Powder processing, rheology, and mechanical properties of feedstock for fused deposition of Si3N4 ceramics

Fused deposition of ceramics (FDC) is a technique in which green parts are fabricated directly from CAD designs. The feedstock for FDC is a 1.778 mm d iameter filament that requires a low viscosity and high column strength. Th is study explores the powder processing science, as well as the rheological and mechanical properties required for a successful FDC feedstock material . GS44 Si3N4 powders were dispersed in RU9 binder using oleyl alcohol (OA). The viscosity of the RU9/OA/Si3N4 mixture was measured as a function of te mperature, solids loading, and OA concentration. The mechanical properties of the filament feedstock were evaluated in compression to establish FDC pr ocess limits. The feedstock material shows a shear thinning behavior with O A acting mainly as a plasticizer. The viscosity of GS44-filled RU9 decrease s with temperature, and increases with solids content. At 185 degrees C and 55 vol% loading, the viscosity was found to be in the range of 49-7 Pa.s f or a corresponding shear rate of 70-1128 s(-1). This was sufficiently low f or FDC. Based on pressure requirements for FDC extrusion (Delta P), and max imum sustainable stress without buckling by the filament (sigma(E)), it has been found that for successful FDC of RU955, 1.1 Delta P < sigma(E).