Abstract: Sintered metal bonded segments with an abrasive action, and containing particles of hard material, for tools for machining or cutting hard and/or brittle materials with a tool support which accommodates the sintered metal bonded segments, which are made up of individual segment modules.

Abstract: A process for preparing amorphous ultrahard material based on boron nitride which has a hardness sufficient to scratch diamond uses hexagonal or turbostratic boron nitride hBN as starting material. The starting material is compressed at pressures of at least 70 Kbar and heated to temperatures of at least of 1650.degree. C. until a boron nitride melt is obtained, the boron nitride melt is quenched by shutting off the heat supply and the quenched boron nitride melt is then relieved of the pressure. In the process, the hexagonal or turbostratic boron nitride employed as a starting material is treated in the presence of crystallisation inhibitors so that the formation of crystals is completely prevented and an amorphous structure is compacted by incorporation of reaction products comprising boron suboxides.

Abstract: A boron nitride, of amorphous structure, which can scratch diamond, is produced from hexagonal or turbostratic boron nitride as starting material. In the process for the production of the amorphous boron nitride, the starting material is subjected to pressures above 70 Kbar and temperatures of at least 1650.degree. C. for a period sufficient for the starting material to be completely melted, followed by quenching the resulting boron nitride melt and thereafter forming grains of amorphous boron nitride. The amorphous structure of the boron nitride is determined by X-ray and electron beam investigation.