Scale bridging evaluation of the fracture behavior of an advanced TiAl alloy
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Advanced intermetallic TiAl alloys are typically used in high-end aerospace and automotive applications. This class of materials outperforms Ni-based superalloys in regard of weight reduction, high-temperature strength, corrosion resistance and creep properties up to 800°C. However, TiAl alloys suffer from a distinct lack of ductility and elongation before fracture at room temperature. Therefore, the fracture properties of a TNM alloy were determined in micro- and nanoscale notched cantilever bending experiments. These in-situ experiments were performed both, in a scanning and transmission electron microscope to track the crack propagation during fracture along selected interface types or phases. Consequently, the conditional fracture toughness, associated J-integral and fracture elongation were determined. To assess the strains prevailing in the initial microstructure, strain maps were recorded using a nanobeam diffraction mapping technique. The experimental results were compared with those obtained from molecular dynamics simulations, where the initial geometric structures were adapted to the real experimental setup. The interaction of the crack tip with an interface and the emerging influence zone were considered for different possible interface variants. The herein presented scale bridging experiments evaluating the fracture properties of a tailored TiAl alloy allow to identify the weakest interfaces or phases within the microstructure. Hence, the results from this investigation will pave the way for an improvement of the critical fracture properties of the alloying system, leading to a wider range of applications.
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