Precipitation and growth behavior of β0 phase in the α2/γ lamellar colonies of an intermetallic Ti-43.5Al-4Nb-1Mo-0.1B alloy

The precipitation and growth behavior of β(β ₀) phases in an intermetallic Ti-43.5Al-4Nb-1Mo-0.1B (at%) alloy were investigated by using X-ray diffraction (XRD), focused ion beam-scanning electron microscopy (FIB-SEM), transmission electron microscopy (TEM) and simulation. The results show that the applied heat treatment changes the volume fraction of the constituting phases and thus the feature of the lamellar microstructure in the alloy. Furthermore, a three-dimensional (3D) reconstruction reveals that β ₀ precipitates mainly form small rods within the α ₂ lamellae. There, the rod-shaped β ₀ precipitates grow in different well-defined directions, and some precipitates are interconnected along their growth paths. TEM investigations indicate that beside the Blackburn orientation relationship (OR): (0001) _{α 2} //{111} _γ, <112̅0> _{α 2} //<11̅0] _γ, the β ₀ precipitates which emerge from the α ₂ lamellae obey the following OR: (0001) _{α 2} //{110} _{β 0} , <112̅0> _{α 2} //<111> _{β 0} . In addition, the {110} planes of β ₀ have multiple variants. As a consequence, they can grow in different <111> directions in the α ₂ lamellae. The low interface energy between β ₀ precipitates and α ₂ lamellar matrix indicates the precipitates are stable.