Electron microscopy nanoscale characterization of ball-milled Cu-Ag powders. Part I: Solid solution synthesized by cryo-milling

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 conventional dark-field imaging, selected area diffraction and energy dispersive X-ray spectrometry (EDS) to more modem 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 morphologies, 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. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.