Fatigue Crack Growth Mechanisms in HCP Single Crystals

2000 Fiscal Year Final Research Report Summary

• Project/Area Number: 11650715
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Structural/Functional materials
• Research Institution: TOKYO INSTITUTE OF TECHNOLOGY
• Principal Investigator: TAKASHIMA Kazuki Precision and Intelligence Laboratory, Tokyo Institute of Technology, 精密工学研究所, 助教授 (60163193)
• Co-Investigator(Kenkyū-buntansha): ANDO Shinji Faculty of Engineering, Kumamoto University, 工学部, 講師 (40222781) ; SHIMOJI Masayuki Precision and Intelligence Laboratory, Tokyo Institute of Technology, 精密工学研究所, 助手 (00242313) ; HIGO Yakichi Precision and Intelligence Laboratory, Tokyo Institute of Technology, 精密工学研究所, 教授 (30016802)
• Project Period (FY): 1999 – 2000
• Keywords: Titanium / Single Crystal / Fatigue / Crystallographic Orientation / Crack Growth Rate / Crack Growth Mechanism / Slip System / Twinning

Research Abstract

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.