Molecular Dynamics Simulation of the Structure and Deformation Behavior of γ/α2 Interface in TiAl Alloys

TiAl alloys with gamma-TiAl and alpha(2)-Ti3Al dual-phase lamellar structure possess not only excellent high temperature performance but also density only about half of traditional superalloys. Such lamellar structure largely determines the mechanical properties of TiAl alloys. However, there is still a lack of understanding on the atomic structure of lamella, as well as their influence on the mechanical behaviors. For this reason, molecular dynamics with an embedded-atom potential is employed to investigate the energies of both the coherent and semi-coherent gamma/alpha(2) interfaces. The interface coherency is found to depend on the thickness ratio of gamma lamellae to alpha(2) lamellae, and there exists a critical lamella thickness, below/above which the interface is coherent/semi-coherent. Tensile loading perpendicular to the lamella interface indicates that the yield strength of coherent interface is higher than that of semi-coherent interface and the crack nucleation behavior varies with the thickness ratio of gamma lamellae to alpha(2), lamellae. The plastic deformation occurs first in the gamma region, forming Shockley partial dislocations and then crosses the gamma/alpha(2), interface via slip transfer, activating stacking faults on the pyramidal plane in the alpha(2) region. In this process, the gamma/alpha(2) interface provides nucleation sites for subsequent dislocations and cracks.