Anisotropy of microstructure and elastic properties of niobium carbide nanopowders

摘要

The peculiarities of microstructure of nanocrystalline powders of nonstoichiometric niobium carbides have been generalized in all homogeneity interval of cubic NbCy phase. Nanocrystalline NbCy powders were produced by high-energy milling of coarse-crystalline powders. For the first time, it is established that the microstructure of nanocrystalline NbCy powders is an inhomogeneous, and contains two cubic fractions differing by particle size and carbon content. Fine details of an inhomogeneous microstructure of NbCy nanopowders have been determined by the time-of-flight neutron high resolution Fourier diffractometry. The analysis of the neutron diffraction data revealed microstrain anisotropy in the nanopowders. The average sizes of the coherent scattering regions and microstrains in nanocrystallites with allowance for the anisotropy of the deformation distortions have been estimated. The consideration of the anisotropy of elastic properties has shown that the splitting of niobium carbide particles during high-energy milling is likely to take place in the (110) or (111) planes in the directions where the shear modulus has the least value.