S699000
Reexamination Certificate
active
06709747
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a diamond composite and a diamond composite produced thereby. This patent application is related to PCT patent application nos. PCT/EP98/04414 and PCT/EP98/05579, and to Russian Patent Application Nos. 98118300 filed Sep. 28, 1998 and 99100821 filed January 26, 1999, which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
There is a general need of extremely hard materials for many fields of application. These extremely hard materials are also called “superhard” when they exhibit a hardness of >40 GPa. These materials are used in a variety of applications such as tools for cutting, turning, milling, drilling, sawing, grinding operations, and the like. The hard materials may also be used for their wear, abrasion and erosion resistance when working as bearings, seals, nozzles or in similar cases. The materials may be working on, or being in contact with, many materials such as cast iron, steel, non-iron metals, wood, paper, polymers, concrete, stone, marble, soil, cemented carbide and grinding wheels of aluminum oxide, silicon carbide, diamond, cubic boron nitride, and the like. As being the hardest material known, mono- or polycrystalline diamond is suitable for these purposes. Other common materials used for their hardness are for instance cubic boron nitride (CBN), boron carbide and other ceramics and cemented carbides, however only diamond or CBN containing materials can reach the superhard group of materials.
It is well known that carbon in the diamond structural form is thermodynamically unstable at ambient temperatures and pressures. Nevertheless the decomposition of diamond to graphite (graphitization) is hindered by kinetic reasons and diamonds found in nature have existed for millions of years. However, by increasing the temperature, graphitization of diamond crystals will occur with a process starting from the surface, where the energy to overcome the kinetic hindrance is highest and where defects or catalytic effects from other surface impurities or the atmosphere will influence this process.
By heating in air it is well known that the decomposition and oxidation of diamonds will take place at temperatures as low as 600-700° C. Carbon solving metals like cobalt may catalyze a reaction already at about 500° C. The graphitization process is delayed to higher temperatures in vacuum or inert atmosphere and diamonds are most stable in hydrogen gas atmosphere, where the environment is strongly reducing—High quality diamond is stable for long times to about 2000° C.
Different composite bodies with bonded diamond particles are known. The diamond particles may be bonded by a matrix comprising metal and/or ceramic phases and produced by sintering diamond particles in a matrix of such materials, or bonded by the infiltration of silicon or silicon alloys into the diamond body, for instance.
By heating a body of diamond powder in a furnace to high temperatures during extended times, a small amount of uncontrolled and undesirable graphitization might occur depending also on the pressure. In previously reported processes to form densely sintered diamond composite bodies this has been an unwanted effect and different ways of avoiding this have been used. The most practiced technique is to use high pressures during the sintering step and stay in the diamond stable area of the phase diagram at 1300-1600° C., in high-pressure chambers with pressures of 30.000-60.000 atm (HP/HT). See for instance
FIG. 4
, in U.S. Pat. No. 4,151,686; for a diamond-graphite phase diagram.
The required extremely high pressures are only achieved by specially made presses and dies. The consequences are high production costs, limited production capacity and limited shapes and sizes of the diamond composite bodies.
There are also methods for production of diamond bodies using lower pressures than needed for the diamond stable area, from about a minimum of 500 psi (about 34 bars) and above, e.g. the method according to U.S. Pat. No. 4,124,401.
In the case where the pressure has been in the graphite stable region, for instance using a furnace with protective inert atmosphere, graphitization has been minimized by using short times at high temperature or reducing the sintering temperature for solidification of the body. An example of the latter is to use metal alloys of silicon that have a significantly lower melting temperature than that of pure silicon.
Several patents reveal techniques to produce materials containing diamond, silicon carbide and silicon without using high pressures. There are a number of variations of the process, mainly concerning the use of different carbonaceous materials (hereafter referring to all kinds of non-diamond carbon materials like carbon black, carbon fibres, coke, graphite, pyrolytic carbon etc). In principal the following steps are followed.
A. Non-coated diamond particles or normally, carbon-coated diamond particles and carbonaceous materials are used as precursor materials. According to the examples, U.S. Pat. No. 4,220,455 starts with adding a thin layer (500-1000 Angstrom) of carbon on the diamonds by a pyrolytic reaction. The pyrolysis is done in vacuum for a few minutes by feeding natural gas or methane, into a furnace with diamond particles at 1200° C. Sometimes diamonds without a pyrolytic carbon layer are used, as in U.S. Pat. No. 4,381,271, EPO 0 043 541, EPO 0 056 596 and JP 6-199571A. Both carbon-coated and non-coated diamonds are mixed with carbonaceous materials as a main source of carbon e.g. carbon black, short carbon fibres or cloth and a binder etc. before the forming of green bodies.
B. Forming of green bodies of the diamond particle/carbon material mixture is done in a mould. The green bodies contain additionally solvents and temporary or permanent binders to facilitate the forming and to increase the strength of the green body.
C. Work-pieces are made by heat treating the green bodies. Some binders are vaporised without leaving any residues e.g. paraffin, other binders are hardened leaving a carbonaceous residue in the work-piece, e.g. phenol-formaldehyde and epoxy resins.
D. Infiltration of the porous work-piece with molten silicon is done to form silicon carbide in a reaction between the carbon and the silicon. The heat treatment is done in such a manner as to minimise the graphitization of diamond, which is considered harmful. In the examples of U.S. Pat. No. 4,220,455 silicon is infiltrated in vacuum when the body is in a mould, at a temperature between 1400-1550° C. for 15 minutes, during which time the reaction between silicon and carbon is completed. U.S. Pat. No. 4,242,106 uses a vacuum of 0,01-2,0 torr during the infiltration. The required time, depending largely on the size of the body, is determined empirically and takes about 15-20 minutes at a temperature above 1400° C., or 10 minutes at 1500° C. U.S. Pat. No. 4,381,271 uses carbon fibres to promote the infiltration of fluid silicon by a capillary action. In most of the patents infiltration is made in a mould. In some earlier patents the infiltration is made outside the mould, like in EPO patent 0 043 541.
Not only silicon has been used for the infiltration and bonding of diamond particles. Several patents describes using silicon alloys instead of pure silicon. U.S. Pat. No. 4,124,401 describes a hot-press method using an eutectiferous silicon alloy for infiltration. U.S. Pat. No. 5,266,236 uses a boron-silicon alloy in a HP/HT method. U.S. Pat. No. 4,664,705 discloses a method that infiltrates a silicon alloy through a PCD body, where the binder has earlier preferably been leached out.
The processes where carbon-coated or non-coated diamonds are mixed with carbonaceous materials might have disadvantages, e.g. difficulties in preparing homogeneous mixtures of these materials, difficulties of silicon infiltration due to very small pore sizes and necessity of special equipment for preparing homogenous mixtures.
In the patent RU 2064399 the addition of carbon by pyrolysis is done only after the fo
Danchukova Lija Vladimirovna
Ekström Thommy
Gordeev Sergey Konstantinovitch
Zhukov Sergey Germanovitch
Moser Patterson & Sheridan
Skeleton Technologies AG
Turner Archene
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