Influence of the wurtzitic boron nitride initial structural state on the formation of the granular structure of the wBN-Based materials. II. Structural transformations in the microstructure formation of the samples of materials based on various types of wBN

The studies of the microstructures of polycrystals produced of five varieties of wurtzitic boron nitride powders at p = 8 GPa in a range of 1600–1800°C have been considered. Particles-platelets of powders differed in size of the developed surface, thickness, and substructure. It has been found that the basic factors responsible for the granular structure and phase composition of polycrystals are the thickness of the initial particles and orientation caused by the formation of the morphological texture in the course of the compaction of the particles-platelets system in sintering. The following structural transformations in particles of wurtzitic boron nitride in sintering: dispersion of the initial particles in mechanical fracture by spalling, plastic fragmentation of them, and as a result the development of slip processes of disoriented fragments at the interface have been affected by the above factors. The maximum grain size and the lowest degree of the phase transformation of the wurtzitic boron phase into the cubic one has been observed in polycrystals based on powders with particles of the highest thickness. And vice versa, these characteristics have the minimum and maximum values, respectively, in polycrystals based on powders with particles of the lowest thickness.