Length scale dependent mechanical/electrical properties of Cu/X(X=Cr, Nb) nano-structured metallic multilayers

By using nanoindentation test and four point probe method, the length scaled dependent mechanical property (hardness/strength) and electrical property (resistivity) of Cu/X(X=Cr, Nb) nanostructured metallic multilayers with equal individual layer thickness were systematically investigated. It is revealed from the microstructural analysis that the modulation structure of Cu/X metallic multilayers is clear, and the preferred growth planes of Cu layer and X layer are {111} and {110}, respectively. The indentation test shows that the hardness/strength of the multilayers increases with reducing modulation period λ. The deformation mechanism of the multilayers transits from the glide of single dislocation in a Cu layer to the interface cutting at a critical modulation period λ ^c (λ ^c≈25 nm). The resistivity of Cu/X multilayers is not only related to the scattering of conduction electrons at surfaces/interfaces and grain boundaries, but also affected by the interface condition at small scale. This significant interface effect on the length scale-dependent resistivity is assessed using a modified FS-MS model. The best combination of strength-resistivity can be achieved by tailoring the microstructure of Cu/X nanostructured metallic multilayers.