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Initial Stages of Lamellae Formation in High Nb Containing γ-TiAl Based Alloys

Published online by Cambridge University Press:  21 September 2018

Limei Cha ,
Christina Scheu ,
Gerhard Dehm ,
Ronald Schnitzer  and
Helmut Clemens
Limei Cha
Affiliation:
Materials Center Leoben Forschung GmbH, Leoben, Austria Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Austria
Christina Scheu
Affiliation:
Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Austria Department Chemistry and Biochemistry Ludwig-Maximilians-University Munich, Germany
Gerhard Dehm
Affiliation:
Department of Materials Physics, Montanuniversität Leoben, and Erich-Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben, Austria
Ronald Schnitzer
Affiliation:
Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Austria
Helmut Clemens
Affiliation:
Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Austria
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Abstract

In this study a two-step heat treatment was applied to high Nb containing γ-TiAl based alloys in order to investigate the initial stage of the lamellae formation in ordered α2-grains as well as in massively transformed γm-grains. The first heat treatment step, conducted in the single α-phase field followed by oil quenching, leads to a microstructure consisting of supersaturated α2-grains and a small volume fraction of γm-grains. The second step of the heat treatment was performed below the eutectoid temperature, i.e. within the (α2+γ)-phase field region and was again followed by oil quenching. There, the formation of ultra-fine γ-lamellae takes place in the α2-grains and (some) fine α2-lamellae are formed in the γm-grains. In both cases the lamellae show a Blackburn orientation relationship with the matrix grain. It was found that the precipitation of γ-laths in the supersaturated α2-grains is faster than the formation of α2-laths in γm-grains. The characteristics of the initial stage of formation were investigated by transmission electron microscopy.

Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1128: Symposium U – Advanced Intermetallic-Based Alloys for Extreme Environment and Energy Applications , 2008 , 1128-U04-07
Copyright
Copyright © Materials Research Society 2009

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