Precipitate effects on the mechanical behavior of aluminum copper alloys: Part I. Experiments
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I. INTRODUCTION
PRECIPITATION-HARDENED alloys are a commercially important group of materials because their mechanical properties can be modified by heat treating and changing the microstructure. Precipitates introduced into the matrix interact with dislocations and affect their mobility, allowing control of the mechanical behavior of the material. Precipitate morphology, orientation, spacing, and degree of coherency with the matrix all contribute to the effectiveness of the precipitate as a barrier to dislocation motion. In addition, the mechanical behavior of a material can be influenced by its microstructure through processing steps during fabrication. These procedures can strengthen the original microstructure by refining the grain size. Orienting the grains in a particular direction can impact the mechanical behavior. To understand the causes of the changing mechanical properties of these materials, it is essential to characterize the microstructure and investigate the underlying deformation mechanisms. The ease of plastic deformation depends on the crystallographic orientation of the material. However, a common microstructural feature of high-strength aluminum-copper alloys are plate-shaped precipitates that form on the cube faces of the fcc structure. These precipitates have an anisotropic contribution to the flow strength of the material such that crystallographically “soft” orientations are hardened by precipitates. In the first part of this series of articles, we will describe this anisotropy with experiments on single crystals of aluminum copper with selected orientations. Since the goal of this work is to develop a physically-based hardenH. SEHITOGLU, C.J. Ganthier Professor and Interim Head, is with the Department of Mechanical and Industrial Engineering, University of Illinois, Urbana, IL 61801. Contact e-mail: [email protected] T. FOGLESONG formerly with the Department of Mechanical and Industrial Engineering, University of Illinois, Urbana, IL 61801, is Research Engineer, with Exxon Mobile Upstream Research Company, Houston, TX 77046. H.J. MAIER, Professor, is with the Department of Materials Science, University of Paderborn, D-33905 Paderborn, Gemany. Manuscript submitted October 6, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS A
ing law that can be incorporated into a polycrystal model and predict the stress-strain behavior through a variety of aging treatments, precipitate-induced anisotropy must also be accounted for in the work hardening description. The modeling is described in Part II of this series of articles. The issues discussed previously are addressed in this work through mechanical experiments and microstructural analysis. The mechanical experiments are conducted under compression loadings at room temperature and the microstructural analysis involves transmission electron microscopy (TEM) of virgin and deformed samples and texture analysis for the polycrystalline cases. Ultimately, the research described in Part I of this series of articles links micromechanical deformation mechanisms
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