Strength and ductility in TiAl alloys

Tensile behavior of two-phase TiAl alloys at room temperature (RT) is analyzed for duplex and lamellar microstructural forms. The Hall-Petch relationship with high constants in fully-lamellar material is explained as a combined function of grain-size and deformation-anisotropy. The low ductility and its inverse relationship with grain size are explained using the anisotropic tensile properties of lamellar structures and assuming that the fracture is controlled by the crack nucleation process involving the pile-ups of dislocations under shear stress. The crack initiation toughness and associated strains near the crack tip are used to explain the inverse relationship between ductility and toughness.