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Creep Behavior and Microstructural Stability of Ti-46Al-9Nb with Different Microstructures

Published online by Cambridge University Press:  26 February 2011

S. Bystrzanowski ,
A. Bartels ,
H. Clemens ,
R. Gerling ,
F.-P. Schimansky  and
G. Dehm
S. Bystrzanowski
Affiliation:
Materials Science and Technology, TU Hamburg-Harburg, D-21073 Hamburg, Germany
A. Bartels
Affiliation:
Materials Science and Technology, TU Hamburg-Harburg, D-21073 Hamburg, Germany
H. Clemens
Affiliation:
Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, A-8700 Leoben, Austria
R. Gerling
Affiliation:
Institute for Materials Research, GKSS-Research Centre, D-21502 Geesthacht, Germany
F.-P. Schimansky
Affiliation:
Institute for Materials Research, GKSS-Research Centre, D-21502 Geesthacht, Germany
G. Dehm
Affiliation:
Max-Planck-Institut für Metallforschung, D-70569 Stuttgart, Germany
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Abstract

In this paper the creep behavior and the microstructural stability of Ti-46Al-9Nb (in at.%) sheet material were investigated in the temperature range of 700°C to 815°C. The study involves three different types of microstructure, namely fully lamellar with narrow lamellar spacing, duplex and massively transformed. Short-term creep experiments conducted at 700°C and 225 MPa confirmed that the lamellar microstructure with narrow lamellar spacing exhibits a much higher creep resistance when compared to the massively transformed and duplex ones. During longterm creep tests up to 1500 hours stress exponents (in the range of 4.4 to 5.8) and apparent activation energies (of about 4 eV) have been estimated by means of load and temperature changes, respectively. Both, stress exponents and activation energies suggest that under the applied conditions diffusion-assisted climb of dislocations is the dominant creep mechanism. The thermal stability of the different microstructures under various creep conditions has been analyzed by electron microscopy and X-ray diffraction. Our investigations revealed considerable stress and temperature induced microstructural changes which are reflected in the dissolution of the α2 phase accompanied by precipitation of a Ti/Nb - rich phase situated at grain boundaries. This phase was identified as a ω-related phase with B82-type structure. It was shown, that in particular the duplex microstructure is prone to such microstructural instabilities.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 842: Symposium S – Integrative and Interdisciplinary Aspects of Intermetallics , 2004 , S7.12
Copyright
Copyright © Materials Research Society 2005

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References

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