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A1→D022 Transformation and Multi-Variant Structure of Ni3V

Published online by Cambridge University Press:  11 February 2011

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

The formation mechanism and morphology of the tetragonal compound Ni3V (D022) quenched from the disordered fcc (A1) state have been examined by TEM using a Ni-25at%V. The alloy is fully transformed to D022 in the quenched state. The resulting microstructure exhibits a fine brick-like “multi-variant structure (MVS)” consisting of one major and two minor variants with c axes perpendicular each other, having coherent interfaces of {102)D022 and {100)D022. The major variant particles with a quadrangular-prism shape are alternately arrayed with two minor variants, one parallel to {102)D022 and the other {100)D022, respectively. The thermal APDs are formed in the all variants, but the average size within the major is larger than that in the minors. The c/a ratio of the D022 in the MVS is 2.006, much smaller than the value (2.04) in equilibrium state. From all these facts, the transformation of A1→D022 is assumed to proceed through a selective nucleation and growth of tetragonal A6 phase, followed by ordering to D022. The formation of the tetragonal phase produces an anisotropic strain field due to the contraction and expansion of the a and c axes against the cubic matrix. The strain field makes {102)D022 and {100)D022 with the invariant lines become habit, and also drives the selective nucleation and growth of minor variants to minimize the elastic strain energy, thereby leading to the multi-variant structure.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 753: Symposium BB – Defect Properties and Related Phenomena in Intermetallic Alloys , 2002 , BB5.31
Copyright
Copyright © Materials Research Society 2003

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References

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