Acta Materialia 50 (2002) 4695–4709 www.actamat-journals.com Electron microscopy nanoscale characterization of ball- milled Cu–Ag powders. Part I: Solid solution synthesized by cryo-milling S. Zghal a,b , M.J. Hy ¨tch c , J.-P. Chevalier c,d , R. Twesten a , F. Wu b , P. Bellon a,b,* a Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA b Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA c Centre d’Etudes de Chimie Me ´tallurgique, CNRS, 15, rue Georges Urbain, Vitry-sur-Seine 94407, France d Chaire des Mate ´riaux Industriels, Conservatoire National des Arts et Me ´tiers, 2, rue Conte ´, Paris 75003, France Received 25 October 2001; received in revised form 8 May 2002; accepted 4 July 2002 Abstract We present a study of nanostructured Cu–Ag material obtained by low temperature ball milling. The microstructural characterization is carried out using a wide variety of transmission electron microscopy (TEM) techniques from conven- tional dark-field imaging, selected area diffraction and energy dispersive X-ray spectrometry (EDS) to more modern techniques of scanning TEM high-angle dark-field imaging (HAADF), nanodiffraction and high resolution imaging (HREM). A novel method of HREM image analysis is also presented which consists of calculating geometric phase images by Fourier filtering. Real-space maps of lattice spacings and lattice rotations are thus obtained. The analysis addresses the following essential points of nanostructural characterization: dislocation densities, grain sizes and morpho- logies, grain boundaries and local lattice rotations, local textures, local variations in lattice parameters. A new description of the microstructure emerges from the observations, quite different to that expected. Analytical modeling suggests that large lattice rotations can be expected in nanomaterials produced by intense deformation.  2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved. Keywords: Ball milling; Transmission electron microscopy; Alloys (copper, silver); Nanomaterials; Cold-working 1. Introduction Nanostructured materials in general have drawn considerable attention [1] over the past decade for * Corresponding author. Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. Tel.: +1 217 265 0284; fax: +1-217- 333-2736. E-mail address: bellon@uiuc.edu (P. Bellon). 1359-6454/02/$22.00.  2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved. PII:S1359-6454(02)00285-9 a number of reasons. Specific and interesting properties are anticipated, ranging, for example, from higher yield strain and superplastic forming, to magnetic properties and catalytic activity. From a fundamental point of view, the validity of the extrapolation of properties, both physical and chemical, to such small grain sizes is of major interest. Ball milling (or mechanical alloying) is a convenient means of obtaining nanostructured materials, as well as other non-equilibrium phases,