Abstract: The proposed polycrystalline superhard material comprises sintered particles of cubic boron nitride coated over the whole surface thereof with a layer of a crystalline compound of the chemical formula B.sub.x N.sub.y C.sub.z, where x, y and z can assume any value from 0 to 1, said compound binding together the particles of the cubic boron nitride.According to the present invention the proposed material is produced in the following way: particles of cubic boron nitride are placed in a flow of a gas containing carbon for a carbon layer 1-100 A thick to be built up on the whole surface of said particles. Then the particles of cubic boron nitride with the carbon layer built up over the whole surface of the particles are subjected to sintering at a temperature and under a pressure corresponding to the region of thermodynamic stability of cubic boron nitride.The herein-proposed material is highly uniform and features mechanical properties superior to those of the known cubic boron nitride materials.

Abstract: The method of preparing superhard articles consists of placing a mixture of powdered hard-alloy matrix material and diamond grains into a hard-alloy envelope formed from a hard-alloy material, preferably of exactly the same composition as the hard-alloy matrix material of the mixture, with the thickness of the hard-alloy envelope over the entire area thereof exceeding by at least 3-4 times the maximum space between any two adjacent diamond grains within the mixture. The mixture in the envelope is then subjected to sintering in a free condition thereof, without any external mechanical loads being applied thereto.

Abstract: The proposed polycrystalline superhard material comprises sintered particles of cubic boron nitride coated over the whole surface thereof with a layer of a crystalline compound of the chemical formula B.sub.x N.sub.y C.sub.z, where x, y and z can assume any value from 0 to 1, said compound binding together the particles of the cubic boron nitride.According to the present invention the proposed material is produced in the following way: particles of cubic boron nitride are placed in a flow of a gas containing carbon for a carbon layer 1-100 A thick to be built up on the whole surface of said particles. Then the particles of cubic boron nitride with the carbon layer built up over the whole surface of the particles are subjected to sintering at a temperature and under a pressure corresponding to the region of thermodynamic stability of cubic boron nitride.The herein-proposed material is highly uniform and features mechanical properties superior to those of the known cubic boron nitride materials.