Rheological Properties of Cemented Tungsten Carbide Feedstock for Micro Powder Injection

Abstract

The rheological behavior of feedstock needs to be examined for manufacturing parts without defects by micro powder injection molding (μPIM). In this study, submicron tungsten carbide (WC) and cobalt (Co) were milled for several hours. The distribution and morphology of the powder mixture were analyzed by laser diffraction and scanning electron microscopy. After measurement of critical powder loading, cemented tungsten carbide (WCCo) powder was mixed with a thermoplastic/paraffin wax binder with a powder loading volume from 50% to 52% to obtain feedstock. The flow properties of the WCCo feedstock were evaluated using a capillary rheometer at different temperatures. It was found that feedstock exhibit a pseudoplastic flow behavior, which is one of the main requirements for μPIM. Feedstock is also shown to be highly sensitive to temperature at high powder loading. Low powder loading led to low viscosity at a high shear rate that cannot be used in μPIM because it results in powder and binder separation.