Nanoscale metallic multilayers formed by alternating layers of two dissimilar metals with layer thicknesses in the nanoscale range have very attractive properties including high hardness, strength and thermal stability. Nevertheless, most of the mechanical characterization of metallic nanolaminates has been carried out by means of nanoindentation or micropillar compression and very little information is available on the tensile behaviour of free-standing nanolaminate films. Thus, there is a lack of information on the deformation and fracture mechanisms of these systems in tension.
In this investigation, the mechanical behaviour of Cu/Nb nanolaminates manufactured by accumulated roll bonding were studied by means of tensile tests carried out within a transmission electron microscope (TEM). Tensile specimens with the loading axis parallel and perpendicular to the laminate were milled using a focus ion beam gun and attached to a push-pull loading device which was introduced in the TEM. Load and deformation were recorded during the in situ tensile deformation, together with the mechanisms of deformation, crack propagation and crack arrest at the Cu/Nb interfaces. Evidence of plastic deformation by confined layer slip was found in both orientations for Cu and Nb, but important differences were found in the fracture mechanisms between both orientations. Crack nucleation and propagation was localized in the thickest Cu layer when the nanolaminate was perpendicular to the loading axis. In the parallel orientation, crack was nucleated in a Cu layer but was stopped at the Cu/Nb interface, leading to a rough crack path. The influence of the orientation on the deformation and fracture mechanisms was discussed to the light of the observations provided by the in situ mechanical tests.