Transmission of the deformation through γ-γ interfaces in a polysynthetically twinned TiAl alloy II. Twin interfaces (180° rotational)

Abstract

The transfer mechanisms of the deformation at γ-γ twin 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 crossing of the interface by ordinary dislocations occurs by cross-slip if they are of screw character when lying in the interface plane. If they are not of screw character when lying in the interface plane, these ordinary dislocations are locked at the interface and no emission of dislocations is observed in the neighbouring lamella. For the case of incident twinning dislocations. twins and ordinary dislocations are emitted in the mirror plane of the neighbouring lamella. All the results of this paper and of the companion paper are then discussed with the aim of understanding the role of these interfaces on the mechanical properties of lamellar TiAl alloys.