Samples of a range of polycrystalline alloys which were based upon TiAl were examined by using optical microscopy, analytical scanning and transmission electron microscopy to understand the role of the a2 phase in controlling plastic deformation in alloys with a lamellar structure. In grains having the hard orientation, where the stress axis was either parallel or perpendicular to [00▪1]a2, fracture occurred preferentially along a2/γ interfaces. Transmission electron microscopy showed that twinning in the γ phase could be transmitted into the a2 phase via the generation of dislocations with Burgers vectors along <11▪6> on {20▪1} planes. Slip along <11▪0> directions was also observed in a2 when the stress axis was perpendicular to [00▪1]a2. When crystals were stressed parallel to [00▪1]a2, the only dislocations which were observed in a2 had their Burgers vector aligned along <11▪6>.

The Role of the a2 Phase in the Transmission of Slip in Lamellar TiAl-Based Alloys A.Godfrey, D.Hu, M.H.Loretto: Philosophical Magazine A, 1998, 77[2], 287-97