On the Formation of Solid Solutions at Thermobaric Sintering of PcBN Composites of cBN–MeN–Al and cBN–MeC–Al Systems

Using the x-ray diffraction method, we study in detail a series of polycrystalline cu bic boron nitride (PcBN) composites of the cBN-{TiN, ZrN, HfN, VN, NbN}-Al and cBN-{TiC, ZrC, HfC, VC, NbC, TaC}-Al systems (with a charge composition of 60 : 35 : 5 vol.%) sintered at high pressures and high temperatures (HPHT): 7.7 GPa, 1600-2450 C.As shown, the crystal structure of each nitride MeN or carbide MeC (Me = Ti, Zr, Hf, V, Nb, Ta) existing in these composites belongs to a modified NaCl-type structure with the additional position for nitrogen atoms that results in the accumulation of N-atoms' excess in the near-surface layers of composites.Al atoms of the charge are embedded into the MeC crystal lattice at certain sintering temperatures forming substitutional solid solutions based on a relevant metal Me.The existence ranges of temperature and composition of MeN 1 + d , MeCN d , and Me 1 - x Al x CN d solid solutions formed at HPHT sintering are determined.As shown, the crystal-structure features revealed in these solid solutions are in a good agreement with theoretical assumptions on the solid-phase interaction of the charge components at sintering.Thus, the accumulation of nitrogen in MeN and MeC phases is described within the atomistic diffusion model.Using the data on the excess of N in nitrides as the reference values, the main parameters of nitrogen diffusion (activation energy and rate constant) within the cBN-{TiN, HfN, VN, NbN}-Al composites are determined.The formation of Al solid solutions at cer-