Orientation relationships between γ plates and α2 matrix in a Ti-39 at.%Al alloy

Microstructural development and creep deformation in equiaxed γ, γ+α 2, and γ+α 2+B2 titanium aluminides

“…Instead of growth of ␣ into grains, which would subsequently form lamellar regions upon cooling, plates precipitate within ␥ grains on {111} planes. Presumably, this occurs at stacking faults or twins by a mechanism similar to that suggested by Yang and Wu [41] and Wang et al [24] Since a hexagonal phase precipitating on the {111} planes of a tetragonal phase is expected to have four distinct variants, this would account for the multiple plate orientations seen in most ␥ grains. Confirmation of four ␣ variants in a similar structure was shown by Muraleedharan et al [42] As the temperature of the sample reaches the annealing temperature, the heating rate reduces, and during this period and during the hold at the annealing temperature, any remaining ␣ that has not yet formed from the supersaturated ␥ has sufficient time to nucleate and grow in the form of grains.…”