Deformation structure in a Ti-24Al-11Nb alloy

Abstract

A Ti-24Al-11Nb alloy has been heat-treated so as to obtain a microstructure of coarse α2 particles (D019 structure based on Ti3Al) in a matrix of the ordered βo phase (B2 structure based on Ti2AlNb). Dislocation structures generated by tensile strains of ∼2 pct at room temperature have been analyzed by transmission electron microscopy The βo phase is shown to deform inhomogeneously on {110}, {112}, and {123} planes by α/〈211〉 slip. The slipband structure is complex, consisting of segments of heavily pinned edge dislocations with periodic cross slip of screw components on to secondary slip planes. Incompatibility stresses at α2/βo interfaces can generate fine α[100] slip as well. The α2 phase deforms independently by α dislocation slip. Slipbands in the βo phase can shear the α2 phase by activatingc +a/2 slip on $$\left\{ {2\overline 2 01} \right\}$$ and $$\left\{ {22\overline 4 2} \right\}$$ slip planes, as well asa slip on higher order pyramidal planes, where the parallelism of the specific slip system is permitted by the Burgers relationship between the two phases.