Effect of Alumina Nanoparticles on the Rheological Behavior of Aluminum-Binder Mixtures for Powder Injection Molding

Preparation of appropriate powder-binder mixtures is the crucial step of powder injection molding process. Hence, the rheological properties of powder-binder mixture are important factors in production of sound parts using powder injection molding. Nowadays, the use of nanoparticles in powder injection molding is increasing due to the improved properties and dimensional precision of the final parts. On the other hand, nanoparticles can initiate problems such as agglomeration and loss of rheological properties and homogeneity. In the present study, the rheological behavior of aluminum mixtures containing nanoalumina particles was investigated. Two powder loadings of aluminum powder (54 vol% and 60 vol%), in which 0, 3, 6 and 9 wt% of aluminum was replaced with nanoalumina, were used. The powder systems were blended with the molten binder system in a banbury internal mixer and the rheological properties of the resulting mixtures were evaluated. All feedstocks showed pseudo-plastic behavior. The presence of nanoparticles increased the viscosity of feedstocks. Due to overwhelming particles cohesion by hydrodynamic forces, the viscosity of the mixtures decreased at high shear rates. Tap density results confirmed an improvement in packing compressibility of the mentioned powders. Shear rate sensitivity decreased with incorporation of nanoparticles into the mixtures. This phenomenon improved the injection capability through further reduction in viscosity