The cyclic deformation behavior and dislocation structure of Ti-5at%Al single crystals, oriented for single prism slip, were studied. It was found that samples which were tested under total strain control (Δt/2) exhibited an initial slight cyclic hardening, followed by a marked softening period. Saturation was reached at 0.2 to 1.0%; except at very low strain amplitudes (0.2%), where the initial hardening was replaced by an immediate cyclic softening. The saturation stage occupied most of the lifetime. The cyclic stress-strain curve comprised a clear stress plateau region within the plastic shear-strain amplitude of 0.039 to 1.68%. The plateau shear-stress was about 85MPa. Single (1¯1▪0) prism slip was observed on the surface of fatigued specimens, and this became denser as the cyclic strain amplitude or number of cycles increased. The typical dislocation structure on the primary slip plane was a saturation bundle structure which consisted mainly of dense screw dislocations, parallel to the [11▪0] direction, and dislocation bundles which were nearly perpendicular to the [11▪0] direction, that was closely parallel to the [00▪1] direction. Some dislocation slabs were observed in (00▪1) foils. The dislocation structure evolved from elongated screw dislocation lines along [11▪0], during the first cyclic hardening stage, to parallel screw dislocation lines together with dislocation bundles nearly along [00▪1] in the cyclic softening stage. Finally, a well-developed saturation bundle structure formed in the saturation stage.

Cyclic Deformation Behaviour and Structural Bundle Structure in Ti-5at%Al Single Crystals Deforming by Single Prism Slip. L.Xiao, Y.Umakoshi: Philosophical Magazine, 2003, 83[30], 3407-26