Fatigue Crack Growth Mechanisms in HCP Single Crystals

关于HCP晶体中疲劳裂纹扩展机制的研究很少。这在一定程度上可能是由于HCP晶体的滑移系统往往尚未被准确识别的事实。此外，由于HCP金属中滑移系的数量有限，因此在HCP晶体中可能会发生机械孪生以适应变形。这也可能使人们很难弄清HCP金属中的疲劳裂纹扩展机制。在hcp晶体中，a-钛及其合金因其优异的比强度和耐腐蚀性而被应用于航空航天结构和发动机部件。因此，重要的是要解决这些材料中的基本机制。本文研究了室温空气中α-钛单晶的疲劳裂纹扩展行为。制备了两种不同缺口取向的CT试件E和F。在E型和F型试样中，缺口平面为(0001)，缺口方向分别为[1010]和[2110]。在E和F两种试件中，裂纹大致平行于基面扩展，并在裂纹面附近发现了与{1012}孪晶相对应的痕迹。在疲劳表面观察到平行于&lt；1010&gt；的脊线，以及由{1012}孪晶引起的痕迹和带状组织。这些结果表明，裂纹的扩展可能是通过激活微孪晶来实现的。

There have been few studies on fatigue crack growth mechanisms in HCP crystals. This may be partly due to the fact that the slip systems of HCP crystals have often not yet been identified precisely. In addition, mechanical twinning may occur in HCP crystals to accommodate deformation, since the number of slip systems in HCP metals is limited. This may also make it difficult to clarify fatigue crack growth mechanisms in HCP metals. Among HCP crystals, a-titanium and its alloys have been applied to aerospace structures and engine components because of their excellent specific strength and corrosion resistance. Therefore, it is important to address fundamental mechanisms in such materials. In this investigation, the fatigue crack growth behavior of a-titanium single crystals has been investigated in laboratory air at room temperature. Two types of CT specimens E and F with different notch orientations were prepared. In the E- and the F-specimens, the notch plane was (0001), and the notch directions were [1010] and [2110], respectively. The crack propagates roughly parallel to the basal plane in both the E- and the F-specimens, 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.