Advanced Technology and Manufacturing Institute (ATAMI)

Silicon carbide (SiC) and aluminum nitride (AlN) exhibit a combination of thermal and mechanical properties that are relevant to applications in electronics, aerospace, defense and automotive industries. However, the successful translation of these properties into final applications lies in the net-shaping of these ceramics into fully dense microstructures. Increasing the packing density of the starting powders is one effective route to achieve high sintered density and dimensional precision. The current research presents an in-depth study on the effects of nanoparticle addition on the powder injection molding (PIM) of SiC and AlN powder-polymer mixtures. In particular, bimodal mixtures of nanoscale (n) and sub-micrometer (μ) particles were found to have significantly increased powder packing characteristics (solids loading) in the powder-polymer mixtures. The influence of nanoparticle addition on the multi-step PIM process was examined by comparing the rheological and thermal properties of the novel bimodal μ-n powder-polymer mixtures to conventional monomodal μ powder-polymer mixtures. Additionally, the effect of nanoparticle addition on the mold filling behavior of the powder-polymer mixtures was examined. Subsequently, the effects of increased powder content and reduced particle size owing to nanoparticle addition were studied in the context of the polymer removal kinetics. Finally, nanoparticle addition was found to expedite the liquid phase formation during the sintering stage. The sintered parts of bimodal μ-n mixtures exhibited higher sintered densities, lower shrinkage and better thermal properties than the corresponding monomodal powder mixtures. The above results provide new perspectives which could impact a wide range of materials, powder processing techniques and applications.