Effects of γ/γ lamellar interfaces on interlamellar crack propagation behaviors of TiAl alloys

Abstract

Interlamellar fracture is one of the failure modes of fully lamellar (FL) TiAl alloys. Here, the effects of three types of γ/γ lamellar interfaces, which are termed true twin (TT), 120° rotational order fault (ROF), and pseudo-twin (PT), subjected to uniaxial tensile loading on the interlamellar crack propagation behaviors of an FL γ-TiAl alloy have been investigated by molecular dynamics method. The results show that the introduction of the PT and ROF interface weakens the tensile strength of single crystal TiAl, while the introduction of the TT interface can effectively improve the tensile strength of the material. Moreover, the cracks in the three interfaces exhibit different propagation behaviors and propagation rates. Specifically, the ROF and PT interfaces exhibit the most desirable and least desirable crack resistances, respectively, which are related to the geometric compatibilities of the interfaces and plastic deformation of crack tips. We also found that the sequence of fracture toughness (ROF > TT > PT) is consistent with that of the flow stresses (ROF > TT > PT). In addition, in the early stage of crack propagation, deformation twins serve as a toughening mechanism that reduces crack tip stress and retards crack extension.