Deformation mechanisms in composite nano-layered metallic and nanowire structures

Using molecular dynamics simulations, the deformation behavior of two types of nanocomposite metallic materials (nano-layered thin films and composite nanowires) is investigated and compared with that of the bulk materials. The first structure is a hybrid nano-layered metallic composite formed by alternating layers of Cu, Ni, Cu, and Nb layers. The nanocomposite has a pre-existing dislocation structure inside it, generated by initially loading a perfect structure to a high strain to nucleate dislocations, then completely unloading it, and loading it again. Four different structures are considered all having the same Cu and Ni layers thickness and varying Nb thickness. Comparison of the deformation behavior between the different structures revealed that the addition of Nb layer makes the material stronger. However, this behavior has a critical limit below which the strength of the material decreases. This is attributed to the extended shearing of the interface that results from the accumulation of dislocations in the Cu/Nb interface. The second structure discussed is a composite nanowire made of a Ni layer sandwiched between two Cu layers. We show that the natural development of coherency stresses at the interfaces between the two layers increases the ability of the wire to deform by a twinning process under tensile loading. This process results in the reorientation of the composite nanowire that, under unloading, forces the nanowire to completely recover the straining, leading to a pronounced pseudoelastic behavior.