In our study, we investigated the additive manufacturing (AM) of ceramic-based functionally graded materials (FGM) by the direct AM technology thermoplastic 3D printing (T3DP). Zirconia components with varying microstructures were additively manufactured by using thermoplastic suspensions with different contents of pore-forming agents (PFA), which were co-sintered defect-free. Different materials were investigated concerning their suitability as PFA for the T3DP process. Diverse zirconia-based suspensions were prepared and used for the AM of single- and multi-material test components. All of the samples were sintered defect-free, and in the end, we could realize a brick wall-like component consisting of dense (<1% porosity) and porous (approx. 5% porosity) zirconia areas to combine different properties in one component. T3DP opens the door to the AM of further ceramic-based 4D components, such as multi-color, multi-material, or especially, multi-functional components.

To combine the benefits of Additive Manufacturing (AM) with the benefits of Functionally Graded Materials (FGM) to ceramic-based 4D components (three dimensions for the geometry and one degree of freedom concerning the material properties at each position) the Thermoplastic 3D-Printing (CerAM -T3DP) was developed. It is a direct AM technology which allows the AM of multi-material components. To demonstrate the advantages of this technology black-and-white zirconia components were additively manufactured and co-sintered defect-free.Two different pairs of black and white zirconia powders were used to prepare different thermoplastic suspensions. Appropriate dispensing parameters were investigated to manufacture single-material test components and adjusted for the additive manufacturing of multi-color zirconia components. Video LinkThe video component of this article can be found at https://www.jove.com/video/57538/ 14,15,16,17 . CerAM -T3DP is based on the selective deposition of single droplets of particle filled thermoplastic suspensions. By utilizing multiple dosing systems, different thermoplastic suspensions can be deposited beside each other layer by layer to produce bulk material as well as property gradients within the additively manufactured green components 18 . Unlike indirect AM processes, in which previously deposited materials solidify selectively over the entire layer, the CerAM -T3DP process does not require the additional effort of removing any non-solidified material prior to the deposition of the next material, making it more suitable for the AM of multi-material components.Although utilizing the CerAM -T3DP process allows the AM of FGM and the realization of ceramic-based components with unprecedented properties, there are challenges to overcome regarding the necessary thermal treatment after the AM process, in order to obtain a multimaterial composite. In particular, the paired powders in the composite material need to be successfully co-sintered, for which the sintering of the components has to be performed at the same temperature and atmosphere. Therefore, it is a prerequisite for all materials to have a comparable sintering temperature and behavior (starting temperature of sintering, shrinkage behavior). In order to avoid critical mechanical stress during cooling, the coefficient of thermal expansion of all materials has to be approximately equal 11 . The combination of materials with different properties in one component opens the door to components with unprecedented properties for manifold applications. E.g. stainless steel-zirconia composites can be used as cutting tools, wear resistant components, energy, and fuel cell Journal of Visualized Experiments

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Additive manufacturing technologies offer the possibility of tool-free production of components with extremely complex geometry that cannot be attained by any other shaping technique. In our project we are developing a completely new approach for ceramic multi-material additive manufacturing that will allow series production of customized and multifunctional components for manifold applications. In several case studies demonstrators for personalized medical products – micro surgical tools, implants, and remedies – will be manufactured starting with the patient-specific physical dimensions and ending with components validated under practically relevant conditions.

Multi-material jetting (CerAM MMJ, previously T3DP) enables the additive manufacturing of ceramics, metals, glass and hardmetals, demonstrating comparatively high solid contents of the processed materials. The material is applied drop by drop onto a substrate. The droplets can be adapted to the component to be produced by a large degree of freedom in parameterization. Thus, large volumes can be processed quickly and fine structures can be displayed in detail, based on the droplet size. Data-driven methods are applied to build process knowledge and to contribute to the optimization of CerAM MMJ manufacturing processes. As a basis for the computational exploitation of mass sensor data from the technological process chain for manufacturing a component with CerAM MMJ, a data management plan was developed with the help of an engineering workflow. Focusing on the process step of green part production, droplet structures as intermediate products of 3D generation were described by means of droplet height, droplet circularity, the number of ambient satellite particles, as well as the associated standard deviations. First of all, the weighting of the factors influencing the droplet geometry was determined by means of single factor preliminary tests, in order to be able to reduce the number of factors to be considered in the detailed test series. The identification of key influences (falling time, needle lift, rising time, air supply pressure) permitted an optimization of the droplet geometry according to the introduced target characteristics by means of a design of experiments.