Extrusion moulding of hard-metal powder using a novel binder system

A powder extrusion moulding (PEM) process based on a novel binder system, and a 92 wt.% tungsten carbide +8 wt.% cobalt composite powder as a test material, are described. The binder system is comprised of major fraction of a mixture of low molecular weight components (LMWCs) and a minor fraction of very finely dispersed polymer. The feedstocks are mixed as a thick slurry at a suitable temperature and are rapidly homogenized by stirring at an adequate shear force. The binders are removed by thermal debinding. The thermal debinding mechanism has been investigated by thermogravimetry (TG) and differential thermogravimetry (DTG). In the first stage of debinding, the LMWCs are removed. These open up pore channels which allows much faster removal of the remaining polymer component during the subsequent stage. The microstructures of the moulded green parts are observed by SEM. The debinded samples are sintered or sinter/HIPed at different temperatures. The properties of the sintered samples are measured.