High green density ceramic components fabricated by the slurry-based 3DP process

The 3DP process has been modified to directly fabricate high green density parts using submicron powder. The slurry-based 3DP process deposits the powder bed by spraying a dispersed slurry of the component material onto a piston. Alumina, silicon nitride, and lead zirconate titanate components with green densities as high as 67% have been fabricated by the slurry-based 3DP process. Solution phase binder systems have proven to be successful for the new process. Substantially improved surface finish over the conventional dry powder-based 3DP process has been demonstrated. Layer heights less than 50 Jlm can be prepared with this process. Thus, the stepped surface topography commonly observed in solid free form parts is substantially reduced. Introduction Structural ceramic components require fine-grained starting powders and high green density in order to achieve near theoretical density after firing. Wet processing techniques such as slip casting and injection molding are commonly used in ceramic forming processes to produce parts that meet these criteria. Structural ceramic components have been fabricated in the past with 3DP using spray-dried powders. These powders are -50 J.lm agglomerates of submicron powder. Spray-dried powders were easily spread into uniform layers, but printed components had packing densities less than 35%. Post-processing was required to achieve sufficient density prior to firing. The slurry-based 3DP process has been developed to overcome the difficulties of spreading fine submicron powder and also to enable layers as thin as 10 J.lm to be deposited. This paper discusses the slurry-based 3DP process and initial results with different ceramic materials systems. The process is sufficiently generic to be adapted to new materials systems. Our preliminary experiments have been performed on two types of ceramic materials, high purity alumina (several grades of Ceralox HPA) and sintered silicon nitride compositions (HC Stark MIl, 6 wt. % Ah03, 6 wt. % Y203). Firing conditions were 1650°C for 1 hr in air for the alumina samples and 1755°C for 1 hr under 2 psig N2 for the silicon nitride. The slurry-based 3DP process The slurry-based 3DP process was developed to fabricate high green density components from submicron powders using wet processing techniques. Figure I shows a schematic of the slurry-based 3DP process. The primary difference from the standard 3DP process