Synthesis and characterizations of ball-milled nanocrystalline WC and nanocomposite WC-Co powders and subsequent consolidations

The room-temperature ball-milling technique has been successfully employed for fabrication of nanocrystalline powders of equiatomic WC by high-energy ball milling of elemental W and C powders. The progress of the solid state reaction has been monitored by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM). A complete single phase of hcp-WC was obtained after 295 ks of milling. Increasing the milling time to 432 ks leads to dramatic grain refinement and the powder of this end-product consists of nanocrystalline grains of less than 5 nm in diameter. The fabricated WC powders possess excellent morphological characteristics, such as homogeneous shape (spherical-like morphology) with fine and smooth surface relief and uniform size (less than 0.5 mum in diameter). Part of the powders of the end-product were further ball-milled, 259 ks together with different concentrations of metallic Co to obtain spherical fine nanocomposite WC-coated Co powders with an average particle size of less than 5 mum in diameter. Both WC free Co and composite WC-Co powders were then consolidated into fully dense (>99.5%) compacts using cold and hot pressing techniques. The as-consolidated samples still maintained their nanocrystalline characteristics with an average grain size of less than 100 nm. Some of physical and mechanical properties of the consolidated samples are reported. (C) 2000 Elsevier Science B.V. All rights reserved.