Additive manufacturing of high loading concentration zirconia using high-speed drop-on-demand material jetting

Zirconia-based ceramic has generated considerable interest in specialist structural/engineering ceramics. Among current available additive manufacturing methods for fabrication of ceramic components, the conventional material jetting systems are able to create local deposition of thin layers, dense green bodies, and complex shapes. However, this method is mainly limited to low viscous ceramic inks (mostly in the range of 20-40 mPa/s) with often less than 25 vol% solid loading which has restricted the widespread adoption of this technique. In this work, we employed a novel in-house developed hybrid drop-on-demand material jetting system (DODMJ) to deposit a highly viscous paste (up to 72 wt% solid content, a viscosity of 2100 mPa/s) of yttria-stabilized-zirconia (YSZ), with approximately 20 times higher speed than the current material jetting methods, for the first time. For this study, tetragonal zirconia polycrystal containing 8 wt% Y2O3(5Y-TPZ), which is commonly used to produce dental restorations by subtractive manufacturing, was utilized. The printability of several visible light-curable zirconia pastes was studied in terms of the rheology, paste composition, solid content, and printing parameters. The density and porosity measurements as well as a two-stage sintering process to achieve fully dense and crack-free parts were carried out. The microstructure and internal features of the printed parts were also explored by X-ray nano-computed tomography (CT) scanning and scanning electron microscopy (SEM). In this work, standard test methods were also utilized to study the Vickers hardness and fracture toughness of the sintered 5Y-TPZ parts for the first time. The results showed that specimens produced with the paste containing 62.3 wt% solid loading yielded a relative density of 99.5% and presented an average fracture toughness and micro-hardness of 5.62 MPa/m(0.5)and 1516 HV, respectively. Overall, the outcomes presented in this work confirmed that the novel DODMJ technique adopted for this study has great potential in the development of a feasible, high-speed, and cost-effective manufacturing system to produce zirconia ceramic parts with adequate mechanical and structural properties that meet the demanding requirements for various applications such as dental crowns restoration.