The TiAl(Mn) alloy with lamellar structure of the α2- and γ-phases is of superior mechanical property in comparison with single α2- and γ-phases because the α2-γ and γ-γ interfaces play an important role in improving the ductility. In order to understand their growth mechanism and the deformation behaviour of the lamellar structure, the fine structures of α2-γ and γ-γ interfaces were investigated on the atomic scale using transmission electron microscopy and high-resolution electron microscopy. The hierarchy of lamellar structures was firstly detected on the nanometre scale. Some boundaries, stacking faults and dislocations were found in the γ stripes. There are also some twins in which the [111]M and [111]T directions are not parallel with each other accurately and have 2d' deviation between them because of their tetragonality. Two atomic structure models of the α2-γ interface were suggested and the perfect α2-γ interface is actually a mixture of these two models. There are also some dislocation ledges and strain concentrations at the α2-γ interface and these ledges are arranged on the interface at regular distance. In the composite interfaces, the γ-γ interfaces show a twin relationship and no α2 slice between them. A new kind of α2-γB-γA-γB-α2 interface was also found. The formation of this composite interface was deduced to be transformed from the α2-γB-γB-α2 interface.
Philosophical Magazine A
Volume 67, 1993 - Issue 5