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Microcrack Nucleation and Crack Propagation in Equiaxed γ TiAl

Published online by Cambridge University Press:  11 February 2011

Martin A. Crimp ,
Boon-Chi Ng ,
Benjamin A. Simkin  and
Thomas R. Bieler
Martin A. Crimp
Affiliation:
Department of Chemical Engineering and Materials Science, Michigan State University East Lansing, MI 48824, USA
Boon-Chi Ng
Affiliation:
Department of Chemical Engineering and Materials Science, Michigan State University East Lansing, MI 48824, USA
Benjamin A. Simkin
Affiliation:
Department of Chemical Engineering and Materials Science, Michigan State University East Lansing, MI 48824, USA
Thomas R. Bieler
Affiliation:
Department of Chemical Engineering and Materials Science, Michigan State University East Lansing, MI 48824, USA
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Abstract

To gain a better understanding of the ductility limitations in TiAl alloys, the mechanisms involved in deformation strain transfer and/or microcrack initiation at grain boundaries have been examined in an equiaxed near-γ alloy. These studies have been carried out on both in-situ and ex-situ deformed bulk samples using scanning electron microscopy (SEM) techniques for both orientation analysis and deformation defect imaging. Selected area electron channeling patterns (SACPs) have allowed determination of grain orientations, eliminating ambiguity between the a and c axes. Deformation twins and dislocations have been imaged in the bulk samples using electron channeling contrast imaging (ECCI). A combination of ECCI contrast analysis and trace analysis based on orientations determined from SACP has allowed identification of the active deformation systems. Microcracks have been found to initiate at γ-γ boundaries as a result of an inability to adequately transfer twin strain from grain to grain. Once initiated, cracks propagate through cleavage and re-nucleation of grain boundary microcracks in front of the advancing crack. A geometric based predictive factor has been developed that accounts for microcrack initiation at γ-γ boundaries based in deformation twinning and strain accommodation by ordinary dislocations.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 753: Symposium BB – Defect Properties and Related Phenomena in Intermetallic Alloys , 2002 , BB3.8
Copyright
Copyright © Materials Research Society 2003

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References

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