Crack resistance of α₂|γ and γ|γ interfaces within a TiAl alloy determined by in situ nano-fracture experiments

This study examines the fracture behavior and mechanisms of a TiAl alloy by assessing individual α₂|γ and γ|γ interfaces as well as individual α₂ and γ lamellae through in situ nano-mechanical investigations. Utilizing a TNM⁺ TiAl alloy with a fully lamellar microstructure, notched bending beams were tested within a transmission electron microscope to assess their mechanical response and type of fracture. The notched specimens were prepared to enable real-time observation of crack initiation and propagation along these distinct interfaces and phases. Results indicate that α₂|γ interfaces demonstrate a more brittle response, while γ|γ interfaces exhibit increased fracture resistance. This could be attributed to dislocation emissions and crack tip blunting within the γ phase. The notched γ lamella exhibited enhanced plastic deformation, as evidenced by higher conditional J integral values of 100 J/m². In contrast, the notched α2 lamellae reached 35 J/m² due to limited available glide systems and easy cleavage of the basal plane. Hence, the α₂ phase decreases ductility and promotes a brittle fracture. Thus, this study enhances the understanding of how specific interfaces and phases affect failure tolerance in TiAl alloys. These insights could guide the design rules of TiAl alloys with improved fracture toughness and reliability for demanding structural applications.