Application of Polyethylene Glycol and Polymethyl Methacrylate as a Binder for Powder Injection Moulding of Hardmetals

Abstract

A binder system is successfully developed for powder injection moulding of tungsten carbide-cobalt (WC-Co) hardmetal components. The binder comprises a major fraction of polyethylene glycol (PEG), which can be removed rapidly by water leaching and a minor fraction of a finely dispersed polymethyl methacrylate (PMMA), which retains rigidity of the components. PMMA can be removed by pyrolysis during ramping up to the sintering temperature. Studies have been made to the feedstock compositions and to the process parameters in order to achieve high density components. Feedstocks having a powder loading of the WC-Co powder mixture up to 60 vol% can be injection moulded successfully. Density and strength of the specimens tend to increase with increasing PMMA content. The mouldings have green strength in the range 14-17 MPa. Specimens can retain their shapes during and after solvent debinding. The final density achieved is higher than 95% of the theoretical value.