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 beta(beta(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 beta(0) precipitates mainly form small rods within the alpha(2) lamellae. There, the rod-shaped beta(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)(alpha 2)//{111}(gamma), < 1120 >( alpha 2)// < 110](gamma), the beta(0) precipitates which emerge from the alpha(2) lamellae obey the following OR: (0001)(alpha 2)//{110}(beta 0), < 1120 >(alpha 2)//< 111 >(beta 0). In addition, the {110} planes of beta(0) have multiple variants. As a consequence, they can grow in different <111> directions in the alpha(2) lamellae. The low interface energy between beta(0) precipitates and alpha(2) lamellar matrix indicates the precipitates are stable.