日本金属学会誌

J. Japan Inst. Metals, Vol. 62, No. 8 (1998),
pp. 708-717

Crystallographic Dependence of Fatigue Crack Growthin Titanium Single Crystals

Yoji Mine1, Shinji Ando1, Hideki Tonda1,Kazuki Takashima2 and Yakichi Higo2

1Department of Materials Science and Mechanical Engineering, Faculty of Engineering, Kumamoto University, Kumamoto 860-8555
2Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama 226-8503

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.


(Received March 20, 1998; In Final Form May 11, 1998)

Keywords:

fatigue crack growth, titanium, single crystal, slip system, mechanical twinning


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