The Role of Interfaces in Deformation Twinning of Lamellar TiA1/Ti3A1Crystals

The role of intakes in deformation twiming of Iamellar TiAl (ywl~l (a*) crystals creep deformed at an ekvated temperature have been investigated. Since the multiplication of lattice dislocations within both y and etzlamellae is very limited as a result of a refined lamekr microstmture, the gliding of interfheii dislocations on both y/a2 and y/y interfaces (i.e. interface sliding) becomes an important d40rmation mechanism. The movement of interfhcial dislocations, which glide in a cooperative fashion along the Iamellar interke.s, can be impeded by obstacles such as interface ledges, impinged lattice dislocations, and grain boundaries. The impediment of dislocation motion subsequently causes a dislocation pile-up in front of obstacle as creep strain accumulates. When the crystals deform at high stress kve~ deformation twinning becomes a predominant deformation mechanism. Deformation twins are fand to nucleate from the interfhees as a result of a local stress concentration generated from the dislocation pile-up. It is suggested that the deformation twinning in kunellar TiA1/Ti~l crystals can be viewed as a stress relaxation process to relieve the local stress concentration caused by the pile-up of interfhcial dislocations. An interfiwe-assisted twinning mechanism is accordingly proposed.