Nanograined WC-Co composite powders by chemical vapor synthesis

Nanograined tungsten carbide (WC)-Co composite powders were prepared by a chemical vapor synthesis (CVS) process that has previously been used for preparing the aluminides of titanium and nickel and other metallic and intermetallic powders at the University of Utah. To determine the optimum condition for producing nanograined WC-Co composite powders, the effects of carburization temperature, CH(4) to WCl(6) ratio, CH(4) to H(2) ratio, CoCl(2) contents, and residence time of WC on the powder composition and particle size were investigated. The reduction and carburization of the vaporized chlorides by CH(4)-H(2) mixtures produced nanograined WC and Co composite powder, which sometimes contained small levels of W(2)C, W, or the eta (Co(3)W(3)C) phase. The presence of these incompletely carburized phases can be tolerated because they can be fully carburized during the subsequent sintering process. These phases can also be fully carburized by a separate post-treatment. The products were characterized by using X-ray diffraction (XRD) and a transmission electron microscope (TEM). As a result, nanograined WC-Co composite with the particle size less than 30 nm was obtained.