Introduction

1. Nanostructured Materials in CuAg by Cyclic Cold Rolling Michael O. Cole1, Ke Han2 1Physics-Engineering (Dual Degree) Department, Morehouse College, Atlanta, Georgia 30314 2Division of Materials Science and Technology, National High Magnetic Field Laboratory of Florida State University, Tallahassee, Florida 32310 Introduction Creating nanostructured materials through cold rolling is a process that has been used and documented for some time now. This process generally compresses the material, making it harder, stronger, and alters the appearance. Cu and Ag both have the face-centered-cubic crystallographic structure and have relatively low strain-hardening rate at room temperature (≈ 295K). Therefore, rolling has limited strengthening impact. By making the composite of Cu and Ag, one creates a large number of interphase interfaces in the materials, enhances the strain hardening rate significantly, therefore yielding a significantly higher strength. Cu and Ag are very good conductors and relatively inexpensive, making them both viable candidates to be used in magnets. This research studies Cu at 84% Ag at 16% because the relationship between the conductivity to strength is optimized at this composition. Sample 2 was rolled both in the original rolling and transverse direction, alternating between each pass until the 9th, where all subsequent passes were only in the rolling direction. After both samples had been rolled to around 0.18 mm, the samples were then cut, mounted in a conductive mount, polished with 1200 grade grit paper, placed in the VibroMat machine for 2.5 hours, etched with a 25% nitric acid solution and then examined under the scanning electron microscope. Results Sample 1: F. Thickness 0.18mm; T. Reduction 71.4%; 12 Passes Sample 2: F. Thickness 0.19mm; T. Reduction 69.8%; 13 Passes While the total reduction only differs by 1.6%, note that sample 2 experienced 1 more pass than sample 1. Cold Rolling reduces the lamellar spacing between Cu and Ag. Rolling in both the rolling and cross direction also caused complications (i.e. instability and fracture) after the 4th pass where the sample seemed to reach its shear strength in local areas. Due to these complications, one must trim the fractured pieces of the sample off before continuing the rolling process in order to yield any further reduction without completely fracturing the entire alloy. Rolling in multiple directions also created a phenomenon known as shear band in both orientations, whereas rolling in one direction only results in shear band in one direction. The shear banks are marked by arrows. Conclusion The cold rolling process produces lamellar structured Cu-Ag nanocomposites that offer high strength. Reduction in lamellar spacing also increases the electrical resistance of the nanostructured composite. The shear bands are considered as defects and may render a poorer performance of the composite than those without shear bands. However, it is unclear if one can produce nanostructured composites without shear bands. Acknowledgements First and foremost I would like to thank Dr. Ke Han for working with me and always having his door open for questions. I have truly learned a great deal from his guidance. I would also like to thank Bob Goddard and Bill Starch for taking the time out of their days to teach me how to use the SEM and the rolling mill. Finally, I would like to thank Jose Sanchez and the rest of Mag Lab REU faculty for accepting me into this program and giving me the opportunity to learn and gain experience in the field of research. Why Rolling? Rolling is one method of deforming an alloy. If done correctly, rolling can reduce the size of Both Cu and Ag in the samples so that nanostructured materials can be created. Nanostructured composites have high density of interfaces and therefore have a high strength. By rolling an alloy to the correct reduction, a maximum strength can be attained. If this process is not done with precision, necking and ultimately fracture will occur. Mag: 15k Mag: 20k References William D. Callister Jr., Fundamentals of Materials Science and Engineering, Second Edition J.M. Alexander & R.C. Brewer, Manufacturing Properties of Materials B. Z. Cui, K. Han, D. S. Li, H. Garmestani, J. P. Liu, N. M. Dempsey, H.J. Schneider-Muntau, Magnetic-field-induced Crystallographic Texture Enhancement in Cold-Deformed FePt Nanostructured Magnets B.Z. Cui, J. Clark, J.W. Su, K. Han, S.A. Shaheen, Textured Anisotropic FePd/ -Fe Nanocomposite Foils by Sheath Repetitive Cold-Rolling Procedure: First, two 7.62 cm X 7.62 cm rolled samples of the Cu 84.0, Ag 16.0 alloy were cut. Immediately after that the samples were rolled in a rolling mill with the roll of 6.27 cm radius. Sample 1 was rolled in the original rolling direction for 12 passes which allowed it to endure more strain and ultimately a greater reduction in area. Mag: 50k Mag: 75k