Deformation-induced γ⇆α phase transformation in a hot-forged Ti-45Al-10Nb alloy

Deformation-induced gamma --> alpha(2) and alpha(2) --> gamma phase transformations in a hot-forged Ti-45Al-10Nb alloy have been investigated by using high-resolution transmission electron microscopy (HREM). The gamma --> alpha(2) transformation is an interface-related process, which involves the emission of the interfacial superdislocations from the misoriented semi-coherent alpha(2)/gamma interface. These superdislocations further react with each other or with the moving dislocations in gamma phase and results in the formation of alpha(2) phase. On the other hand, the deformation-induced alpha(2) --> gamma phase transformation nucleates either at the alpha(2)/gamma interfaces or at the stacking faults on the basal plane of alpha(2) phase. The growth of gamma plate is accomplished by the moving of a/6 < <10(1)over bar 0> > Shockley partials on alternate basal plane (0001)(alpha 2). The interfaces as well as the crystallographic orientation relationship between the as-cast or deformation-induced alpha(2) and gamma phase have been analyzed. The mechanisms for the deformation-induced gamma --> alpha(2) and alpha(2)-gamma phase transformations were also discussed. (C) 1997 Elsevier Science S.A.