Twinning Behavior in Lamellar γ-TiAl Alloy Deformed Cyclically at Room Temperature

Twinning behavior of a lamellar γ-TiAl alloy deformed in cyclic compression has been studied using transmission electron microscopy (TEM) at room temperature. The experimental results reveal that the deformation twins occurred in this processing have an obvious relationship with the orientation of lamellar. At a favorable orientation a large number of deformation twins appeared at a specific angle with lamellar boundary, and at an unfavorable orientation no deformation twins were found. Meanwhile, two types of deformation twins were observed in a single lamellar lath, and determined to be (111)〈1̄12] and (111) 〈112̄] twins by the analyses of unidirectivity of twinning shear and Schmid factor of twinning shear in a triangle 〈001〉-〈110〉-〈100〉. Twinning and slipping can compensate each other, in which when twinning is restricted by the boundary of lamellar laths, slipping will activated in the barrier laths, and deforming alone the twinning direction will continue. This variation is very helpful to release the stress concentration due to the twinning deformation and restraining the cracks initiation. As a result, the plasticity of this alloy are improved considerably.