Dominant factor controlling the fracture mode in nanostructured Cu/Cr multilayer films

It was recently suggested that the fracture mode in nanostructured metallic multilayer films (NMFs) is related to the strengthening mechanism. Here, based on extensive experimental examinations on the nanoscale damage of Cu/Cr NMFs with wide ranges of modulation period (from 10 nm to 250 nm) and modulation ratio (from 0.11 to 3.0), we conclude that the dominant factor controlling the fracture mode in NMFs is the constraint effect from the ductile layer on the brittle layer, rather than the strengthening mechanism. This constraint effect is quantitatively assessed using a fracture mechanism-based micromechanical model, which yields predictions in broad agreement with the experimental observations.