Transmission of the deformation through γ-γ interfaces in a polysynthetically twinned TiAl alloy I. Ordered domain interfaces (120° rotational)

Abstract

The transfer mechanisms of the deformation at ordered domain interfaces in a polysynthetically twinned TiAl alloy are studied by in-Situ straining experiments performed at room temperature in a transmission electron microscope. Several situations which differ in the nature of the incident dislocations and in the orientation of the applied stress are analysed. Some cases for which no dislocations are emitted in the second lamella are also presented. The interpretation of the results is based on a geometric analysis of the different situations encountered and on the calculation of the stress distribution due to the applied stress and to the pile-up of dislocations at the interface. Emission of dislocations is found to occur if the applied stress and the internal stress are favourable. When the incident system is formed by a twin, ordinary and superlattice dislocations are emitted in the second lamella in the plane in continuation to the glide plane of the incident dislocations. When the incident system consists of ordinary dislocations, Shockley dislocations resulting from the dissociation of the incident dislocations are emitted in one plane containing their Burgers vectors.