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.