Characterizations of ball-milled nanocrystalline WC–Co composite powders and subsequently rapid hot pressing sintered cermets

Abstract

Nanostructured WC–Co cemented carbides, combining high hardness and high toughness, are expected to be widely applicable. In this study, nanocrystalline WC–10Co–0.8VC–0.2Cr 3C 2 (wt.%) composite powders, whose average grain size is bout 25 nm, were fabricated by a unique ball milling technique with variable rotation rate and repetitious circulation in 32 min. The high energy ball milling process was optimized and the as-prepared nanocrystalline powders were characterized and analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis (DTA). Furthermore, a low temperature, high heating rate, short soaking time and pressure sintering technique, that is, rapid hot pressing sintering, was used in the sintering process, by which nanostructured WC–Co cemented carbides with mean grain size of 250 nm were produced. The material exhibits high hardness of 93.6 HRA and transverse rapture strength of 2746 MPa. In the sintered composites, the distribution of elements W, Co, V and Cr is homogeneous, and it is small quantity of miropores and extraordinary coarse tungsten carbide phase that negatively influence the transverse rapture strength of nanostructured WC–Co cemented carbides.