Nano-lamellar Structures in a Rolled Cu-Ag Alloy
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Nano-lamellar Structures in a Rolled Cu-Ag Alloy Mark T. Lyttle and D.A. Hughes Materials Research Department, Sandia National Laboratories Livermore, California 94550, U.S.A. ABSTRACT The microstructural evolution and texture development in a Cu-Ag eutectic during rolling are systematically investigated. A directionally solidified Cu-Ag alloy with a single dominant texture is deformed to several rolling reductions. At each of these strains, the microstructure and texture are characterized. Rapid divergence of local crystal orientations leads to the early development of high-angle Cu-Ag boundary/interface orientations, while less misorientation accumulation occurs within the individual copper and silver layers. With increasing deformation, orientations of the copper and silver phases in a single region are observed to diverge to two distinct textures, and within each of the single phases, there is a greater spread of orientations of individual cells while still retaining an identifiable preferred orientation. INTRODUCTION The evolution of microstructure and texture in a Cu-Ag eutectic during rolling deformation is examined. Much work has been performed to characterize the microstructures that develop during the deformation of single phase fcc metals, but there has been relatively little investigation of the related two-phase materials. Specifically, the texture and microstructural evolution of copper (and to a lesser extent, silver) during deformation has been heavily examined, but the question remains whether the structures within the individual phases of a CuAg eutectic will develop in the same manner as observed in the pure metals, or if any new characteristic structures or textures develop. Technologically, the development of a fine layered Cu-Ag eutectic is desirable for high strength, high conductivity applications [1]. Current methods for constructing this layered structure, such as, vapor deposition and Taylor wire, can produce only small specimens and are expensive to develop and maintain. The ability to produce a very small-scale layered structure by mechanical deformation would enable much larger products to be more efficiently produced. The potential for high strength and high conductivity in the Cu-Ag eutectic and other similar Cu-based eutectics, i.e. a subset of the so-called in situ composites, has been long known [2,3]. Most of the previous research on these Cu-based eutectics has focused on quantifying the strength increases due to various production techniques and deformation conditions [4-6]. Other than brief qualitative assessment of micrographs, little work has been done to characterize the structures and textures that develop during these deformation processes and directly contribute to the increase in strength. Deformation has been observed to produce similar microstructures in a wide variety of fcc pure metals and related alloys. Largely independent of deformation mode, a general framework has been developed to describe the types of structures that have been seen repeatedly in aluminum, copp
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