ИСТИНА

Tungsten carbide (WC) is one of the most prospective and, at the same time, most available hard materials in science and industry. Present work is focused on specific features of formation of nanocrystalline WC by sintering process. We have synthesized WC nanopowder by means of milling and then sintering of W/C60 mixture (20.4 weight % of C60 and 79.6 weight % of W) by electric current short pulse. Afterwards the sample was examined in transmission electron microscope (TEM). WC particles have size from nanometers to tens of nanometers. Almost all of them possess stacking faults in {111} planes. As it was shown earlier [1], such a defect (a stacking fault also analogous to the shift of a neighbor plane) is equivalent to the rotation of the crystal lattice cells within the “layer” of the stacking fault at 90°. Analysis of our high resolution TEM data have shown that these stacking faults in our sample serve as seams connecting fragments of the crystal lattice rotated at 90° relatively to one another and composing a single nanoparticle in such a way. Certain combination of such stacking faults along the same direction, perpendicular to one of the {100} planes forms a polytype of WC, which was not reported earlier. Atomic planes {100} alternate with shifted atomic planes thus forming a new sequence which can be seen in high resolution TEM images. We propose a model of this polytypic structure. Apparently, the formation of WC polytypes and nanoparticles consisting of differently oriented lattice fragments takes place at the stage of WC sintering during the carbon diffusion through the tungsten nanoparticles.