A study by high-resolution electron microscopy of an α2+ γ two-phase Ti–40 at.% Al alloy

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Abstract
High-resolution electron microscopy observation of a Ti-40 at.% Al alloy shows some microstructures which cannot be resolved by conventional transmission electron microscopy. The α2-γ interface with or without a ledge is found to be related to the misfit dislocations at the α2-γ interface. A transition lamella with the structure in between D019 and L10 is suggested as a way to grow the γ lamella from the α2 matrix. This lamella is formed by stacking faults occurring on every third close-packed plane. The ½[011]γ ledge dislocation can dissociate into a ⅙[112]γ partial dislocation which induces the atomic shuffle on the (111)γ plane in the [112]γ direction and causes the twinning γT to form in the γ lamella. The formation mechanisms of γT associated with a single ledge or a ‘ledge pair’ at the α2-γ interface are also proposed. γT with multilayers of (111)γ planes becomes a real twin in the γ lamella.