Crystallography and phase transformation mechanisms in TiAl-based alloys – A synthesis

The variation in cooling rates of Ti–46.8Al–1.7Cr–1.8Nb (at. %) alloy from the high-temperature α domain produces lamellar, Widmanstätten, feathery-like (α2 + γ) structures, as well as γ-massive phase, often coexisting together. Earlier reported crystallographic and morphological details of each of these structures are compiled together and a combined view on the generation of their crystallographic related possible variants and their solid phase transformation mechanisms is proposed. Sympathetic nucleation is suggested as a common mechanism for the lamellar structure at slow cooling rate, the Widmanstätten structure and the feathery-like structure.