Effects of precipitates in Cu upon impact fracture: An ultra-high-vacuum study with local probe scanning Auger/electron microscopy

In situ fracture under ultra-high vacuum (UHV) conditions of copper-alloys containing copper sulfide precipitates exhibits areas in the form of pits. The wide variety of morphologies depends significantly on the size of the existing precipitate. For large precipitates. the fractured surface reveals loops surrounded by step-terrace like structures with sulfur remaining preferentially on straight ledges as nanometer scale Auger images reveal in comparison with scanning electron images. For smaller precipitates (< 3-4 mu m). only well defined Facets are formed having an almost uniform distribution of sulfur. Qualitatively the loop and Facet formation could be explained due to accommodation of the Cu sulfide to the Cu matrix. leading for small precipitates to Facet Formation. and for large ones to step-terrace structures. Asymmetry in loop structures could be attributed to asymmetry of precipitate shape, while in some areas plasticity effects are also present. Finally, a comparison with distinctly different behavior in Cu-Bi alloys is made. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.