| 摘要 |
A polycrystalline compact of synthesized diamond embedded in a metal matrix prepared by the method of the invention (see Division C1), is used as an abrasive material. The diamond compact may or may not be attached to a tool holder.ALSO:<FORM:1000702/C1/1> <FORM:1000702/C1/2> A diamond compact is synthesized by subjecting carbonaceous material to high temperatures and pressures in the presence of a metal catalyst, diamond growth being confined to the carbonaceous materialmetal catalyst combination by a metal shield, in the form of an enclosure, which does not melt under the high temperature-high pressure conditions of the reaction, and which has a higher melting point than the catalyst. The shield, 32, which is of nickel, iron, chromium, or their alloys, may be regular or irregular in shape, e.g. tube, sphere, rectangular parallelepiped, and contains catalyst discs, 37, 38, of chromium, manganese, tantalum, or a Group VIII metal, together with carbonaceous material, 35, e.g. graphite, coke, coal, sugar or charcoal, the remaining volume of 32 being also filled with graphite. The catalyst may take the form of discs, spheres, wires or tubes, and may assume various positions within the metal enclosure. 32 is placed in the reaction vessel, which comprises a hollow cylinder of pyrophilite, talc, or carlinite, containing a graphite tube and a liner of alumina or graphite, and subjected to 75,000 atmos. by means of a press apparatus and heated electrically to 1300-1450 DEG C., the temperature and pressure being subsequently reduced to atmospheric. The diamond compact, 31, is then removed from the reaction vessel, and the metal shield is either stripped from it, or retained to facilitate soldering, or brazing of the compact on to a part, e.g. wheel, grinding, or cutting element, of a suitable tool. Alternatively, the reaction vessel may be subjected to a "ratcheting" process whereby the pressure is increased to 75,000 atmos., and the temperature raised to 1200 DEG C., these conditions being maintained for 10 minutes, after which time the reaction vessel is cooled to atmospheric temperature by interrupting the electric power for 2 minutes, and then reheated to 1350-1450 DEG C. over a period of 20-30 minutes, before finally reducing the temperature and pressure to atmospheric. Compacts of various shapes may be formed, e.g. by employing end discs which do not touch the sides of the cylindrical metal shield, by varying the spacing between the catalyst disc assemblies, by using end discs which have hemispherical portions removed from them, and by including a spool member within the metal tube to define an annular volume. Specifications 830,210 and 830,743 are referred to.
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