Slip transfer of deformation twins in duplex gamma-based Ti-Al alloys. Part II. Transfer across gamma-alpha(2) interfaces

The interactions of 1/6[112]{111}gamma slip dislocations in deformation twi ns with {111}(gamma)-(0001)alpha (2) interphase interfaces, intersecting al ong both [101](gamma) (30 degrees -type) and [110]gamma (edge-type) directi ons. 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 i dentified by image matching between experimental and computed images. Slip transfer of 30 degrees -type 1/6[112]{111}, twinning dislocations across th e gamma-alpha (2) interface into 1/3[1120]{1100}(alpha2) slip dislocations has been confirmed and completely characterized. In addition to this: prima ry slip system a new secondary slip system of 1/3[1(1) over bar 20](3(3) ov er bar 01}alpha (2) is activated within the alpha (2) phase under condition s of high levels of plastic strain. This new slip system has also been obse rved to be the favoured route for slip transfer of incoming 30 degrees -typ e 1/6[112]{111}(gamma) twinning dislocations when the plane of the gamma-al pha (2) interface deviates significantly from {111}(gamma)-(0001)alpha (2) and the line of intersection is no longer close to [101](gamma). For the in teraction involving edge-type 1/6[112]{111}(gamma) twinning dislocations wi th {111}(gamma)-(0001)(alpha2) gamma-alpha (2) interfaces, no significant t ransfer of dislocations into the alpha (2) phase was observed. Instead, str ess relief of the incoming twinning dislocation pile-up at the yat interfac e occurs via 1/2[110]{001}(gamma) slip dislocations 'reflecting' back into the gamma phase coupled with the generation of a new twinned gamma grain at the gamma-alpha (2) interface. No dislocation reactions involving c-compon ent dislocations in the alpha (2) phase were observed for any of the intera ctions investigated.