Effects of γ/γ lamellar interfaces on translamellar crack propagation in TiAl alloys

Lamellar interfaces and their structures play a significant role in the fracture behavior of fully lamellar (FL) TiAl alloys. However, the effects of different lamellar interfaces on crack tip behavior are not clear. To this end, the interaction between three types of γ/γ lamellar interfaces, which are termed by true-twin, rotational-order, and pseudo-twin interfaces, and a translamellar crack in FL-TiAl alloy have been investigated by molecular dynamics simulation. By analyzing the atomic structure evolution of crack propagation and the effects of interfaces on the crack growth rate, we found that the introduction of γ/γ lamellar interfaces enhanced the crack resistance of a crack model without interfaces. Furthermore, the resistances of the γ/γ lamellar interfaces against translamellar crack propagation are in the order of rotational-order> pseudo-twin> true-twin. Specifically, crack growth is almost arrested at the rotational-order interface; the crack propagation nearly stops after crossing through the pseudo-twin interface; while the crack penetrates the true-twin interface and continues to propagate in adjacent lamellae. In addition, as crack resistance of the lamellar interface improves, the dislocation density in the corresponding model also increases. Among the three kinds of γ/γ lamellar interfaces, the true-twin interface effectively screens the stress field at the crack tip, whereas the pseudo-twin and rotational-order interfaces do not.