B19 phase in Ti–45Al–8.5Nb–0.2W–0.2B–0.02Y alloy

•The α2 laths in lamellar colonies are composed of the modulated α2 + B19 phases.•Thin γ plates can nucleate within the B19 phase to release the lattice misfit.•The B19 phase can be eliminated at high temperature.•The pure α2 phase observed at room temperature is not in the equilibrium state.

The B19 phase is widely observed in the α2 laths in Ti–45Al–8.5Nb–0.2W–0.2B–0.02Y alloy, forming a modulated structure together with the α2 phase. The distortion between the α2 and B19 phases exists only along the [11¯00]α2 direction and is very difficult to detect. Thin γ laths precipitate regularly within the α2 + B19 structure to accommodate the lattice misfit, whereas the sizes of the γ laths are limited to a small scale. The B19 phase, however, is unstable and was eliminated after annealing at 900 °C for 30 min, followed by air-cooling. The pure α2 phase observed in the air-cooled sample is not in the equilibrium state. The B19 phase can be a stable phase in some temperatures below 900 °C but be repressed under rapid cooling.