Slip transfer of deformation twins in duplex γ-based Ti–Al alloys. Part II. Transfer across γ–α₂ interfaces

Abstract

The interactions of ⅙<112]{111}_γ slip dislocations in deformation twins with {111}_γ-(0001)_α2 interphase interfaces, intersecting along both <101]_γ (30°-type) and <110]_γ (edge-type) directions, in duplex Ti–Al alloys after room-temperature deformation in tension, have been investigated by transmission electron microscopy. The dislocation reactions involved in each of these types of interaction have been fully identified by image matching between experimental and computed images. Slip transfer of 30°-type ⅙<112]{111}_γ twinning dislocations across the γ–α₂ interface into ⅓<1120>{1100}_α2 slip dislocations has been confirmed and completely characterized. In addition to this primary slip system a new secondary slip system of ⅓<1120>{3301}_α2 is activated within the α₂ phase under conditions of high levels of plastic strain. This new slip system has also been observed to be the favoured route for slip transfer of incoming 30°-type ⅙<112]{111}_γ twinning dislocations when the plane of the γ-α₂ interface deviates significantly from {111}_γ-(0001)_α2 and the line of intersection is no longer close to <101]_γ. For the interaction involving edge-type ⅙<112]{111}_γ twinning dislocations with {111}_γ-(0001)_α2 γ-α₂ interfaces, no significant transfer of dislocations into the α₂ phase was observed. Instead, stress relief of the incoming twinning dislocation pile-up at the γ-α₂ interface occurs via ½<110]{001)_γ slip dislocations ‘reflecting’ back into the γ phase coupled with the generation of a new twinned γ grain at the γ-α₂ interface. No dislocation reactions involving c-component dislocations in the α₂ phase were observed for any of the interactions investigated.