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

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 γ_T to form in the γ lamella. The formation mechanisms of γ_T associated with a single ledge or a ‘ledge pair’ at the α₂-γ interface are also proposed. γ_T with multilayers of (111)_γ planes becomes a real twin in the γ lamella.