Degenerated lamellar microstructure with an increased propensity for 120°-rotational boundaries in a Ti-48Al alloy formed upon annealing

The lamellar structures of the γ(TiAl)-phase coexisting with a small amount of α2(Ti3Al)-phase in two-phase TiAl-based alloys were studied. The γ-lamellae and α2-lamellae have the orientation relationships of {111}γ∥(0001)α(2) and 〈110〉γ∥〈1120〉α(2). Large kinks were observed at the boundaries of coarsened γ-lamellae. Within these thick lamellae, there were thin γ-lamellae and an increased number of α2-plates with the sharp ends. The formation mechanism of the degenerated structures was associated with the nucleation of the α-phase, which may be more favorable at pseudo-twin and true-twin interfaces than at 120°-rotational interfaces upon heating into the α+γ two-phase field.