Plastic Deformation Behavior and Microstructural Evolution of Al-Core/Cu-Sheath Composites in Multi-pass Caliber Rolling
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INTRODUCTION
CORE-SHEATH composites with wire or bar shapes are widely used in structural materials[1–3] and functional materials.[4–7] Several fabricating processes for the core-sheath composites, such as extrusion,[8–10] drawing,[11,12] rolling forming,[13–18] and solid state diffusion,[19] have been used successfully. However, insufficient interface bonding is a significant problem in the core-sheath composites that are used for structural applications, as in other types of composite materials (e.g., particulate, fibrous, or layered). In order to improve the interface bonding and reliability of the layered and core-sheath composites, multiple pass and/ or elevated temperature processing is recommended. Severe plastic deformation (SPD)[20–24] is a multiple pass or repeating metal forming process for superplasticity/strength enhancement through grain refinement. In addition to the strengthening effect, multiple pass processing can enhance the homogeneity of the deformation (stress and strain) in workpieces, typically through rolling,[25,26] pressing,[27,28] and extrusion.[8–10] It should be noted that the enhanced homogeneity in the JUNG GI KIM, Research Assistant, is with the Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea. MARAT I. LATYPOV and DONG JUN LEE, Postdoctoral Research Associates, SUNGHAK LEE and HYOUNG SEOP KIM, Professors, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784, Korea. Contact e-mail: [email protected] HA-GUK JEONG, Director, and JONG BEOM LEE, Researcher, are with the Production Technology R&D Department, Korea Institute of Industrial Technology (KITECH), Incheon, 406-840, Korea. Manuscript submitted February 3, 2014. Article published online October 15, 2014 260—VOLUME 46A, JANUARY 2015
deformation is related to the stress saturation with increased strain; that is, it decreases the strain-hardening rate with strain in most metallic materials. Recently, caliber rolling has garnered significant attention, particularly in the material science and engineering communities, due to its capability of excellent grain refinement and relatively easy-to-handle processing.[29] Caliber rolling has been predominantly applied to single materials; however, it is worthwhile attempting to apply caliber rolling to core-sheath composites for strengthening through cold forming (i.e., grain refinement and dislocation density increase) as well as improving interface bonding through multiple processing. In general, core materials are harder and less ductile while sheath materials, which receive more deformation than the core material, should be softer and more ductile. However, this combination is not absolute. Numerical analyses in caliber rolling have been conducted in single material workpieces in order to investigate the temperature changes in multiple pass processing[30,31] and the relationship between the equivalent strain distribution and microstructure.[32] From these resu
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