Features оf structural phase transitions at high pressure and temperature in the system of ultra-fine diamonds and turbostratic boron nitride powders


I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Electron Microscopy and Strength of Materials - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2019, #25


Using research methods such as X-ray phase analysis (XRD), X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (X-ray diffraction), transmission electron microscop In the present work, results of a study of the structural-phase transformations during sintering (at P = 7,7 GPa, Т = = 1600°С) of nanodisperse powders of diamond and turbostratic BN (whose content was ∼17% (mass)) are presented. The main size range of initial particles in the powders was 5―7 nm. The oxygen content in diamond powders attained 10% (mass), and its content in BN was at most 4―5% (mass.). For investigation, polycrystalline specimens with a density of 3,0―3,06 g/cm3 were used. XRD investigations revealed that the main components of specimens were cubic diamond and BN phases in combination with a diamond-like phase of composition BС2.5N. TEM investigations revealed that specimens contained predominantly structural elements with sizes ∼1―2 nm, i. e. during sintering, the dispersion of particles of the initial components occurred. A HR TEM study showed that residual diamond in the microstructure was present in the form of particles with sizes ∼3―4 nm, which are present in the matrix in the form of finer particles of d-l phases . It was established that It was established for the first time that the formation of diamond-like phases of compositions B―C, B―C―N, B―C―O, B―N―O, as well as chemical dispersion of particles of the starting components due to their interaction can occur in B―N―C―O systems. The diamond-like phases known to date, which are formed at high pressures in these systems, are superhard. This is determined experimentally or established by calculation methods. Full text download