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

摘要

The interactions of 1/6[112]{111}gamma slip dislocations in deformation twins with {111}(gamma)-(0001)alpha (2) interphase interfaces, intersecting along both [101](gamma) (30 degrees -type) and [110]gamma (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 degrees -type 1/6[112]{111}, twinning dislocations across the gamma-alpha (2) interface into 1/3[1120]{1100}(alpha2) slip dislocations has been confirmed and completely characterized. In addition to this: primary slip system a new secondary slip system of 1/3[1(1) over bar 20](3(3) over bar 01}alpha (2) is activated within the alpha (2) 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 degrees -type 1/6[112]{111}(gamma) twinning dislocations when the plane of the gamma-alpha (2) interface deviates significantly from {111}(gamma)-(0001)alpha (2) and the line of intersection is no longer close to [101](gamma). For the interaction involving edge-type 1/6[112]{111}(gamma) twinning dislocations with {111}(gamma)-(0001)(alpha2) gamma-alpha (2) interfaces, no significant transfer of dislocations into the alpha (2) phase was observed. Instead, stress relief of the incoming twinning dislocation pile-up at the yat interface 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-component dislocations in the alpha (2) phase were observed for any of the interactions investigated. [References: 20]