In this study, an easily controlled transformation similar to the β + α → β + α + γ and the analysis of metastable phases in a β solidifying Ti-44.5Al-8Nb-2.5V alloy were investigated. Therefore, a liquid alloy copper-quenching followed by annealing at an application temperature (850 °C) has been carried out. Following quenching, a microstructure composed of several supersaturated phases—the basket-weave β 0 (β bv ) phase, the plate-like α 2 (α p ) phase and the stripe-like γ (γ s ) phase—was obtained. In the annealing processes, phase transformations in the prior β bv and α p phases domain corresponded nicely to the β + α → β + α + γ transformation during solidification. Also, in the annealed γ s phase, the kinetics of the phase transformations involving the metastable L1 2 phase was firstly detected by transmission electron microscopy (TEM). The L1 2 phase had a lattice structure similar to the γ phase, whereas the composition of the phase was similar to the α 2 phase. The formation of the γ pre-twin phase with an anti-phase boundary (APB) was detected in the γ s phase of the matrix. The orientation relationships between the γ s and precipitated: γ (γ p ) phase are <101]γ s //<114]γ p , (10 1 ˉ )γ s //( 1 ˉ 10)γ p and (0 1 ˉ 0)γ s //(22 1 ˉ )γ p .
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