Cyclic deformation behavior and substructure in monocrystalline Ti–5at%Al alloy with different orientations fatigued at Δεt/2 = 0.4% were examined. The selected loading orientation included: single prism slip, A; double prism slips [2¯1▪0], B; pyramidal slip, C; and twinning [00▪1], D. The results showed that the crystallographic orientation had a

marked effect upon the cyclic stress response and the plastic deformation mode of Ti–5at%Al single crystals. The crystals exhibited an initial cyclic hardening followed by a striking softening period, and then a saturation stage was reached in specimens A and B. In contrast, an obvious cyclic saturation stage was obtained after first cyclic hardening up to fracture in specimens C and D. Trace analysis of the surface of specimens with an optical microscope showed that (1¯1▪0) single prism slip operated in specimen A during cycling. The (10▪0) and (1¯1▪0) double prism slips could be distinguished from the traces on the (00▪1) surface in specimen B. The (1¯1▪1) pyramidal slip and the (1¯1▪0) prism slip were activated simultaneously in specimen C. Twinning was the primary plastic deformation mode in specimen D. The twinning types included {11▪1}, {10▪1}, {11▪2} and {10▪2}. The substructure in the fatigued specimens was examined using transmission electron microscopy. The typical dislocation configuration was a well-developed saturation bundle structure in specimen A, while it was the planar edge dislocations which were tangled on the primary (10▪0) plane and arranged parallel to the [00▪1] direction in specimen B. Fully developed loop patches were formed in specimen C. Typical deformed structures were the twin bundles and dislocations among twins in specimen D. The effects of plastic deformation mode upon the cyclic stress response and the corresponding dislocation configuration of Ti–5at%Al single crystals were considered.

Orientation Dependence of Cyclic Deformation Behavior and Dislocation Structure in Ti–5at%Al Single Crystals. L.Xiao, Y.Umakoshi: Materials Science and Engineering A, 2003, 339[1-2], 63-72