Observation of pseudoelastic behavior in large Cu-Ni composite multilayer nanowires
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Observation of pseudoelastic behavior in large Cu-Ni composite multilayer nanowires N. Abdolrahim1, I.N. Mastorakos1, D. Bahr2, and H.M. Zbib1 1
School of Mechanical and Materials Engineering
Washington State University, Pullman, WA 99164 2
School of Materials Engineering,
Purdue University, 701 West Stadium Avenue, West Lafayette IN 47907-2045 ABSTRACT In recent years, studies have shown that single crystal metallic nanowires (NWs) can exhibit unique pseudoelastic behavior when their cross-sectional area is smaller than a certain critical value, which is on the order of a few nms. The mechanism responsible for this behavior is the formation of partial dislocations (twinning). In this paper we demonstrate using molecular dynamics simulations that thicker composite nanowires can exhibit pseudoelastic behavior at large cross-sectional dimensions to 28 nm and higher, as long as the individual layer thickness do not exceed a critical value of 1.8-2 nm, thus making their manufacturing feasible and more attractive.
In two previous papers1,2 we studied the possibility of increasing the critical dimensions of nanowires for exhibiting pseudoelasticity by adding the coherency stresses found in coppernickel (Cu-Ni) interfaces, using molecular dynamics (MD) simulations. In particular, our simulations showed that trilayer composite nanowires, made of alternating copper and nickel layers, would still exhibit pseudoelastic behavior for total thicknesses that are about 3 times larger than that of single crystalline nanowires2. In this paper we expand this work to composite nanowires with several numbers of layers with total dimensions much larger (15 times and more) than single crystalline nanowires. Our results show that even these ”thick” structures exhibit pseudoelasticity. The key parameter to this behavior is the restriction of the individual layer thickness below a critical value that is related to the maximum thickness of a single metal nanowire to exhibit pseudoelasticity. The resulted structures could maintain their pseudoelastic behavior with very few residual dislocations under several loading/unloading processes. It is our belief that these composite wires can be manufactured from nano-metallic multilayers3 using already established techniques. Metallic nanowires have many potential applications in nanoscale electromechanical systems2,3 (NEMS)4,5 due to their unique physical, electronic, magnetic and optical properties that are coupled with their mechanical behavior6-9. Hence, it is important to understand the mechanical properties of nanowires to recognize their future applications in nanotechnology10. Among metallic nanowires, fcc nanowires exhibit very unique behavior of pseudoelasticity11-13 upon applying and removal of tensile loading. They can recover plastic strains of up to 40% which is far beyond the limits for conventional shape memory bulk materials that is about 5-8%14 . This behavior of pseudoelasticity is very important in the area of self-healing materials used as
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