Abstract: Twinning in γ TiAl base alloys has attracted great attention in the last few years and is considered to play an important role in plastic deformation, hardening and fracture of the alloys because γ TiAl has a tetragonal structure with a low symmetry. In single phase γ TiAl, deformation twin interaction plays important roles. In multi phase γ TiAl base alloys, deformation twin interacts strongly with γ/α 2/γ lamellae which may be considered as transformation twins. The interactions must be considered in the understanding of the toughening and fracture mechanisms of the alloys. In this paper, crystallography of the twinning and twin interactions in γ TiAl alloys is described in details, and possible interaction mechanisms are suggested. Future trend in the study is also proposed.

Key words: tw inning, γ-T iA l base alloys, p last ic defo rmat ion