Microinhomogeneity of the structure of nanocrystalline niobium and vanadium carbides

The evolution of the microstructure of nonstoichiometric niobium carbides NbC$_y$ ($y=0.77, 0.84, 0.96$) and vanadium carbide V$_8$C$_7$ subjected to high-energy milling has been studied by the time-of-flight neutron diffraction method. It has been found that milled nanocrystalline powders have microinhomogeneous structure: two fractions with different sizes of particles have been identified in them. The content of the nanofraction is more than $90$ wt $\%$; the size of particles of this fraction varies from $90$ to $250$ Å, depending on the composition of the initial carbide and the duration of milling. The size of particles of the second fraction is more than $2000$ Å. Anisotropic deformation distortions have been revealed. The mean size of coherent scattering regions and microstrains in nanocrystallites have been estimated.