Fedoran Y. Regularities for formation of nanocrystalline boron-nitride-based tool material for precision edge cutting processing.

The dissertation work is devoted to study the features of phase and structural changes in the nanoscale wurtzite boron nitride during sintering with high pressures and temperatures to obtain polycrystalline superhard material with nanocrystalline grain structure. It has studied the influence of conditions of obtaining and preparing the initial powders of wurtzite boron nitride on their dispersion, morphology and structural state. It has established that all types of particles wBN are characterized by significant size heterogeneity in the developed surface and thickness. Deformation of the powders with overlay shear stress provides a thin equal thickness plates with developed plane (001), which size can be classified as the nanometer range. It has established that compaction of wurtzite boron nitride nanopowders with high presser and temperature corresponds to general laws consolidation of fine powders with the influence on them of phase and structural transformations that accompany the sintering process wBN - hBN(norm.) - hBN(comp.) - cBN and wBN - cBN. It is shown the principal possibility to obtain polycrystalline superhard materials with nanocrystalline grain structure of wBN nanopowders. There were investigated the features of formation microstructure of polycrystalline superhard materials of wBN nanopowders and found that in the process of structural transformation, determining the formation structures of grains, the significant role plays the particle thickness and orientation factor. It is shown that polycrystalline superhard nano-wBN-based material has higher mechanical and performance properties compared to traditional materials.