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

摘要

The interactions of (1)/(6)[112]{111}gamma twinning dislocations with {111}gamma-{(1) over bar(1) over bar(1) over bar}(T) coherent twin interfaces, intersecting along both [101]gamma (30 degrees -type) and [110]gamma ledge-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 degrees -type (1)/(6)[112]{111}gamma dislocations across the {111}gamma-{(1) over bar(1) over bar(1) over bar}(T) coherent twin interface occurs via the transmission of (1)/(2)[110]{111}(T) slip dislocations and (1)/(6)[112]{111}(T) twinning dislocations into the twinned gamma phase in association with the motion of (1)/(6)[112]{111}gamma-(T) twinning dislocations in the plane of the coherent twin interface. For the interaction involving incoming edge-type (1)/(6)[112]{111}gamma dislocations with {111}gamma-{(1) over bar(1) over bar(1) over bar}(T) coherent twin interfaces, transfer occurs via (1)/(2)[110][001}(T) slip dislocations which are transmitted into the twinned gamma phase in association with (1)/(2)[110]{001}gamma slip dislocations which are 'reflected' back into the matrix gamma phase, and under some circumstances this is also coupled with the motion of (1)/(6)[112]{111}(gamma -T) twinning dislocations in the plane of the coherent twin interface. [References: 28]