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Effects of long-period superstructures on plastic properties in Al-rich TiAl single crystals

Published online by Cambridge University Press:  26 February 2011

Takayoshi Nakano ,
Koutaro Hayashi ,
Yukichi Umakoshi ,
Yu-Lung Chiu  and
Patrick Veyssière
Takayoshi Nakano*
Affiliation:
Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2–1, Yamada-oka, Suita, Osaka 565–0871, Japan
Koutaro Hayashi
Affiliation:
Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2–1, Yamada-oka, Suita, Osaka 565–0871, Japan
Yukichi Umakoshi
Affiliation:
Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2–1, Yamada-oka, Suita, Osaka 565–0871, Japan
Yu-Lung Chiu
Affiliation:
Laboratoire d'Etude des Microstructures, CNRS-ONERA, BP72, 92322 Châtillon cedex, France
Patrick Veyssière
Affiliation:
Laboratoire d'Etude des Microstructures, CNRS-ONERA, BP72, 92322 Châtillon cedex, France
*
*) E-mail: nakano@mat.eng.osaka-u.ac.jp
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Abstract

In Al-rich TiAl crystals, several long-period superstructures may appear depending on Al composition, annealing temperature and annealing time. Amongst these, Al5Ti3 and h-Al2Ti contain pure Al (002) layers, as in the L10 structure of the matrix, alternating with Ti (002) layers that exhibit an ordered arrangement of the Al atoms in excess. In single crystals with compositions ranging from Ti-54.7at.%Al to Ti-62.5at.%Al annealed at 1200°C, the Al5Ti3 long-period superstructure embedded in the L10 matrix develops with increasing Al concentration to finally transform fully into h-Al2Ti for Ti-62.5at.%Al. On the other hand, Al5Ti3 precipitates grow with annealing time at 500°C in Ti-58.0at.%Al.

The effects of the Al5Ti3 and h-Al2Ti superstructures on slip properties of 1/2<110] ordinary dislocations are examined both at a macroscopic and a microscopic level. The CRSS for 1/2<110] ordinary slip increases with Al5Ti3 ordering depending on Al composition, or of annealing time in the case of Ti-58.0at.%Al. Dislocations with 1/2<110] Burgers vector group into fourfold configurations to avoid the trailing of extended APBs in Al5Ti3. The CRSS for slip in the <110] direction further increases with the formation of h-Al2Ti particles within the L10 matrix in Ti-62.5at.%Al. By contrast, Ti-62.5at.%Al fully transformed into Al5Ti3 exhibits a CRSS significantly lower than that of the two-phase alloy.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 842: Symposium S – Integrative and Interdisciplinary Aspects of Intermetallics , 2004 , S7.4
Copyright
Copyright © Materials Research Society 2005

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References

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