2004 Fiscal Year Final Research Report Summary
Alloy Design for Austenitic Heat-resisting Steels Strengthened by Intermetallic Compounds
| Project/Area Number |
14205102
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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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 Tokyo institute of Technology, Dept Metallurgy and Ceramics Science, Associate Professor, 大学院・理工学研究科, 助教授 (30251622)
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| Co-Investigator(Kenkyū-buntansha) |
YAMAMOTO Yukinori Tokyo institute of Technology, Dept Metallurgy and Ceramics Science, Assistant Professor, 大学院・理工学研究科, 助手 (30334543)
MATSUO Takashi Tokyo institute of Technology, Dept Metallurgy and Ceramics Science, Professor, 大学院・理工学研究科, 教授 (10089823)
HASHIMOTO Kiyoshi Materials Design Technology Co., Ltd, Director, 研究部長
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| Project Period (FY) |
2002 – 2004
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| Keywords | C14 structure / C15 structure / DO_<22>structure / Lattice Parameters / Lattice misfit / Phase equilibria / Precipitation morphology / Microstructure control |
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| Research Abstract |
This research has focused on the phase equilibria, phase transformations and precipitation behavior of TCP and GCP compounds in Fe-Ni-M(M : transition metals) ternary systems at elevated temperatures, in order to get insight into a new concept for alloy development of austenitic heat resisting steels strengthened by intermetallic phases. As strengthening species, Fe_2Nb Laves(TCP) and Ni_3V(GCP) phases are used.
Among Fe-Ni-M ternary systems, Fe_2Nb with C14 crystal structure has an extended composition homogeneity region and it can be in equilibrium with γ-Fe phase (Al). For example, Ni atoms can substitute for more than a half of Fe sublattice, and Zr atoms for twp-third of the Nb sublattice sites. Thus, solid solution alloying controls the lattice parameters of C14 structure, and the Laves phase can homogeneously precipitates in the γ matrix when its lattice parameter ratio (c/a) becomes 1.633. Based on these findings, we proposed a model Fe-Ni-Cr-Nb alloy.
The Ni_3V with DO_<22> structure quenched from the high-temperature disordered Al (fcc) phase region consists of an unique multi-variant structure (MVS) with two habits planes of {010}と{101} due to its tetragonality (a_<DO22><a_<Al><c_<DO22>). We identified the formation mechanism and its composition region of MVS. The morphology of the Al/DO_<22> two-phase MVS can be intentionally changed to either "Maze" or "Chessboard", by controlling the misfit. We extended these findings to multi-component system by substituting Ni with Fe and V with Nb, and showed ways to develop austenitic steels strengthened by the intermetallic phases.
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