Process-property-performance relationship for fused deposition of ceramics (FDC) feedstock materials

Fused deposition of ceramics (FDC) is an extrusion based layered manufacturing process. It uses a high solids loaded (>50 vol. % ceramic or metal powder) thermoplastic binder in filament form as the feedstock material. The filament acts as both the piston driving the extrusion process and the feedstock material being deposited in the X-Y direction onto a Z-stage platform. The primary mode of failure of the filament during the FDC process is via buckling. Earlier work has shown that the filament compressive modulus and the feedstock viscosity control the buckling behavior of the filament material in FDC. A study was conducted to investigate the effect of particle/polymer interface on the viscosity and compressive modulus of the PZT filled ECG9 system. The relative viscosity of the untreated and the surface treated particle filled systems increases with solids loading. It is found that both of the surface treated materials (stearic acid and titanate coupling agent) exhibit a lower relative viscosity than the untreated material. A rheological model (Krieger-Dougherty model) was used to investigate the possible reasons for the decrease in relative viscosity due to the surface treatment of particles. The investigation showed that the coupling agent acted as a dispersant (increasing value of φ_m) and thereby decreased the viscosity. The stearic acid may act as a dispersant (increasing value of φ_m) and as a lubricant (decreasing value of K_E). The compressive modulus of all the different systems studied showed an increase with solids loading. A generalized Nielsen model was used to describe the relative modulus vs. solids loading behavior for all the different systems studied. Also, the measured compressive modulus of the filled system was found to be insensitive to the modifications in the particle surface treatment.