| Project/Area Number |
09450258
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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 | Tokyo Institute of Technology |
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Principal Investigator |
TAKEYAMA Masao Dipt. Metallurgy and ceumes Science Graduate Sch of Science an Engineering Associate Professor, 大学院・理工学研究科・材料工学専攻, 助教授 (30251622)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUO Takashi Dipt. Metallurgy and ceumes Science Graduate Sch of Science an Engineering Associate Professor, 大学院・理工学研究科・材料工学専攻, 教授 (10089823)
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| Project Period (FY) |
1997 – 1999
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| Project Status |
Completed (Fiscal Year 1999)
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| Budget Amount *help |
¥14,000,000 (Direct Cost: ¥14,000,000)
Fiscal Year 1999: ¥1,500,000 (Direct Cost: ¥1,500,000)
Fiscal Year 1998: ¥8,200,000 (Direct Cost: ¥8,200,000)
Fiscal Year 1997: ¥4,300,000 (Direct Cost: ¥4,300,000)
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| Keywords | Ni_3 Nb-S / Ni-Nb-M / Lattice misfit / Crystal structure / Misfit dislocation / Symmetry of crystal / Precipitation / Micrpstructure contral / 構造緩和 / ミスフィット転位 / 格子定数 / Ni_3 Nb-S / Nib Nb sl-η / 一方向擬固 / 結晶方位関係 / Nb / 対称性 |
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| Research Abstract |
The intermetallic compound Ni_3Nb (δ) is of interest as a strengthener of Ni base alloys because of its phase stability up to the melting temperature. The crystal structure of the δ phase is ordered orthorhombic (DO_a structure), the lowest crystal symmetry among the A_3B compounds with close-packed structure. Thus, in order to use the δ phase as a strengthener, it is important to find the way to change its precipitation morphology more fine and uniform. The misfit accommodation between the δ and γ phases by alloying is one of the effective ways to change its morphology. In this study, phase equilibria among the phases including γ-nickel solid solution and Ni_3Nb-δ in Ni-rich corner of Ni-Nb-M (M : Fe, Co, Al, Ti, V) ternary systems at elevated temperatures have been examined. We have found that the solid solubility of δ phase field in these systems, and the crystal structure becomes more symmetrical by the addition these element but Al.
Based on the knowledge of phase diagrams and crystal symmetry, , the effect of Fe, for example, on precipitation of the δ phase in the γ Ni solid solution was studied. The addition of Fe drastically refines the morphology of the δ precipitates. TEM weak beam analysis revealed the a-axis misfit dislocation density increases with Fe content. This is because of the increase in the lattice misfit along the a-axis. The introduction of the misfit dislocations makes the growth kinetics sluggish, which is responsible for the refinement of the δ precipitates in Fe containing alloys. The effects of other elements on the precipitation kinetics and morphology of the δ phase have been demonstrated, and the alloy design using the δ phase by controlling the morphology has been demonstrated.
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