Many natural materials have exceptional mechanical properties, which are difficult to reproduce in materials engineering. One example are teeth which are astoundingly resistant under the harsh fatigue and environmental loading conditions. They possess potent strengthening and toughening mechanisms to hinder crack formation and propagation. Zirconia materials have found increasing interest for tooth replacements, because of their toughness, biocompatibility and aesthetic appearance. In contrast to teeth, they are prone to brittle fracture despite the inbuilt transformation toughening mechanism of certain zirconia formulations. We investigated possibilities to further increase the toughness of zirconia-based ceramic constructs by implementing hierarchical features into the structure, that were shown to be important for the fracture resistance of teeth. Electrophoretic deposition (EPD) has been shown a very promising method to produce multi-layered zirconia constructs of variable shape, consisting of alternating layers of cubic stabilized zirconia and tetragonal partially stabilized zirconia . Preceding mechanical studies of such structures showed promising results.
We have proposed a new method for the investigation of fatigue in hierarchically structure ceramics on the nanoscale up to 50 cycles  and we showed that nanoindentation is a useful tool for the local analysis of the influence of layers, gradients and material inhomogeneities on the fatigue behaviour. On the poster we will present new results in this areas based on a higher number of cycles now focusing on potential crack propagation initialization. We also investigated the mechanical properties of multi-layered samples with bending tests and we will show the influences of the number and thickness of the layers and their sequence. Moreover results of light microscopy and scanning electron microscopy will be presented illustrating the crack propagation through the different layers.
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2. R. Zehbe, et al., Electrophoretic deposition of multilayered (cubic and tetragonal) zirconia ceramics for adapted crack deflection, J Eur Ceram Soc (2015)
3. C. Müller, A. Maerten, W.-D. Müller, C. Fleck, Investigation of fatigue and crack propagation of hierarchically structured ceramic materials using nanoindentation, LCF8 (2017)