Effects of γ/γ interfacial structures on continuous coarsening of lamellar microstructure in TiAl alloy during aging

The effects of gamma/gamma interfacial structures on continuous coarsening of the fully lamellar microstructure in Ti-48Al alloy aged at 1150degreesC were investigated by using transmission electron microscopy (TEM). Continuous lamellar coarsening can be achieved not only by migration of interface faults(such as ledges, edges and curved interfaces) but also by migration and decomposition of perfect gamma/gamma lamellar interfaces. Thermal grooves, initiative positions of interfacial dissociation, can frequently form at the triple point junctions between the 120degrees-rotational ordered gamma domain boundaries within gamma lamellae and the lamellar interfaces. During the early stage of aging at 1150degreesC, the interface migration and dissociation took place preferentially at the 120degrees-rotational ordered lamellar interfaces. Comparing the relative thermal stability of the true-twin, pseudo-twin and 120degrees-rotational ordered gamma/gamma lamellar interfaces shows that the 120degrees-rotational ordered lamellar interface is the most unstable. The reason of this phenomenon was analyzed through the comparisons of the interfacial energies and atomic arrangements of the three types of gamma/gamma lamellar interfaces.