A novel PEG/PMMA based binder composition for void-free metal injection moulding of Ti components

Abstract

The use of polyethylene glycol (PEG) and poly methylmethacrylate (PMMA) as a binder for metal injection moulding (MIM) operation results in void formation in the MIM feedstock. In order to formulate a practicable PEG/PMMA binder system, we identified a crystallisation inhibitor - polyvinyl acetate (PVAc) – to suppress the void formation. Rheological behaviour of the feedstocks with varying amounts of PVAc was compared with a previously reported feedstock based on the crystallisation inhibitor polyvinypyrrolidone (PVP). The analysis of rheology tests reveals that the incorporation of PVAc into PEG/PMMA binder system does not affect the overall rheology of the feedstocks. Differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and microstructural analysis along with impurity measurement of the sintered samples were carried out for complete evaluation. The DSC analysis suggests interactions between components of the binder system. These interactions were further verified using Fourier-transform infrared spectroscopy (FTIR), which reveals possible complex hydrogen bonding interactions in the ternary blend systems. Overall, the results show that the addition of PVAc into the PEG/PMMA binder system produces Ti-MIM feedstocks with good rheological properties resulting in void-free injection moulded samples, and acceptable mechanical properties (tensile strength ~550 MPa; elongation ~10%).