Powder Processing, Rheology, and Mechanical Properties of Feedstock for Fused Deposition of Si ₃ N ₄ Ceramics

Abstract

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 diameter filament that requires a low viscosity and high column strength. This study explores the powder processing science, as well as the rheological and mechanical properties required for a successful FDC feedstock material. GS44 Si 3 N 4 powders were dispersed in RU9 binder using oleyl alcohol (OA). The viscosity of the RU9/OA/Si 3 N 4 mixture was measured as a function of temperature, solids loading, and OA concentration. The mechanical properties of the filament feedstock were evaluated in compression to establish FDC process limits. The feedstock material shows a shear thinning behavior with OA acting mainly as a plasticizer. The viscosity of GS44‐filled RU9 decreases with temperature, and increases with solids content. At 185°C and 55 vol% loading, the viscosity was found to be in the range of 49–7 Pa·s for a corresponding shear rate of 70–1128 s − 1 . This was sufficiently low for FDC. Based on pressure requirements for FDC extrusion (Δ P ), and maximum sustainable stress without buckling by the filament (σ E ), it has been found that for successful FDC of RU955, 1.1Δ P < σ E .