Plastic Behaviour of Cu / Ni Multilayers

In order to study the plasticity in Cu-Ni multilayers deposited on single crystals of Cu and etched Si, we have investigated the mechanical properties of the multilayers both by nanoindentation measurements, and by the transmission of well characterized dislocations from the underlying substrate by tensile deformation of Cu single crystals.Various multilayers were deposited by physical vapor deposition with layer thicknesses varying between 1000 and 20 Angstroms (for a total thickness between 0.8 and 1 μm). Two types of experiments were designed. The first one aimed at injecting, in a controlled way, some dislocations from the substrate into the multilayers; the second type of experiment concerned the structure of the multilayer surface after having plastically pushed the material away from a nanoindenter.This communication reports the results from the nanoindentation measurements, as well as the observations of slip on the surface. We observed through the injection of dislocations by nanoindentation that the multilayers increase in strength with refinement of the layer structure but at thicknesses below 35Å exhibits a softening behaviour. Also observation of the upheaval around the nanoindent showed an evolution from slip lines to more spread plasticity with refinement of the layer structure.