| Project/Area Number |
15360361
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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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 | TOHOKU UNIVERSITY |
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Principal Investigator |
MARUYAMA Kouichi Tohoku University, Graduate School of Environmental Studies, Professor, 大学院・環境科学研究科, 教授 (90108465)
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| Co-Investigator(Kenkyū-buntansha) |
KOIKE Jun-ichi Tohoku University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (10261588)
SUZUKI Mayumi Tohoku University, Graduate School of Environmental Studies, Research Associate, 大学院・環境科学研究科, 助手 (20292245)
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| Project Period (FY) |
2003 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥15,300,000 (Direct Cost: ¥15,300,000)
Fiscal Year 2004: ¥6,700,000 (Direct Cost: ¥6,700,000)
Fiscal Year 2003: ¥8,600,000 (Direct Cost: ¥8,600,000)
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| Keywords | Intermetallics / Titanium Aluminide / Nano lamellar Structure / Lamellar Boundary Design / Strengthening of Materials / Hall-Petch Relation / High Temperature Creep / Microstructural Degradation / ナノ層状組織 / ホール・ペッチの関係 / ミスフィット転位 / シミュレーション |
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| Research Abstract |
TiAl alloys are the most promising light material for high temperature structural applications. The alloys take a lamellar structure consisting of α_2Ti_3Al and γ TiAl phases, and their strength increases with decreasing lamellar thickness. However there is an upper limit in the strengthening. In this study the causes of the upper limit were examined and it was proposed how to improve the upper limit.
1.Misfit dislocations on α_2/γ lamellar boundaries disappear when lamellar thickness λ is reduced below 50nm, resulting in loss of boundary resistance to dislocation motion. Therefore, the yield stress vs. 1/√<λ> curve deviates from the Hall-Petch relation and yield stress has an upper limit at fine λ.
2.The upper limit of yield stress can be improved if we can introduce the misfit dislocations to α_2/γ lamellae less than 50nm thickness. Lattice misfit determines the lower limit of lamellar thickness for the introduction of misfit dislocations, and a lattice misfit larger than 1.5% is required to improve the upper limit.
3.Coarsening and sphoroidization of lamellae are the major microstructural degradation that cause loss of deformation resistance. The degradation is driven by the interfacial energy and is faster in finer lamellar structure. The degradation proceeds by the migration of lamellar boundaries, and can be retarded by reducing the mobility of lamellar boundaries.
4.TiAl alloys contain four types of lamellar boundaries, and the α_2/γ boundaries have the lowest mobility. It was confirmed that a material having a high density of α_2/γ boundaries shows better creep deformation resistance due to its improved microstructure stability.
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