On the role of microstructure in fatigue-crack growth of γ-based titanium aluminides1

Room temperature fatigue-crack growth behavior is investigated in a wide range of γ-based titanium aluminide microstructures. The influence of microstructural variables such as lamellar colony size and volume fraction of equiaxed γ grains are systematically analyzed in terms of their effects on crack growth resistance. It is found that the coarse lamellar microstructures exhibit the best resistance to cyclic crack growth, while the duplex and single-phase γ microstructures exhibit the worst. Additionally, a wide range in fatigue-crack growth resistance is observed for the various lamellar microstructures investigated. These trends in material properties are explained in terms of extrinsic crack-tip shielding mechanisms, including crack closure and uncracked (shear) ligament bridging, the potency of which are functions of microstructure.