Petrusha I. Phase and Structure Transformations of Boron Nitride Pyrolytic Materials at High Pressures

The thesis deals with the studies on the regularities of phase and structure transformations of BN dense pyrolytic materials at high pressures and preparation of cBN polycrystalline materials of an enhanced strength for cutting materials on their basis. The main concept of the studies of the possibility to produce high-strength materials of cBN amounts to the necessity of forming the material structures as a result of solid-phase transformations that take place in the initial dense products of graphite-like boron nitride at sufficiently high pressures and temperatures. The resulting polycrystalline structure of cBN is the structure of purely recrystallization origin and is characterized by perfect intergranular boundaries and, hence, high intergranular cohesion and strength. The key to the scientific problem has laid with the studying of the structural mechanisms and regularities of cBN formation as functions of the characteristics of the pyronitride real structure (ordering, phase composition, texture, density). The applied aspect of the work consisted in developing a highly efficient cutting material. The development has further elaborated traditional methods of production of cBN-based ceramic and composite materials.