Composition change during creep in colonies oriented for easy-slip of Ti–46.5Al–2Cr–3Nb–0.2W

Alloy Ti–46.5Al–2Cr–3Nb–0.2W with fully lamellar microstructure was crept under 1073 K and 270 MPa, and element distribution before and after creep deformation has been compared. In the undeformed microstructure, Cr concentrates in the α2 phase, W concentrates in α2 phase and segregates at the γ/α2 interface and Nb concentrates in the γ phase. An explanation based on site occupying and electronic bonding has been given. During creep deformation, α2→β phase transformation occurs. The segregation of W atoms at the γ/α2 interface promotes nucleation of β phase precipitates, then β phase precipitates grow with the help of the immigration of Cr and W atoms from α2 phase to β phase, and Cr and W do not concentrate in α2 phase any more. During migration, Cr atoms diffuse in the α2 phase directly and W atoms mainly diffuse along the γ/α2 interface. The composition of sub-lamellae in deformed microstructure has also been studied; the composition of α2 laths in sub-lamellae is influenced significantly by the formation of β phase precipitates.