HRTEM study of defects in twin boundaries of ultra-fine grained copper

Abstract

Twin boundaries (TBs) in ultra-fine grained (UFG) copper prepared by powder metallurgy were investigated using high-resolution transmission electron microscopy (HRTEM) and geometric phase analysis (GPA). Specimens were analyzed both before and after mechanical deformation (compression of 40%) and emphasis placed on the study of TB defects. Twin boundaries in the as-processed specimens are mainly disoriented from the perfect Σ3 coincidence. They present a faceted structure with coherent {111} and incoherent {112} facets. The latter have a 9R structure and the {111}/{112} junctions are associated with sessile dislocations of Frank type . Shockley glissile dislocations with Burgers vector of type are also present. This microstructure is interpreted in terms of the absorption and decomposition at room temperature of lattice dislocations (60° type). After mechanical deformation, an enrichment of twins at dislocations and a decrease of step density and height is observed and quantified by statistical analysis. Deformation mechanisms of UFG copper are discussed in light of these observations.

Acknowledgements

The authors would like to thank Cyril Langlois, Jean-Louis Bonnentien and Patrick Langlois for providing the UFG Cu specimens, and Cécilie Duhamel and Sandrine Guerin for carrying out the compression tests. Professor Louisette Priester is gratefully acknowledged for valuable discussions and her critical reading of the manuscript.

Notes

†Currently at CEMES-CNRS, 28 rue Jeanne Marvig, 31055 Toulouse, France.

Additional information

Notes on contributors

M. J. Hÿtch†

†Currently at CEMES-CNRS, 28 rue Jeanne Marvig, 31055 Toulouse, France.