Self-grown monopoly compact grit

Details Self-grown monopoly compact grit Self-grown monopoly compact grit

2001-08-21

2003-09-09

Jenkins, Daniel J. (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Compositions

Consolidated metal powder compositions

C419S011000, C423S446000, C051S307000

Reexamination Certificate

active

06616725

ABSTRACT:

THE FIELD OF THE INVENTION
The present invention relates generally to methods of forming synthetic diamond or polycrystalline diamond (PCD). More specifically, the present invention relates to a new, high pressure-high temperature (HPHT) sintered/synthesized, self-grown, monopoly compact grit and methods of preparation thereof.
BACKGROUND OF THE INVENTION
Diamond is a gemstone known for its rarity and beauty. As an industrial material, its superior hardness and wear resistance make diamond a preferred material in a variety of applications. For example, diamond is used extensively as an abrasive in polishing operations. Additionally, diamond-tipped drills and cutting tools are indispensable in shaping and cutting extremely hard materials such as sintered carbide and quartz. In order to help meet the industrial demand for these types of tools, a number of techniques have been developed for the production of synthetic diamonds. While natural diamond is still used in many industrial applications, diamond synthesis is emerging as the solution to the problem of inadequate supply of this unique material.
Diamond has a cube lattice, in which each carbon atom is covalently bonded to four other carbons to form a tetrahedron. This structure is repeated throughout the crystal and it is believed that this configuration of carbon—carbon bonds produces the extreme hardness of diamond. It has been discovered that at high temperatures and pressures, the conversion of carbon to diamond occurs at an appreciable rate. This phenomenon gave rise to the first synthetic high-pressure diamonds fabricated in the early 1950's.
A synthetic diamond grit manufacturing method is disclosed in U.S. Pat. No. 2,947,609 (1960) to Herbert M. Strong, hereby incorporated by reference. A polycrystalline diamond compact with a metal bonded carbide substrate is described in U.S. Pat. No. 3,745,623 (1975) to Robert Wentorf Jr. et al, hereby incorporated by reference. Similarly, a polycrystalline cubic boron nitride with a metal bonded carbide substrate is disclosed in U.S. Pat. No. 3,743,489 to Robert Wentorf Jr. et al, also hereby incorporated by reference. A great deal of effort has been expended to increase the economy of preparing diamond grits under the HPHT conditions, however, commercial production of synthetic diamond grits, using the HPHT process is still a very expensive operation. Therefore, continuous attempts have been made both for the manufacturing of quality diamond grits and to develop an optimum HPHT diamond synthesis process for converting less expensive forms of carbon, such as graphite, into expensive diamonds.
There are two methods for the synthesis of diamond crystals at ultra-high pressure and high temperatures, which are generally well known in the art. The first method is the “temperature gradient method,” and the second is the “thin film solvent method.”
The “temperature gradient method,” involves using transitional metal elements, i.e. Fe, Co, Ni, Cr, Mn, Pt, etc. or alloys thereof, as a solvent metal. By this method, a diamond seed crystal is separated from a carbon source by the solvent metal so that the carbon source and the diamond seed crystal are not in contact with one another. By maintaining the temperature of the seed crystal at a relatively lower level than that of the contact surface of the carbon source and solvent metal, and allowing this assembly to stand at a high pressure and high temperature causes epitaxial growth of diamond on the seed crystal. See U.S. Pat. Nos. 4,034,066 and 4,632,817, which are hereby incorporated by reference.
The “thin film solvent method” can be performed in two different ways. The first way consists of creating a reaction mixture of a non-diamond carbon source powder, a solvent metal powder, and seed crystal. The reaction mixture is then placed under temperature and pressure conditions in the diamond stable region, sufficient to convert the non-diamond carbon source into diamond in a relatively short time. The second way is by creating a reaction system which includes a plate of a non-diamond carbon source, or a laminate thereof, a plate of solvent metal, and optionally a seed crystal, and placing the system at a temperature and pressure within the diamond stable range, such that the non-diamond carbon source is converted into diamond within a relatively short period of time.
The above described temperature gradient method is capable of synthesizing a relatively large grain size crystal. However, it presents several problems. First, the synthesis reaction takes a very long time, thus increasing the operation costs of the apparatus required to affect the carbon to diamond transition. Additionally, because the method requires a temperature gradient to be created in a relatively small sample chamber, the number of crystals which can be produced in a single reaction is small. Therefore, the small crystal yield increases the production costs of each crystal.
The “thin film solvent method”, solves many of the problems inherent in the “temperature gradient method”, but increases the frequency of other problems such as spontaneous nucleation. Such problems give rise to great difficulty in synthesizing crystals of a large grain size, and make the crystals produced inferior in quality as they may be contaminated with many inclusions.
In the typical diamond synthesis from carbonaceous materials utilizing a catalyst solvent material, a process for yielding a higher commercial quality valued diamond is the key to success. Needless to say, a higher commercial value diamond is directly related to both a higher product quality and a larger crystal size. The higher the crystal quality and the larger the size, the higher the value of the diamond. Product quality is generally graded according to the compressive and impact strength of the crystal. Crystal shape and internal clarity are also barometers of quality. A large size crystal is more valued as compared to a small size crystal. However, the manufacturing cost for growing larger diamond in the HPHT process is higher because of the required longer reaction/synthesis time and a relatively lower yield under HPHT conditions.
Large diamond crystals (up to 1.0 carat) are commercially produced using the technique of a seed diamond being placed in contact with the catalyst solvent and an available carbon source under long duration of high temperature and high pressure conditions. Such a process is cost and quality prohibitive from being utilized on a mass production scale.
The typical grit size which is used in the construction industry for items such as diamond saws and drill bits, is in the range of 20/30, 30/40, and 40/50 mesh. Although the current HPHT diamond synthesis processes have been significantly improved over a decade of active research and development efforts, these processes are still below desirable level for the efficient production of large crystals (20~50 mesh). Therefore, none of the current processes have so far been fully satisfactory in the super hard materials manufacturing industry.
Another problem inherent to many diamond grit applications such as diamond saw blades, grinding wheels and drill bits is obtaining a crystal shape which provides greater performance than that of existing crystals. Desirable shapes include cubic, octahedral, and needle-like shapes. The production of crystals having such shapes is not readily commercially available.
Yet another problem inherent in typical polycrystalline diamond (PCD) and cubic boron nitride compact (PCBN) applications, such as turning tools and wire dies, is producing ultra-fine grained (0.1~0.5 &mgr;m) microstructure which provides a mirror-like surface finish to the product (optical lenses, aluminum, etc.). The production of such fine grained PCD or PCBN is not commercially and economically readily available.
For all intents and purposes, the quality and performance of diamond grits incorporated into tools such as saw blades, other cutting tools, and drill bits is primarily based upon the length of time which the grit will last under the impact

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