Direct ink writing of hierarchical porous ultra-high temperature ceramics (ZrB2)

Abstract

An approach to producing hierarchical multi-scale porous ultra-high temperature ceramics (zirconium diboride, ZrB2) using 3D printing has been developed. Porous ceramic filaments can be 3D printed via Direct Ink Writing (DIW) (paste extrusion). Millimeter scale porosity is created by the 3D printed scaffold filaments. We introduce 20-micron-scale porosity into the scaffold filaments with the addition of oil to produce capillary suspension paste inks. Micron-scale porosity is also developed by partial sintering of the ceramic. The rheological (flow) properties of the capillary suspension paste inks suitable for printing by extrusion through the needle of the 3D printer have been characterized. The samples are strengthened by partial sintering at high temperatures. Complex-shaped components can be printed and sintered into crack-free components, but distortion during drying and sintering lead to poor shape and tolerance control. X-ray tomography is used to characterize the internal structure of the printed components. Printed test bars measured in 4-point bend testing exhibit high strength to density ratio. Such materials potentially have applications as insulation near very high-temperature surfaces in aerospace applications.