In Situ Fracture Behaviour of Tailored TNM Alloys

Titanium aluminium alloys are constantly evolving as tremendous efforts have been set to improve their mechanical properties at elevated temperatures. Thus, new alloys were developed and tailored via heat treatments to fulfil the demanding requirements of aviation and automotive applications. However, these optimizations notoriously have led to decreased room temperature ductility and reduced fracture toughness. Within this study, two advanced TNM alloys have been investigated by in-situ micromechanical notched cantilever tests and sophisticated transmission electron microscopy techniques. Using these methods, the mechanical properties of distinct interfaces regarding the fracture toughness, <i>J-</i>integral and fracture stress could be evaluated at any point during the experiment. Furthermore, the crack propagation could be tracked in-situ and sudden fracture events were linked to the failure of distinct microstructural components. The presented method allowed to identify strengthening mechanisms such as e.g. particles along common α₂/γ interfaces or bridging. To further deepen the understanding of the fracture mechanisms along this interface type, strain maps of the fully lamellar microstructure were conducted edge-on for both alloys. To do so, 4D scanning transmission electron microscopy including scanning nanobeam electron diffraction was performed. From these experiments, strain accumulations caused by misfit dislocations or silicide particles were identified and linked to fracture events. Furthermore, these results were discussed in the light of existing literature.<br/>Based on these results, further alloy design and tailored microstructures will be adapted to enable a higher room temperature ductility and fracture toughness of these alloys.