Layered and Functionally Graded Nanocomposite Thin Films with Unique Mechanical Properties
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Layered and Functionally Graded Nanocomposite Thin Films with Unique Mechanical Properties Stephen L. Farias1, Patrick C. Breysse2, Chai-Ling Chien3, Robert C. Cammarata1 1
Deptartment of Materials Science & Engineering, Johns Hopkins University, Baltimore, MD Eberly College of Science, Pennsylvania State University, University Park, PA 3 Deptartment of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 2
Abstract A novel electrochemical deposition method for manufacturing functionally graded, oxide-dispersion strengthened metal matrix nanocomposites will be presented. Using a rotating disk electrode and depositing from an electrolyte containing a suspension of oxide nanoparticles, metal-ceramic nanocomposites have been produced. This method leads to precise control over the volume fraction of the oxide in the nanocomposite and allows for the manufacturing of compositionally uniform, periodically layered, or functionally graded structures. In the higher order structures the composition variation can be finely tuned with nanometer resolution, and the characteristic microstructural length scale (e.g., individual layer thickness) can range from microns up to millimeters. Using indentation methods, the nanocomposites are shown to display enhanced and tunable mechanical properties. Introduction Hierarchical ordered materials have grown as a topic of research interest over the past decade. Natural materials with these unique constructions have strength to weight ratios and failure properties vastly superior to any manmade materials to date1,2,3. These materials have controlled composite structures at nanometer length scales as well as higher order structures with length scales ranging from nanometer to 100 microns. Simulations and analytical models on these structures indicate that manufactured artificial hierarchical materials would display superior properties compared to those produced by most current industry technologies4.5. Although extensive research efforts have been devoted to studying natural materials, limited progress has been made in manufacturing materials with these unique structures and properties. Much of the difficulty in manufacturing these hierarchical structures has come in controlling them at both nanosize and macroscopic length scales. While there are many refined techniques for creating nanostructures and processing bulk materials, generating these nanostructures in bulk quantities and organizing them over large scales has proved challenging. Electrochemical deposition provides unique means of tackling many of the difficulties that have hindered the synthesis of artificial high order composite structures. Deposition rates can be finely tuned to nanometers/minute, but these same systems can also be robust enough to deposit at rates on the order of microns/minute. Additionally, total deposition thicknesses of the order of millimeters can be achieved. We have shown in previous work that electrodeposition can also be used to create uniform metal-ceramic nanocomposite structures6. By using
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