Structural Ceramic Components by 3D Printing
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Several technical challenges exist in adapting Three Dimensional Printing (3DP) to processing of dense ceramic structures. The sintering rate of particulate bodies depends on the sintering mechanism, average powder size, and initial packing density. Fine powders are necessary to ensure appreciable densification rates from powders which sinter by solid state transport. A critical packing density exists for such powders below which densification does not occur. Special build strategies are, therefore, required for 3DP of ceramic structures. We have successfully demonstrated five approaches to produce dense ceramic components by 3DP. First, spray-dried granules of fine ceramic powders are spread in the existing 3DP equipment and bound using a latex binder through an ink-jet print head. The resulting components are then isostatically pressed to raise the green density to a point that the parts will fully densify when fired. A second approach uses glass powders that sinter by a viscous sintering mechanism. Such bodies sinter to full density at all initial green densities. Spray-dried granules of fine glass powders are spread and bound with latex followed by directly sintering to full density. Both of these approaches produce rather large linear shrinkage because of the low overall packing density. Large glass particles have a much higher packing density and produce bodies that sinter to full density because of the rapid viscous sintering. This third technique produces fully dense parts with linear shrinkage of about 15%. The fourth approach involves glass infiltration of porous ceramic bodies. Our results indicate that this technique can produce dense parts with less than 1% linear shrinkage. Finally, the 3DP process has been modified to permit deposition of fine powders as slurries, rather than dry powders. The resulting process considerably increases the bed density and the resulting fine ceramic parts can be sintered to full density without intermediate isopressing.