Abrasive tool making process – material – or composition – Miscellaneous
Patent
1986-06-19
1989-10-17
Lieberman, Paul
Abrasive tool making process, material, or composition
Miscellaneous
51307, 51308, 51309, B24D 300
Patent
active
048743984
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an improved method of producing a diamond compact possessing sufficiently high degrees of abrasiveness, hardness and mechanical strength so as to permit the compact to be employed usefully in the cutting, turning and drilling of hard materials such as rocks, ceramics and carbides.
Many different kinds of diamond compacts and diamond composites have been described in the literature and their properties vary widely. Generally speaking, a diamond compact is understood to mean a polycrystalline body possessing substantial abrasiveness and hardness and low or negligible porosity, comprised of more than 50 percent by volume of diamond crystals, in which a large proportion of diamond-to-diamond contacts occur.
In one class of diamond compacts, which usually contain more than 80 percent by volume of diamond crystals, the diamonds are joined at their contacts by diamond-to-diamond bonding. This means that the diamond crystalline structure is essentially continuous between adjacent diamond crystals and the strengths of the bonds between adjacent crystals are comparable with the strength of the carbon to carbon bonds within single diamond crystals.
A second class of diamond compacts exists which are composed of more then 50 percent by volume of diamond and less than 50 percent by volume of non-diamond bonding materials, wherein the diamonds themselves are only weakly bonded at their mutual contacts and the cohesion of the compact is provided mainly by bonding between the diamonds and the non-diamond bonding material. The difference between these two classes is readily revealed when the compact is leached with a solvent which selectively dissolves the non-diamond bond. If true diamond-to-diamond bonding exists, the diamond crystals remain strongly bonded. However, if this kind of bonding is not present, the individual diamonds can readily be separated, after dissolution of the compact, using, for example, a steel needle or scalpel.
It will be appreciated by those skilled in the art that the qualities displayed by diamond compacts proposed in the literature vary over an extremely broad range, according to their composition, structures, nature of their bonds and their pressures, temperatures and times of formation. Many compacts, particularly those produced at pressures below 40 kbars, may display high hardness and abrasiveness, but are lacking in toughness and compressive strength. These can be useful for grinding and general abrasive purposes, but cannot be practically utilized in applications where a combination of high hardness with high toughness and compressive strength is required, for example, in drilling, turning and machining hard rocks, hard ceramics and carbides. Diamond compacts in this category should possess compressive strengths of at least 10 kbars and preferably greater than 20 kbars.
Diamond compacts suitable for use as drilling bits, cutting tools, wire-drawing dies, nozzles and related applications can be made by several techniques. One such technique (U.S. Pat. Nos. 3,745,623; 3,609,818) places a mass of polycrystalline diamond in juxtaposition with an appropriate metallic catalyst or metallic carbide substance and subjects the entire body to high pressures and temperatures in the thermodynamic stability field of diamond (e.g. 60 kbars, 1500.degree. C.). A related process described by H. Katzman and W. Libby (Science 172, 1132, 1971) mixes a minor proportion of an appropriate metallic catalyst with a major proportion of diamond crystals and subjects the entire mixture to high pressures and temperatures in the diamond thermodynamic stability field at temperatures above the melting point of the respective diamond-catalyst eutectic temperature. These processes are capable of producing mechanically strong and hard compacts containing extensive diamond-to-diamond bonding between adjacent crystals. These processes possess certain disadvantages, however. They require highly specialized and expensive apparatus in order to produce the very high pressures and temperatures. Moreover,
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Lieberman Paul
Thompson Willie J.
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