2005 Fiscal Year Final Research Report Summary
Development of Characterization Method of Microstructural Constituents using Micro-Sized Specimens
| Project/Area Number |
16560608
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Structural/Functional materials
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| Research Institution | KUMAMOTO UNIVERSITY (2005)
Tokyo Institute of Technology (2004) |
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Principal Investigator |
TAKASHIMA Kazuki Kumamoto University, Faculty of Engineering, Professor, 工学部, 教授 (60163193)
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| Co-Investigator(Kenkyū-buntansha) |
OTSU Masaaki Kumamoto University, Faculty of Engineering, Lecturer, 工学部, 講師 (20304032)
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| Project Period (FY) |
2004 – 2005
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| Keywords | Fracture Toughness / TiAl / Lamellar Structure / Micro Testing / Micro-Sized Specimen / Interface Strength / Crack Growth Resistance |
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| Research Abstract |
TiAl based alloys with a fully lamellar structure exhibit superior fracture properties compared to those with other microstructures. This is mainly due to the activation of extrinsic toughening mechanisms including crack deflection and shear ligament bridging. These extrinsic toughening mechanisms are controlled by the mechanical properties of lamellae, in particular the lamellar interface fracture strength. It is, therefore, extremely important to evaluate the fracture properties of lamellar colonies to improve the fracture toughness of such TiAl based alloys. In this investigation, a micro-sized testing technique is applied to investigate the fracture properties of lamellar colonies in a TiAl based alloy. A fully lamellar, Ti-46Al-5Nb-1W, alloy was used in this work. Micro-sized cantilever specimens with a size 【approximately equal】 10 x 15 x 50 μm^3 were prepared from one lamellar colony by focused ion beam machining. Notches with a width of 0.5 μm and a depth of 5 μm were also introduced into the micro-sized specimens by focused ion beam machining. Fracture tests were successfully completed using a mechanical testing machine for micro-sized specimens at room temperature. The fracture toughness values were obtained in the range 0.2-6 MPam^<1/2>. Fracture surface observations indicate that these variations are attributable to differences in local lamellar orientations ahead of the notch. These fracture toughness values are also lower than those having been previously reported in conventional samples. This may be due the absence of significant extrinsic toughening mechanisms in these micro-sized specimens. Fracture mechanisms of these alloys are also considered on the micrometer scale. The results obtained in this investigation give important and fundamental information on the development of TiAl based alloys with high fracture toughness.
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