Effects ofγ/γinterfacial structures on continuous coarsening
of lamellar microstructure in TiAl alloy during aging①
of lamellar microstructure in TiAl alloy during aging①
(Beijing Institute of Aeronautical Materials, Beijing 100095, China)
Abstract: The effects ofγ/γinterfacial structures on continuous coarsening of the fully lamellar microstructure in Ti48Al alloy aged at 1 150℃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 perfectγ/γlamellar interfaces. Thermal grooves, initiative positions of interfacial dissociation, can frequently form at the triple point junctions between the 120°-rotational orderedγdomain boundaries within γlamellae and the lamellar interfaces. During the early stage of aging at 1 150℃, the interface migration and dissociation took place preferentially at the 120°-rotational ordered lamellar interfaces. Comparing the relative thermal stability of the true-twin, pseudo-twin and 120°-rotational orderedγ/γlamellar interfaces shows that the 120°-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 ofγ/γlamellar interfaces.
Key words: titanium aluminide; lamellar microstructure; continuous coarsening;γ/γlamellar interface; orientation relationship; aging