EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

In order to improve the efficiency of modern turbines in aviation technology with simultaneous reduction of exhaust gas emissions, intermetallic TiAl alloys are implemented as structural material for highly durable turbine blades. Fourth-generation TiAl alloys typically exhibit an excellent high-temperature behavior, promising oxidation resistance and represent a lightweight alternative for heavy Ni-base alloys. However, at ambient temperatures, TiAl alloys are lacking ductility and therefore possess a certain risk of brittle failure. As the preferred fully-lamellar microstructure consists of α₂/γ colonies, the fracture toughness of single phases or interfaces within the compound is crucial for lifetime predictions or foreign object damage estimation. Thus, two alloy variants were analyzed by complementary in-situ notched cantilever experiments and SEM video recording to study phase and interface dependent fracture properties. Here, the J-integral as well as the conditional fracture toughness were determined, which allowed to unveil the fracture process and path. This allows to assign the mechanical response of the material to the particular phase or interface. The propagation of the crack length was determined from both, cantilever stiffness and by the use of computer vision, which were in excellent agreement with each other. Based on these results, further alloying design and heat treatment development can be realized to enhance the ductility and toughness of this material system.