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A Mechanism of Polycrystallization in Fully Lamellar Ti-48Al-8Nb Single Crystal Alloy Aged at Elevated Temperatures

Published online by Cambridge University Press:  11 February 2011

Yukinori Yamamoto ,
Masao Takeyama  and
Takashi Matsuo
Yukinori Yamamoto
Affiliation:
Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2–12–2 Ookayama, Meguro-ku, Tokyo 152–8552, Japan
Masao Takeyama
Affiliation:
Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2–12–2 Ookayama, Meguro-ku, Tokyo 152–8552, Japan
Takashi Matsuo
Affiliation:
Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2–12–2 Ookayama, Meguro-ku, Tokyo 152–8552, Japan
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Abstract

Polycrystallization mechanism of a fully lamellar microstructure during aging at 1473 and 1273 K has been examined using Ti-48Al-8Nb fully lamellar single crystal, which consists mostly of γ/γ interfaces (variant, perfect-twin and pseudo-twin boundaries). After a certain period of aging, a few γ grains are formed within the lamellae and the lamellar microstructure collapses rapidly to become a γ grained microstructure at both temperatures. An EBSP analysis for aged sample revealed that most of the grains follow the orientation of variant domains in the lamellar microstructure. A kinetic analysis of the grain growth during aging revealed that the activation enthalpy of the growth rate is estimated to be 390 kJ/mol, which is very close to that for volume diffusion coefficient of Al and Nb in γ-TiAl. Based on the results, it is concluded that the formation of the grains is attributed to coarsening of variant domains within the lamellar plates and coalescence of the same variant domains across the lamellae, leading to a γ grained microstructure following the orientation of variant domains. These reactions also make the number of the variant domains decrease during aging, which remains only two variant domains with perfect-twin relationship.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 753: Symposium BB – Defect Properties and Related Phenomena in Intermetallic Alloys , 2002 , BB5.5
Copyright
Copyright © Materials Research Society 2003

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