Mechanical alloying assisted spark plasma sintering of Tungsten diboride ceramics

Abstract

Herein, we demonstrate the fabrication of tungsten boride from high-purity tungsten (W) and boron (B) powders through mechanical alloying (MA), followed by spark plasma sintering (SPS) for the first time. First, WB2 powders are synthesized by mechanical alloying, which is achieved by high energy ball milling for 50 h. The phase composition and microstructure of the as-milled powders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-milled WB2 powders possess an AlB2-type structure, with a crystallite size of 5–10 nm. The as-synthesized powders are sintered by SPS at 1600 °C, under the pressure of 30 MPa, for 10 min and 5 wt % of MgO is added as a sintering aid. Furthermore, the as-sintered WB2 and MgO-added WB2 ceramics are characterized by XRD, SEM and microindentation. The results reveal that the metastable AlB2-type WB2 phase has been transformed into a stable WB2-type WB2 phase after sintering. Moreover, a slight increase in the Vickers hardness is observed due to the addition of MgO, which can be ascribed to the grain refinement effect in the presence of sintering aid.