Microinhomogeneity of the Structure of Nanocrystalline Niobium and Vanadium Carbides

Resumo

The evolution of the microstructure of nonstoichiometric niobium carbides NbC_y (y = 0.77, 0.84, 0.96) and vanadium carbide V₈C₇ 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.