Zhen Xiong

PREPARATION OF WC-Co POWDER BY DIRECT REDUCTION AND CARBONIZATION

A new approach to produce superfine WC-Co powder by direct reduction and carbonization is proposed. Water-soluble salts containing W and Co were used as raw materials. Tungsten and cobalt oxide powder (CoWO4/WO3) was first formed by a spray-pyrolysis technique, which was then mixed with carbon black and converted to WC-Co composite powder at 950°C for 4 h in N2 atmosphere. The resulting powder has a particle size of 100–300 nm.

Properties of Carbide-Metal Cermets Prepared from Composite Powders by Direct Reduction and Carburization Process

The transition-metal carbide cemented by metal has excellent combined properties. In this study, cermets were prepared by vacuum sintering from carbide-metal composite powders. The transition- metal oxides (Cr2O3, MoO3, V2O5, Nb2O5 and TiO2), cementing-metal oxides (Co3O4 and NiO), and carbon black were used as raw materials to pre-synthesize composite powders such as Cr3C2-Co, Mo2C-Co, VC-Co, NbC-Co and TiC-Ni, by a direct reduction and carburization process in vacuum. Results show that the participation of Co3O4 and NiO as well as the vacuum circumstance were greatly propitious to the carburization of transition-metal oxides into carbides. The carbothermal condition was greatly improved by the direct reduction and carburization process.

The Core / Rim Structure in Cobalt / Tungsten Carbide Nanocomposite Powder

A nanocomposite WC-Co powder consisting of grains with a Co core / WC rim structure was prepared by precipitation covering - continuous reduction / carburization method. Its morphological, microstructure and chemical features were characterized by field emission scanning electron microscopy and transmission electron microscopy. The main cause of the change in the microstructures of a Co core / WC rim system was investigated.

Consolidation and Properties of Tungsten Carbide Target with Low Cobalt Content by Hot-Press Sintering

Tungsten carbide (WC) targets with low cobalt (Co) content (0.1 - 0.2 wt.%) were prepared by hot-press sintering at 1700°C for 60 minutes in argon, from element starting powders of tungsten, cobalt and carbon. Results show that the as-fabricated targets yield relatively high relative density above 99% and high HRA above 92. WC with low Co content is formed easily than pure WC. The hot-press sintering process, while element starting powders are used, is an in-situ reaction technique for accelerating the WC’s diffusion rate to obtain a dense sintered body.