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Crystallography of Bcc/T1/T2 Three-Phase Microstructure in the Directionally Solidified Mo-Nb-Si-B Alloy

Published online by Cambridge University Press:  09 February 2015

Naoki Takata ,
Nobuaki Sekido ,
Masao Takeyama  and
John H. Perepezko
Naoki Takata
Affiliation:
Dept. Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo, 152-8552, Japan
Nobuaki Sekido
Affiliation:
Research Center for Strategic Materials, National Institute for Materials Science, 1-2-1 Sengen Tsukuba, Ibaraki, 305-0047, Japan
Masao Takeyama
Affiliation:
Dept. Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo, 152-8552, Japan
John H. Perepezko
Affiliation:
Dept. Materials Science and Engineering, University of Wisconsin-Madison, 1509 University Avenue, Madison, WI 53706, U.S.A.
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Abstract

In the present study, the crystallographic features of bcc/T1/T2 three-phase microstructure in a directionally solidified Mo–32.2Nb–19.5Si–4.7B (at.%) alloy have been examined by electron back-scattering diffraction (EBSD) analysis. The alloy was directionally solidified using an optical floating zone (OFZ) furnace in a flowing Ar gas atmosphere at a constant growth rate of 10 mm/hour. The microstructure of the directionally solidified alloy is characterized by an elongated T2 phase surrounded by inclusions of bcc and T1 phases with an interwoven morphology. The T2 grains are faceted on the (001) planes and elongated along the [110] direction. The T2 phase has an orientation relationship of (001)T2 // (011)bcc and [130]T2 // [2${\rm{\bar 1}}$1]bcc with the bcc phase, whereas any particular orientation relationships of T1 phase with bcc and T2 phases have not been found. These crystallographic features of bcc/T1/T2 three-phase microstructure suggest that the primary T2 phase crystallizes and grows along the [110] direction in liquid phase, followed by nucleation of the bcc phase on the interface between T2 and liquid phases, resulting in bcc/T1 two-phase eutectic reaction surrounding the elongated T2 phase.

Keywords

directional solidificationmicrostructurescanning electron microscopy (SEM)
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1760: Symposium YY – Advanced Structural and Functional Intermetallic-Based Alloys , 2015 , mrsf14-1760-yy03-03
Copyright
Copyright © Materials Research Society 2015 

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References

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