Abstract A transmission electron microscope investigation has been performed on the thermal instability of the nonequilibrium α 2 γ interfacial structure in a hot-forged Ti-45Al-10Nb-2.5Mn-0.05B alloy. The distinctiveness of these nonequilibrium α 2 γ interfaces in the hot-deformed sample is the misorientation from the conventional orientation relationship {111}γ//{0001}α2, 〈 110 〉γ// 〈 1120 〉α2. The structure of this nonequilibrium interface boundary is characterized by numerous interfacial ledges containing 1 3 [111] Frank partial dislocations. The analysis points towards the formation of this type of nonequilibrium α 2 γ interface being caused by the relative rotation of α2 and γ plates in the lamellar structure. Further TEM studies of microstructural changes during annealing for 4 min/1000 °C of the nonequilibrium α 2 γ lamellar structure generated by hot-forging revealed that many low-angle grain boundaries are formed in the γ plates of lamellar colonies, resulting in a γ subgrain microstructure; necking of α2 plates occurs preferentially at α2 subgrain boundaries; subsequently disintegration of the original α2 plates takes place resulting in spheroidized α2 particles which are aligned at the prior α 2 γ boundaries.