Process for the production of polycrystals of a boron nitride consisting of dense modifications

摘要

The invention relates to extremely hard materials and in particular to a process for the production of polycrystals of a boron nitride consisting of dense modifications. The process for the production of polycrystals of a boron nitride consisting of dense modifications comprises the preparation of a batch from the hexagonal boron nitride with or without addition of alloy, the pressing of the batch at a pressure of 3 to 8 kbar, the action of high pressures and temperatures on the semi-finished product obtained in two stages, the semi-finished product being exposed initially to the action of a pressure of 100 to 150 kbar at a temperature of 290 to 1500 K. The treatment time for this stage must be sufficient for the conversion of at least 15% by weight of hexagonal boron nitride to the wurtzite modification. In the second stage, the compacted material obtained is exposed to the action of pressure of 40 to 90 kbar at a temperature of 1600 to 3200 K. The treatment time for the second step must be sufficient for the complete conversion of the hexagonal boron nitride to its dense modifications. The invention will find its use in the production of cutting tools such as chisels, boring crowns, milling machines and the like for the machining of very hard articles.