Slip transfer of deformation twins in duplex γ-based Ti–Al alloys. Part I. Transfer across γ–γ coherent twin interfaces

Abstract

The interactions of ⅙<112]{111}_γ twinning dislocations with {111}_γ-{111}_T coherent twin 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 that describe the slip transfer processes have been fully identified using image matching between experimental and computed images and are discussed and interpreted in terms of the direction of the applied tensile stress. Slip transfer of incoming 30°-type ⅙<112]{111}_γ dislocations across the {111}_γ-{111}_T coherent twin interface occurs via the transmission of ½[110]{111}_T slip dislocations and ⅙<112]{111}_T twinning dislocations into the twinned γ phase in association with the motion of ⅙<112]{111}_γT twinning dislocations in the plane of the coherent twin interface. For the interaction involving incoming edge-type ⅙<112]{111}_γ dislocations with {111}_γ-{111}_T coherent twin interfaces, transfer occurs via ½<110]{001)_T slip dislocations which are transmitted into the twinned γ phase in association with ½<110]{001)_γ slip dislocations which are ‘reflected’ back into the matrix γ phase, and under some circumstances this is also coupled with the motion of ⅙<112]{111}_γ-T twinning dislocations in the plane of the coherent twin interface.