Microstructural properties, as grain size, grain shape, texture and/or porosity can have a large impact on the structural and functional response of ceramic materials. Powder preparation, the forming process as well as the sintering step contribute to the development of ceramic microstructures. Focus of this work is to explore a non-conventional sintering route to tailor the microstructure and properties of equiaxed and textured alumina fabricated using stereolithographic additive manufacturing. A pressure-less rapid sintering technology with high heating rates of ~450 °C/min and short dwell times of 2 - 16 min at 1300 - 1600 °C was employed to sinter both equiaxed and textured samples.
In the case of 3D printed parts, manufactured using equiaxed alumina suspensions, grain growth was impeded and resulted in microstructures with grain sizes below 1 µm and relative densities of ~97 %. It is shown that a biaxial strength increase of ~200 MPa can be achieved in comparison to conventionally sintered equiaxed alumina (grain size ~4 µm). In addition, by applying slightly different dwell times the grain size could be tailored.
When 3D printed samples contained 2.5 vol% high aspect ratio templates in the alumina slurries, templated grain growth could be induced during rapid sintering using dwell times as low as 2 min at temperatures of 1600 °C. The addition of sintering additives to form a liquid phase during sintering has led to an improvement of densification and resulted highly textured microstructures.
The application of pressure-less rapid sintering technology opens the path to reduce the processing time for 3D-printed complex ceramics and enables the tailoring of microstructure and properties.