Near-nano and coarse-grain WC powders obtained by the self-propagating high-temperature synthesis and cemented carbides on their basis. Part I: Structure, composition and properties of WC powders

Abstract

Near-nano WC powders with mean grain sizes of about 200nm were prepared by the SHS method including the reduction of WO3 by Mg in the presence of carbon and regulating additives. The chemical leaching and refinement of the SHS reaction products allowed one to obtain stoichiometric WC containing only traces of oxygen and magnesium. The thermal reduction of WO3 and V2O5 by magnesium in the presence of carbon resulted in obtaining two carbide phases of WC and complex carbide (W,V)C with the fcc crystal lattice having a grain size of less than 300nm. It was established that the tungsten oxide reduction by magnesium in the presence of carbon cannot be used to synthesize coarse-grain WC powders. Coarse-grained WC powders were obtained using the W+C mixture heated to high temperatures by a simultaneous exothermic reaction of interaction between magnesium perchlorate Mg(ClO4) and magnesium. The coarse-grain WC powder synthesized in such a way is nearly stoichiometric and consists of sintered round-shaped agglomerates with the average grain size of up to 16μm and containing only traces of magnesium and oxygen. The agglomerates comprise WC single-crystals of roughly 1μm to 8μm in size.