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Strain-Rate Dependence of the Brittle-to-Ductile Transition Temperature in TiAl

Published online by Cambridge University Press:  21 March 2011

M. Khantha ,
V. Vitek  and
D. P. Pope
M. Khantha
Affiliation:
Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104–6272
V. Vitek
Affiliation:
Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104–6272
D. P. Pope
Affiliation:
Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104–6272
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Abstract

The brittle-to-ductile transition (BDT) and the strain-rate dependence of the brittle-to-ductile transition temperature (BDTT) have been recently investigated in single crystals of TiAl [1]. It was found that the activation energy associated with the BDTT is 1.4 eV when the slip is dominated by ordinary dislocations and 4.9 eV when it is dominated by superdislocations. Despite this difference in the activation energies, the BDTT, while varying with the strain-rate, remains in the same temperature range, viz., between 516–750C and 635–685C for ordinary and superdislocations, respectively. In this paper, we examine how the activation energy of the BDTT can vary with the type of dislocation activity and explain why it can attain values which are clearly much larger than the activation energy for dislocation motion. We describe a strain-rate dependent mechanism of cooperative dislocation generation in loaded solids above a critical temperature and use it to explain the characteristics of the BDT in TiAl. We show that the activation energy associated with the BDTT is a composite value determined by two or more inter-dependent thermally activated processes and its magnitude can be much larger than the activation energy for dislocation motion in certain materials. The predictions of the model are in good agreement with observations in TiAl.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 646 , 2000 , N1.11.1
Copyright
Copyright © Materials Research Society 2001

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References

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