Feedstock properties and injection molding simulations of bimodal mixtures of nanoscale and microscale aluminum nitride

Powder injection molding (PIM) is useful to manufacture small, complex metal and ceramic components in high production volumes. Mixing nanoparticles (n) with microparticles (μ) has been previously identified in our research group as a promising approach to achieve high sintered density and low shrinkage in injection molded AlN. Sintering studies showed a liquid phase formation at ∼1500°C in bimodal μ–n AlN samples, a temperature that is atleast 100°C lower than typically reported values in the literature. Sintered parts of bimodal μ–n AlN mixtures exhibited comparable sintered density but lower shrinkage (∼14%) than corresponding monomodal μ-AlN (∼20%). These benefits in sintered attributes are a direct consequence of a significant increase in the packing density in powder–polymer mixtures with the addition of nanoparticles. However, there are few studies focused on understanding the effects of nanoparticle addition on the rheological and thermal properties of the bimodal feedstock. The present study combines experimental measurement feedstock properties with models for estimating properties over a range of powder content. The properties were subsequently used in mold-filling simulations to understand the effects of powder content on process parameters and defect evolution in PIM. These protocols and findings can be used to improve PIM design practices in material selection, component geometry attributes, and optimized process parameters.