Modification of PEG/PMMA binder by PVP for titanium metal injection moulding

Polyethylene glycol (PEG), with polymethyl methacrylate (PMMA) as the backbone binder component, is a common primary binder component in the design of water soluble binder systems for metal injection moulding (MIM). However, PEG crystallises upon cooling, producing voids in the injection moulded parts. These voids ultimately lead to porosity and degraded mechanical properties in the sintered bodies. We have previously reported on the use of polyvinylpyrrolidone (PVP) as a crystallisation inhibitor in the PEG/PMMA binder system to suppress void formation. In this paper, PEG/PMMA/PVP binder-based feedstocks were prepared with a 67 vol% solid loading in order to evaluate the effects of PVP incorporation on the PEG/PMMA binder for titanium MIM. The homogeneity and rheological behaviours of the feedstocks with varying amounts of PVP were compared with the base PEG/PMMA binder-based feedstock. Microstructural observation, impurity measurement and mechanical testing were carried out. It was found that incorporation of 20 wt% PVP into the PEG produced a void-free, high quality Ti-MIM component, with an average final density of 98% and a tensile elongation of 9.5%.