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Phase Equilibria and Lattice Parameters of Fe2Nb Laves Phase in Fe-Ni-Nb Ternary System at Elevated Temperatures

Published online by Cambridge University Press:  26 February 2011

Masao Takeyama ,
Nobuyuki Gomi ,
Sumio Morita  and
Takashi Matsuo
Masao Takeyama
Affiliation:
Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2–12–1 Ookayama, Meguro-ku, Tokyo 152–8552, JAPAN
Nobuyuki Gomi
Affiliation:
Graduate Student
Sumio Morita
Affiliation:
Graduate Student
Takashi Matsuo
Affiliation:
Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2–12–1 Ookayama, Meguro-ku, Tokyo 152–8552, JAPAN
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Abstract

Phase equilibria in Fe-Ni-Nb ternary system at elevated temperatures have been examined, in order to identify the two-phase region of γ-Fe (austenite) and ε-Fe2Nb (C14). The ε single phase region exists in the range of 27.5 to 35.5 at.% Nb in the Fe-Nb binary system, and it extends toward the equi-niobium concentration direction up to 44 at.% Ni in the ternary system at 1473 K, indicating that more than half of the Fe atoms in Fe2Nb can be replaced with Ni. Thus, the γ+ε two-phase region exists extensively, and the solubility of Nb in γ phase increases from 1.5 to 6.0 at.% with increase in Ni content. The lattice parameters of a and c in the C14 Laves phase decrease with increasing Ni content. The change in a axis is in good agreement with calculation based on Vegard's law, whereas that of c axis is much larger than the calculated value. The result suggests that atomic size effect is responsible for a-axis change and the binding energy is dominant factor for the c-axis change. To extend these findings to development of new class of austenitic steels strengthened by Laves phase, an attempt has been made to control the c/a ratio by alloying. The addition of Cr is effective to make the c/a ratio close to the cubic symmetry value (1.633).

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 842: Symposium S – Integrative and Interdisciplinary Aspects of Intermetallics , 2004 , S5.37
Copyright
Copyright © Materials Research Society 2005

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References

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