The nature of the steps on lamellar γ/α2 interfaces in this ternary TiAl-based alloy was studied by using high-resolution transmission electron microscopy. Most of the steps were found to be identical to those observed previously in a low-misfit quinternary alloy, where equal even numbers of {111}γ and (00•2)α2 planes matched across the step riser, and the Burgers vectors depended upon the height and sense of the step. Occasional steps were also observed for unequal numbers of {111}γ and (00•2)α2 planes across the step riser; including a ¾ step with b = 1/3[¯1¯1¯1] and a 7/8 step with b = 1/3[¯21¯2]. All of the Burgers vectors were consistent with the steps being perfect interfacial disconnections, as described by Pond’s topological theory of interfacial defects. This implied that the γ lamellae in the alloy grew via diffusion-controlled step migration, rather than via the previously-proposed glide of partial dislocations.

High-Resolution Electron Microscopy of Steps on Misfitting Lamellar Interfaces in a Ti-44Al-8at%Nb Alloy. P.Shang, T.T.Cheng, M.Aindow: Philosophical Magazine Letters, 2000, 80[1], 1-10