The influence of sintering procedure and porosity on the properties of 3D printed alumina ceramic cores

In order to obtain 3D printed alumina ceramic cores with isotropic shrinkage, a pore former was added into the photocurable slurry, and combined with an optimization of the sintering procedure. Micron scale pores were observed in the sintered ceramics when the pore former was present compared with the samples without pore former. The addition of the pore former significantly improved the pore interconnectivity and pore size of the 3D printed ceramics, due to the volatilization of the pore former. The resulting shrinkage of the ceramic parts in three directions was more uniform and smaller when they were fabricated using a slurry containing the pore former in comparison to those without pore former. The bulk density, shrinkage, and flexural strength of the ceramics increased with increasing the sintering temperature. Triple sintering significantly improved the flexural strength, and also lead to anisotropic shrinkage of the samples, due to the enhanced binding force between layers deriving from the increased number of sintering cycles. In addition, the triple sintering process enabled healing of the cracks developed during sintering, differently from a single sintering. The use of a pore former and the triple sintering procedure provides a new optimized strategy for the fabrication of 3D printed ceramic cores with suitable properties.