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In-Situ TEM Study of Plastic Stress Relaxation Mechanisms and Interface Effects in Metallic Films

Published online by Cambridge University Press:  01 February 2011

Marc Legros
Affiliation:
CEMES-CNRS, 29 rue J. Marvig, 31055 Toulouse -France
Gerhard Dehm
Affiliation:
Erich Schmid Institute for Materials Science and University of Leoben, Department Materials Physics, Jahnstr. 12, 8700 Leoben - Austria
T. John Balk
Affiliation:
Dept. of Chemical and Materials Engineering, University of Kentucky, Lexington, KY, USA
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Abstract

To investigate the origin of the high strength of thin films, in-situ cross-sectional TEM deformation experiments have been performed on several metallic films attached to rigid substrates. Thermal cycles, comparable to those performed using laser reflectometry, were applied to thin foils inside the TEM and dislocation motion was recorded dynamically on video. These observations can be directly compared to the current models of dislocation hardening in thin films. As expected, the role of interfaces is crucial, but, depending on their nature, they can attract or repel dislocations. When the film/interface holds off dislocations, experimental values of film stress match those predicted by the Nix-Freund model. In contrast, the attracting case leads to higher stresses that are not explained by this model. Two possible hardening scenarios are explored here. The first one assumes that the dislocation/interface attraction reduces dislocation mobility and thus increases the yield stress of the film. The second one focuses on the lack of dislocation nucleation processes in the case of attracting interfaces, even though a few sources have been observed in-situ.

Type
Research Article
Copyright
Copyright © Materials Research Society 2005

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