Studies on the deformation behaviour of interfaces in (γ + α₂) titanium aluminide by high-resolution transmission electron microscopy

Abstract

The deformation behaviour of two-phase (γ + α₂) titanium aluminide was investigated by high-resolution transmission electron microscopy. Specimens were deformed in compression at room temperature well beyond the yield point. The α₂-Ti₃Al lamellae within the γ-TiAl matrix were observed to deform by shearing when intersected by twins. In addition to dislocation slip, plastic deformation in γ-TiAl was found to proceed by (a/6)<112] twinning partial dislocations, as revealed by the steps on twin interfaces, and by the creation of a three-plane (9R) deformation-induced structure parallel to pre-existing twin interfaces. Formation of the 9R structure is due to an antitwinning operation on every third plane. The core structure of (a/6)<112] twinning partial dislocation steps appears narrow compared with similar (a/6)<112] partial dislocations associated with growth ledges at the γ-α₂ interface. These observations and deformation mechanisms are discussed in terms of the structure of γ-α₂ and twin interfaces.