Cyclic deformation features in high purity titanium bicrystals

High purity α-titanium bicrystals were prepared using a strain-annealing method after refining twice in a vacuum electric arc furnace and then growing crystals three times in a vacuum floating zone melting furnace. Reverse push-pull cycling tests were performed on bicrystals with grain boundaries oriented at about 90°, 70° and 35° to the stress axis. The cyclic stress-strain curves of bicrystals were determined by a multiple-step test method. The position of the cyclic stress-strain curves has no direct dependence on the angle between the grain boundary plane and the stress axis. {1121}, {1122}, {1011} and {1012} types of twinning occurred during cycling. Grain boundaries sliding was observed in the specimen whose grain boundary plane is about 35° inclined to the stress axis. Bunched slip bands in a braid-like pattern were observed. Fatigue cracks initiated along slip bands and grain boundaries owing to grain boundary extrusion or grain boundary sliding.