Powder Injection Moulding of Cemented Carbides : Feedstock Preparation and Injection Moulding

A composite binder system, successfully developed earlier for powder injection moulding of stainless steels, CoCrMo and NiCrSiB alloys, has been adapted for tungsten carbide-cobalt (WC-Co) cemented carbides. The binder consists of a major fraction of polyethylene glycol (PEG), which can be removed rapidly by leaching with water, a minor fraction of a finely dispersed polymethyl methacrylate (PMMA), which retains rigidity of the components and sometimes with stearic acid (SA) to act as a lubricant. The adjustments made to powder characteristics, binder compositions and process parameters to achieve successful injection moulding are reported. Feedstocks containing a powder loading of the WC-Co up to 60 vol% can be moulded successfully. The moulded specimens had good green strength, in the range 12-17 MPa for three point bend tests.