Nucleation and growth of α phase in hot extruded Ti–46.6Al–2Mo–1.4Mn intermetallic alloy produced by hot extrusion of elemental powders

The present study is concerned with nucleation and growth of α phase during heat treatment in Ti–Al–Mo–Mn intermetallic alloys processed by hot extrusion of elemental powders. TEM and X-ray diffraction analysis show that the microstructure of the as-hot extruded alloy consists of γ, α2 and B2 phases. The volume fractions of α2 and B2 phases are 16 and 20%, respectively, which shows that B2 phases that contain significant amounts of Mo have an orientation relationship with γ plates inside them. Microstructural evolution during heat treatment reveals that the α2 phase nucleates and grows in lamellar form by edgewise and sidewise mechanism. Edgewise growth of the α2 phase is more rapid than sidewise growth due to the coherent interface between α2 and γ phases along the sidewise direction. Sidewise growth of the α2 phase occurs by a ledge mechanism. It has been shown that α phase nucleates in γ plates located at the lamellar boundaries and grows along a direction that can produce an incoherent interface. γ phase present in the B2 phase affects the growth of the α phase by providing a preferential site for α growth.