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Influence of Quenching Rates on the Transformation of Ternary Phases in Nb-rich γ-TiAl Alloys

Published online by Cambridge University Press:  20 January 2011

Andreas Stark ,
Michael Oehring  and
Florian Pyczak
Andreas Stark
Affiliation:
Institute of Materials Research, Helmholtz-Zentrum, Geesthacht Centre for Materials and Coastal Research, Max-Planck-Str. 1, D-21502 Geesthacht, Germany
Michael Oehring
Affiliation:
Institute of Materials Research, Helmholtz-Zentrum, Geesthacht Centre for Materials and Coastal Research, Max-Planck-Str. 1, D-21502 Geesthacht, Germany
Florian Pyczak
Affiliation:
Institute of Materials Research, Helmholtz-Zentrum, Geesthacht Centre for Materials and Coastal Research, Max-Planck-Str. 1, D-21502 Geesthacht, Germany
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Abstract

Intermetallic γ-TiAl based alloys with additional amounts of the ternary bcc β phase attracted increasing attention in recent years due to their improved workability at elevated temperatures. At lower temperatures the ductile high-temperature β phase can transform to several ordered phases. However, actually available phase diagrams of these multiphase alloys are quite uncertain and the precipitation kinetics of some metastable phases is far from understood.

In the present study various transformations of the third phase are observed in situ by means of high-energy x-ray diffraction using synchrotron radiation. A Ti-45Al-10Nb (at.%) specimen is subject to a temperature ramp of repeated heating cycles (700 °C - 1100 °C) with subsequent quenching at different rates. Depending on the quenching rate reversible transformations of the B2-ordered βo phase to different ω related phases are observed in Ti-45Al-10Nb. At low quenching rates the hexagonal B82-ordered ωo phase is formed while at high quenching rates the metastable intermediate trigonal ω’’ phase can be preserved. The results indicate that the complete transformation from βo to hexagonal B82-ordered ωo consists of two steps which are both diffusion controlled.

Keywords

phase transformationx-ray diffraction (XRD)crystallographic structure
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1295: Symposium N – Intermetallic-Based Alloys for Structural and Functional Applications , 2011 , mrsf10-1295-n03-07
Copyright
Copyright © Materials Research Society 2011

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