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

Abstract

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 30min, 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.