Within this project, we managed to synthesize metallic nanomaterials as well as nanocomposites starting from input powders, thereby establishing a very versatile additive material synthesis approach. Furthermore, this powder-based material synthesis also enables us to deliberately add doping elements for grain boundary strengthening, which would be impossible utilizing standard processing strategies. Focusing on tungsten as the hard and brittle composite phase, we followed up theoretical predictions to enhance grain boundary cohesion and demonstrate increased ductility with no loss in strength for the grain boundary doped material. The same holds for nanocomposites, where the addition of ductile copper to the nanostructured tungsten reduced the overall strength compared to pure tungsten, but the ductility could be markedly improved. By alloying the softer Cu phase with Zn, we could further strengthen the composite without compromising its fracture toughness. Another strategy to further advance the properties of the softer composite phase copper was to create amorphous grain boundary layers. The powder based synthesis was again successfully completed, and the nanocrystalline copper with amorphous grain boundary films documented very high hardness.
To understand the fundamental mechanisms governing the excellent material behavior, we established detailed micro- and nanomechanical deformation and fracture examinations to unravel the fundamental deformation and fracture processes. Besides employing advanced nanoindentation techniques, we developed elastic-plastic fracture mechanical testing strategies for micro- and nanoscale specimens in the scanning and transmission electron microscope, respectively. Here it is particularly worth mentioning that we possess the unique capability to map the strain field at a crack tip with nanometer resolution and have the capability to conduct these analyses even during in-situ testing in the transmission electron microscope. Accompanying analysis tools were also developed for a better understanding of local strain distribution. Concerning the in-situ experiments on micron-sized specimens conducted in the scanning electron microscope, novel digital vision analysis was designed to aid the continuous identification of the crack advancement process, tremendously aiding the analysis of the respective data. Furthermore, we also implemented micromechanical spectroscopy techniques for sampling grain boundary processes, as well as a transmission microscopy mechanical testing setup in the scanning electron microscope to connect the scanning and transmission worlds in terms of their respective beneficial capabilities. Moreover, we also expanded towards nanoporous but still nanocrystalline tungsten as another promising material to unite high levels of strength, ductility and toughness. We were successful in deriving a novel synthesis technique, establishing a fundamental understanding of the formation process of the nanoporous topology, and could demonstrate that the received material provides again a very attractive combination of materials properties.
Furthermore, we could demonstrate that our novel materials, including nanocrystalline, nanocomposite and nanoporous materials, exhibit excellent performance in harsh conditions, such as elevated temperatures or radiative environments. This renders them as potential go-to materials for the design of new fusion reactor concepts.
Lastly, to broaden the impact of the action we expanded the use of our concepts to microelectronic materials, biological nanocomposites and bio-inspired composites.
These achievements were disseminated in more than 70 peer reviewed publications, including high impact journals such as Nature Communications, Materials Today, Science Advances, as well as numerous works in highly regarded materials science journals such as Acta Materialia or Materials & Design. Furthermore, almost 100 oral contributions were delivered at international workshops and conferences, including two plenary and 36 invited contributions, as well as several outlets to the general public via web pages, newsletters, newspapers, etc.
