Crystallographic dependence of fatigue crack growth in titanium single crystals

Abstract

The fatigue crack growth behavior of α-titanium single crystals has been investigated in laboratory air at room temperature. Six types of CT specimens A, B, C, D, E and F with different notch orientations were prepared. The notch plane and direction in the A-specimen were (1210) and [1010], and those in the B-specimen were (0110) and [2110], respectively. The notch plane of the C-specimen was (0110) and that of the D-specimen was (1210), and the notch direction of both the C- and the D-specimens was [0001]. In the E- and the F-specimens, the notch plane was (0001), and the notch directions were [1010] and [2110], respectively. The crack in the A- and the B-specimens propagates parallel to (0110) [2110]. Therefore, the crack is deduced to extend by alternating shear on two intersecting prismatic slip systems at the crack tip. The crack in the C- and the D-specimens propagates close to the basal plane which is perpendicular to the notch directions. This indicates that the fatigue crack is difficult to grow along [0001] compared with parallel to the basal plane. In the E- and the F-specimens, the crack propagates roughly parallel to the basal plane and the traces which correspond to {1012} twin systems are found near the crack plane. Ridges parallel to 〈1010〉 and traces and bands due to {1012} twinning are observed on the fatigue surfaces. These results suggest that the crack growth might occur plausibly by the activation of micro-twins. A definite crystallographic dependence of fatigue crack growth behavior in α-titanium is obtained.