Low Temperature Phase Transformations in Copper-Quenched Ti-44.5Al-8Nb-2.5V Alloy

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 [Formula: see text])γ(s)//([Formula: see text] 10)γ(p) and (0 [Formula: see text] 0)γ(s)//(22 [Formula: see text])γ(p).