Fracture of convoluted and lamellar α2 + γ TiAl alloys

Fracture toughness tests are conducted at room temperature and 923 K (650 °C) on SENB (Single Edge Notched Bend) specimens of three different (α2 + γ) TiAl-based alloys. One alloy is a conventional near fully lamellar Ti-45Al–2Mn–2Nb + 0.8%vol TiB2 XD alloy. The second and third have a composition of Ti–46Al–8Ta, with a novel “convoluted” cast microstructure developed for turbine applications and a coarse near fully lamellar microstructure, respectively. The novel alloy displays fracture toughness values of 13 ± 2 MPa m at room temperature and 19 MPa m at 923 K (650 °C); these values approach data for lamellar microstructures, known to be optimal for this class of alloy. In particular, shear ligament toughening is observed with a role of retained lamellar colonies in toughening the convoluted microstructure.