A short and facile process to synthesize WC-Co cemented carbides

Abstract

WC-Co cemented carbides are widely used in the fields of military, aerospace, mining and cutting industry etc. In this paper, a new two-step method for the preparation of WC-Co cemented carbides was proposed. First, the mixture of yellow tungsten trioxide (WO3) and cobaltic oxide (Co2O3) were reduced by carbon black to remove all the oxygen. Then, the carbothermic reduction products were precisely mixed with an appropriate amount of carbon black to directly prepare WC-Co cemented carbides. The effects of C/WO3 ratio on the phase composition, morphological evolution, particle size and mechanical properties of products are investigated. The experimental results revealed that when the C/WO3 molar ratio was above 2.7, all oxygen in the raw material mixture were removed by carbon black and a mixture of W2C and η-phase were obtained after the first step of carbothermic reduction at 1150 °C for 2 h; then, the mixture of carbothermic reduction product and an appropriate content of carbon black was compacted, and the green compact was first carbonized at 1200 °C for 2 h and then sintered at 1450 °C for 4 h to prepare cemented carbides. With the increase of C/WO3 ratio at the first stage, the content of η-phase with a low melting point increased, which resulted in the large grain size of WC in the finally prepared cemented carbide. Compared with the traditional method of preparing cemented carbides, the cemented carbides prepared by the current method showed a higher hardness and toughness. Furthermore, the addition of a proper content of the VC in the second stage can significantly inhibit the grain growth of WC and further increase the hardness of cemented carbides.