Compositions: ceramic – Ceramic compositions – Carbide or oxycarbide containing
Patent
1988-11-15
1991-04-23
Bell, Mark L.
Compositions: ceramic
Ceramic compositions
Carbide or oxycarbide containing
501 86, 501 88, 423345, 423439, 423446, 51307, C04B 3556, C04B 3558, B24D 300
Patent
active
050100432
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
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, machining, milling, drilling, grinding and working of ultra-hard materials. These ultrahard materials include advanced ceramics such as silicon carbide, boron carbide, silicon nitride, sialons, alumina, partially stabilized zirconia and beryllia, metallic materials such as tungsten carbide, titanium carbide, titanium boride and high temperature nickel and cobalt-based alloys, and very hard natural minerals and rocks such as semi-precious and precious gems, quartzite and banded iron formations.
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 amount of diamond to diamond contact occurs.
In one class of diamond compacts, which usually contains more than about 85 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 chemical bonds within single diamond crystals. These compacts possess very high hardness and compressive strengths because of their diamond-to-diamond bonding.
A second class of diamond compacts exists which are composed of more than 50 percent by volume of diamond and less than 50 percent by volume of non-diamond bonding materials. The diamonds are packed sufficiently closely so that a substantial or major proportion are in direct contact, which also causes these compacts to possess high compressive strengths. However, the diamonds themselves are only weakly bonded at their mutual contacts and the cohesion or tensile strength 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 diamond-to-diamond bonding exists, the diamond crystals remain strongly bonded. However, if this kind of bonding is not present or only weakly developed, the individual diamonds can readily be separated, after dissolution of the bonding agent, using, for example, a steel needle or scalpel. The present invention relates to a diamond compact of this second class, in which the non-diamond bonding matrix is composed mainly of silicon carbide.
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 compositions, structures, nature of their bonds and their pressures, temperatures and times of fabrication. Many compacts, particularly those produced at pressures below 10 kilobars, may display substantial abrasiveness, but are lacking in toughness and compressive strength. They may 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, shaping and machining very hard ceramics, carbides, rocks and minerals. Diamond compacts in this category should possess compressive strengths of at least 10 kilobars and preferably greater than 20 kilobars. This invention relates to a compact in this latter category.
However, even though a diamond compact may possess considerable hardness, compressive strength and toughness, these attributes do not guarantee that the compact will have the capacity t
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Bell Mark L.
Green Anthony J.
The Australian National University
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