Mechanistic modeling of deformation and fracture behavior in TiAl and Ti3Al

Phase stability and bulk properties of TiAl and Ti3Al are investigated based on the first-principles local-density-functional approach, and deformation and fracture behavior of two-phase lamellar γ-TiAl alloys are analyzed using the linear elasticity theory applied to interfaces, dislocations, and cracks. In terms of the calculated elastic constants, Youngʹs and shear moduli are higher in Ti3Al than in TiAl. The coupling effect due to elastic incompatibility reduces the misfit strain at an interface when a tensile stress is applied normal to it. The mode mixity of stress concentration by a dislocation pile-up plays an important role in determining whether slip transfer or microcracking occurs at the interface. The fracture morphology reported in notched polysynthetically twinned crystals is explained in terms of the elastic interaction of a (112)[110] crack with an α2-Ti3Al plate. Additional factors that are involved in the brittle-to-ductile transition behavior of TiAl are discussed.