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High-Temperature Phase Transformation in Cr Added TiAl Base Alloy

Published online by Cambridge University Press:  10 February 2011

E. Abe ,
K. Niinobe ,
M. Nobuki ,
M. Nakamura  and
T. Tsujimoto
E. Abe
Affiliation:
National Research Institute for Metals, Tsukuba, JAPAN,
K. Niinobe
Affiliation:
Ibaraki University, Faculty of Engineering, Hitachi, JAPAN.
M. Nobuki
Affiliation:
National Research Institute for Metals, Tsukuba, JAPAN,
M. Nakamura
Affiliation:
National Research Institute for Metals, Tsukuba, JAPAN,
T. Tsujimoto
Affiliation:
Ibaraki University, Faculty of Engineering, Hitachi, JAPAN.
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Abstract

We have investigated a microstructure evolution of a Ti-48Al-3.5Cr (in at.%) alloy at high-temperatures (>1473K). In the alloy annealed at 1673K for 1.8ks, followed by air-cooling, a characteristic microstructure with a feathery fashion was uniformly formed. From a cooling-rate-controlling study, it was found that formation of the feathery structure is accomplished during continuous cooling from 1673K to 1573K, within the α+γ two-phase region. Transmission electron microscopy revealed that the feathery structure is composed of lamellar colonies (5–10µm) which are crystallographicaly tilted slightly (a few degree) with their neighbors. A surprising fact is that lamellae in each colony are mostly the γphase with few α2 phase less than 5% in volume. This suggests that the feathery structure is a metastable product and has not resulted from the α → α+γ transformation above 1573K. Instead, the feathery structure formation should be attributed to the non-equilibrium α → γtransformation which occurs at high-temperatures with a small degree of supercooling. We discuss this interesting phase transformation in terms of the α→γ massive transformation, based on the continuous-coolingtransformation (CCT) diagram constructed for the present alloy.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 552: Symposium KK – High-Temperature Ordered Intermetallic Alloys VIII , 1998 , KK2.10.1
Copyright
Copyright © Materials Research Society 1999

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References

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