Dislocation-based modeling of the mechanical behavior of epitaxial metallic multilayer thin films

A 3D dislocation cellular automaton model is employed to simulate yield and hardening in nanostructured metallic multilayer thin films during in-plane, biaxial tensile loading. The films consist of two types of alternating, single-crystalline FCC layers with (0 0 1) epitaxy, a mismatch in stress-free lattice parameter, but no elastic modulus mismatch. The simulations monitor the operation of interfacial and threading sources with lengths greater than the individual layer thickness. At larger layer thickness, strength increases with decreasing layer thickness, due to slip confinement to individual layers. At sufficiently small layer thickness, slip confinement is not possible, even during initial stages of plastic deformation. Consequently, strength is not controlled by layer thickness but rather by source length, as well as coherency stress and interfacial barrier strength. Here, strength may increase, decrease, or reach a plateau depending on how source length and barrier strength vary with layer thickness.