THE STUDY OF INTERFACES BETWEEN TIAL AND TI3AL PHASES IN THE INTERMETALLIC COMPOUND TI50.7AL48MN1.3

The TiAl(Mn) alloy with lamellar structure of the alpha2- and gamma-ph ases is of superior mechanical property in comparison with single alph a2- and gamma-phases because the alpha2-gamma and gamma-gamma interfac es play an important role in improving the ductility. In order to unde rstand their growth mechanism and the deformation behaviour of the lam ellar structure, the fine structures of alpha2-gamma and gamma-gamma i nterfaces were investigated on the atomic scale using transmission ele ctron microscopy and high-resolution electron microscopy. The hierarch y of lamellar structures was firstly detected on the nanometre scale. Some boundaries, stacking faults and dislocations were found in the ga mma stripes. There are also some twins in which the [111]M and [111]T directions are not parallel with each other accurately and have 2-degr ees deviation between them because of their tetragonality. Two atomic structure models of the alpha2-gamma interface were suggested and the perfect alpha2-gamma interface is actually a mixture of these two mode ls. There are also some dislocation ledges and strain concentrations a t the alpha2-gamma interface and these ledges are arranged on the inte rface at regular distance. In the composite interfaces, the gamma-gamm a interfaces show a twin relationship and no alpha2 slice between thei n. A new kind of alpha2-gamma(B)-gamma(A)-gamma(B)-alpha2 interface wa s also found. The formation of this composite interface was deduced to be transformed from the alpha2-gamma(B)-gamma(B)-alpha2 interface.