Crack propagation behavior under cyclic loading in α-titanium single crystals

Abstract

The fatigue crack growth behavior of α-titanium single crystals has been investigated in laboratory air at room temperature. SEN specimens A, B and C with different notch orientations were prepared by a strain-annealing technique. The notch plane and direction in the A-specimen were close to (1210) and [1010], those in the B-specimen were (0110) and [2110], and those in the C-specimen were close to (1010) and [0001], respectively. A definite dependence of crystallographic orientation on fatigue crack growth behavior was obtained. The crack in the A-specimen propagated parallel to (0110) [2110] and two sets of prismatic slip traces ((1100) [1120] and (1010) [1210]) were found near the crack tip. The crack in the B-specimen propagated parallel to the [2110] notch direction. Therefore, the cracks in both the A- and the B-specimens are deduced to extend by alternating shear on two intersecting prismatic slip systems ((1100) [1120] and (1010) [1210]). The fatigue crack propagated along the [0001] direction in the C-specimen. Although very fine traces due to twinning were observed near the crack surface, large slip bands were not found. Ridges and valleys which are deduced to be associated with twin interfaces were observed on the fatigue surface. This suggests that the crack may grow by the separation of twin interfaces.