Coarsening Mechanism of Ordered Precipitates in the Concentrated Al-Li Alloys and their Properties
| Project/Area Number |
02650513
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
金属材料(含表面処理・腐食防食)
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
SATO Tatsuo Tokyo Institute of Technology, Department of Metallurgical Engineering, Associate Professor, 工学部, 助教授 (90126318)
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| Project Period (FY) |
1990 – 1991
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| Project Status |
Completed (Fiscal Year 1991)
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| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1991: ¥200,000 (Direct Cost: ¥200,000)
Fiscal Year 1990: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Keywords | Al-Li alloys / Phase Decomposition / Ordered Structure / Ostwald Ripening / Coarsening / Particle Size Distribution / 粗大化現象 / 急冷凝固 / 機械的性質 / 高分解能電子顕微鏡 |
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| Research Abstract |
Decomposition phenomena of supersaturated solid solution and coarsening behavior of the delta' phase were experimentally investigated for four Al-Li alloys containing 1.80 mass%Li (6.65 mol%Li) up to 3.33 mass%Li (11.8mol%Li). The decomposition of the Al-Li binary alloy was found to take place as follows :
alpha -> homogeneous ordering -> ordered domain -> delta' delta
Both the homogeneous ordering structures and ordered domains were precursors to the metastable delta' phase and contained less Li than that of the stoichiometric composition, 25mol%Li. The delta' phase was most effective to increase the mechanical strength of Al-Li alloys. The coarsening behavior of the delta' phase was also quantitatively analyzed. The delta' precipitates were clearly observed in the TEM dark field images. The mean radius, particle size distribution, standard deviation and skewness were determined using an image analysis system. The coarsening of the delta' phase took place in accordance with the well-kno
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wn r^3 - t law (r : mean radius, t : aging time) for all alloys investigated. The coarsening rate constant, k, increased with increasing delta' volume fraction and temperature. The derived value of the interfacial energy for the delta'/matrix interface was - 0.2 J/m^2.
The delta' particle size distribution (PSD) was found to have no strong dependence on aging time within the present investigation. The PSD, however, became more symmetrical with increasing volume fraction of the delta' phase. Although any of the particle-coarsening theories did not fully explain the experimentally obtained results for the delta' phase, the LSEM theory taking into account the encounter effect between particles explains weel the coarsening rate constant and PSDs. The small additional element Zr was found to produce fine composite particles and was effective to improve the mechanical properties. The obtained results are applicable to control and predict the precipitate microstructures and improve the properties of Al-Li alloys. Less
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Report
(3 results)
Research Products
(3 results)
