Fatigue Crack Growth Mechanisms in Titanium Single Crystals

本文研究了α-钛单晶在室温空气中的疲劳裂纹扩展行为。制备了A、B、C、D、E和F六种不同切口方向的CT标本。A试样的缺口平面和方向分别为（1210）和[1010]，B试样的缺口平面和方向分别为（0110）和[2110]。C试样的缺口平面为（0110），D试样的缺口平面为（1210），缺口方向均为[0001]; E试样的缺口平面为（0001），缺口方向分别为[1010]和[2110]。A和B样本中的裂纹平行于（0110）[2110]扩展。因此，裂纹扩展是由两个相交的棱柱滑移系在裂纹尖端的交替剪切。在C-和D-试样中的裂纹扩展接近基面垂直于缺口方向。这表明，与平行于基面相比，疲劳裂纹难以沿着[0001]扩展。在E-和F-试样中，裂纹大致平行于基面扩展，并在裂纹面附近发现对应于{1012}孪晶系统的痕迹。在<1010>疲劳表面上观察到平行于{1012}孪晶的脊、痕迹和条带。这些结果表明，裂纹扩展可能是由于微孪晶的激活而发生的。获得了α-钛疲劳裂纹扩展行为的晶体学依赖性。

The fatigue crack growth behavior of alpha-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 alpha-titanium is obtained.