3D printing, strengthening and functionalization of advanced ceramic lattices

Abstract

Ceramic lattices have shown significant potential as lightweight structural materials. 3D printing of these lattices enables innovative designs that improve their specific strength and stiffness. However, the sensitivity of the ceramic lattices to defects and tensile stress concentrations makes them prone to catastrophic failure, limiting their application in various engineering fields. Therefore, tailoring the ceramic paste formulation to enable 3D printing of defect-free ceramic lattices and exploring various strengthening and toughening strategies for the ceramic lattices are of great interest to both academic research and industry. Furthermore, functionalizing the 3D printed ceramic lattices by coating or filling them with a secondary phase could pave the way to create high-performance functional-structural hybrid composite materials, but which has not been explored extensively yet.

In this work, the 3D printing ceramic pastes were first modified by adding a non-reactive plasticizer, polyethylene glycol (PEG), to tune the paste rheological behaviour and reduce debinding induced delamination and warpage defects in yttria stabilized zirconia (YSZ) ceramics. Systematic studies showed that with the increase of PEG addition from 5 wt% to 20 wt%, the viscosity of YSZ paste dramatically decreased and correspondingly the yield stress under shearing as well, which could potentially reduce printing defects. With 20 wt% PEG, no visible warpage or delamination was observed in the 3D printed ceramic green bodies after debinding. The mechanism for the reduction of these defects has been discussed thoroughly. The flexural strength of the obtained YSZ ceramics can reach 725.9 ± 70.2 MPa, which is comparable to YSZ fabricated using conventional method. The developed PEG-modified pastes have been used to successfully print complex ceramic lattice structures such as density-graded simple cubic and gyroid lattices, which exhibit highly structure-dependent, and not defect-dominated mechanical properties.

Functionalization of 3D printed YSZ ceramic simple cubic lattices by in-situ growing Vertically Aligned Carbon Nanotubes (VACNTs) at the empty spaces inside the lattices has been explored. The integration of VACNTs enhances the electrical and thermal conductivities of the ceramic lattices. The electrical resistivity was drastically reduced from insulating levels to ~0.97 kΩ/mm, while the thermal conductivity tripled from 1.1 to 3.3 W/m·K. The composites also exhibit excellent electromagnetic interference (EMI) shielding effectiveness of 36 dB while maintaining a high compressive strength of ~115-230 MPa. By introducing a density gradient to the YSZ ceramic lattice design, directional and asymmetrical EMI shielding can be realized.

Strengthening and toughening of the ceramic lattices have also been investigated by infiltrating epoxy into the lattices to form an interpenetrating phase composite (IPC). The IPCs display compressive strengths up to 120% greater, and energy absorption twice of that of the iso-strain combined properties of the ceramic lattice and epoxy. Failure analysis and finite element simulations were employed to investigate the factors influencing fracture behaviours and the mechanisms behind the increased strength and energy absorption. Additionally, these IPCs show enhanced retention of mechanical strength and dimensional stability at elevated temperatures compared to many traditional particle or fibre-reinforced epoxy matrix composites.

This work has provided a systematic in-depth study of various aspects of ceramic lattices, from paste formulation to enable a successful 3D printing of defect-free ceramic lattices, to various strategies to enhance their mechanical, thermal and electrical properties. The attractive properties bestowed by incorporating a second phase in the 3D printed ceramic lattices may enable many potential applications, such as directional EMI shielding and lightweight support structures with high strength and high fracture toughness. The present work could thus arouse great interest to further explore various 3D printed ceramic lattices and derived composites to unlock many structural and functional properties that previously were not possible to achieve.