Effect of yttrium barrier on the preparation of precursor powders of WC-Co cemented carbide and properties of sintered bulk

Abstract

Effects of yttrium on the calcination of ammonium paratungstate (APT), reduction of tungsten oxide, carbonization of tungsten and sintering of cemented carbides were studied during the preparation of yttrium-doped cemented tungsten carbide. The phase compositions, particle sizes and morphologies of all the components were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, respectively. The results showed that 1%Y-doped tungsten oxide consisted of WO3 and Y2WO6 phases. After hydrogen reduction, the size of Y-doped tungsten decreased remarkably and a yttrium barrier was observed in the cross-sectional morphology of the 1%Y-doped tungsten powder. During carbonization, a part of the Y2WO6 phase transformed to Y15C19 and WC. The flexural strength and fracture toughness of 1%Y-doped WC-6wt.%Co cemented carbide were 2458 MPa and 12.15 MPa m1/2, showing improvements of 18.97% and 8.87%, respectively. A refining mechanism for tungsten and a strengthening mechanism for WC-Co cemented carbides were proposed.