A maximum in ductility and fracture toughness in nanostructured Cu/Cr multilayer films

In Cu/Cr multilayers with modulation period (λ) ranging from 10 to 250 nm, maxima are observed for both tensile ductility and fracture at a critical λ ∼ 50 nm, different from the monotonic λ dependence known for monolithic films. This unusual behavior is explained, via quantitative assessments based on a micromechanical model, by considering the competing thickness effects on the size of the microcracks initiated in the Cr layers and on the role of the ductile Cu layer in blocking crack propagation.