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Mechanical Behaviour of Nanocrystalline Copper Related to Grain-boundary Structure

Published online by Cambridge University Press:  01 February 2011

Y. Champion ,
P. Langlois ,
S. Guérin-Mailly ,
C. Langlois  and
M. J. Hÿtch
Y. Champion
Affiliation:
Centre d'Etude de Chimie Métallurgique – CNRS, 15 rue Georges Urbain 94407 Vitry-sur-Seine, France
P. Langlois
Affiliation:
LIMHP-CNRS, Université Paris XIII, 99 av. J.B Clément, 93430 Villetaneuse, France.
S. Guérin-Mailly
Affiliation:
Centre d'Etude de Chimie Métallurgique – CNRS, 15 rue Georges Urbain 94407 Vitry-sur-Seine, France
C. Langlois
Affiliation:
Centre d'Etude de Chimie Métallurgique – CNRS, 15 rue Georges Urbain 94407 Vitry-sur-Seine, France
M. J. Hÿtch
Affiliation:
Centre d'Etude de Chimie Métallurgique – CNRS, 15 rue Georges Urbain 94407 Vitry-sur-Seine, France
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Abstract

Understanding the mechanical behaviour of metallic nanostructures is a key issue for their development. On the one hand, knowledge of the plastic behaviour at various temperatures is essential to control the synthesis, forming, and machining of such materials. Equally, a clear understanding of atomic and mesoscopic mechanisms, involving defects and their interactions, is essential for the control of ageing and functional properties. Regarding plastic deformation at room temperature, there is now evidence for unusual behaviour in nanostructured metals. In addition to high resistance and ductility, tensile testing reveals peculiar elasto-plastic deformation. Such behaviour was initially attributed to grain-boundary sliding. However, intergranular areas (including triple junctions) may possess special properties compared to their microcrystalline counterparts. For example, low activation energies have been measured for grain-boundary diffusion and it has been observed that grain-boundaries may act as dislocation sources and nucleation sites for deformation twinning.

In this paper, we report on analysis on bulk copper nanostructures. Grain-boundaries are studied, by cross-correlating information from mechanical tensile testing and structural analysis, including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Macroscopic bulk specimens (with grain size of about 80 nm) are prepared by powder metallurgy techniques, modified to fit to the special properties of nanocrystalline powders. Processing includes coldisostatic pressing, sintering and differential extrusion. The powders used (grain size of 40 nm) are synthesised by evaporation and cryo-condensation of a metallic vapour within liquid nitrogen. Results on mechanical testing and structural analysis will be reported. Emphasis will be placed on the structure of grain-boundaries (type of grain-boundary, grain-boundary thickness) studied by TEM and high resolution TEM image analysed using the geometric phase technique. The nanostructure was revealed to be consist in agglomerate of nano-size grains separated by low angle grain-boundaries. Agglomerates are themselves separerated by general high angle boundaries. These observations will then be related to the unusual mechanical true stress-true strain curves of the metallic nanostructures.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 727: Symposium R – Nanostructured Interfaces , 2002 , R3.2
Copyright
Copyright © Materials Research Society 2002

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